New virus catalog reveals which pathogens pose the greatest threat

In a typical year, scientists discover two or three viruses that have never been seen in people before. The number fluctuates, but the trend has been fairly steady since the 1960s. Most of these viruses attract little attention, and my colleagues and I have often had to search through old medical papers to find any mention of them. Some viruses disappear entirely and are all but forgotten. At the other extreme, the discovery of HIV-1 in 1983 and Sars-CoV-2 in 2020 presaged the AIDS and COVID pandemics, respectively. Both have killed tens of millions . The next time a scientist finds an unusual or unknown virus in a patient—probably in the next few months—how will they know whether it could lead to a public health emergency on the same scale as AIDS or COVID? My team at the University of Edinburgh has been using the lessons of virus history to help answer this question . Pandemics come in many forms, but in recent times the biggest culprits have been viruses with genomes made from RNA (rather than the more familiar DNA). Thousands of RNA virus species have been identified , and there may be millions , but only 239 infect humans. We recently published a catalog that helps pinpoint the riskiest ones. The type and severity of disease are important indicators, but there will be no pandemic unless the virus can spread between people. That could involve physical contact, or inhaling airborne particles, or exposure to blood or feces, or the bite of a mosquito or tick. For two-thirds of the viruses on our list, an infected person is highly unlikely to pass their infection on. These are known as zoonotic viruses, meaning people usually catch them from animals rather than other people. Rabies is one example. That sounds reassuring, but viruses evolve quickly and there is an understandable concern that a zoonotic virus might acquire the ability to spread among humans. That’s why scientists are so worried about bird flu . But there is no documented example of an RNA virus doing