Viruses are the most numerous organisms on Earth. Thousands are already known, but there are millions yet to be discovered. To enter the host they need to live, viruses deploy different strategies. After analysing 12,000 virus-host associations, a research group from the Institute for Integrative Systems Biology (I2SysBio) – a joint centre of the University of Valencia (UV) and the Spanish National Research Council (CSIC) – has observed that enveloped viruses – those with a lipid outer shell – are more capable of infecting multiple species and are at greater risk of jumping from animals to humans. The work, which contradicts previous studies, is published in the PNAS journal.

Led by University of Valencia researcher Rafael Sanjuán, the study investigates the properties that make a virus more or less likely to infect new species and, in particular, to jump from animals to humans. To do this, the I2SysBio team used data obtained by various methods, including metagenomics (a tool capable of detecting the genetic material of viruses in environmental samples) to study 5,149 viruses and 1,599 host species, by analysing a total of 12,000 interactions. Their results are highlighted in the latest issue of the Proceedings of the National Academy of Sciences.
Wrapped for camouflage or to better bind

The lipid envelope of some viruses is derived from the surface of the cells it infects. This envelope gives viruses a greater ability to enter cells of different types, including cells of other species. The study reveals that enveloped viruses tend to infect more host species and are more likely to infect humans than non-enveloped viruses, while other viral traits such as genome composition, structure, size, or replication compartment viruses play a minor role.

“We have been able to analyse the viral properties associated with the host jump, on the one hand, and the infection in humans, on the other, with greater reliability than previous studies had”, says Rafael Sanjuán, who leads an Advanced Grant from the European Research Council (CKD). “The results are in contrast to the earlier idea that viral envelopes have little or even reduced zoonotic risk, which should help to better prioritize outbreak prevention efforts”, he adds.

Knowing which type of virus is most likely to cross the species barrier can help guide surveillance programs for new viruses, something whose importance has become clear with the outbreak of the epidemic caused by SARS-CoV-2. “It is no coincidence that the vast majority of emerging human viruses such as HIV, the Zika and Ebola viruses, SARS-CoV-2 or monkeypox, among others, are enveloped viruses. This suggests that we should prioritise surveillance of this type of viruses”, sums up Sanjuán.

Reference: Ana Valero-Rello, Rafael Sanjuán, Enveloped viruses show increased propensity to cross-species transmission and zoonosis, PNAS Vol. 119, No. 50, December 13, 2022.