A bat-borne virus is any virus whose primary reservoir is any species of bat. The viruses species include coronaviruses, hantaviruses, lyssaviruses, lassa virus, Ebola virus and Marburg virus. Bat-borne viruses are among the most important of the emerging viruses.
Bat-borne viruses are transmitted via bat bite and transfer via saliva, as well as aerosolization of salvia, feces, and/or urine. Like rabies virus, newly emerging bat-borne viruses can be transmitted to humans directly by bats. These include Ebola virus, SARS, and the Middle East respiratory syndrome coronavirus.
Left unrecognized and untreated, the interval between transmission of rabies virus strains until the disease manifests in the victims, varies from hours to years. Most victims are not aware of either having been bitten by a bat or exposed to a bat's secretions. This can be due to a lack of awareness of a bat's presence in the same space, such as when sleeping, not feeling the bite if aware of the bat's presence, and/or exposure to bat saliva, urine, and/or feces in closed environments. These include caves and human living spaces such as attics, basements, barns and sheds. Bats invading human living and working spaces will normally offensively attack by biting and urinating on the victim to mark the victim's location.
It is believed that bat behaviours, which include the ability to fly, roosting habits, reproductive cycle, migration, hibernation, produce a natural susceptibility to viruses. In addition, bats are known to have persistent viral infections at a rate higher than other mammals. This is believed to be due to a shorter antibody half-life. 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.
Bats versus rodents as reservoirs
Bats harbor more viruses than rodents and are capable of spreading disease over a wider geographic area owing to their ability to fly and their migration and roosting patterns. In addition, certain species of bat, like the brown bat, favor roosts in attic spaces of human dwellings from which they often invade spaces in other parts of the structure. This brings them into contact with humans. Rodents, on the other hand, are more confined to their geographic location and seek seasonal shelter in underground burrows and in human dwellings and buildings in the immediate area.
The 2009 outbreak of severe acute respiratory syndrome (SARS), and the 2012 outbreak of Middle East respiratory syndrome have been traced to have an origin in bats. Coronaviruses are positive-sense, single-stranded RNA viruses with four genera, Alphacoronaviruses, betacoronaviruses, gammacoronaviruses, and deltacoronaviruses. Of these four, alphacoroanviruses and betacoronaviruses are bat-borne.
Rabies Virus (family Rhabdoviridae, genus Lyssavirus)
Approximately 55,000 human deaths from rabies annually are attributed to twelve known species acquired from bat bites. A rabies-like virus was first described in ancient times, but it was not until the 19th century when Louis Pasteur isolated the virus from rabbit spinal cord. Pasteur also formulated a vaccine for postexposure prophylaxis.
Hantaviruses, usually found in rodents and shrews, were discovered in two species of bats. The Mouyassué virus (MOUV) was isolated from banana pipestrelle bats captured near Mouyassué village in Cote d'Ivoire, West Africa. The Magboi virus was isolated from hairy split-faced bats found near the Magboi River in Sierra Leone in 2011. They are single-stranded, negative sense, RNA viruses in the Bunyaviridae family.
The filoviruses are responsible for fatal hemorrhagic infections in humans and monkeys. These include Marburgviruses (MARV) and Ebolaviruses (EBOV).
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