A team of researchers from Nagoya University in Japan has revealed that human behavior, such as confinements and isolation measures, can affect the evolution of new strains of SARS-CoV-2, the virus that causes Covid-19. The study, published in Nature Communications, provides new insights into the relationship between people’s behavior and disease-causing agents.
The coronavirus evolved to become more transmissible earlier in its life cycle. The findings suggest that viruses like any other living organism evolve over time with those that have survival advantages becoming dominant. Many environmental factors influence this evolution, including human behavior. By isolating sick people and using lockdowns to control outbreaks, humans can alter the evolution of the virus in different ways.
An important concept in this interaction is the viral charge or the amount or concentration of a virus present per ml of a body fluid. In the case of SARS-CoV-2, a higher viral load in respiratory secretions increases the risk of transmission through droplets. Viral load relates to potential to transmit a virus to other people with viruses like Ebola having an exceptionally high viral load while common cold has a low one.
The research group led by Professor Shingo Iwami identified trends using mathematical models with an artificial intelligence component to investigate previously published clinical data. They discovered that SARS-CoV-2 variants that were most successful in spreading had an earlier and higher peak in viral load as well as a shorter duration of infection. They also found that decreased incubation period and higher proportion of asymptomatic infections recorded as the virus mutated also affected the evolution of the virus.
Iwami and his colleagues suggest that human behavior changes designed to limit transmission were increasing selection pressure on the virus. This caused SARS-CoV-2 to be transmitted primarily during the asymptomatic and pre-symptomatic periods which occur earlier in its infectious cycle. As a result, peak viral load advanced to this period to spread more effectively in early pre-symptomatic stages. Scientists suggest that when evaluating public health strategies in response to Covid-19 and potentially pandemic causing pathogens in future it is necessary to consider impact of changes human behavior on virus evolution patterns.
Overall, this study highlights how important it is for scientists and public health officials to consider human behavior when developing treatments and interventions for diseases caused by viruses like SARS-CoV