Viruses can be identified by biophysical and biochemical methods. Like most other parasites, viruses stimulate host antibody production. Several hundred different viruses infect humans. Because many have been only recently recognized, their clinical effects are not fully understood. Viruses that primarily infect humans are spread mainly via respiratory and enteric excretions.
Some viruses have oncogenic properties.
Herpesviruses exhibit latency. Diagnosis usually requires testing. Histopathology can sometimes be helpful. Specific diagnostic procedures are described elsewhere in The Manual. Many state health laboratories and the Centers for Disease Control and Prevention offer diagnostic help.