Paolo Rossi Castelli 29 April 2021 6 min read

Mapping the viruses that can make the “jump”

A new archive at California University catalogues infective microorganisms typically found in wild fauna and which, like SARS-CoV-2, seem capable of passing to other species, including man.

Named SpillOver (after the process when a microorganism passes from its host species to another never infected before), it is the new interactive archive on the web created by researchers at University of California, Davis to provide real-time monitoring of potentially hazardous viruses using a global network which is open to all.

SpillOver was presented in the PNAS scientific magazine, in an article which explains its potential. The article also outlines how it works, and its intuitive approach for professionals in the field as well as non-specialists.

The aim is also to help political “decision-makers” take prompt, coordinated measures when needed, to prevent situations such as those which fostered the spread of the pandemic of the SARS-CoV 2 coronavirus, which is responsible for the Covid-19 disease.

A calculated risk

Researchers have taken three aspects into consideration in gauging the risk of a “species jump” from wild animals to men, as was likely the case with SARS-CoV-2 and indeed Ebola: the characteristics of the virus, those of the host (the animal in which the virus reproduces) and those of the environment which the animals inhabit.

Using data obtained from other public registers for 509,721 viral samples (taken from 74,635 wild animals), academics then entered an initial list of 887 zoonotic viruses into the SpillOver archive: viruses which are typical in wild animals but which, following a series of mutations, might also infect other species, including mankind.

The behaviour and ability of some of these viruses to cause disease were already known to researchers. Others were only familiar from the genetic standpoint. The 25 families entered on the database include numerous coronaviruses, along with dozens of other viruses, many of which were identified in a major international project called PREDICT, which ran from 2009 to 2020 and was also coordinated by California University.

The Top 12

According to the Californian academics, the 12 most hazardous viruses have a high probability of managing, under certain conditions, to infect man.

Somewhat surprisingly, SARS-CoV-2 is only in second place, between Lassa fever, the most fearsome of all (which causes a haemorrhagic fever), and Ebola, firmly in third place.

But the top 20 also includes another coronavirus considered at high risk, named PREDICT_CoV-35.

Given that the archive is open to the international scientific community at large, and that it is based on a combination of no less than 32 risk factors which can, by way of example, be customised by country, the system is expected to improve as new data is added. Algorithms borrowed from actuarial calculation (the kind of mathematics banks and insurers use for predicting risk) mean the programme should learn on its own, and allocate increasingly sophisticated and specific risk priorities.

The basic idea is to create a platform where experts – including those from other disciplines – can discuss and share information in order to process data which is useful and constantly updated.

“SARS-CoV-2 is just one of the many viruses which pose a potential threat to man,” the researchers write in PNAS. “It is thought that around 1.67 million viruses yet to be described exist in mammals and birds”. And we might add, it is necessary to understand which have the ability, even if only potentially, to spread to man.


Paolo Rossi Castelli

Journalist since 1983, Paolo has been dealing with scientific divulgation for years, especially in the fields of medicine and biology. He is the creator of Sportello Cancro, the site created by on oncology in collaboration with the Umberto Veronesi Foundation. He collaborated with the pages of the Science of Corriere della Sera for several years. He is the founder and director of PRC-Comunicare la scienza.