Why are there so many species of bats?

Why are there so many species of bats?

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I read that roughly 20% of all species of mammals are bats. Is there a good explanation for why bats have diversified so much compared to other mammals? Is it because bats' ability to fly allows them to fill niches that are completely out of reach (pun intended) of other mammals? If so, how is this reconciled with the coexistence of bat populations and bird populations?

Indeed, good question. There's tiny bats, large bats, and so many different species of them! A clue can be found in the observation that each bat species is almost always restricted to a small geographical region. With this in mind, it has been shown that an animal lineage's ability to diversify quickly in new environments depends largely on its diet. Bats have an incredible variety of dietary sources. Plant nectar, insects (there's so many different kinds of insects… ), blood-feeding, and more! So, as you can imagine, bat species are restricted because they have specialized diets and because they are very good at taking up new diets over evolutionary time. Unfortunately for them, it restricts them to a geographical location much of the time. Geographical restriction is always a good starting point for speciation events, and there have been many in the bat clade. But why bats, specifically, you might ask? Well - it is argued (below) that it is due to the characteristics of their skulls, rather than their wings.

Dumont, E. R., Dávalos, L. M., Goldberg, A., Santana, S. E., Rex, K., & Voigt, C. C. (2012). Morphological innovation, diversification and invasion of a new adaptive zone. Proc. R. Soc. B, 279(1734), 1797-1805.

Bats are hosts to a range of viruses but don’t get sick – why?

Keith Grehan is affiliated with the University of Leeds as a postdoctoral researcher.


University of Leeds provides funding as a founding partner of The Conversation UK.

The Conversation UK receives funding from these organisations

Bats harbour many diverse viruses, including coronaviruses. Indeed, Sars, Mers and COVID-19 – which are all caused by coronaviruses – are thought to have emerged from bats. These diseases can be deadly to humans, yet bats seem to be unaffected by them.

Like all animal species, bats possess their own range of pathogens – viral, bacterial and fungal. Organisms are part of an interconnected system of other living things that evolved to exploit and be exploited in turn. Bats have therefore evolved with a set of viruses that infect them and continuously circulate through the bat population.

SARS-CoV-2, the virus that causes COVID-19 is a member of a family of viruses called the coronaviridae (coronaviruses). Coronaviruses, or “CoVs”, infect a variety of animals, with human infections ranging from HCoV-229E, which causes some cases of the common cold, to MERS-CoV, which is fatal in up to 30% of cases.

Since the original SARS-CoV outbreak in 2002, coronaviruses closely related to SARS-CoV have been discovered in bats from countries all over the world. Scientists in China studying Chinese horseshoe bats in 2013, identified several SARS-like CoVs that use the same ACE2 receptor to bind to cells as the current SARS-CoV-2. These viruses were similar enough to SARS-CoV that they were termed SARS-like coronaviruses. New viruses have been added to this group since then. So there is a significant diversity of coronaviruses circulating in bats, which may increase the probability that one of these viruses has the potential to become a zoonotic infection – in other words, can jump to humans.

Bats are excellent hosts for viruses in general and coronaviruses as a group have been particularly successful at infecting and diversifying within bats. The highly social nature of many bat species leads to the constant exchange of viral pathogens between bats – and this may act to drive viral diversification within a population.

Why are there so many species of bats? - Biology

Thomas G. Barnes
Associate Extension Professor
Department of Forestry
University of Kentucky
[email protected]

  • Most bats are not rabid.
  • Bat droppings in buildings are usually not a source of histoplasmosis.
  • Bats are not filthy and will not infest homes with dangerous parasites.
  • Bats are not aggressive and will not attack people or pets.
  • Kentucky bats do not feed on blood. (The vampire bat, which does feed on blood, lives in Latin America, more than 1,000 miles from Kentucky. )

Bat Facts and Biology

Bats are interesting and useful animals. People often fail to realize that bats benefit humans. One benefit is their ability to
consume large amounts of insects. A single little brown bat (one of the most common house-dwelling bats) may eat 600
mosquitoes in an hour. Many landowners report a noticeable reduction in insects around their property when bats are present.
All Kentucky bats eat insects and capture flying insects at night, using their tail and wing membranes. They are the only major
predator of night-flying insects. Another benefit provided by bats includes pollination and dispersal of seeds for many tropical plants. The local grocery store would not be the same without products that depend on bats for their survival. Wild stocks of bananas, avocadoes, dates, figs, peaches, mangoes, cloves, cashews, and agave are pollinated by bats. These wild plant ancestors are an important genetic source for developing new disease-resistant strains of commercial varieties, reinvigorating old commercial varieties, andproducing new, highly productive varieties. Bats have also contributed to medical research in birth control and artificial insemination techniques, navigational aids for the blind, vaccines and drugs, and new low-temperature surgical techniques. Without bats, we would suffer great economic losses, and our quality of life would be reduced.

Bats are not rodents. They belong to their own special group of mammals called Chiroptera, which means "hand wing".
Bat wings are actually modified finger bones attached by a thin skin membrane. Bats are more closely related to primates
(monkeys, apes, and humans) than to rodents. Like other mammals, bats are warm-blooded and furry, and they nurse their
young. Bats are the only mammals that exhibit true flight. Bats are not blind, and like dolphins, they navigate, avoid obstacles,
and detect food using a very sophisticated system called echolocation. Echolocation works when bats emit high-frequency
sounds that bounce off objects. The bat then hears the rebounding echo and reacts accordingly. This system is so precise and
sophisticated that bats can detect obstacles as small as a gnat or a human hair in total darkness. With such sophistication they
are unlikely to blunder into people. Kentucky bats mate in the fall and early winter. The females hold sperm in their reproductive tracts until spring when fertilization occurs. Pregnant females then move from their winter hibernating sites (called hibernacula) to maternity sites or nursery colonies.

Most bats produce a single offspring six to eight weeks after fertilization. This is an exceptionally low reproductive rate
for a small mammal. Thus, their populations are quite vulnerable and require a long time to recover. Many bats do not breed
until they are two years old and may survive for 30 years. Young bats grow rapidly and are able to fly in five weeks. While females are attending to the young in nursery colonies, males congregate in separate groups called bachelor colonies. Groups of bats found in buildings throughout Kentucky are usually nursery colonies. Cold winter temperatures force many Kentucky bats to migrate for the winter. Their migrations are usually less than 300 miles. Bats look for a cave or other hibernating site with an optimum temperature varying from 41 to 58°F. Big brown bats, commonly found in buildings, can survive subzero temperatures and may hibernate in walls, attics, cliff faces, and rock shelters.

Fall migrations usually begin in August, and the bats return in April and May. Bats have amazing homing abilities and return to the same summer or winter quarters every year, much like some birds. Kentucky bats live in a variety of habitats. Some species like the red bat and the hoary bat spend their summers roosting among tree leaves and migrate south for the winter. Others, especially endangered bats like Indiana and gray bats, are cave-dwelling animals in the winter. Another endangered bat, the Virginia big-eared bat, hibernates in caves and spends the summer along sandstone cliff faces, crevices, and rock shelters. Several common bats, like the big brown and little brown bat, summer mostly in buildings but occasionally can be found in hollow trees or rock crevices.

Kentucky has 15 species of bats which can be found throughout most of the state. Some species are common, and others have been placed on the state or federal endangered species list. Fifty-seven percent of Kentucky's bat fauna is listed as rare, threatened, or endangered. Bat populations have been declining in the United States and Kentucky for the past 20 years.

Dealing with Unwanted House Guests

Most bat species found in Kentucky are not likely to become a nuisance. Many species, including rare, threatened, and
endangered bats, are never encountered by most humans. Many of the more common species go unnoticed by everyone
except avid bat enthusiasts. Only big brown and little brown bats, two of our most common bat species, are likely to take up
residence in buildings. Proper control measures must provide a long-term solution to the problem. Many short-term control measures areillegal and provide numerous hazards to both bats and humans. There are no pesticides, not even Rozol tracking powder, registered for controlling bats in Kentucky. Insect bombs and commercial fumigation using methylbromide are against the law in Kentucky and pose significant health hazards to humans. Home remedies including moth balls, ultrasonic devices, bright lights, chemical repellents including aerosol dog and cat repellents, sulfur candies, strong wind currents, or glue boards are not completely successful or recommended. The only permanent solution in dealing with problem bats is to build them out or "bat-proof" the building. Because bats cannot gnaw new holes or reopen old ones, once openings are closed they should remain that way. Bats can enter a hole as small as 3/8 inch in diameter. You must find ALL openings larger than 3/8 inch and seal them because bats will continue to use the building as long as they have an entry point. Openings can be anywhere because bats do not need to fly through an opening to enter or escape.

Time spent locating and sealing all entrances the first time will save additional time and frustration in the future because
bats return each year to their nursery colony. Thus, they will be back next year if you don't take the time to find and seal their
points of entry. The first step in building out bats is to locate entrance points. There are several methods you can use to locate bat entry points. Inspect the ground at the base of the house for bat droppings which accumulate below entrances. Also look on the side of the building for spattered droppings. On bright sunny days climb into the attic and observe where light from the outside is coming. Or, after dark, place a bright light such as a lantern inside the attic and observe places where light is shining through. Another method is to position several people around the outside of the building before dusk and watch for bats
emerging. However, this method may not locate all entrances for two reasons: bats may use other nonpreferred entrances, and
people often have difficulty seeing bats emerge, recognizing them only when they are actively flying.

The best time of day to seal bat openings is several hours after sundown when bats are feeding. Because most bats migrate, the best time of year to bat-proof the building is during late November through early March. Never seal openings from mid-May through July because flightless young may be present. Sealing bats inside a building causes the bats to quickly starve, creating an unsanitary and smelly problem. The best method to use in sealing openings is to seal all but two or three major entry points at your convenience. Once the bats have adjusted to using these openings, seal these openings after dark or during late fall and winter. You can seal them with a variety of materials depending on each individual situation. Because bats do not chew like rodents, you can use insulating material as a stop-gap measure until a permanent material is found. Cracks near the roofline or areas where pipes or wires enter a building can be sealed with latex, acrylic or silicone caulk. Metal flashing can be used to seal joints in the house, and mortar can be used to seal cracks in the foundation. Weatherstripping can be used to seal cracks around door and windowsills. Open vents and belfry louvers should be sealed with 1/4-inch hardware cloth which will allow proper ventilation. Rust-resistant spark arrestors or bird screens should be installed on chimneys to prevent bats from entering.

One alternative to closing the remaining holes after dark is to install a valve-like bat-proofing device in the remaining
holes. This allows bats to depart during the evening but prevents their reentry. Eventually, these holes will need to be sealed
permanently to prevent reentry. Bat excluder devices are available from 3E Corporation, 401 Kennedy Blvd., P.O. Box 177,
Somerdale, NJ 08083 or Bay Area Bat Protection, 1312 Shiloh Road, Sturgeon Bay, WI 54235. Homeowners can make their own simple bat-excluding device by using 1/2-inch plastic bird netting available at local garden or hardware stores. Cut a piece of netting several feet larger than the opening so that at least two feet hang to the side of and below the entry hole. Hang the netting, during the day, several inches above the entry hole. The sides may be stapled, taped, or nailed to the building, but the bottom must be allowed to hang free.

Another way to keep your house free from bats is to provide them with a dwelling of their own. A properly constructed bat house can give bats a place to roost and raise their young, thereby concentrating their insect-eating activities nearby, but some distance away from, your living quarters.

Not every bat house will be used. Just like birds, bats are fussy about the design and location of their living quarters. Bat nurseries should have a fairly stable temperature of 80-110°F depending on the species. Thus, the house should be made as airtight as possible. Glue all external joints and seal them with silicone caulk to prevent heat loss. Bats are also very susceptible to chemicals. Therefore, do not use treated wood, and do not paint or varnish the completed house. Use rough lumber because it is easier for the bats to secure a good foothold. If rough lumber is not available, roughen the inside of the house with a file or other tool. Be sure to place the rough sides inward. You may also wish to cut 1/16 inch grooves in each partition to help the bats climb and roost. Western red cedar is the recommended construction material because it withstands outdoor exposure. Houses can also be built of redwood or cypress if western red cedar is not available at your local lumber store. To ensure that temperatures remain constant, the house should be oriented to receive maximum sunlight, especially in the early morning. You may need to experiment to determine the direction the house should face. South-facing houses will be warmer than north-facing houses. By testing several choices and recording the high and low temperatures inside the house, you can determine which
direction is best. Europeans sometimes mount four houses in a group, each facing a different direction to provide a wide range
of temperatures for the bats to select from. You may have to place tar paper or dark shingles on the top of the house to
increase heat absorption.

Bat houses should be erected from 10 to 15 feet above the ground and protected from the prevailing (north and west) winds. Never place a house where the entrance is obstructed by tree limbs or vegetation. A good site for a house is on an old building or home. Houses placed near a permanent water source are more likely to attract bats. Don't be discouraged if bats don't occupy the house right away. Most bat houses are not used the first year they are erected, and some may never be used. However, most bat houses are used eventually.

Little Brown Bat (Myotis lucifugus). A small brown bat weighing about 10 grams. Common throughout Kentucky, it can sometimes be found in attics of buildings or roosting on boat docks. One of bats most commonly encountered by humans.
Lives in colonies, hibernates.

Southeastern Bat (Myotis austroriparius). May be confused with little brown bat because of numerous similarities. Found in western Kentucky. State endangered species and candidate for federal endangered species. Found in buildings, caves, culverts, or tree cavities. Lives in colonies, hibernates.

Gray Bat (Myotis grisescens). Similar to other Myotis bats but larger. It can be identified by the wing membrane attached to the ankle instead of base of toes. Found in inner Bluegrass and cave region of south-central Kentucky. Federal endangered species. Lives in colonies, hibernates.

Northern Long-eared Bat (Myotis septentrionalis). Similar to little brown bat except for its longer ears and a long pointed tragus (inner ear membrane). Rare. A state special concern species. Found in caves, rockhouses or shelters, old mines, and buildings. Lives singly or in small colonies, hibernates.

Indiana Bat (Myotis sodalis). Difficult to distinguish from other Myotis. Federal endangered species. Found in winter
throughout Kentucky cave regions. Lives in forested areas during summer, roosting in snags and under tree bark. Lives in
colonies, hibernates.

Small-footed Bat (Myotis leibii). Very tiny bat identified by small size, small forearm and foot, and keeled calcar (a long bone spur on one of the ankle bones). Found in eastern and central cave regions of Kentucky. State endangered species and candidate for federal endangered species list. Lives in colonies, hibernates.

Big Brown Bat (Eptesicus fuscus). Abundant statewide resident. The bat most commonly found in buildings. A large bat about twice the size of the little brown bat. In Kentucky, this species is by far the most commonly encountered by people. Lives in colonies, hibernates.

Silver-haired Bat (Lasionycteris noctivagans). Medium-sized black bat with white-tipped fur. Usually found during spring migration. Seasonally solitary, migrates. Some hibernate in caves, mines, and rock crevices in Kentucky.

Eastern Pipistrelle (Pipistrellus subflavus). Tiny bat with tricolored fur. Abundant statewide resident. Prefers caves in winter and trees and buildings in the summer. Hibernates, singly scattered through caves and mines.

Red Bat (Lasiurus borealis). Abundant statewide resident. Fur is rusty red, washed with white. Cannot be confused with any other species. Seeks daytime refuge in trees. Solitary, migrates. In June, females laden with young (up to four) often fall onto lawns.

Hoary Bat (Lasiurus cinereus). Rare, but found throughout Kentucky. Larger than Big Brown Bat. Color is grayish
yellow-brown, overcast with grayish white. Spends summer days in tree foliage. Solitary, migrates.

Evening Bat (Nycticeius humeralis). Found in western and southern Kentucky. State threatened species. Found in trees and buildings avoids caves. Lives in colonies, migrates.

Virginia Big-eared Bat (Plecotus townsendii virginianus). Known only from eastern Kentucky cave region. Federal
endangered species. Largest known winter colony occurs in one eastern Kentucky cave. Lives in colonies, hibernates.

Rafinesque's Big-eared Bat (Plecotus rafinesquii). Uncommon but scattered throughout the state. Occurs in caves, mines, wells, and abandoned buildings. Very similar in appearance to Virginia big-eared bat. State threatened species and candidate for federal endangered species list. Lives in colonies, hibernates.

Brazilian Free-Tailed Bat (Tadarida brasiliensis). Accidental. Autumn wanderer from the south.

America's Neighborhood Bats: Understanding and Learning to Live in Harmony with Them. by M.D. Tuttle. University of
Texas Press, 1988, 104 pp.

Bats: A Natural History. by J.E. Hill and J.D. Smith. University of Texas Press, 1984, 243 pp.

Just Bats. by M.B. Fenton. University of Toronto Press, 1983, 165 pp.

"Most 'Facts' About Bats are Myths". by B. Strohm. In National Wildfire Magazine, 1982, 20(5):35-39.

Tiny and Elusive

They may be tiny, but there's a lot to love about microbats.

The creatures use echolocation—or built-in sonar—to catch many insects, including pests such as mosquitoes. They also pollinate plants, including agave, the base ingredient of tequila. (Related: "Tequila's Savior May Be the 'Bat Man' of Mexico.")

And they're surprisingly long-lived for such small-bodied animals. The oldest recorded microbat in the wild died at 41, which goes against the belief that small creatures live fast and die young, Lentini says.

Yet little is known about these long lives, partly because they're notoriously tough to study, says Merlin Tuttle, bat expert and founder of Bat Conservation International.

Not only are microbats nocturnal, every time an individual is caught, examined, or disturbed during hibernation, "we're increasing the odds that the bat will learn to avoid us, or will die prematurely," Tuttle says.


Viruses have been found in bat populations around the world. Bats harbor all groups of viruses in the Baltimore classification, [7] representing at least 28 families of viruses. [6] Most of the viruses harbored by bats are RNA viruses, though they are also known to have DNA viruses. [8] Bats are more tolerant of viruses than terrestrial mammals. [8] A single bat can host several different kinds of viruses without becoming ill. [9] Bats have also been shown to be more susceptible to reinfection with the same viruses, whereas other mammals, especially humans, have a greater propensity for developing varying degrees of immunity. [10] [11] Their behavior and life history also make them "exquisitely suitable hosts of viruses and other disease agents", with long lifespans, the ability to enter torpor or hibernate, and their ability to traverse landscapes with daily and seasonal movement. [1]

Though bats harbor diverse viruses, they are rarely lethal to the bat host. Only the rabies virus and a few other lyssaviruses have been confirmed to kill bats. [7] Various factors have been implicated in bats' ability to survive viral infections. One possibility is bats' use of flight. Flight produces a fever-like response, resulting in elevated temperature (up to 38 °C (100 °F)) and metabolic rate. Additionally, this fever-like response may help them cope with actual fevers upon getting a viral infection. [7] Some research indicates that bats' immune systems have allowed them to cope with a variety of viruses. A 2018 study found that bats have a dampened STING response compared to other mammals, which could allow them to respond to viral threats without over-responding. [8] STING is a signaling molecule that helps coordinate various host defense genes against pathogens. [12] The authors of the study concluded that "the weakened, but not entirely lost, functionality of STING may have profound impact for bats to maintain the balanced state of 'effective response' but not 'over response' against viruses." [8]

Additionally, bats lack several inflammasomes found in other mammals [8] other inflammasomes are present with a greatly reduced response. [13] While inflammation is an immune response to viruses, excessive inflammation is damaging to the body, and viruses like severe acute respiratory syndrome coronavirus (SARS-CoV) are known to kill humans by inducing excessive inflammation. Bats' immune systems may have evolved to be more tolerant of stressors such as viral infections compared to other mammals. [14]

Transmission to humans Edit

The vast majority of bat viruses have no zoonotic potential, meaning they cannot be transmitted to humans. [6] The zoonotic viruses have four possible routes of transmission to humans: contact with bat body fluids (blood, saliva, urine, feces) intermediate hosts environmental exposure and blood-feeding arthropods. [15] Lyssaviruses like the rabies virus are transmitted from bats to humans via biting. Transmission of most other viruses does not appear to take place via biting, however. Contact with bat fluids such as guano, urine, and saliva is an important source of spillover from bats to humans. Other mammals may play a role in transmitting bat viruses to people, with pig farms a source of bat-borne viruses in Malaysia and Australia. [15] [16] Other possible transmission routes of bat-borne viruses are more speculative. It is possible but unconfirmed that hunting, butchering, and consuming bat meat can result in viral spillover. While arthropods like mosquitoes, ticks, and fleas may transmit viral infections from other mammals to humans, it is highly speculative that arthropods play a role in mediating bat viruses to humans. There is little evidence of environmental transmission of viruses from bats to humans, meaning that bat-borne virus do not persist in the environment for long. However, a limited number of studies have been conducted on the subject. [15]

Bats compared to other viral reservoirs Edit

Bats and their viruses may be the subject of more research than viruses found in other mammal orders, an example of research bias. A 2015 review found that from 1999 to 2013, there were 300–1200 papers published about bat viruses annually, compared to 12–45 publications for marsupial viruses and only 1–9 studies for sloth viruses. The same review found that bats do not have significantly greater viral diversity than other mammal groups. Bats, rodents, and primates all harbored significantly more zoonotic viruses than other mammal groups, though the differences among the aforementioned three groups were not significant (bats have no more zoonotic viruses than rodents and primates). [4] A 2020 review of mammals and birds found that the identity of the taxonomic groups did not have any impact on the probability of harboring zoonotic viruses. Instead, more diverse groups had greater viral diversity. Bat life history traits and immunity, while likely influential in determining bat viral communities, were not associated with a greater probability of viral spillover into humans. [5]

Sampling Edit

Bats are sampled for viruses in a variety of ways. They can be tested for seropositivity for a given virus using a method like ELISA, which determines whether or not they have the corresponding antibodies for the virus. They can also be surveyed using molecular detection techniques like PCR (polymerase chain reaction), which can be used to replicate and amplify viral sequences. Histopathology, which is the microscopic examination of tissue, can also be used. Viruses have been isolated from bat blood, saliva, feces, tissue, and urine. Some sampling is non-invasive and does not require killing the bat for sampling, whereas other sampling requires sacrificing the animal first. A 2016 review found no significant difference in total number of viruses found and new viruses discovered between lethal and non-lethal studies. Several species of threatened bat have been killed for viral sampling, including the Comoro rousette, Hildegarde's tomb bat, Natal free-tailed bat, and the long-fingered bat. [17]

Adenoviruses Edit

Adenoviruses have been detected in bat guano, urine, and oral and rectal swabs. They have been found in both megabats and microbats across a large geographic area. Bat adenoviruses are closely related to those finds in canids. [18] The greatest diversity of bat adenoviruses has been found in Eurasia, though the virus family may be undersampled in bats overall. [7]

Herpesviruses Edit

Diverse herpesviruses have been found in bats in North and South America, Asia, Africa, and Europe, [18] including representatives of the three subfamilies, alpha-, beta-, and gammaherpesviruses. [7] Bat-hosted herpesviruses include the species Pteropodid alphaherpesvirus 1 and Vespertilionid gammaherpesvirus 1. [19]

Papillomaviruses Edit

Papillomaviruses were first detected in bats in 2006, in the Egyptian fruit bat. They have since been identified in several other bat species, including the serotine bat, greater horseshoe bat, and the straw-colored fruit bat. Five distinct lineages of bat papillomaviruses have been recognized. [18]

Anelloviruses Edit

No anellovirus is known to cause disease in humans. [7] The first bat anellovirus, a Torque teno virus, was found in a Mexican free-tailed bat. [20] Novel anelloviruses have also been detected in two leaf-nosed bat species: the common vampire bat and Seba's short-tailed bat. The bat anelloviruses and one opossum anellovirus have been included in the proposed genus Sigmatorquevirus. [21]

Circoviruses Edit

Circoviruses, family Circoviridae, are among the most diverse of all viruses. [22] Like anelloviruses, circoviruses are not associated with any disease in humans. [7] About a third of all circoviruses are associated with bats, found in North and South America, Europe, and Asia. [22] A study of horseshoe and vesper bats in China identified circoviruses from the genera Circovirus and Cyclovirus. [23]

Parvoviruses Edit

Several kinds of parvoviruses are considered important for human and animal health. Several strains of parvovirus have been identified from bat guano in the US states of Texas and California. Serum analysis of the straw-colored fruit bat and Jamaican fruit bat led to the identification of two new parvoviruses. Bat parvoviruses are in the subfamily Parvovirinae, closely resembling the genera Protoparvovirus, Erythrovirus, and Bocaparvovirus. [18]

Reoviruses Edit

Nelson Bay orthoreoviruses, also known as Pteropine orthoreoviruses, identified from 1968 to 2014 [24]
Virus name Year identified Host Location
Nelson Bay virus 1968 Bat Australia
Pulau virus 1999 Bat Malaysia
Melaka virus 2006 Human Malaysia
Kampar virus 2006 Human Malaysia
HK23629/07 2007 Human Hong Kong
Miyazaki-Bali/2007 2007 Human Indonesia/Japan
Sikamat virus 2010 Human Malaysia
Xi River virus 2010 Bat China
Indonesia/2010 2010 Bat Indonesia/Italy

Zoonotic Edit

Some disease-causing reovirus species are associated with bats. One such virus is Melaka virus, which was linked to illness in a Malaysian man and his two children in 2006. [25] [26] The man said that a bat had been in his home a week before he became ill, and the virus was closely related to other reoviruses linked to bats. Kampar virus was identified a few months later in another Malaysian man. Though he had no known contact with bats, Kampar virus is closely related to Melaka virus. Several other reovirus strains identified in ill humans are known as Miyazaki‐Bali/2007, Sikamat virus, and SI‐MRV01. No reoviruses linked to bats have caused death in humans. [25]

Other Edit

Reoviruses include many viruses that do not cause disease in humans, including several found in bats. One reovirus species associated with bats is Nelson Bay orthoreovirus, sometimes called Pteropine orthoreovirus (PRV), which is an orthoreovirus several virus strains of it have been identified in bats. The type member of Nelson Bay orthoreovirus is Nelson Bay virus (NBV), which was first identified in 1970 from the blood of a gray-headed flying fox in New South Wales, Australia. NBV was the first reovirus to be isolated from a bat species. Another strain of Nelson Bay orthoreovirus associated with bats is Pulau virus, which was first identified from the small flying fox of Tioman Island in 2006. Other viruses include Broome orthoreovirus from the little red flying fox of Broome, Western Australia Xi River virus from Leschenault's rousette in Guangdong, China and Cangyuan virus also from Leschenault's rousette. [25] Several mammalian orthoreoviruses are associated with bats, including at least three from Germany and 19 from Italy. These were found in pipistrelles, the brown long-eared bat, and the whiskered bat. [25]

Orbiviruses have been isolated from bats, including Ife virus from the straw-colored fruit bat, Japanaut virus from the common blossom bat, and Fomédé virus from Nycteris species. [25]

Astroviruses Edit

Astroviruses have been found in several genera of bat in the Old World, including Miniopterus, Myotis, Hipposideros, Rhinolophus, Pipistrellus, Scotophilus, and Taphozous, [18] though none in Africa. [7] Bats have very high prevalence rates of astroviruses studies in Hong Kong and mainland China found prevalence rates approaching 50% from anal swabs. No astroviruses identified in bats are associated with disease in humans. [18]

Caliciviruses Edit

Bat caliciviruses were first identified in Hong Kong in the Pomona roundleaf bat, [18] and were later identified from tricolored bats in the US state of Maryland. Bat caliciviruses are similar to the genera Sapovirus and Valovirus, with noroviruses also detected from two microbat species in China. [27]

Coronaviruses Edit

SARS-CoV, SARS-CoV-2, and MERS-CoV Edit

Several zoonotic coronaviruses are associated with bats, including severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome-related coronavirus (MERS-CoV). [28] Severe acute respiratory syndrome coronavirus 2 is another zoonotic coronavirus likely originating in bats. [29] [30] SARS-CoV causes the disease severe acute respiratory syndrome (SARS) in humans. The first documented case of SARS was in November 2002 in Foshan, China. [28] It became an epidemic, affecting 28 countries around the world with 8,096 cases and 774 deaths. [28] The natural reservoir of SARS-CoV was identified as bats, with the Chinese rufous horseshoe bat considered a particularly strong candidate after a coronavirus was recovered from a colony that had 95% nucleotide sequence similarity to SARS-CoV. [28] There is uncertainty on whether or not animals like palm civets and raccoon dogs were intermediate hosts that facilitated the spread of the virus from bats to humans, or if humans acquired the virus directly from bats. [28] [31]

The first human case of Middle East respiratory syndrome (MERS) was in June 2012 in Jeddah, Saudi Arabia. [28] As of November 2019, 2,494 cases of MERS have been reported in twenty-seven countries, resulting in 858 fatalities. [32] It is believed that MERS-CoV originated in bats, though camels are likely the intermediate host through which humans became infected. Human-to-human transmission is possible, though does not easily occur. [33]

The SARS-CoV-2 outbreak in humans started in Wuhan, China in 2019. [34] Genetic analyses of SARS-COV-2 showed that it was highly similar to viruses found in horseshoe bats, with 96% similarity to a virus isolated from the intermediate horseshoe bat. Due to similarity with known bat coronaviruses, data "clearly indicates" that the natural reservoirs of SARS-COV-2 are bats. It is yet unclear how the virus was transmitted to humans, though an intermediate host may have been involved. [3] Phylogenetic reconstruction of SARS-CoV-2 suggests that the strain that caused a human pandemic diverged from the strain found in bats decades ago, likely between 1950 and 1980. [35]

Other Edit

Bats harbor a great diversity of coronaviruses, with sampling by the EcoHealth Alliance in China alone identifying about 400 new strains of coronavirus. [36] A study of coronavirus diversity harbored by bats in eastern Thailand revealed forty-seven coronaviruses. [37]

Flaviviruses Edit

Most flaviviruses are transmitted via arthropods, but bats may play a role in the ecology of some species. Several strains of Dengue virus have been found in bats in the Americas, and West Nile virus has been identified in fruit bats in South India. Serological studies indicate that West Nile virus may also be present in bats in North America and the Yucatán Peninsula. Saint Louis encephalitis virus has been detected in bats in the US states of Texas and Ohio, as well as the Yucatán Peninsula. Japanese encephalitis virus or its associated antibodies have been found in several bat species throughout Asia. Other flaviviruses detected in bats include Sepik virus, Entebbe bat virus, Sokuluk virus, Yokose virus, Dakar bat virus, Bukalasa bat virus, Carey Island virus, Phnom Penh bat virus, Rio Bravo bat virus, Montana myotis leukoencephalitis virus, and Tamana bat virus. [18]

Picornaviruses Edit

Several genera of picornaviruses have been found in bats, including Kobuvirus, Sapelovirus, Cardiovirus, and Senecavirus. [18] Picornaviruses have been identified from a diverse array of bat species around the world. [7]

Arenaviruses Edit

Arenaviruses are mainly associated with rodents, though some can cause illness in humans. The first arenavirus identified in bats was Tacaribe mammarenavirus, which was isolated from Jamaican fruit bats and the great fruit-eating bat. Antibody response associated with Tacaribe virus has also been found in the common vampire bat, the little yellow-shouldered bat, and Heller's broad-nosed bat. It is unclear if bats are the natural reservoir of Tacaribe virus. There has been one known human infection by Tacaribe virus, though it was accidentally acquired in a laboratory setting. [18]

Hantaviruses Edit

Hantaviruses, family Hantaviridae, naturally occur in vertebrates. All bat-associated hantaviruses are in the subfamily Mammantavirinae. Of the four genera within the subfamily, Loanvirus and Mobatvirus are the genera that have been documented in various bats. Almost all bat hantaviruses have been identified from microbats. [38] Mouyassue virus has been identified from the banana pipistrelle in Ivory Coast and the Cape serotine in Ethiopia [38] Magboi virus from the hairy slit-faced bat in Sierra Leone Xuan Son virus from the Pomona roundleaf bat in Vietnam Huangpi virus from the Japanese house bat in China Longquan loanvirus from several horseshoe bats in China [18] Makokou virus from Noack's roundleaf bat in Gabon Đakrông virus from Stoliczka's trident bat in Vietnam [38] Brno loanvirus from the common noctule in the Czech Republic [38] and Laibin mobatvirus from the black-bearded tomb bat in China. [39] As of 2019, only Quezon mobatvirus has been identified from a megabat, as it was identified from a Geoffroy's rousette in the Philippines. [38] Bat hantaviruses are not associated with illness in humans. [18] [38]

Filoviruses Edit

Marburgvirus and Ebolavirus Edit

Filoviridae is a family of virus containing two genera associated with bats: Marburgvirus and Ebolavirus, which contain the species that cause Marburg virus disease and Ebola virus disease, respectively. Though relatively few disease outbreaks are caused by filoviruses, they are of high concern due to their extreme virulence, or capacity to cause harm to their hosts. Filovirus outbreaks typically have high mortality rates in humans. Though the first filovirus was identified in 1967, it took more than twenty years to identify any natural reservoirs. [40]

Ebola virus disease is a relatively rare but life-threatening illness in humans, with an average mortality rate of 50% (though individual outbreaks may be as high as 90% mortality). The first outbreaks were in 1976 in South Sudan and Democratic Republic of the Congo. [41] The natural reservoirs of ebolaviruses are unknown. [42] [43] [44] However, some evidence indicates that megabats may be natural reservoirs. [40] [41] Several megabat species have tested seropositive for antibodies against ebolaviruses, including the hammer-headed bat, Franquet's epauletted fruit bat, and little collared fruit bat. [40] Other possible reservoirs include non-human primates, [42] rodents, shrews, carnivores, and ungulates. [45] Definitively stating that fruit bats are natural reservoirs is problematic as of 2017, researchers have been largely unable to isolate ebolaviruses or their viral RNA sequences from fruit bats. Additionally, bats typically have low level of ebolavirus-associated antibodies, and seropositivity in bats is not strongly correlated to human outbreaks. [44]

Marburg virus disease (MVD) was first identified in 1967 during simultaneous outbreaks in Marburg and Frankfurt in Germany, and Belgrade, Serbia. MVD is highly virulent, with an average human mortality rate of 50%, but as high as 88% for individual outbreaks. [46] MVD is caused by Marburg virus and the closely related Ravn virus, which was formerly considered synonymous with Marburg virus. [47] Marburg virus was first detected in the Egyptian fruit bat in 2007, [40] which is now recognized as the natural reservoir of the virus. [46] Marburg virus has been detected in Egyptian fruit bats in Gabon, Democratic Republic of the Congo, Kenya, and Uganda. [40] Spillover from Egyptian fruit bats occurs when humans spend prolonged time in mines or caves inhabited by the bats, [46] though the exact mechanism of transmission is unclear. [40] Human-to-human transmission occurs through direct contact with infected bodily fluids, including blood or semen, or indirectly through contact with bedding or clothing exposed to these fluids. [46]

Other Edit

Lloviu virus, a kind of filovirus in the genus Cuevavirus, has been identified from the common bent-wing bat in Spain. [40] Another filovirus, Bombali ebolavirus, has been isolated from free-tailed bats, including the little free-tailed bat and the Angolan free-tailed bat. [48] Neither Lloviu virus nor Bombali ebolavirus is associated with illness in humans. [49] [48] Genomic RNA associated with Mengla dianlovirus, though not the virus itself, has been identified from Rousettus bats in China. [48]

Rhabdoviruses Edit

Rabies-causing viruses Edit

Lyssaviruses (from the genus Lyssavirus in the family Rhabdoviridae) include the rabies virus, Australian bat lyssavirus, and other related viruses, many of which are also harbored by bats. Unlike most other viruses in the family Rhabdoviridae, which are transmitted by arthropods, lyssaviruses are transmitted by mammals, most frequently through biting. All mammals are susceptible to lyssaviruses, though bats and carnivores are the most common natural reservoirs. The vast majority of human rabies cases are a result of the rabies virus, with only twelve other human cases attributed to other lyssaviruses as of 2015. [50] These rarer lyssaviruses associated with bats include Duvenhage lyssavirus (three human cases as of 2015) European bat 1 lyssavirus (one human case as of 2015) European bat 2 lyssavirus (two human cases as of 2015) and Irkut lyssavirus (one human case as of 2015). Microbats are suspected as the reservoirs of these four uncommon lyssaviruses. [50] [51]

After transmission has occurred, the average human is asymptomatic for two months, though the incubation period can be as short as a week or as long as several years. [50] Italian scientist Antonio Carini was the first to hypothesize that rabies virus could be transmitted by bats, which he did in 1911. This same conclusion was reached by Hélder Queiroz in 1934 and Joseph Lennox Pawan in 1936. Vampire bats were the first to be documented with rabies in 1953, an insectivorous bat in Florida was discovered with rabies, making it the first documented occurrence in an insectivorous species outside the vampire bats' ranges. [52] Bats have an overall low prevalence of rabies virus, with a majority of surveys of apparently healthy individuals showing rabies incidence of 0.0–0.5%. [50] Sick bats are more likely to be submitted for rabies testing than apparently healthy bats, known as sampling bias, [53] with most studies reporting rabies incidence of 5–20% in sick or dead bats. [50] Rabies virus exposure can be fatal in bats, though it is likely that the majority of individuals do not develop the disease after exposure. [50] In non-bat mammals, exposure to the rabies virus almost always leads to death. [51]

Globally, dogs are by far the most common source of human rabies deaths. [54] Bats are the most common source of rabies in humans in North and South America, Western Europe, and Australia. [55] Many feeding guilds of bats may transmit rabies to humans, including insectivorous, frugivorous, nectarivorous, omnivorous, sanguivorous, and carnivorous species. [55] The common vampire bat is a source of human rabies in Central and South America, though the frequency at which humans are bitten is poorly understood. [56] Between 1993 and 2002, the majority of human rabies cases associated with bats in the Americas were the result of non-vampire bats. [51] In North America, about half of human rabies instances are cryptic, meaning that the patient has no known bite history. [50] While it has been speculated that rabies virus could be transmitted through aerosols, studies of the rabies virus have concluded that this is only feasible in limited conditions. These conditions include a very large colony of bats in a hot and humid cave with poor ventilation. While two human deaths in 1956 and 1959 had been tentatively attributed to aerosolization of the rabies virus after entering a cave with bats, "investigations of the 2 reported human cases revealed that both infections could be explained by means other than aerosol transmission". [57] It is instead generally thought that most instances of cryptic rabies are the result of an unknown bat bite. [50] Bites from a bat can be so small that they are not visible without magnification equipment, for example. Outside of bites, rabies virus exposure can also occur if infected fluids come in contact with a mucous membrane or a break in the skin. [57]

Other Edit

Many bat lyssaviruses are not associated with infection in humans. These include Lagos bat lyssavirus, Shimoni bat lyssavirus, Khujand lyssavirus, Aravan lyssavirus, Bokeloh bat lyssavirus, West Caucasian bat lyssavirus, and Lleida bat lyssavirus. [51] [50] Lagos bat lyssavirus, also known as Lagos bat virus (LBV), has been isolated from a megabat in sub-Saharan Africa. [50] This lyssavirus has four distinct lineages, all of which are found in the straw-colored fruit bat. [58]

Rhabdoviruses from other genera have been identified in bats. This includes several from the genus Ledantevirus: Kern Canyon virus, which was found in the Yuma myotis in California (US) Kolente virus from the Jones's roundleaf bat in Guinea [59] Mount Elgon bat virus from the eloquent horseshoe bat in Kenya Oita virus from the little Japanese horseshoe bat and Fikirini virus from the striped leaf-nosed bat in Kenya. [60]

Orthomyxoviruses Edit

Orthomyxoviruses include influenza viruses. While birds are the primary reservoir for the genus Alphainfluenzavirus, a few bat species in Central and South America have also tested positive for the viruses. These species include the little yellow-shouldered bat and the flat-faced fruit-eating bat. Bat populations tested in Guatemala and Peru had high seropositivity rates, which suggests that influenza A infections are common among bats in the New World. [18]

Paramyxoviruses Edit

Hendra, Nipah, and Menangle viruses Edit

Paramyxoviridae is a family that includes several zoonotic viruses naturally found in bats. Two are in the genus Henipavirus—Hendra virus and Nipah virus. Hendra virus was first identified in 1994 in Hendra, Australia. Four different species of flying fox have tested positive for Hendra virus: the gray-headed flying fox, little red flying fox, spectacled flying fox, and black flying fox. [61] Horses are the intermediate host between flying foxes and humans. Between 1994 and 2014, there were fifty-five outbreaks of Hendra virus in Australia, resulting in the death or euthanization of eighty-eight horses. Seven humans are known to have been infected by Hendra virus, with four fatalities. [16] Six of the seven infected humans were directly exposed to the blood or other fluids of sick or dead horses (three were veterinarians), while the seventh case was a veterinary nurse who had recently irrigated the nasal cavity of a horse not yet exhibiting symptoms. It is unclear how horses become infected with Hendra virus, though it is believed to occur following direct exposure to flying fox fluids. There is also evidence of horse-to-horse transmission. In late 2012, a vaccine was released to prevent infection in horses. [61] Vaccine uptake has been low, with an estimated 11–17% of Australian horses vaccinated by 2017. [62]

The first human outbreak of Nipah virus was in 1998 in Malaysia. [16] It was determined that flying foxes were also the reservoir of the virus, with domestic pigs as the intermediate host between bats and humans. Outbreaks have also occurred in Bangladesh, India, Singapore, and the Philippines. In Bangladesh, the primary mode of transmission of Nipah virus to humans is through the consumption of date palm sap. Pots set out to collect the sap are contaminated with flying fox urine and guano, and the bats also lick the sap streams flowing into the pots. It has been speculated that the virus may also be transmitted to humans by eating fruit partially consumed by flying foxes, or by coming into contact with their urine, though no definitive evidence supports this. [63]

An additional zoonotic paramyxovirus that bats harbor is Menangle virus, which was first identified at a hog farm in New South Wales, Australia. Flying foxes were once again identified as the natural reservoirs of the virus, with the black, spectacled, and gray-headed seropositive for the virus. Two employees of the hog farm became sick with flu-like illnesses, later shown to be a result of the virus. [16] Sosuga pararubulavirus is known to have infected one person—an American wildlife biologist who had conducted bat and rodent research in Uganda. [16] The Egyptian fruit bat later tested positive for the virus, indicating that it is potentially a natural reservoir. [64]

Other Edit

Bats host several paramyxoviruses that are not known to affect humans. Bats are the reservoir of Cedar virus, a paramyxovirus first discovered in flying foxes South East Queensland. [16] The zoonotic potential of Cedar virus is unknown. [65] In Brazil in 1979, Mapuera orthorubulavirus was isolated from the saliva of the little yellow-shouldered bat. Mapuera virus has never been associated with disease in other animals or humans, but experimental exposure of mice to the virus resulted in fatality. [16] Tioman pararubulavirus has been isolated from the urine of the small flying fox, which causes fever in some domestic pigs after exposure, but no other symptoms. Tukoko virus has been detected from Leschenault's rousette in China. [16] Bats have been suggested as the host of Porcine orthorubulavirus, though definitive evidence has not been collected. [16]

Togaviruses Edit

Togaviruses include alphaviruses, which have been detected in bats. Alphaviruses cause encephalitis in humans. Alphaviruses that have been detected in bats include Venezuelan equine encephalitis virus, Eastern equine encephalitis virus, and Western equine encephalitis virus. Sindbis virus has been detected from horseshoe bats and roundleaf bats. Chikungunya virus has been isolated from Leschenault's rousette, the Egyptian fruit bat, Sundevall's roundleaf bat, the little free-tailed bat, and Scotophilus species. [18]

Retroviruses Edit

Bats can be infected with retroviruses, including the gammaretrovirus found in horseshoe bats, Leschenault's rousette, and the greater false vampire bat. Several bat retroviruses have been identified that are similar to the Reticuloendotheliosis virus found in birds. These retroviruses were found in mouse-eared bats, horseshoe bats, and flying foxes. The discovery of varied and distinct gammaretroviruses in bat genomes indicates that bats likely played important roles in their diversification. Bats also host an extensive number of betaretroviruses, including within mouse-eared bats, horseshoe bats, and flying foxes. Bat betaretroviruses span the entire breadth of betaretrovirus diversity, similar to those of rodents, which may indicate that bats and rodents are primary reservoirs of the viruses. Betaretroviruses have infected bats for a majority of bat evolutionary history, since at least 36 million years ago. [66]

Hepadnaviruses Edit

Hepadnaviruses are also known to affect bats, with the tent-making bat, Noack's roundleaf bat, and the halcyon horseshoe bat known to harbor several. The hepadnovirus found in the tent-making bat, which is a New World species, was the closest relative of human hepadnoviruses. [66] Though relatively few hepadnaviruses have been identified in bats, it is highly likely that additional strains will be discovered through further research. As of 2016, they had been found in four bat families: Hipposideridae and Rhinolophidae from the suborder Yinpterochiroptera and Molossidae and Vespertilionidae from Yangochiroptera. The high diversity of bat hosts suggests that bats share a long evolutionary history with hepadnaviruses, indicating bats may have had an important role in hepadnavirus evolution. [67]

Why are pollinating bats, birds, bees, butterflies, and other animals important?

Do you enjoy a hot cup of coffee, a juicy peach, an-apple-a-day, almonds, rich and creamy dates, a handful of plump cashews, or vine-ripened tomatoes? Do you enjoy seeing the native flowers and plants that surround you?

If so, you depend on pollinators.

Wherever flowering plants flourish, pollinating bees, birds, butterflies, bats and other animals are hard at work, providing vital but often-unnoticed services. About three-fourths of all native plants in the world require pollination by an animal, most often an insect, and most often a native bee. Pollinators are also responsible for one in every three bites of food you take, and increase our nation’s crop values each year by more than 15 billion dollars.

Loss of pollinators threatens agricultural production, the maintenance of natural plant communities, and the important services provided by those ecosystems, such as carbon cycling, flood and erosion control, and recreation. Without pollinators providing the transportation of pollen from flower to flower, about 75 percent of all native North American plants could gradually become extinct as they lose the ability to reproduce.

Since bees are so small and accommodating, we can all do our own part by eliminating non-native weeds and shrubs and encouraging wildflowers to grow on our properties. Adding native flowering plants to even the smallest yard can help. The pollen and nectar from only about 5 flowers supports the food needs of a bee from egg to adulthood.


Scope of WNS threat

The estimated geographic extent of where WNS has been confirmed varied over each species’ range, existing over a large part of the range of M. sodalis (93%), M. septentrionalis (79%), and P. subflavus (59%) to about one-third of the range for the more widespread species, M. lucifugus (36%) and E. fuscus (32%) (Fig. 2). The scope of WNS threat was pervasive for M. sodalis and M. septentrionalis, large for P. subflavus and M. lucifugus, and restricted for E. fuscus (Fig. 2 Table 1).

Species Scope of WNS threat (%) Percent severity of WNS threat (95% credible interval) Scope level Severity level Impact of WNS threat
Myotis septentrionalis 79 100 (97, 100) pervasive extreme very high
Myotis lucifugus 36 98 (96, 100) large extreme high
Perimyotis subflavus 59 93 (90, 100) large extreme high
Myotis sodalis 93 28 pervasive moderate medium
Eptesicus fuscus 32 35 (13, 54) restricted serious medium
  • Percent overlap of species and WNS occurrence ranges weighted by proportion of sites with observed declines.
  • Estimate of percent mean declines at hibernacula with WNS establishment 95% credible interval from Eq. 1.
  • Due to extreme skew in colony sizes and variation in declines of M. sodalis, estimates of severity of WNS threat ranged from 84% (95% credible interval 78–100%) based on Eq. 1 to 28% based on mean site-level declines derived from Eq 3. Severity and impact is 28% based on our best understanding of the model fit and data (Appendix S2).

Severity of WNS threat

Declines in winter colonies were most variable among regions and states or provinces during the invasion stage (Fig. 4 & Appendix S2). Generally, estimates at state and provincial jurisdictions had high levels of uncertainty due to low sample size (fewer than ∼5 sites surveyed) or lacked enough sites (at least >1 site surveyed) to estimate declines independently (Fig. 4 Appendices S2 & S3). Regional estimates of declines coalesced toward study-wide averages during the epidemic and established disease stages for most species, but declines were generally least variable and most severe in the northeast and least severe in the southeast (Fig. 4 & Appendix S2).

Changes in species incidence at sites

The proportion of sites where a species occurred in our count record decreased significantly from prearrival to disease establishment for M. septentrionalis, P. subflavus, M. lucifugus, and M. sodalis but not E. fuscus (Appendices S2 & S3). Incidence of M. septentrionalis decreased the most dramatically from 98% (CRI: 96−100%) in the prearrival stage to 21% (CRI: 9–36%) by disease establishment (Appendix S2). Declines in incidence were less dramatic for M. lucifugus, P. subflavus, and M. sodalis, whose incidence at sites decreased from near 100% in prearrival to 92% (CRI: 86−96%), 93% (CRI: 87−97%), and 93% (CRI: 87−97%) by disease establishment, respectively (Appendix S2). Incidence of E. fuscus at sites changed from 98% (CRI: 95−100%) in prearrival to 93% (CRI: 82−98%) by disease establishment, but this decrease was not significant (Appendix S2).

Changes to size classes of observed winter colonies

We found that 90% of the few sites where M. septentrionalis remained by disease establishment had fewer than 10 bats (Fig. 5 & Appendix S2). Where P. subflavus persisted in disease establishment, 63% of sites had fewer than 10 bats and no large colonies (>1000 bats) remained (Fig. 5 & Appendix S2). Distribution of remaining M. lucifugus colony sizes in disease establishment became strongly skewed toward sites with fewer than 10 bats (44%) or fewer than a hundred bats (33%), and only a single very large colony (>10,000 bats) persisted (Fig. 5 & Appendix S2). For M. sodalis, sites with fewer than 10 bats also increased (from 20% prior to Pd arrival to 27% in disease establishment), but the proportion of large colony sizes remained largely unchanged through disease progression (Fig. 5 & Appendix S2). Similarly, for E. fuscus, the proportions of colony size classes did not change by disease establishment (Fig. 5 & Appendix S2).

Suppress, then tolerate

The impressive ability of bats to ward off disease has long been remarked upon. A 1932 scholarly note on fruit bats in Australia states, “No reliable evidence of the occurrence of epidemics among the fruit-bat population was discovered.” And a 1957 paper on the southeastern myotis bat notes that “disease is apparently unimportant. During the course of this study, which involved observations on over a million bats in every known cave colony in Florida, I have never found a dead bat, and have seen only one which appeared diseased.”

Certainly, bats in the United States are in trouble today: The Eurasian fungus behind white nose syndrome has been killing large numbers of many bat species for more than a decade. But with few exceptions — including rabies and the more obscure Tacaribe virus — when bats get infected with viruses they don’t appear to get sick.

“There seems to be no pathology associated with these infections — no clinical signs associated. They can remain in good health and display no discernible signs of disease,” says Raina Plowright, an infectious disease ecologist and wildlife veterinarian at Montana State University in Bozeman who coauthored a new review on bats and viruses.

Infectious disease: Making — and breaking — the animal connection

Betting on bats for genetic treasures

The challenge of conducting clinical research during a pandemic

Building a mouse squad against Covid-19

When a host, whether bat or human, is infected with a disease-causing pathogen, the ensuing interaction is often described as a battle: The host’s immune system pulls out the big guns to fight and eradicate the invader. In immunology parlance, this is known as resistance its end game is destroying the pathogen.

But there’s a growing appreciation of the importance of disease tolerance, a “keep calm and carry on” approach in which the immune system limits collateral damage to the host but doesn’t worry about getting rid of every trace of a pathogen. And several recent studies suggest that this tolerance model captures how bats interact with many of the viruses they carry.

Many details are missing: There are some 1,300 bat species — they are the second largest order of mammals, outnumbered only by rodents — and studies typically focus on one or a handful. But a rough picture is emerging. Research suggests that the bat immune system deals with marauding viral invaders in two key ways: First, the bats mount a speedy but nuanced offensive that stops the virus from multiplying with abandon. Second, and perhaps more important, they dial down the activity of immune foot soldiers that might otherwise cause a massive inflammatory response that would do more damage than the virus itself.

“Bats have a lot of this good immune response — suppressing virus replication — that protects them,” Banerjee says. “And they have very little of the not-so-good immune response, which is inflammation.”

Key players in this two-part bat immune response are interferons, small signaling molecules that got their name because of their talent for interfering with virus replication. They’re a first line of defense for mammals in general: When cells are infected by viruses, they release various interferons as an alarm signal, as do some immune system cells.

But bats seem to go one better. To start with, some species have an outsize number of genes for making interferons: Large flying foxes (Pteropus vampyrus) and little brown bats (Myotis lucifugus) have dozens of genes for making even just one kind, called type 1 interferons the Egyptian fruit bat (Rousettus aegyptiacus), a natural host of Marburg virus, has 46 (humans have about 20).

Fruit-eating Egyptian rousette bats (Rousettus aegyptiacus), roosting here in Python Cave in Uganda, are a natural host for Marburg virus, a relative of Ebola that is often deadly in people. The bats have several immune-system tricks that allow them to tolerate the virus, including ways to prevent inflammation from getting out of control.


Black flying foxes (Pteropus alecto) seem to use another strategy: In this species — as well as the lesser short-nosed fruit bat (Cynopterus brachyotis) — some genes for making interferons are always turned on, even when there’s no viral invader to contend with. In the black flying foxes, these “always on” interferons, among other things, kick-start production of an enzyme that chops up viral genetic material.

Black flying foxes and big brown bats (Eptesicus fuscus) have yet another trick up their wings. They have an extra-strong version of a protein whose job is to flip the “on” switch for some interferon genes. Experiments by Banerjee and colleagues using genetically altered human and bat cells found that in either kind of cell, the bat protein was better than the human version at keeping viral numbers down after exposure to a cousin of the rabies virus.

Bats, in other words, seem to have multiple layers of interferon protection: one that stands at the ready to quickly curtail viral replication, and another, more standard-issue one that ramps up activity after a viral invader has appeared. But it’s not just a blunt one-two punch. The sheer number of interferon genes some bats have hints at a flexible, more nuanced response.

Having many, many copies of a gene presents opportunities, says Thomas Kepler, a computational immunologist at Boston University’s medical school, who’s done much of the Egyptian fruit bat research. Some of the genes can ramp up or down their activity even as other ones keep normal functions going. Rather than all of the interferons sounding the standard “prepare for war” alarm, some may tell cells to hold their fire and sit tight.

The message, Kepler says, may be, “We’ve got a virus, let’s use soft power for as long as we can.”

Watch “Preventing the Next Pandemic: Exploring the Origins and Spread of Animal Viruses,” an online event held on December 16, 2020. Raina Plowright is one of the speakers. Additional resources available here.

Why are there so many species of bats? - Biology

Bats act as reservoirs for over 200 viruses, many of which cause severe, often life-threatening, diseases in humans, livestock and wildlife. Examples include rabies virus, SARS and MERS coronaviruses and Ebola virus. Surprisingly many of these viruses cause asymptomatic infections in bats. In fact it has been postulated that these viral infections may even confer a benefit (as yet unknown) to the bat host. Research into the molecular and cellular biology of the virus-host interaction and studies on the immune systems of the bat hosts are providing new insights into these fascinating viruses and are essential first steps for the development of novel strategies for the prevention of bat-borne zoonotic infections.

In this multi-authored volume, international experts review the current hot-topics in this field. Chapters have extensive reference sections that should encourage readers to pursue each subject in greater detail. The book opens with an introductory chapter that is followed by six chapters (chapters 2-7) reviewing different important families of bat-borne viruses. The following two chapters (chapters 8-9) focus on the bat immune system. Chapters 9-12 cover in vitro isolation, in vivo models and metagenomics for viral discovery in bats. The book closes with a fascinating look at the special ability of bats to act as reservoirs for so many different types of viruses.

This book is an invaluable reference source of timely information for students, virologists, immunologists, medical and veterinary professionals, and scientists working on bat-borne diseases. It is also highly recommended for all university libraries.

"an invaluable reference source . highly recommended " from Southeastern Naturalist (2020) 19: B1

". very valuable. This volume provides a much-needed synthesis . including experimental studies, knowledge gaps and challenges, and guidance for future directions. As a panoramic review of bats and viruses spanning virology, immunology, and its subdisciplines . a mine of useful information and thoughtful synthesis and guidance, made all the more urgent by the COVID-19 pandemic . the book provides good syntheses on bat biology, solid summaries of (some) bat-borne viruses, and careful surveys of a range of methods" from Quarterly Review of Biology

(EAN: 9781912530144 9781912530151 Subjects: [medical microbiology] [molecular microbiology] [virology] )

Alterations in Immune Genes Make Bats Great Viral Hosts

Abby Olena
Oct 27, 2020

ABOVE: Cave nectar bat (Eonycteris spelaea)

B ats act as reservoirs for lots of viruses—including coronaviruses such as those that cause Middle East respiratory syndrome, severe acute respiratory syndrome, and possibly COVID-19—but they don’t often get sick themselves. How they avoid viral illness has been an open question. Researchers reported in PNAS yesterday (October 26) that various species of bats have slightly different ways of suppressing inflammation, all centered on changes in genes responsible for triggering innate immune responses.

The authors demonstrate a number of the mechanisms in bats that seem to support their capacity to tolerate viruses that make other mammals really sick, says Cara Brook, a postdoc at the University of California, Berkeley, who was not involved in the work. “This follows a series of other publications that really highlight a dampened inflammatory response in bats that suggests that they are uniquely resistant and resilient to the consequences of immunopathology . . . and don’t experience the kind of autoimmune disease that we often incur against ourselves.”

In a study published in 2013, Linfa Wang, an immunologist at Duke-NUS Medical School in Singapore, and colleagues compared the genomes of two bat species: the fruit bat (Pteropus alecto) and insectivorous bat (Myotis davidii). They found that both species had lost a gene called AIM2, which in other mammals encodes a protein that senses pathogenic DNA and triggers inflammasomes, protein complexes that activate proinflammatory signals that in turn promote the maturation of cytokines, small signaling proteins that can be released by immune cells and regulate inflammation and immunity.

What’s nice about this paper is that it points to the fact that different species have evolved different mechanisms for achieving the same ends.

In the current study, Wang’s group followed up on AIM2 to figure out what affect its loss has on cellular responses to pathogenic DNA. They compared macrophages, the innate immune system’s primary effector cells, from mice and fruit bats. The mouse cells, which have a functional gene, make the aggregates of AIM2 and its protein binding partner, which together trigger the inflammasome pathway when cells are exposed to double-stranded DNA. None of this occurred in the fruit bat cells. When the researchers added in a copy of the human version of AIM2 to fruit bat kidney cells aggregates still formed, but did not activate other inflammasome-related genes, including those that encode the effector enzyme caspase-1, which activates the proinflammatory cytokine IL-1β.

“We hypothesized that further downstream activation of the inflammasome pathway may be affected in bats and decided to investigate these signaling components in an effort to detect any alteration in their function,” Wang writes in an email to The Scientist.

The researchers determined that the faulty caspase-1 response was due to bat-specific mutations in two sites within the fragment of the enzyme that must be cleaved in order for it to be activated. When they engineered the equivalent human amino acids back into the coding sequence, the bat enzyme worked just as the human protein does. The reverse experiment confirmed these mutations were responsible for the impaired enzyme function. Introducing both bat-specific mutations into the gene for the human protein resulted in a loss of function of human caspase-1.

In contrast, they found, the Myotis genus of bats has functional caspase-1, but these animals’ genomes instead contain mutations in IL-1β that prevent the cytokine’s cleavage and subsequent for cellular secretion. A third species, the cave nectar bat (Eonycteris spelaea) had diminished, though not completely suppressed, function of both caspase-1 and IL-1β, resulting from a handful of mutations.

When people “find something about one species of bats, they assume that every bat species does the same thing, and that’s not true,” says Vikram Misra, a virologist at the University of Saskatchewan who did not participate in the study “What’s nice about this paper is that it points to the fact that different species have evolved different mechanisms for achieving the same ends.”

“It’s very small changes in specific amino acids, where you have one change . . . that can completely change the function of a protein,” Karen Mossman, a virologist at McMaster University who did not participate in the work, tells The Scientist. In the future, it will be “interesting to really understand how all of these subtle changes in these proteins work collectively to give the bats their immune system,” she adds. “It’s so similar to the human immune system the components of the pathways are very similar. And yet, there’re these vast, vast changes and differences in how they respond, say, to a viral infection.”

Although many species of bats don’t seem to get sick from viruses, inflammation in bats does exist, such as when they’re exposed to fungal diseases, Misra says. “Even though inflammation because of the viral infection is dampened, there’ve got to be other pathways that bring out inflammation. That’s something that I think we haven’t, as a group of bat researchers, addressed completely at this point.”

G. Goh et al., “Complementary regulation of caspase-1 and IL-1β reveals additional mechanisms of dampened inflammation in bats,” PNAS, doi:10.1073/pnas.2003352117, 2020.