Herpesviruses are extremely common and around 100 have been identified in a variety of animal species. All of the herpesviruses are members of one family, the Herpesviridae, and have certain characteristics in common, such as their ability to establish latency during primary infection. This means that following initial infection the virus remains dormant, to be reactivated by certain triggers such as an individual’s immune status, stress or sunlight.

To date, eight human herpesviruses have been identified. These include:

• Epstein-Barr virus, which causes infectious mononucleosis (also known as ‘mono’ and ‘glandular fever’);

• Varicella zoster, which causes chickenpox and shingles;

Typical rash of chickenpox in an adult.	Typical rash of chickenpox in an adolescent.	Typical rash of chickenpox in an adult.		Typical herpes zoster rash.

• Herpes simplex virus type 1, the cause of cold sores;

• Herpes simplex virus type 2, the most common cause of genital herpes.

The human herpesviruses have been divided into the alpha, beta and gamma herpesviruses (see table).

• Members of the alpha herpesvirus subfamily are classified on the basis of their relatively short reproductive cycle, a variable host range, efficient destruction of infected cells and their ability to establish latent infections primarily in sensory ganglia.

• Each of the beta herpesviruses has a long reproductive cycle and a restricted host range. Infected cells often become enlarged. Latency can be maintained in the white cells of the blood, kidneys, secretory glands and other tissues.

• The experimental host range of the gamma herpesviruses is restricted to the family or order to which the natural host belongs. This subfamily of viruses is specific for either T or B lymphocytes, and latency is often demonstrated in lymphoid tissue.