Date Published: August 9, 2018
Publisher: Public Library of Science
Author(s): Léa Joffrin, Muriel Dietrich, Patrick Mavingui, Camille Lebarbenchon, Rebecca Ellis Dutch.
Although bat bites may be the main transmission route coming to mind, pathogen transmission involving bat bites has been documented mostly for rabies virus (Rhabdoviridae). The common vampire bat (Desmodus rotundus) can, for instance, naturally transmit rabies to other species when biting to feed on blood, particularly to livestock and sometimes to humans . Mycoplasma has also been detected in common vampire bat blood and saliva and might be transmitted between bats, for instance, during aggressive behaviors . Obligate blood-feeding bats are, however, restricted to Central and South America and represent only a very small proportion of the bat species diversity (<0.005%; 3/1,200). Most bat species do not naturally bite humans unless intentional contacts occur (e.g., veterinarian and field biologists involved in bat capture and handling, people trying to remove bats from houses). Infection of wild animals such as apes, monkeys, and antelopes with bat-borne infectious agents may also play a role in the transmission chain to humans, such as for Ebola virus . In the case of the severe acute respiratory syndrome (SARS) coronavirus, civets (Paguma larvata) got infected with a virus circulating in horseshoe bats (Rhinolophus sp.) and would have then acted as an intermediate amplifying host . Natural bat predation by other animals (e.g., monkeys, domestic cats) and its consequences on infectious agents transmission are poorly documented [13,14] but could also favor spillover opportunities to other hosts. A large diversity of arthropods, such as mosquitoes, mites, flies, fleas, and ticks , can be found in habitats occupied by bats, particularly in cave systems. Some bat ectoparasites (e.g., fleas and ticks) might incidentally bite humans , but ectoparasite-mediated transmission of bat-borne infectious agents to humans is difficult to demonstrate and has rather been speculated, such as for the transmission of Ebola virus . Nevertheless, the presence of the bacterium Bartonella mayotimonensis, the etiologic agent of endocarditis in humans, both in bat blood and fleas, suggests that transmission to humans by flea bites or their fecal droppings may occur . With the advance of metagenomic technologies, a large diversity of potentially zoonotic bacteria (e.g., Rickettsia, Bartonella ) have been described in bat ectoparasites, but such investigations remain scarce for other infectious agents, such as haemosporidian parasites and viruses . Dengue virus (DENV) was recently detected simultaneously in bat flies (Streblidae) and in their host (Desmodus rotundus), although DENV transmission from bat flies to humans has never been reported . To date, the role of blood-feeding arthropods in pathogen spillover to humans therefore remains highly speculative. Environmental transmission or indirect transmission through the contamination of habitats used by infected hosts has been described as a major mechanism in the epidemiology of wildlife diseases. For bat infectious agents, a limited number of experimental and field studies have been performed to assess their persistence in the environment. Henipaviruses can persist in liquids and on solid surfaces for several days under laboratory conditions and filoviruses for several weeks [28,29]. Bat-borne Leptospira could be a source of contamination to other hosts, as this bacterial genus is known to persist in moist environments . Transmission may also occur by bat guano (i.e., accumulation of bat excrement in the environment). Indeed, guano from cave-dwelling bats is commonly used in agriculture as fertilizer worldwide . Reports of human infection with bat guano are usually restricted to histoplasmosis, also known as “cave disease,” a lung infection caused by a fungus (Histoplasma capsulatum). The detection of coronavirus RNA in bat guano has been demonstrated , although there was no evidence of long-time maintenance of infectious viral particles by virus isolation. Longitudinal sampling of environmental material (water, guano, and soil) exposed to bat secretions for the detection, quantification, and isolation of infectious agents is needed to better assess the risk associated with this transmission route. Transmission of infectious agents is highly dynamic in bats and is associated with significant changes in bat population structure (e.g., birth pulse in maternity colonies) . Periods of high prevalence of infected bats with Hendra and Marburg viruses have been shown to coincide with the timing of infectious agent spillover to other hosts [1,33]. Although several studies have focused on these aspects, a precise assessment of the diversity of transmission routes involved in disease epidemiology in bats is still lacking, especially when considering the extreme diversity of bat species and associated ecological and biological features. Such information is not only relevant from a fundamental perspective but can provide major information for the development of biosafety measures, therefore limiting emergence risk. Source: http://doi.org/10.1371/journal.ppat.1007134