EDINBURGH — A team at the University of Edinburgh published a catalog designed to help identify viruses with high-risk potential. The catalog focuses on RNA viruses, and for two-thirds of the viruses listed, human-to-human transmission is considered highly unlikely.

The catalog includes viruses such as Zaire ebolavirus, Chikungunya, Zika, Oropouche viruses, and mpox. Zaire ebolavirus caused an outbreak in West Africa in 2014, and Bundibugyo ebolavirus is currently spreading in central Africa. Andes hantavirus, which caused a recent outbreak on a cruise ship, and Bundibugyo ebolavirus do not have the characteristics to initiate a global pandemic, despite spreading for weeks prior to detection. SARS-CoV-2 also spread for weeks before detection.

In 2019, data published by the University of Edinburgh team indicated that highly transmissible viruses are typically closely related to other human-spread viruses but emerge separately from animals. Mark Woolhouse, professor of infectious disease epidemiology, stated, "In 2019, my team showed that highly transmissible viruses tend to be closely related to other viruses that spread between humans, but they emerge separately from animals." He added, "That turned out to be a perfect description of SARS-CoV-2, very similar to the original SARS coronavirus but independently (and perhaps indirectly) acquired from bats." The World Health Organization (WHO) had proposed a SARS-like coronavirus as a candidate for Disease X in 2018.

Only 239 out of thousands of identified RNA virus species infect humans. Zoonotic viruses, such as rabies, are typically transmitted from animals to humans rather than directly between humans. There are tens of thousands of human rabies cases annually. There is no documented instance of an RNA virus evolving the ability for sustained human-to-human spread from a state of only animal-to-human transmission. Viruses like measles, mumps, and rubella likely originated from animal viruses that already possessed the capacity to spread among people. Scientists typically discover two or three unknown human viruses each year, a rate that has been consistent since the 1960s. HIV-1 was discovered in 1983, and SARS-CoV-2 was discovered in 2020. AIDS and COVID-19 have each resulted in tens of millions of fatalities.