Inapparent (asymptomatic) infection

Many virus infections are inapparent, asymptomatic or subclinical, there being no apparent outward symptoms of disease. This is not due to a lack of virus replication or of cell damage and/or death within the host, but cellular damage is limited and hence not translated into obvious clinical symptoms. This is generally the case in the immune host, where there has been recovery and virus eradication by the immune system following a previous infection or vaccination. In this case, the immune system rapidly recognizes and curtails virus replication in the host following reinfection and hence the level of cell damage is limited to below detection levels. However, there are also several viruses (e.g. respiratory viruses and enteroviruses) that do not produce clinical symptoms in non- immune individuals. In the majority of individuals infected with poliovirus, the virus replicates in the epithelial cells of the gastrointestinal tract and is excreted in the feces, but causes no symptoms.