Correlations between virus infection and pathogenicity in humans

Infection is not synonymous with disease. Infection refers to the multiplication or the persistence of a virus in tissues while pathogenicity refers to the emergence of disease in the infected host. Pathogenicity is the result of a competition between the growth of the virus and the host response to infection, and its genesis involves many intricate factors. Consequently, most viruses of medical interest exhibit a wide spectrum of pathogenicity ranging from asymptomatic infection to lethal disease. The study of pathogenicity is far more complex than the recognition of infection. Cell cultures, animal models and molecular biology investigations have provided substantial insights both into the virulence of viruses and the susceptibility of the host. However, the prediction of disease often remains hazardous whereas the detection of a virus can now be obtained in most cases by the combination of classical methods with recent molecular techniques. Therefore the prevention of virus diseases transmitted by biologicals is logically founded on the prevention of virus infections, which implies a constant adaptation of safety control procedures to the rapid evolution of knowledge in medical virology.