A virus population is usually composed of a collection of variants of virus particles. In order to  investigate whether virus particles (virions) can cause an infection independently from each other, and therefore individually, the researchers set up an experiment with two marked virus variants. They exposed a population of hosts (caterpillars) to both variants.The experiment showed that exposure to a low dosage of virus particles resulted in a small number host infections (20%). The majority of these hosts (86%) turned out to be infected by a single virus genotype. In contrast, exposure to a high dosage of virus particles resulted in virtually all the hosts (99%) becoming infected, where most of the hosts were infected by both types of virus. Only 14% were infected by only one of the two variants.Based on the assumption that every virus particle operates independently from all other virus particles, the researchers set up a probability model.

This model predicts how many virus particles have caused an infection and how many different virus genotypes are present in infected hosts, such as plants, insects or people. If there are few virus particles that lead to an infection, the number of virus particles determines the degree of diversity that can be present within the host. This is an important finding because the interactions between virus variants, such as competition and exchanging genetic information, determine the progression of disease and the evolution of the virus. Until now, it was unclear whether a virus must be seen as an individual that can infect a host independently, or whether a cloud of viruses cooperates to cause an infection.

Regards
ALEX JOHN
Editorial Assistant
Journal of infectious disease and dignosis