Herpesviruses

Herpesviruses are highly successful viruses because they transmit to many individuals in all populations, often without causing obvious symptoms. However, they are responsible for significant diseases, including herpes simplex encephalitis, genital herpes, chickenpox, infectious mononucleosis, cytomegalic inclusion disease, exanthem subitum and Kaposi's sarcoma. They also cause severe opportunistic disease in patients with T-cell immunodeficiency. Antiviral drugs have greatly reduced the burden of disease caused by herpesviruses. Aciclovir and penciclovir (with their pro-drugs valaciclovir and famciclovir, respectively) are safe in clinical practice. Ganciclovir (and its pro-drug valganciclovir) and foscarnet have significant toxic effects but are clearly indicated for either pre-emptive therapy or prophylaxis of the immunocompromised host. Ganciclovir is indicated for neonates born with symptoms of congenital cytomegalovirus (CMV) infection. Vaccine development has been slow for herpesviruses but a live attenuated vaccine for varicella-zoster virus has already reduced the incidence of chickenpox and deaths from chickenpox following universal immunization in the USA. Vaccines for CMV, herpes simplex virus and Epstein–Barr virus are undergoing clinical trials.