Deciphering Human-to-Animal Virus Transmission: Revelations from Genomic Analysis
Watan-A recent scientific study has found that humans transmit viruses to pets and wildlife more than we acquire from them, according to a new primary genome analysis conducted by researchers at the University of California.
For a long time, scientists have warned that the next pandemic threat could arise from infections transferring from animals to humans, but a new study suggests that the opposite might be true.
The scientific study, published in the journal Nature Ecology & Evolution, indicates that a team of scientists conducted an analysis of all publicly available viral genome sequences to reconstruct the pathways through which viruses jumped from one host to infect other vertebrate species.
Zoonotic Origin Diseases
It turns out that most emerging infectious diseases stem from viruses circulating in animals. When these viruses jump from animals to humans, a process known as zoonotic spillover, they can cause outbreaks and pandemics like Ebola, influenza, or COVID-19.
Given the enormous impact of zoonotic diseases on public health, humans have generally been viewed as a “reservoir” for viruses rather than a source. The transmission of viruses from humans to animals has received much less attention.
Viral Genome Analysis
The research team developed and applied methodological tools to analyze nearly 12 million viral genomes deposited in public databases to date.
By leveraging this data, they reconstructed the evolutionary history and previous host jumps of viruses across 32 viral families, examining segments of the viral genome that acquired mutations during host jumps.
According to the study published on the Phys.org website, scientists found that almost twice the number of host jumps were inferred from humans to other animals (known as anthroponoses) rather than the reverse.
This pattern was consistent across most of the viral families examined. Additionally, they found more host jumps from one animal to another, excluding humans.
The team’s work highlighted a significant and largely underappreciated fact that human viruses frequently spread from humans to both wild and domestic animals.
Just One Knot
Co-author Professor Francois Balloux from the Institute of Genetics at the University of California, Los Angeles, stated: “We must consider humans as just one knot in a vast network of hosts exchanging disease-causing agents ad infinitum.”
Results also show that viral host jumps, on average, are associated with an increase in genetic changes, or mutations, in viruses compared to their continuous evolution alongside a single host animal, reflecting how viruses adapt to exploit their new hosts better.
Furthermore, viruses already infecting various animal species show weaker signs of this adaptive process, indicating that broad-host-range viruses may inherently possess traits making them more capable of infecting a diverse range of hosts.
If a virus carried by humans infects a new animal species, the virus may continue to thrive even if eradicated among humans, or it may develop new adaptations before re-infecting humans.
Cell Entry
Cell entry is generally seen as the first step in virus infection of the host. However, the team found many modifications associated with host jumps were not found in viral proteins enabling them to bind to and enter host cells. This suggests that viral host adaptation is a complex process that still needs to be fully understood.
Co-author Dr. Lucy van Dorp from the Institute of Genetics at the University of California, Los Angeles, said: “Our research would not have been possible without countless research teams openly sharing their data through public databases.”
She added, “The main challenge moving forward is integrating knowledge and tools from diverse disciplines including genomics, epidemiology, and ecology to enhance our understanding of host jumps.”
