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The bat virome is the
group of viruses associated with
bats. Bats host a diverse array of viruses, including all seven types described by the
Baltimore classification system
Baltimore classification is a system used to classify viruses based on their manner of messenger RNA (mRNA) synthesis. By organizing viruses based on their manner of mRNA production, it is possible to study viruses that behave similarly as a d ...
: (I)
double-stranded DNA viruses; (II)
single-stranded DNA viruses
A DNA virus is a virus that has a genome made of deoxyribonucleic acid (DNA) that is replicated by a DNA polymerase. They can be divided between those that have two strands of DNA in their genome, called double-stranded DNA (dsDNA) viruses, and ...
; (III)
double-stranded RNA viruses
Double-stranded RNA viruses (dsRNA viruses) are a polyphyletic group of viruses that have double-stranded genomes made of ribonucleic acid. The double-stranded genome is used to transcribe a positive-strand RNA by the viral RNA-dependent RNA ...
; (IV)
positive-sense single-stranded RNA viruses; (V)
negative-sense single-stranded RNA viruses; (VI)
positive-sense single-stranded RNA viruses that replicate through a DNA intermediate; and (VII)
double-stranded DNA viruses that replicate through a single-stranded RNA intermediate. The greatest share of bat-associated viruses identified as of 2020 are of type IV, in the family ''
Coronaviridae
''Coronaviridae'' is a family of enveloped, positive-strand RNA viruses which infect amphibians, birds, and mammals. The group includes the subfamilies '' Letovirinae'' and ''Orthocoronavirinae;'' the members of the latter are known as coronavi ...
''.
Bats harbor several viruses that are
zoonotic
A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...
, or capable of infecting humans, and some bat-borne viruses are considered important
emerging viruses.
These zoonotic viruses include the
rabies virus,
SARS-CoV,
MERS-CoV,
Marburg virus
Marburg virus (MARV) is a hemorrhagic fever virus of the '' Filoviridae'' family of viruses and a member of the species '' Marburg marburgvirus'', genus '' Marburgvirus''. It causes Marburg virus disease in primates, a form of viral hemorrhagi ...
,
Nipah virus, and
Hendra virus
Hendra virus (HeV), scientific name ''Hendra henipavirus'', is a bat-borne virus that is associated with a highly fatal infection in horses and humans. Numerous disease outbreaks in Australia among horses have been caused by Hendra virus. The Hend ...
. While research clearly indicates that
SARS-CoV-2
Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19 (coronavirus disease 2019), the respiratory illness responsible for the ongoing COVID-19 pandemic. The virus previously had a ...
originated in bats,
it is unknown how it was transmitted to humans, or if an intermediate host was involved. It has been speculated that bats may have a role in the
ecology
Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...
of the Ebola virus, though this is unconfirmed. While transmission of rabies from bats to humans usually occurs via biting, most other zoonotic bat viruses are transmitted by direct contact with infected bat fluids like urine,
guano
Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. G ...
, or saliva, or through contact with an infected, non-bat
intermediate host
In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' ( symbiont). The guest is typically provided with nourishment and shelter. Examples include ...
. There is no firm evidence that butchering or consuming
bat meat can lead to viral transmission, though this has been speculated.
Despite the abundance of viruses associated with bats, they rarely become ill from viral infections, and
rabies
Rabies is a viral disease that causes encephalitis in humans and other mammals. Early symptoms can include fever and tingling at the site of exposure. These symptoms are followed by one or more of the following symptoms: nausea, vomiting, ...
is the only viral illness known to kill bats. Much research has been conducted on bat
virology
Virology is the scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, the ...
, particularly bat
immune response
An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, parasites, and fungi which coul ...
. Bats'
immune system
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
s differ from other mammals in their lack of several
inflammasome
Inflammasomes are cytosolic multiprotein oligomers of the innate immune system responsible for the activation of inflammatory responses. Activation and assembly of the inflammasome promotes proteolytic cleavage, maturation and secretion of pro-in ...
s, which activate the body's inflammatory response, as well as a dampened
stimulator of interferon genes
Stimulator of interferon genes (STING), also known as transmembrane protein 173 (TMEM173) and MPYS/MITA/ERIS is a protein that in humans is encoded by the STING1 gene.
STING plays an important role in Innate immune system, innate immunity. STING ...
(STING) response, which helps control host response to pathogens. Preliminary evidence indicates bats are thus more tolerant of infection than other mammals. While much research has centered on bats as a source of zoonotic disease, reviews have found mixed results on whether bats harbor more zoonotic viruses than other groups. A 2015 review found that bats do not harbor more zoonotic viruses than
primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includin ...
s or
rodent
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...
s, though the three groups harbored more than other mammal
orders
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
.
In contrast, a 2020 review found that bats do not have more zoonotic viruses than any other bird or mammal group when viral diversity is measured relative to host diversity, as bats are the second-most diverse order of mammals.
Viral diversity
Viruses have been found in bat populations around the world. Bats harbor all groups of viruses in the
Baltimore classification,
representing at least 28 families of viruses.
Most of the viruses harbored by bats are
RNA virus
An RNA virus is a virusother than a retrovirusthat has ribonucleic acid ( RNA) as its genetic material. The nucleic acid is usually single-stranded RNA (ssRNA) but it may be double-stranded (dsRNA). Notable human diseases caused by RNA virus ...
es, though they are also known to have
DNA virus
A DNA virus is a virus that has a genome made of deoxyribonucleic acid (DNA) that is replicated by a DNA polymerase. They can be divided between those that have two strands of DNA in their genome, called double-stranded DNA (dsDNA) viruses, and ...
es.
Bats are more tolerant of viruses than terrestrial mammals.
A single bat can host several different kinds of viruses without becoming ill.
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. 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
Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the time ...
or hibernate, and their ability to traverse landscapes with daily and seasonal movement.
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.
Various factors have been implicated in bats' ability to survive viral infections. One possibility is bats' use of flight. Flight produces a
fever
Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...
-like response, resulting in elevated temperature (up to ) and metabolic rate. Additionally, this fever-like response may help them cope with actual fevers upon getting a viral infection.
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.
STING is a
signaling molecule
In biology, cell signaling (cell signalling in British English) or cell communication is the ability of a Cell (biology), cell to receive, process, and transmit signals with its environment and with itself. Cell signaling is a fundamental property ...
that helps coordinate various host defense genes against pathogens. 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."
Additionally, bats lack several
inflammasome
Inflammasomes are cytosolic multiprotein oligomers of the innate immune system responsible for the activation of inflammatory responses. Activation and assembly of the inflammasome promotes proteolytic cleavage, maturation and secretion of pro-in ...
s found in other mammals;
other inflammasomes are present with a greatly reduced response. While inflammation is an immune response to viruses, excessive inflammation is damaging to the body, and viruses like
severe acute respiratory syndrome coronavirus
Severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1; or Severe acute respiratory syndrome coronavirus, SARS-CoV) is a strain of coronavirus that causes severe acute respiratory syndrome (SARS), the respiratory illness responsible for ...
(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.
Transmission to humans
The vast majority of bat viruses have no
zoonotic
A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...
potential, meaning they cannot be transmitted to humans.
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.
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 farm
Pig farming or pork farming or hog farming is the raising and breeding of domestic pigs as livestock, and is a branch of animal husbandry. Pigs are farmed principally for food (e.g. pork: bacon, ham, gammon) and skins.
Pigs are amenable to ...
s a source of bat-borne viruses in Malaysia and Australia.
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
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s like
mosquito
Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...
es,
tick
Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living ...
s, and
flea
Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, ...
s 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.
Bats compared to other viral reservoirs
Bats and their viruses may be the subject of more research than viruses found in other mammal
orders
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
, 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
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in ...
viruses and only 1–9 studies for
sloth
Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their l ...
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).
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.
Sampling
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
The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay uses a solid-phase type of enzyme immunoassay (EIA) to detect the presen ...
, which determines whether or not they have the corresponding
antibodies
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of ...
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
Histopathology (compound of three Greek words: ''histos'' "tissue", πάθος ''pathos'' "suffering", and -λογία '' -logia'' "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Sp ...
, 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
Threatened species are any species (including animals, plants and fungi) which are vulnerable to endangerment in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of '' critical depe ...
bat have been killed for viral sampling, including the
Comoro rousette,
Hildegarde's tomb bat,
Natal free-tailed bat, and the
long-fingered bat.
Double-stranded DNA viruses
Adenoviruses
Adenovirus
Adenoviruses (members of the family ''Adenoviridae'') are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from ...
es have been detected in bat guano, urine, and oral and rectal swabs. They have been found in both
megabat
Megabats constitute the family Pteropodidae of the order Chiroptera ( bats). They are also called fruit bats, Old World fruit bats, or—especially the genera ''Acerodon'' and '' Pteropus''— flying foxes. They are the only member of the s ...
s and
microbats across a large geographic area. Bat adenoviruses are closely related to those finds in
canids.
The greatest diversity of bat adenoviruses has been found in Eurasia, though the virus family may be undersampled in bats overall.
Herpesviruses
Diverse
herpesviruses have been found in bats in North and South America, Asia, Africa, and Europe,
including representatives of the three subfamilies,
alpha-,
beta-, and
gammaherpesviruses.
Bat-hosted herpesviruses include the species ''
Pteropodid alphaherpesvirus 1'' and ''
Vespertilionid gammaherpesvirus 1''.
Papillomaviruses
Papillomaviruses were first detected in bats in 2006, in the
Egyptian fruit bat
The Egyptian fruit bat or Egyptian rousette (''Rousettus aegyptiacus'') is a species of megabat that is found in Africa, the Middle East, the Mediterranean, and the Indian subcontinent. It is one of three '' Rousettus'' species with an African-M ...
. They have since been identified in several other bat species, including the
serotine bat
The serotine bat (''Eptesicus serotinus''), also known as the common serotine bat, big brown bat, or silky bat, is a fairly large Eurasian bat with quite large ears. It has a wingspan of around and often hunts in woodland. It sometimes roosts ...
,
greater horseshoe bat, and the
straw-colored fruit bat. Five distinct lineages of bat papillomaviruses have been recognized.
Single-stranded DNA viruses
Anelloviruses
No
anellovirus is known to cause disease in humans.
The first bat anellovirus, a
Torque teno virus
''Alphatorquevirus'' is a genus of viruses in the family ''Anelloviridae'', in group II in the Baltimore classification. It encompasses many species of the virus formerly known as TTV, transfusion transmitted virus, or torque teno virus, SENV, S ...
, was found in a Mexican free-tailed bat. Novel anelloviruses have also been detected in two
leaf-nosed bat species: the
common vampire bat
The common vampire bat (''Desmodus rotundus'') is a small, leaf-nosed bat native to Latin America. It is one of three extant species of vampire bat, the other two being the hairy-legged and the white-winged vampire bats. 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''.
Circoviruses
Circovirus
''Circovirus'' is a genus of viruses, in the family '' Circoviridae''. Birds (such as pigeons and ducks) and pigs serve as natural hosts, though dogs have been shown to be infected as well. It is a single stranded DNA virus (ssDNA). There are 49 ...
es, family ''Circoviridae'', are among the most diverse of all viruses.
Like anelloviruses, circoviruses are not associated with any disease in humans.
About a third of all circoviruses are associated with bats, found in North and South America, Europe, and Asia.
A study of
horseshoe
A horseshoe is a fabricated product designed to protect a horse hoof from wear. Shoes are attached on the palmar surface (ground side) of the hooves, usually nailed through the insensitive hoof wall that is anatomically akin to the human ...
and
vesper bats in China identified circoviruses from the genera ''
Circovirus
''Circovirus'' is a genus of viruses, in the family '' Circoviridae''. Birds (such as pigeons and ducks) and pigs serve as natural hosts, though dogs have been shown to be infected as well. It is a single stranded DNA virus (ssDNA). There are 49 ...
'' and ''
Cyclovirus''.
Parvoviruses
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
''Protoparvovirus'' is a genus of viruses in the '' Parvovirinae'' subfamily of the virus family '' Parvoviridae''. Vertebrates serve as natural hosts. There are 15 species in the genus including '' Rodent protoparvovirus 1'' for which the exem ...
'', ''
Erythrovirus'', and ''
Bocaparvovirus
''Bocaparvovirus'' is a genus of viruses in the subfamily ''Parvovirinae'' of the virus family ''Parvoviridae''. Humans, cattle, and dogs serve as natural hosts. There are 28 species in this genus. Diseases associated with this genus include, in ...
''.
Double-stranded RNA viruses
Reoviruses
Zoonotic
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.
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.
Other
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
''Nelson Bay orthoreovirus'', often called Nelson Bay virus (NBV) is a novel double-stranded RNA orthoreovirus species first isolated from a flying fox (Pteropus poliocephalus) near Nelson Bay in New South Wales, Australia.Gard G, Compans RW. Stru ...
'', 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
)
, nickname =
, image_map = New South Wales in Australia.svg
, map_caption = Location of New South Wales in AustraliaCoordinates:
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, es ...
, 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
Pulau may refer to:
* Pulau virus (PuV), a novel strain of Nelson Bay orthoreovirus species
* Pulau River, a river of West Papua and Papua New Guinea
See also
*List of islands of Malaysia
A ''list'' is any set of items in a row. List or lists ...
, which was first identified from the
small flying fox
The small flying fox, island flying fox or variable flying fox (''Pteropus hypomelanus'') is a species of flying fox in the family Pteropodidae. It is found in Australia, Cambodia, Indonesia, Malaysia, the Maldives, Myanmar, Papua New Guinea, t ...
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
Guangdong (, ), alternatively romanized as Canton or Kwangtung, is a coastal province in South China on the north shore of the South China Sea. The capital of the province is Guangzhou. With a population of 126.01 million (as of 2020 ...
, China; and
Cangyuan virus also from Leschenault's rousette.
Several
mammalian orthoreovirus
''Mammalian orthoreovirus'' (MRV) is a double-stranded RNA virus. It is a part of the family ''Reoviridae'', as well as the subfamily '' Spinareovirinae''. As seen in the name, the Mammalian Ortheoreovirus infects numerous mammalian species and ...
es are associated with bats, including at least three from Germany and 19 from Italy. These were found in
pipistrelles, the
brown long-eared bat
The brown long-eared bat or common long-eared bat (''Plecotus auritus'') is a small Eurasian insectivorous bat. It has distinctive ears, long and with a distinctive fold. It is extremely similar to the much rarer grey long-eared bat which was o ...
, and the
whiskered bat
The whiskered bat (''Myotis mystacinus'') is a small European bat with long fur. Although uncommon, ''M. mystacinus'' is often found around human habitation and around water; it is similar to Brandt's bat (''Myotis brandtii''), from which it ...
.
Orbivirus
''Orbivirus'' is a genus of double-stranded RNA viruses in the family ''Reoviridae'' and subfamily '' Sedoreovirinae''. Unlike other reoviruses, orbiviruses are arboviruses. They can infect and replicate within a wide range of arthropod and ver ...
es 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.
Positive-sense single-stranded RNA viruses
Astroviruses
Astroviruses have been found in several genera of bat in the
Old World
The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by thei ...
, including ''
Miniopterus'', ''
Myotis'', ''
Hipposideros
''Hipposideros'' is one of the most diverse genera of bats, with more than 70 species. They are collectively called roundleaf bats after the shape of their nasal ornament. It is the type genus of the family Hipposideridae. It is divided into s ...
'', ''
Rhinolophus'', ''Pipistrellus'', ''
Scotophilus
''Scotophilus'' is a genus of vesper bat, vespertilionid bats commonly called yellow bats. They are found in southern Asia and Africa. They are the only members of the Tribe (biology), tribe Scotophilini.
Species
* East African yellow bat, ' ...
'', and ''
Taphozous'',
though none in Africa.
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.
Caliciviruses
Bat
caliciviruses were first identified in
Hong Kong
Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (abbr. Hong Kong SAR or HKSAR), is a List of cities in China, city and Special administrative regions of China, special ...
in the
Pomona roundleaf bat
The Pomona roundleaf bat, Pomona leaf-nosed bat, or Andersen's leaf-nosed bat (''Hipposideros pomona'') is a species of bat in the family Hipposideridae that is endemic to India.
Taxonomy
It was described as a new species in 1918 by Danish mam ...
,
and were later identified from
tricolored bat
The tricolored bat (''Perimyotis subflavus'') is a species of microbat native to eastern North America. Formerly known as the eastern pipistrelle, based on the incorrect belief that it was closely related to European ''Pipistrellus'' species, t ...
s in the US state of Maryland. Bat caliciviruses are similar to the genera ''
Sapovirus'' and ''
Valovirus'', with
norovirus
Norovirus, sometimes referred to as the winter vomiting disease, is the most common cause of gastroenteritis. Infection is characterized by non-bloody diarrhea, vomiting, and stomach pain. Fever or headaches may also occur. Symptoms usually devel ...
es also detected from two microbat species in China.
Coronaviruses
SARS-CoV, SARS-CoV-2, and MERS-CoV
![MERS-CoV electron micrograph1](https://upload.wikimedia.org/wikipedia/commons/8/87/MERS-CoV_electron_micrograph1.jpg)
Several zoonotic coronaviruses are associated with bats, including severe acute respiratory syndrome coronavirus (SARS-CoV) and ''
Middle East respiratory syndrome-related coronavirus'' (MERS-CoV).
Severe acute respiratory syndrome coronavirus 2
Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19 (coronavirus disease 2019), the respiratory illness responsible for the ongoing COVID-19 pandemic. The virus previously had a ...
is another zoonotic coronavirus likely originating in bats. SARS-CoV causes the disease
severe acute respiratory syndrome
Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''sev ...
(SARS) in humans. The first documented case of SARS was in November 2002 in
Foshan
Foshan (, ), alternately romanized as Fatshan, is a prefecture-level city in central Guangdong Province, China. The entire prefecture covers and had a population of 9,498,863 as of the 2020 census. The city is part of the western side of the ...
, China.
It became an
epidemic
An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of patients among a given population within an area in a short period of time.
Epidemics of infectious ...
, affecting 28 countries around the world with 8,096 cases and 774 deaths.
The natural reservoir of SARS-CoV was identified as bats, with the
Chinese rufous horseshoe bat
The Chinese rufous horseshoe bat (''Rhinolophus sinicus'') is a species of bat in the family Rhinolophidae. It is found in Bhutan, China, India, Nepal, and Vietnam.
The species is most easily confused with '' R. affinis'', from which it is bes ...
considered a particularly strong candidate after a coronavirus was recovered from a colony that had 95% nucleotide sequence similarity to SARS-CoV.
There is uncertainty on whether or not animals like
palm civets and
raccoon dog
The common raccoon dog (''Nyctereutes procyonoides''), also called the Chinese or Asian raccoon dog, is a small, heavy-set, fox-like canid native to East Asia. Named for its raccoon-like face markings, it is most closely related to foxes. Common ...
s were intermediate hosts that facilitated the spread of the virus from bats to humans, or if humans acquired the virus directly from bats.
The first human case of
Middle East respiratory syndrome (MERS) was in June 2012 in
Jeddah
Jeddah ( ), also spelled Jedda, Jiddah or Jidda ( ; ar, , Jidda, ), is a city in the Hejaz region of the Kingdom of Saudi Arabia (KSA) and the country's commercial center. Established in the 6th century BC as a fishing village, Jeddah's pro ...
, Saudi Arabia.
As of November 2019, 2,494 cases of MERS have been reported in twenty-seven countries, resulting in 858 fatalities. It is believed that MERS-CoV originated in bats, though
camel
A camel (from: la, camelus and grc-gre, κάμηλος (''kamēlos'') from Hebrew or Phoenician: גָמָל ''gāmāl''.) is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. ...
s are likely the intermediate host through which humans became infected. Human-to-human transmission is possible, though does not easily occur.
The
SARS-CoV-2
Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19 (coronavirus disease 2019), the respiratory illness responsible for the ongoing COVID-19 pandemic. The virus previously had a ...
outbreak in humans started in
Wuhan
Wuhan (, ; ; ) is the capital of Hubei Province in the People's Republic of China. It is the largest city in Hubei and the most populous city in Central China, with a population of over eleven million, the ninth-most populous Chinese city a ...
, China in 2019. 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
The intermediate horseshoe bat (''Rhinolophus affinis'') is a bat species of the family Rhinolophidae (“nose crest”) that is very widespread throughout much of the Indian subcontinent, southern and central China and Southeast Asia. It is li ...
. 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.
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.
Other
Bats harbor a great diversity of
coronavirus
Coronaviruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the co ...
es, with sampling by the
EcoHealth Alliance in China alone identifying about 400 new strains of coronavirus. A study of coronavirus diversity harbored by bats in eastern Thailand revealed forty-seven coronaviruses.
Flaviviruses
![West Nile Virus Image](https://upload.wikimedia.org/wikipedia/commons/1/1e/West_Nile_Virus_Image.jpg)
Most
flaviviruses are transmitted via arthropods, but bats may play a role in the ecology of some species. Several strains of ''
Dengue virus
''Dengue virus'' (DENV) is the cause of dengue fever. It is a mosquito-borne, single positive-stranded RNA virus of the family '' Flaviviridae''; genus '' Flavivirus''. Four serotypes of the virus have been found, a reported fifth has yet to ...
'' have been found in bats in the Americas, and ''
West Nile virus
West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family '' Flaviviridae'', from the genus '' Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The v ...
'' 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
The Yucatán Peninsula (, also , ; es, Península de Yucatán ) is a large peninsula in southeastern Mexico and adjacent portions of Belize and Guatemala. The peninsula extends towards the northeast, separating the Gulf of Mexico to the north ...
. ''
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.
Picornaviruses
Several genera of
picornavirus
Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are viruses that represent a large family of small, positive-sense, single-stranded RNA viruses with a 30 nm ...
es have been found in bats, including ''
Kobuvirus
''Kobuvirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae''. Humans and cattle serve as natural hosts. There are six species in this genus. Diseases associated with this genus include: gastroenteritis. ...
'', ''
Sapelovirus
''Sapelovirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae
Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are virus ...
'', ''
Cardiovirus
Cardiovirus are a group of viruses within order ''Picornavirales'', family ''Picornaviridae''. Vertebrates serve as natural hosts for these viruses.
Taxonomy
There are currently six species in the genus:
* '' Cardiovirus A''
* '' Cardiovirus B' ...
'', and ''
Senecavirus
''Senecavirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae''. Pig and maybe also cow serve as natural hosts. There is only one species in this genus: ''Senecavirus A''. ''Senecavirus'' is a replication-c ...
''.
Picornaviruses have been identified from a diverse array of bat species around the world.
Negative-sense single-stranded RNA viruses
Arenaviruses
Arenavirus
An arenavirus is a bisegmented ambisense RNA virus that is a member of the family ''Arenaviridae''. These viruses infect rodents and occasionally humans. A class of novel, highly divergent arenaviruses, properly known as reptarenaviruses, have ...
es are mainly associated with
rodent
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...
s, 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
The little yellow-shouldered bat (''Sturnira lilium'') is a bat species from South and Central America. It is a frugivore
A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, sho ...
, 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.
Hantaviruses
Hantaviruses
''Orthohantavirus'' is a genus of single-stranded, enveloped, negative-sense RNA viruses in the family '' Hantaviridae'' within the order ''Bunyavirales''. Members of this genus may be called orthohantaviruses or simply hantaviruses.
Orthohantav ...
, 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.
Mouyassue virus has been identified from the
banana pipistrelle in
Ivory Coast
Ivory Coast, also known as Côte d'Ivoire, officially the Republic of Côte d'Ivoire, is a country on the southern coast of West Africa. Its capital is Yamoussoukro, in the centre of the country, while its largest city and economic centre i ...
and the
Cape serotine in Ethiopia;
Magboi virus from the
hairy slit-faced bat
The hairy slit-faced bat (''Nycteris hispida'') is a species of slit-faced bat widely distributed throughout forests and savanna
A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) ecosystem characterised by the trees ...
in
Sierra Leone
Sierra Leone,)]. officially the Republic of Sierra Leone, is a country on the southwest coast of West Africa. It is bordered by Liberia to the southeast and Guinea surrounds the northern half of the nation. Covering a total area of , Sierr ...
;
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;
Makokou virus
Makokou is the regional capital of the Ogooué-Ivindo province in Gabon. Its coordinates are . Its altitude is 308 m. Its population in 2004 is around 16,600.
The city lies on the Ivindo River and the N4 road. It grew around iron ore min ...
from
Noack's roundleaf bat in Gabon;
Đakrông virus from
Stoliczka's trident bat in Vietnam;
''
Brno loanvirus'' from the
common noctule
The common noctule (''Nyctalus noctula'') is a species of insectivorous bat common throughout Europe, Asia, and North Africa.
Description
The common noctule's short fur is dark brown after moulting in June (males) or July/August (females); late ...
in the Czech Republic;
and ''
Laibin mobatvirus'' from the
black-bearded tomb bat in China. As of 2019, only ''
Quezon mobatvirus'' has been identified from a megabat, as it was identified from a
Geoffroy's rousette in the Philippines.
Bat hantaviruses are not associated with illness in humans.
Filoviruses
''Marburgvirus'' and ''Ebolavirus''
![Skraidantis egipto šuo (cropped)](https://upload.wikimedia.org/wikipedia/commons/4/4c/Skraidantis_egipto_%C5%A1uo_%28cropped%29.jpg)
''
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
Ebola, also known as Ebola virus disease (EVD) and Ebola hemorrhagic fever (EHF), is a viral hemorrhagic fever in humans and other primates, caused by ebolaviruses. Symptoms typically start anywhere between two days and three weeks after becom ...
, respectively. Though relatively few disease outbreaks are caused by filoviruses, they are of high concern due to their extreme
virulence
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...
, 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.
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
South Sudan (; din, Paguot Thudän), officially the Republic of South Sudan ( din, Paankɔc Cuëny Thudän), is a landlocked country in East Africa. It is bordered by Ethiopia, Sudan, Central African Republic, Democratic Republic of th ...
and
Democratic Republic of the Congo
The Democratic Republic of the Congo (french: République démocratique du Congo (RDC), colloquially "La RDC" ), informally Congo-Kinshasa, DR Congo, the DRC, the DROC, or the Congo, and formerly and also colloquially Zaire, is a country in ...
.
The natural reservoirs of ebolaviruses are unknown.
However, some evidence indicates that megabats may be natural reservoirs.
Several megabat species have tested
seropositive for
antibodies
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of ...
against ebolaviruses, including the
hammer-headed bat,
Franquet's epauletted fruit bat, and
little collared fruit bat
The little collared fruit bat (''Myonycteris torquata'') is a species of megabat in the family Pteropodidae found in Angola, Cameroon, the Central African Republic, the Republic of the Congo, the Democratic Republic of the Congo, Ivory Coast, Eq ...
.
Other possible reservoirs include non-human
primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includin ...
s,
rodents, shrews, carnivores, and ungulates. 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.
Marburg virus disease (MVD) was first identified in 1967 during simultaneous outbreaks in
Marburg
Marburg ( or ) is a university town in the German federal state (''Bundesland'') of Hesse, capital of the Marburg-Biedenkopf district (''Landkreis''). The town area spreads along the valley of the river Lahn and has a population of approximat ...
and
Frankfurt
Frankfurt, officially Frankfurt am Main (; Hessian: , " Frank ford on the Main"), is the most populous city in the German state of Hesse. Its 791,000 inhabitants as of 2022 make it the fifth-most populous city in Germany. Located on it ...
in Germany, and
Belgrade, Serbia
Belgrade ( , ;, ; names in other languages) is the capital and largest city in Serbia. It is located at the confluence of the Sava and Danube rivers and the crossroads of the Pannonian Plain and the Balkan Peninsula. Nearly 1,166,763 mill ...
. MVD is highly virulent, with an average human mortality rate of 50%, but as high as 88% for individual outbreaks.
MVD is caused by
Marburg virus
Marburg virus (MARV) is a hemorrhagic fever virus of the '' Filoviridae'' family of viruses and a member of the species '' Marburg marburgvirus'', genus '' Marburgvirus''. It causes Marburg virus disease in primates, a form of viral hemorrhagi ...
and the closely related
Ravn virus, which was formerly considered synonymous with Marburg virus. Marburg virus was first detected in the
Egyptian fruit bat
The Egyptian fruit bat or Egyptian rousette (''Rousettus aegyptiacus'') is a species of megabat that is found in Africa, the Middle East, the Mediterranean, and the Indian subcontinent. It is one of three '' Rousettus'' species with an African-M ...
in 2007,
which is now recognized as the natural reservoir of the virus.
Marburg virus has been detected in Egyptian fruit bats in Gabon, Democratic Republic of the Congo, Kenya, and Uganda.
Spillover from Egyptian fruit bats occurs when humans spend prolonged time in mines or caves inhabited by the bats,
though the exact mechanism of transmission is unclear.
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.
Other
Lloviu virus, a kind of filovirus in the genus ''
Cuevavirus
The species ''Lloviu cuevavirus'' ( ) is the taxonomic home of a virus that forms filamentous virion, ''Lloviu virus'' (LLOV). The species is included in the genus '' Cuevavirus''. LLOV is a distant relative of the commonly known Ebola virus a ...
'', has been identified from the
common bent-wing bat
The common bent-wing bat (''Miniopterus schreibersii''), also known as the Schreibers's long-fingered bat or Schreibers's bat, is a species of insectivorous bat. They appear to have dispersed from a subtropical origin and distributed throughout ...
in Spain.
Another filovirus, ''
Bombali ebolavirus'', has been isolated from
free-tailed bat
The Molossidae, or free-tailed bats, are a family of bats within the order Chiroptera.
The Molossidae is the fourth-largest family of bats, containing about 110 species as of 2012. They are generally quite robust, and consist of many strong-flyi ...
s, including the
little free-tailed bat
The little free-tailed bat (''Chaerephon pumilus'') is a species of the genus ''Chaerephon'' in the family Molossidae. It is widely distributed across Africa and islands around the continent.
Description
The little free-tailed bat is one of t ...
and the
Angolan free-tailed bat
The Angolan free-tailed bat (''Mops condylurus'') is a species of bat in the family Molossidae. It is found in Angola, Benin, Botswana, Burkina Faso, Burundi, Cameroon, the Republic of the Congo, the Democratic Republic of the Congo, Ivory Coa ...
.
Neither Lloviu virus nor ''Bombali ebolavirus'' is associated with illness in humans.
Genomic RNA associated with ''
Mengla dianlovirus'', though not the virus itself, has been identified from ''
Rousettus'' bats in China.
Rhabdoviruses
Rabies-causing viruses
Lyssaviruses (from the genus ''Lyssavirus'' in the family ''
Rhabdoviridae
''Rhabdoviridae'' is a family of negative-strand RNA viruses in the order '' Mononegavirales''. Vertebrates (including mammals and humans), invertebrates, plants, fungi and protozoans serve as natural hosts. Diseases associated with member ...
'') 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.
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.
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.
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 bat
Vampire bats, species of the subfamily Desmodontinae, are leaf-nosed bats found in Central and South America. Their food source is blood of other animals, a dietary trait called hematophagy. Three extant bat species feed solely on blood: the ...
s 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. 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%.
Sick bats are more likely to be submitted for rabies testing than apparently healthy bats, known as sampling bias, with most studies reporting rabies incidence of 5–20% in sick or dead bats.
Rabies virus exposure can be fatal in bats, though it is likely that the majority of individuals do not develop the disease after exposure.
In non-bat mammals, exposure to the rabies virus almost always leads to death.
![Wound from canine teeth of Eptesicus fuscus](https://upload.wikimedia.org/wikipedia/commons/b/be/Wound_from_canine_teeth_of_Eptesicus_fuscus.jpg)
Globally, dogs are by far the most common source of human rabies deaths. Bats are the most common source of rabies in humans in North and South America, Western Europe, and Australia.
Many
feeding guilds of bats may transmit rabies to humans, including insectivorous, frugivorous, nectarivorous, omnivorous, sanguivorous, and carnivorous species.
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. Between 1993 and 2002, the majority of human rabies cases associated with bats in the Americas were the result of non-vampire bats.
In North America, about half of human rabies instances are
cryptic
Cryptic may refer to:
In science:
* Cryptic species complex, a group of species that are very difficult to distinguish from one another
* Crypsis, the ability of animals to blend in to avoid observation
* Cryptic era, earliest period of the Earth ...
, meaning that the patient has no known bite history.
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".
It is instead generally thought that most instances of cryptic rabies are the result of an unknown bat bite.
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
A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...
or a break in the skin.
Other
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''.
''Lagos bat lyssavirus'', also known as Lagos bat virus (LBV), has been isolated from a megabat in sub-Saharan Africa.
This lyssavirus has four distinct lineages, all of which are found in the straw-colored fruit bat.
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
The Yuma myotis (''Myotis yumanensis'') is a species of vesper bat native to western North America.
Description
The Yuma myotis is a relatively small myotis, measuring in head-body length, with an average wingspan of and a weight of about . T ...
in California (US);
Kolente virus from the
Jones's roundleaf bat
Jones's roundleaf bat (''Hipposideros jonesi'') is a species of bat in the family Hipposideridae. It is endemic to southern West Africa. Its natural habitats are subtropical or tropical dry forest, savanna, subtropical or tropical dry lowland gr ...
in Guinea;
Mount Elgon bat virus from the
eloquent horseshoe bat in Kenya;
Oita virus from the
little Japanese horseshoe bat
The little Japanese horseshoe bat (''Rhinolophus cornutus'') is a species of bat
Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mamm ...
; and
Fikirini virus from the
striped leaf-nosed bat
The striped leaf-nosed bat (''Macronycteris vittatus'') is a species of bat native to eastern and southern Africa. It was formerly considered part of '' M. commersoni'', which is now viewed as being restricted to Madagascar. Both ''commersoni'' an ...
in Kenya.
Orthomyxoviruses
Orthomyxoviruses include
influenza
Influenza, commonly known as "the flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptom ...
viruses. While birds are the primary reservoir for the genus ''
Alphainfluenzavirus
'' A virus'' (''IAV'') causes influenza in birds and some mammals, and is the only species of the genus ''Alphainfluenzavirus'' of the virus family '' Orthomyxoviridae''. Strains of all subtypes of influenza A virus have been isolated from w ...
'', 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.
Paramyxoviruses
Hendra, Nipah, and Menangle viruses
![Date Palm Sap Collection - Taki - North 24 Parganas 2015-01-13 4731](https://upload.wikimedia.org/wikipedia/commons/c/c8/Date_Palm_Sap_Collection_-_Taki_-_North_24_Parganas_2015-01-13_4731.JPG)
''
Paramyxoviridae'' is a family that includes several zoonotic viruses naturally found in bats. Two are in the genus ''
Henipavirus''—
Hendra virus
Hendra virus (HeV), scientific name ''Hendra henipavirus'', is a bat-borne virus that is associated with a highly fatal infection in horses and humans. Numerous disease outbreaks in Australia among horses have been caused by Hendra virus. The Hend ...
and
Nipah virus. Hendra virus was first identified in 1994 in
Hendra, Australia. Four different species of
flying fox
''Pteropus'' (suborder Yinpterochiroptera) is a genus of megabats which are among the largest bats in the world. They are commonly known as fruit bats or flying foxes, among other colloquial names.
They live in South Asia, Southeast Asia, Aust ...
have tested positive for Hendra virus: the gray-headed flying fox, little red flying fox,
spectacled flying fox
The spectacled flying fox (''Pteropus conspicillatus''), also known as the spectacled fruit bat, is a megabat that lives in Australia's north-eastern regions of Queensland. It is also found in New Guinea and on the offshore islands including Wood ...
, and
black flying fox
The black flying fox or black fruit bat (''Pteropus alecto'') is a bat in the family Pteropodidae. It is among the largest bats in the world, but is considerably smaller than the largest species in its genus, ''Pteropus''. The black flying fox ...
.
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.
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
A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified. was released to prevent infection in horses.
Vaccine uptake has been low, with an estimated 11–17% of Australian horses vaccinated by 2017.
The first human outbreak of Nipah virus was in 1998 in Malaysia.
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.
An additional zoonotic paramyxovirus that bats harbor is
Menangle virus
''Menangle pararubulavirus'', also called Menangle virus, is a virus that infects pigs, humans and bats.
History
Menangle virus was first identified in 1997 after a piggery in Menangle near Sydney, NSW, Australia experienced a high number o ...
, which was first identified at a hog farm in
New South Wales
)
, nickname =
, image_map = New South Wales in Australia.svg
, map_caption = Location of New South Wales in AustraliaCoordinates:
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, es ...
, 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.
''
Sosuga pararubulavirus
''Sosuga pararubulavirus'' is a species of Paramyxovirus which is transmissible to humans. The Egyptian fruit bat is thought to be a natural reservoir species for the virus.
History
In August 2012, following a six-week field trip to South Sud ...
'' is known to have infected one person—an American wildlife biologist who had conducted bat and rodent research in Uganda.
The
Egyptian fruit bat
The Egyptian fruit bat or Egyptian rousette (''Rousettus aegyptiacus'') is a species of megabat that is found in Africa, the Middle East, the Mediterranean, and the Indian subcontinent. It is one of three '' Rousettus'' species with an African-M ...
later tested positive for the virus, indicating that it is potentially a natural reservoir.
Other
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
South East Queensland (SEQ) is a bio-geographical, metropolitan, political and administrative region of the state of Queensland in Australia, with a population of approximately 3.8 million people out of the state's population of 5.1 million. Th ...
.
The zoonotic potential of Cedar virus is unknown. 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.
''
Tioman pararubulavirus
Tioman Island ( ms, Pulau Tioman) is a mukim and an island in Rompin District, Pahang, Malaysia. It is located off the east coast of the state, and is some long and wide. It has seven villages, the largest and most populous being Kampung Tek ...
'' 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.
Bats have been suggested as the host of ''
Porcine orthorubulavirus'', though definitive evidence has not been collected.
Togaviruses
Togavirus
''Alphavirus'' is a genus of RNA viruses, the sole genus in the ''Togaviridae'' family. Alphaviruses belong to group IV of the Baltimore classification of viruses, with a positive-sense, single-stranded RNA genome. There are 32 alphaviruses, ...
es include
alphavirus
''Alphavirus'' is a genus of RNA viruses, the sole genus in the ''Togaviridae'' family. Alphaviruses belong to group IV of the Baltimore classification of viruses, with a positive-sense, single-stranded RNA genome. There are 32 alphaviruses ...
es, which have been detected in bats. Alphaviruses cause
encephalitis in humans. Alphaviruses that have been detected in bats include ''
Venezuelan equine encephalitis virus
Venezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis (VEE). VEE can affect all equine species, such as horses, donkeys, and zebras. After infection, equines m ...
'', ''
Eastern equine encephalitis virus'', and ''
Western equine encephalitis virus
The Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease ''Western equine encephalomyelitis'' (WEE). An alphavirus of the family '' Togaviridae'', the WEE virus is an arbovirus (arthropod-borne vir ...
''. ''
Sindbis virus
''Sindbis virus'' (SINV) is a member of the ''Togaviridae'' family, in the ''Alphavirus'' genus. The virus was first isolated in 1952 in Cairo, Egypt. The virus is transmitted by mosquitoes (''Culex'' and Culiseta). SINV is linked to Pogosta di ...
'' has been detected from horseshoe bats and
roundleaf bats. ''
Chikungunya virus
Chikungunya is an infection caused by the ''Chikungunya virus'' (CHIKV). Symptoms include fever and joint pains. These typically occur two to twelve days after exposure. Other symptoms may include headache, muscle pain, joint swelling, and a ra ...
'' has been isolated from Leschenault's rousette, the Egyptian fruit bat,
Sundevall's roundleaf bat, the little free-tailed bat, and ''Scotophilus'' species.
Positive-sense single-stranded RNA viruses that replicate through a DNA intermediate
Retroviruses
Bats can be infected with
retroviruses, including the
gammaretrovirus found in horseshoe bats, Leschenault's rousette, and the
greater false vampire bat
The greater false vampire bat (''Lyroderma lyra'') is a species of bat in the family Megadermatidae, the false vampire bats. It is native to Asia. It is also known as the Indian false vampire bat or greater false-vampire
Description
This speci ...
. Several bat retroviruses have been identified that are similar to the ''
Reticuloendotheliosis virus
Reticuloendotheliosis (RE) designates a group of pathologic syndromes caused by the reticuloendotheliosis virus (REV) group of avian retroviruses. The disease syndromes associated with REV include 1) a runting disease syndrome, 2) chronic neoplas ...
'' found in birds. These retroviruses were found in
mouse-eared bat
The mouse-eared bats or myotises are a diverse and widespread genus (''Myotis'') of bats within the family Vespertilionidae. The noun "''myotis''" itself is a New Latin construction, from the Greek "''muós'' (meaning "mouse") and "''oûs''" (mea ...
s, 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.
Double-stranded DNA viruses that replicate through a single-stranded RNA intermediate
Hepadnaviruses
Hepadnaviruses are also known to affect bats, with the
tent-making bat
The tent-making bat (''Uroderma bilobatum'') is an American leaf-nosed bat (Phyllostomidae) found in lowland forests of Central and South America. This medium-sized bat has a gray coat with a pale white stripe running down the middle of the back. ...
, Noack's roundleaf bat, and the
halcyon horseshoe bat known to harbor several. The hepadnavirus found in the tent-making bat, which is a New World species, was the closest relative of human hepadnoviruses.
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
The Hipposideridae are a family of bats commonly known as the Old World leaf-nosed bats. While it has often been seen as a subfamily, Hipposiderinae, of the family Rhinolophidae, it is now more generally classified as its own family.Simmons, 20 ...
and
Rhinolophidae from the suborder
Yinpterochiroptera
The Yinpterochiroptera (or Pteropodiformes) is a suborder of the Chiroptera, which includes taxa formerly known as megabats and five of the microbat families: Rhinopomatidae, Rhinolophidae, Hipposideridae, Craseonycteridae, and Megadermatid ...
and
Molossidae and
Vespertilionidae
Vespertilionidae is a family of microbats, of the order Chiroptera, flying, insect-eating mammals variously described as the common, vesper, or simple nosed bats. The vespertilionid family is the most diverse and widely distributed of bat famili ...
from
Yangochiroptera
Yangochiroptera, or Vespertilioniformes, is a suborder of Chiroptera that includes most of the microbat families, except the Rhinopomatidae, Rhinolophidae, Hipposideridae, and Megadermatidae. These other families, plus the megabats, are seen ...
. 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.
See also
*
Histoplasmosis
Histoplasmosis is a fungal infection caused by '' Histoplasma capsulatum''. Symptoms of this infection vary greatly, but the disease affects primarily the lungs. Occasionally, other organs are affected; called disseminated histoplasmosis, it can ...
*
Human virome
The human virome is the total collection of viruses in and on the human body. Viruses in the human body may infect both human cells and other microbes such as bacteria (as with bacteriophages). Some viruses cause disease, while others may be asy ...
References
{{Baltimore classification
Coronaviridae
Hantaviridae
Hemorrhagic fevers