Multiple types of viruses may infect the human nervous system and cause meningitis and encephalitis. Some are specific as to cell type, such as poliomyelitis virus infection of motor neurons, and some are less specific, such as HSV encephalitis. Worldwide, infections of the nervous system by some of the many viruses in the Arbovirus group, such as yellow fever virus, dengue virus, Zika virus, and West Nile virus, are important public health concerns.

Slow virus infections such as the neurological infection subacute sclerosing panencephalitis may be contrasted with latent viral infections. Latent virus infections that have reactivated and new virus infections may cause birth defects including microcephaly.

Atypical agents such as endogenous retroviruses are part of human DNA, and one can consider them as infections or not. Illnesses caused by them may be better considered as degenerative or metabolic illnesses. Other atypical agents such as viroids consist of a simple piece of RNA and require another virus for their replication.

The COVID-19 pandemic has emphasized epidemiology. Some of the epidemiology discussion relates to probability and decision making. Some of the discussion relates to comparisons with clinical medicine, particularly in the great utilization of PCR testing in clinically asymptomatic individuals.