When Viruses Become More VirulentThe evolution of virulence depends on the biology and interplay of

When Viruses Become More Virulent

The evolution of virulence depends on the biology and interplay of infection and transmission, writes Joel O. Wertheim, PhD, associate professor in the Division of Infectious Diseases and Global Public Health at UC San Diego School of Medicine, in the journal Science. 

Virulence is the degree to which a pathogen weakens, sickens or kills its host. More virulent pathogens may be less transmissible because in killing its host, it reduces the opportunity for transmission. But both virulence and transmissibility are forever linked: To maintain or increase infectiousness, a pathogen must be virulent.

In his Science article, Wertheim describes the emergence of a more virulent and transmissible variant of HIV that has spread to 102 known cases, mostly in the Netherlands. These findings, he says, have relevance to SARS-CoV-2 and the COVID-19 pandemic. It’s possible that the coronavirus is evolving toward a more benign, highly transmissible infection, similar to common cold viruses, but that outcome is not guaranteed.

SARS-CoV-2 has displayed an extraordinary ability to rapidly alter its transmissibility and virulence, and how those two factors interact over the coming months will dictate whether SARS-CoV-2 will benignly fade away or continue to be an evolving, global public health threat.

– Scott LaFee