A study published in PNAS Microbiology found that enveloped viruses harbor higher interspecies transmissibility and are more likely to cause zoonotic infections than non-enveloped viruses. The research suggested that viral envelopes help these pathogens evade host immunity.
Study: Enveloped viruses show a higher propensity for cross-species and zoonotic transmission. Image Credit: Kateryna Kon / Shutterstock
Background
Zoonosis refers to the spread of infectious diseases between animals and humans (or between humans and animals). In recent decades, the interspecies transmission of viruses from wild or domestic animals to humans (zoonoses) has given rise to large epidemics. Still, our understanding of this complex process remains limited.
Several well-known zoonoses include human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS), Zika, Ebola, influenza, COVID, and mpox. Therefore, understanding and predicting the emergence of viruses has become a scientific priority. There are several zoonotic risk factors, including depletion of biodiversity and species invasions, viral host variability, frequency of interaction, life history characteristics of reservoir hosts, wildlife trade, and proximity to the host with humans.
However, previous studies have revealed that three factors have been identified as contributing to the risk of zoonotic disease spread: viral genetic material: ribonucleic acid (RNA) viruses may be more susceptible than DNA viruses; site of replication: viruses that replicate in the host’s cytoplasm rather than the nucleus may have an advantage; and genome size: smaller genomes may be more zoonotic.
The enveloped nature of viruses is a characteristic feature that distinguishes them from other organisms. Most of the zoonotic viruses that have caused human disease in the past were enveloped, such as smallpox, mpox, coronaviruses, rabies, measles, and influenza.
The genome of a virus can provide information about host tropism and zoonotic propensity by evaluating features such as codon or dinucleotide usage biases and the degree to which these biases reflect those seen in host gene transcripts. The fundamental characteristics of viruses remain unknown despite these advances in understanding interspecies transmission and zoonoses.
The study
Using a database of more than 12,000 mammalian virus-host interactions, the current work explored key virological properties that influence interspecies transmissibility and zoonotic propensity to better understand which viral characteristics predominantly determine zoonoses.
Here, the researchers examined a large VIRION database containing 5,149 viruses identified through metagenomic studies. This exploratory analysis used the Global Virome in One Network (VIRION) database. Overall, 5,149 viruses belonging to 36 families and 1,599 host species from 20 orders were analysed, revealing 12,888 virus-host associations.
Next, the fundamental characteristics of the viruses were defined based on –their genetic material; single-stranded or double-stranded; segmented or non-segmented, replicated in the cytoplasm or nucleus, enveloped or non-enveloped, and the size of the genome.
For each virus, the number of natural host species, excluding humans, was identified and recorded to reduce the possibility of bias. Mammalian viruses were then examined for their potential pathogenicity, ie, their capacity for zoonoses.
The results
The results showed that the number of host species increased more rapidly for enveloped viruses than for non-enveloped viruses, being approximately double for the former type. This difference was also noticeable when the envelope factor was combined with the other viral characteristics.
All other viral characteristics examined were not significant or were marginally significant. Enveloped viruses were more likely to undergo interspecies transmission than non-enveloped viruses.
It was observed that enveloped viruses tend to have a higher rate of zoonotic spread than non-enveloped viruses. Using binary logistic regression with N ≥5 sequence records, the zoonotic propensity was estimated to be 2.5-fold increased for enveloped viruses compared to non-enveloped viruses. Therefore, enveloped viruses showed a higher propensity for zoonotic contagion than non-enveloped viruses.
Meanwhile, viruses that replicate in the cytoplasm were found to be more likely (1.9 times) to be zoonotic than those that replicate in the nucleus. Segmented viruses increased the chances of zoonoses slightly more than non-segmented viruses. Furthermore, viruses with smaller genomes were more likely to precipitate a zoonotic infection.
The lack of significant effects of these two traits on interspecies transmission meant that their impact on zoonotic propensity could be due to human-specific factors or, more likely, biases within human-infectious virus data sets.
This study also provided information on how enveloped viruses might infect hosts. It was likely that the envelope proteins were structurally less restrictive than the capsid proteins, allowing enveloped viruses to bind to cell receptors of different host species with greater flexibility, to bind to a greater number of receptors. alternative or adapt to host switch mutations without compromising other functions.
Another possible mechanism is apoptotic mimicry, in which viral particles are engulfed by host cells disguised as apoptotic bodies with defined membrane lipid conformations and enter host cells.
Conclution
The results revealed that enveloped viruses infect more host species and are more likely to be zoonotic than non-enveloped viruses. By contrast, other viral characteristics, such as genome composition, structure, size, and viral replication compartment, are less important.
According to this study, viral envelopes did not significantly affect or reduce zoonotic risk, contrary to previous belief, and this may help prioritize outbreak prevention efforts. A viral envelope may facilitate interspecies transmission by facilitating the structural flexibility of receptor-binding proteins and allowing barriers to viral entry to be overcome.
Source: news.google.com