Scientists at Nagoya University (Japan) have discovered that human behavior, such as confinements and isolation measures, can impact the evolution of new strains of SARS-CoV-2, the virus that causes Covid-19. The coronavirus developed to become more transmissible earlier in its life cycle due to these behaviors. The findings, published in Nature Communications, provide new insights into the relationship between people’s behavior and disease-causing agents.
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. Predicting how these changes occur is vital for developing adaptive treatments and interventions.
An important concept in this interaction is viral charge. This refers to 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 the potential to transmit a virus to other people with viruses like Ebola having an exceptionally high viral load while the common cold has a low one.
The research group led by Professor Shingo Iwami used 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. The researchers also found that decreased incubation period and increased proportion of asymptomatic infections recorded as the virus mutated affected virus evolution patterns.
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 asymptomatic and pre symptomatic periods which occur earlier in its infectious cycle. As a result, peak viral load advanced to this period for effective spread in early pre symptomatic stages.
According to scientists evaluating public health strategies response to Covid 19 pandemic causing pathogens future must consider impact changes human behavior on virus evolution patterns