Bats are victims of slander
In a groundbreaking scientific paper published in Biology Lettersan international team of biologists, virologists and environmentalists, including Sébastien Puechmaille of the Institut des sciences de l'environnement de Montpellier (Isem), challenge the conventional wisdom that bats, particularly African bats, are the source of a myriad of viruses harmful to humans. Contrary to popular belief, this in-depth review of published studies provides little substantial evidence, apart from the Marburg and Sosuga viruses, that African bat species serve as reservoirs or intermediate hosts for viruses that spread to humans and cause serious disease.
The scientific community and the public have often been confronted with depictions of bats as carriers of numerous dangerous viruses transmitted to humans. However, the research team, led by Natalie Weber, carried out an exhaustive and critical review of the available literature, focusing specifically on viruses detected in bats in Africa. They meticulously reviewed 162 articles published between 1978 and 2020 and, based on data from over 80,000 individuals belonging to more than 167 bat species, no substantial evidence was found of any bat species other than the Egyptian flying fox playing a central role in the transmission of viruses to humans in this region.
"The aim of our study was to provide a balanced, evidence-based assessment of available knowledge about bat viruses and their relevance to the transmission of bat viruses to humans in Africa. After meticulous review and analysis, we found no convincing evidence to support the prevailing view that bats harbor a large number of viruses that are transmitted to humans.Onthe contrary, our results reveal only two bat-virus systems in which transmission is clearly documented", says Natalie Weber.
A more nuanced approach
The researchers systematically assessed the available data and determined which bat species were sampled, how often and in which country, whether they were sampled lethally or not, what metadata were collected and which viruses were detected with which methodology. The results of these analyses challenge not only the scientific community, but also the general public's perception of bats, underlining the importance of evidence-based understanding. Study co-author DeeAnn Reeder notes that "the results underline the need for a more nuanced and informed approach to public discourse on the role of wildlife in disease emergence". The authors therefore propose a scheme to facilitate standardized assessment of virus hosts in the future, and call for greater interdisciplinary collaboration in bat and virus studies.
This review also revealed that bat misidentification and obsolete species assignments were common in published virus studies. Yet species identification is of great importance for follow-up investigations, particularly when a particular bat is identified as the host of a virus of interest. Furthermore, bats are often regarded as a single entity, but it is crucial to recognize the substantial diversity within this group, which has diversified over tens of millions of years; Africa alone is home to no fewer than 324 different bat species.
"When examining the relationship between bat species and viruses, precision of language is vital. Instead of making the general statement that 'bats harbor the Marburg virus', it is more accurate to specify that 'the Egyptian flying fox, a specific species of bat, harbors the Marburg virus'. This succinct approach preserves precision and avoids wrongly associating all bat species with the Marburg virus", explains Sébastien Puechmaille, co-author of the study and researcher at the Institut des sciences de l'évolution in Montpellier.
Cautious communication
As emerging infectious diseases continue to cause global concern, the researchers hope their work will contribute to a better understanding of the complex dynamics between wildlife, particularly bats, and human health. Their study also raises concerns about the impact of reiterated research communication linking bats to viruses, based on missing evidence, on public perception of bats, as well as on human-bat conflicts and bat conservation efforts.
"Fear and active persecution of bats is increasing dramatically, and populations are likely to decline across Africa. Careful, scientifically-based communication of findings and a balance between potential risks and benefits will be essential to achieve to enable humans and bats to live side by side in our changing world," says study co-author Dina Dechmann. The implications of this research extend beyond Africa, encouraging a more thoughtful, evidence-based approach to the study of zoonotic diseases worldwide.