Varicella Zoster Virus (VZV)
Varicella zoster virus (VZV) infection is known to have two disease outcomes. The first is varicella, a frequent and highly contagious disease of childhood. More commonly known as chickenpox, it is characterized by fever and severe skin rash. The second is zoster, a disease characterized by extremely painful skin rash that occurs much later in life.
Varicella is caused by varicella zoster virus (VZV), a human virus and a member of the herpesvirus group.
The virus can infect and grow in several cell types in the body: blood, skin, and nerve.
Like other herpes viruses, VZV causes a primary acute infection which, following healing, travels up to the nerve root or ganglia and remains silent or dormant for life. Under certain conditions, the dormant VZV can be stimulated to come back down the nerve tract and cause a secondary disease years or decades later.
Infection with VZV occurs through the respiratory tract.
The most common mode of transmission is by person-to-person contact with infected respiratory tract secretions.
Transmission may also occur by aspirating airborne droplets or by direct contact and/or inhalation of aerosols from skin lesion fluids.
Primary Disease: Varicella or Chickenpox
The primary infection occurs in the respiratory tract, where the virus grows at the site of entry in the nasopharynx. From there, it moves into regional lymph nodes, into the blood stream, and then to organs such as the liver and spleen, to nerves, and finally to the skin, where it erupts as a severe and widespread rash with many raised, fluid-filled vesicles.
The disease in healthy children is generally mild with fever up to 102oF for 2-3 days, fatigue and varying levels of rash, itching and irritation. Most symptoms resolve in a few weeks. The disease in healthy adults is generally more severe and prolonged.
Children or adults with cancers or AIDS may develop a very severe form of the disease characterized by high fever, extensive vesicular rash, high complication rates, and very prolonged illness.
Recurrent Disease: Zoster or Shingles
Zoster may occur years or decades after the primary infection if the dormant or latent VZV in the nerve root is reactivated. If reactivated, the virus will follow the nerve down to the skin causing tremendous pain and a vesicular rash all around the specific area supplied by that nerve, most often around the back or trunk of the body or parts of the face. Although the rash will resolve in a few weeks, the nerve pain, or neuralgia, may last up to a year or longer.
Primary disease is generally not treated. When allowed to resolve, it generates life-long immunity to reinfection. Zoster, however, is always a possibility.
Due to complications with varicella and the many complications with recurrent zoster, a varicella vaccine was licensed in 1995 for use in children between 12 and 18 months old and in adolescents and adults that were never infected.
The medicines Acyclovir and Famcyclovir are available to treat chickenpox and shingles in high risk individuals.
Varicella zoster immune globulin is purified from individuals already with high levels of immunity to varicella. It is used following exposure to treat people at high risk for complications.
We have developed a monkey model of varicella for our research studies. A closely related viral species, simian varicella virus (SVV), infects and causes an identical disease in nonhuman primates. We can grow and study this virus in the laboratory.
Experiments with SVV in monkeys are used to answers questions related to infection, disease and development of improved vaccine and treatment methods.
We are currently developing a zoster (shingles) model in monkeys. We have successfully produced animals with latent virus and are currently testing possible methods to reactivate virus to produce shingles in these animals. With this model, we hope to find ways to block reactivation as well as to test potential treatments.
The current vaccine is a live but weakened virus and therefore has some potential for latency and reactivation. We are continuing to generate and test improved vaccine candidates that may reduce these complications.
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