Researchers Unveil Origins of Zoonotic Virus Outbreaks

Study finds no evidence of lab manipulation or prolonged animal host adaptation for COVID-19 and other viruses

Published on Mar. 10, 2026

Got story updates? Submit your updates here. ›

A new study from researchers at the University of California, San Diego has revealed that most zoonotic viruses, including SARS-CoV-2 which causes COVID-19, do not require acquiring adaptive mutations to sustain human-to-human transmission. The findings suggest that many viruses may already possess the basic capacity to infect and spread between humans, and that what matters most is human exposure to a diverse array of animal viruses.

Why it matters

The research provides important insights into the natural origins of zoonotic virus outbreaks, countering theories that COVID-19 and other pandemics may have been caused by laboratory manipulation or prolonged evolution in an intermediate animal host. Understanding the true evolutionary pathways of these viruses is crucial for improving outbreak surveillance, prevention, and pandemic preparedness.

The details

The study analyzed viral genomes from outbreaks caused by influenza A, Ebola, Marburg, mpox, SARS-CoV and SARS-CoV-2, focusing on the evolutionary period immediately preceding human outbreaks. The researchers found that selection pressures before zoonotic emergence were indistinguishable from those acting during routine circulation in animal reservoirs, with measurable changes in selection typically appearing only after sustained transmission began in humans. This suggests that many viruses may already possess the basic capacity to infect and transmit between humans, rather than requiring rare, finely tuned adaptations in animals.

  • The study was published in the journal Cell on March 10, 2026.

The players

Joel Wertheim

Senior author of the study, professor of medicine in the Division of Infectious Diseases and Global Public Health at the University of California, San Diego School of Medicine, and co-corresponding author of the paper.

University of California, San Diego

The institution where the research was conducted.

Got photos? Submit your photos here. ›

What they’re saying

“From an evolutionary perspective, we find no evidence that SARS-CoV-2 was shaped by selection in a laboratory or prolonged evolution in an intermediate host prior to its emergence. That absence of evidence is exactly what we would expect from a natural zoonotic event and it represents another nail in the coffin for theories invoking laboratory manipulation.”

— Joel Wertheim, Professor of medicine (Cell)

“Rather than requiring rare, finely tuned adaptations in animals, many viruses may already possess the basic capacity to infect and transmit between humans. What matters most is human exposure to a diverse array of animal viruses.”

— Joel Wertheim, Professor of medicine (Cell)

What’s next

The researchers see potential applications of their framework in outbreak forensics, viral surveillance, and pandemic preparedness, with the goal of better understanding how pandemics begin in order to focus on prevention and reducing opportunities for viral spillover.

The takeaway

This study provides important evidence that COVID-19 and other zoonotic virus outbreaks likely arose through natural processes, rather than laboratory manipulation or prolonged evolution in animal hosts. Understanding the true evolutionary pathways of these viruses is crucial for improving outbreak detection, prevention, and pandemic preparedness.