Not Just Bats – All Sorts Of Animals Harbor Viruses That Infect Humans

These cute fruitbats have little to do with the horseshoe bats thought to harbor the originator of the SARS-CoV-2 virus. The reason so many viruses come from bats may be because they are such a large and diverse group. Susan Flashman/Shutterstock

The possibility that SARS-CoV-2 jumped to humans from bats has led some to call for the culling of bat populations. However, new evidence suggests this so-called "safety measure" would require destroying all warm-blooded animals as human-infecting viruses exist across mammals and birds, and no animals are particularly threatening. If bats give us coronoviruses, as well as Hendra and rabies, and rats (via fleas) produced the bubonic plague, it is proposed the world would be better off without either of them. Rats have proven elimination resistant (pied pipers aside) but many bat species are quite vulnerable, even without deliberate action.

Dr Nardus Mollentze and Dr Daniel Streicker of the University of Glasgow thought it time to test their reputation as the prime harbor for future epidemics. The duo conducted a literature search for all examples of viruses, whether DNA or RNA, that are known to infect humans and have also been recorded in mammals or birds. They didn't check for bacterial infections, thus letting rats (or gerbils) off the hook for plague, but still found 415 examples.

In Proceedings of the National Academy of Sciences, the pair report that “the proportion of viruses that infect humans varies minimally across reservoir taxonomic orders.” In other words, the next pandemic is as likely to come from zebras as any specific bat species. It's true that more of the viruses identified are hosted by certain groups of animals than others. However, this is not because certain groups of animals are disease-ridden Typhoid Marys, but because the more species of animal a group contains, the more viruses it will host.

If a new virus is more likely to emerge from bats than sloths, the authors conclude, it's because there are more than 1,200 species of bats – making up 20 percent of all living mammal species – whereas sloths and their relatives are scarce. This is one reason why calls to eradicate Australian fruitbats, as some have advocated, make no sense. Bats are an exceptionally diverse group, many of which have little in common with the coronavirus hosts.

In a few cases, the authors think our close relationship to another species makes it more likely a virus will cross over, such as when simian immunodeficiency virus became HIV. More broadly, however, the findings contradict the idea “special reservoirs” pose a heightened risk thanks to characteristics like our own.

Mollentze and Streicker argue this means we instead need to maintain broad surveillance of virus families that could pose a threat to humanity, rather than concentrating on a few animal hosts.

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