A team of researchers from Nagoya University (Japan) has shed light on the impact of human behavior on the evolution of new strains of SARS-CoV-2, the virus that causes Covid-19. The study, published in Nature Communications, reveals that viral load and transmission patterns are influenced by human actions such as confinement and isolation measures.
In the early stages of its life cycle, SARS-CoV-2 evolved to become more transmissible. This is due in part to environmental factors, including human behavior. For instance, when sick individuals are isolated and lockdowns are implemented to control outbreaks, these measures can alter the evolution of the virus in different ways.
One important concept in this interaction is viral charge, which refers to the concentration or amount of a virus present per ml of 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 infectivity potential and can vary greatly among different viruses – for example, Ebola has 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 analyze previously published clinical data. They discovered that SARS-CoV-2 variants that were most successful at spreading had an earlier and higher peak in viral load as well as a shorter duration of infection. The researchers also found that changes in incubation period and proportion of asymptomatic infections affected virus evolution patterns when it mutated.
Iwami and his colleagues suggest that changes in human behavior designed to limit transmission have increased selection pressure on SARS-CoV-2. As a result, it became primarily transmitted during asymptomatic and pre-symptomatic periods which occur earlier in its infectious cycle. This allowed it to advance its peak viral load into this period for more effective spread during early pre-symptomatic stages. Scientists advise public health officials to consider how changes in human behavior impact virus evolution patterns when developing strategies for responding to Covid-19 and potentially pandemic causing pathogens in the future.
Overall, this study provides valuable insights into how our actions can influence disease outcomes by shaping virus evolution patterns over time.