A new study by a team of researchers from Nagoya University (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 coronavirus developed to become more transmissible earlier in its life cycle due to these factors.
The findings, published in Nature Communications, provide new insights into the relationship between people’s behavior and disease-causing agents. By isolating sick people and using lockdowns to control outbreaks, humans can alter the evolution of the virus in different ways. However, predicting how these changes occur is vital for developing adaptive treatments and interventions.
One important concept in this interaction is the 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, identified trends using mathematical models with an artificial intelligence component to investigate previously published clinical data. They discovered that the 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 the decreased incubation period and the 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