The potential of bats, primates and rodents to carry a large number of viral species that could be transmitted to humans is analysed in a study published in Nature. The work identifies factors that influence whether viruses can be passed from animals to humans, and provides a map of the geographic locations and mammals that are most likely to host novel threats to human health.

Most emerging human infectious diseases originate in wild mammals, particularly zoonotic viruses such as HIV, Ebola and SARS. Predicting which viruses are most likely to spread from animals to humans could assist health programmes to monitor emerging diseases and pre-empt future potential outbreaks.

To improve our understanding of the factors influencing cross-species transmission of zoonotic viruses to humans, Kevin Olival, Peter Daszak and colleagues create and analyse a database of over 2,800 mammal–virus associations. Of 586 viral species analysed, 263 (44.8%) have been detected in humans, 188 (71.5% of human viruses) of which are defined as zoonotic, that is, they have been detected at least once in humans and at least once in another mammal species. 

They find that the risk of transmission of zoonotic viruses from host species to humans varies according to the species relatedness to humans, opportunity for contact with humans and underlying viral traits. Bats are shown to harbour the highest proportion of zoonotic viruses, followed by primates and rodents.

When it comes to predicting geographical hot spots for zoonotic viruses, the authors find that the patterns vary according to host species. For example, zoonotic viruses from bats are most prevalent in South and Central America and parts of Asia. Conversely, those from primates tend to be clustered in Central America, Africa and Southeast Asia, and those from rodents are mostly found in parts of North and South America and Central Africa.

These results may help to inform global viral discovery programmes to identify new zoonotic viruses and assess their potential threat to human health, the authors conclude.

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