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 analyzing 12,000 virus-host associations, a research group from the Institute for Integrative Systems Biology (I2SysBio), a joint center of the Higher Council for Scientific Research (CSIC) and the University of Valencia (UV), in Spain, has observed that the Enveloped viruses, those that have a lipid outer shell, have a greater capacity to infect multiple species and present a greater risk of jumping from animals to humans. The findings contradict the conclusions of previous studies.
The study, led by the University of Valencia researcher Rafael Sanjuán, investigates the properties that make a virus more or less prone to infecting new species and, in particular, to jumping from animals to humans. To do this, the I2SysBio team used data obtained by various methods, including metagenomics (a technique capable of detecting the genetic material of viruses in environmental samples), to study 5,149 viruses and 1,599 host species, analyzing a total of 12,000 interactions.
“In recent years, efforts have been made to characterize the viruses present in wild mammals such as bats, rodents and many others,” recalls Rafael Sanjuán. “We analyzed a large number of virus-host interactions and, after reviewing and analyzing this information, we found that viruses that have a lipid envelope are capable of infecting multiple species and present a greater risk of jumping from animals to humans”, sums up the researcher. .
Image captured by an electron microscope and then processed, showing numerous filaments of Ebola virus particles in blue, sprouting from the cell they have infected (in yellow). (Photo: National Institute of Allergy and Infectious Diseases (NIAID))
Wrapped for camouflage or to fit together better
The lipid envelope is a structure that some viruses have derived from the surface of the cells it infects. According to the work of I2SysBio, this envelope gives viruses a greater ability to penetrate cells of different types, including cells of other species. “Our analysis 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 compartment of viral replication play a minor role”, the researchers explain.
The mechanisms by which the lipid envelope favors zoonosis are not clear. One of the hypotheses being considered is that this structure is used by viruses to pass themselves off as cellular debris that is engulfed by cells as part of the physiological process of molecular recycling that occurs in all animals. Another is that the envelopes give the virus’s surface proteins greater flexibility to bind to different types of host proteins. These and other ideas are currently under investigation.
Most emerging human viruses are enveloped
According to Sanjuán, “previous studies were based on a few hundred highly characterized viruses due to their biomedical or economic implications, but this set does not represent the viral diversity existing in nature and, therefore, offered a limited vision of the capacity of a viruses to colonize new hosts. Research techniques capable of detecting new viruses such as metagenomics make the vision of viral diversity increasingly broad.
“We have been able to analyze the viral properties associated with the host jump and the infection in humans with greater reliability than previous studies had,” says the Valencian researcher. The results contrast with the earlier notion that viral envelopes do not significantly affect, or even reduce, zoonotic risk, which should help better prioritize outbreak prevention efforts, according to the I2SysBio researchers.
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. “According to our findings, it is no coincidence that the vast majority of emerging human viruses such as HIV, new strains of influenza, Zika and Ebola viruses, SARS-CoV-2 or monkeypox, among others, are viruses with wrapping This suggests that we should prioritize surveillance of this type of virus”, sums up Sanjuán.
The study is titled “Enveloped viruses show increased propensity to cross-species transmission and zoonosis”. And it has been published in the journal Proceedings of the National Academy of Sciences (PNAS). (Source: CSIC)