Varicella-zoster Virus

Varicella-zoster virus (VZV) is a member of the Herpesviridae family of viruses which are large DNA viruses. VZV belongs to the Alphaherpesvirinae subfamily and it is also called human herpesvirus type 3 (HHV-3). VZV is the cause of varicella, also known as chicken pox, a common childhood illness that causes an itchy rash and vesicles (blisters or pox) all over the body. The first symptoms of chickenpox often are a fever, headache, sore throat, fatigue and loss of appetite. The skin lesions follow in 1-2 days.

Prior to the development of the varicella vaccine chicken pox occurred in over 90% of children. Chicken pox can be very severe in for pregnant women, adults, and people who have immune deficiency syndromes. Following chicken pox VZV remains in a latent, or inactive, state in nervous tissue (dorsal root ganglia), but it can reactivate following periods of stress or many years following chicken pox as immunity wanes. The reactivation usually occurs in nerves that supply a single region of the body or dermatome. This reactivated VZV infection is called zoster or shingles. It presents with severe pain associated with vesicles that occur on the face or trunk. The reactivation VZV can also cause severe infections of the nervous system including meningitis and encephalitis.

Transmission 

Chicken pox or varicella is a highly contagious infection and is transmitted by respiratory secretions by coughing or sneezing, coughs. Fluid from a chickenpox blister is also infectious. Shingles can be transmitted by close contact with vesicles to a non-immune person who has never been exposed to VZV and can thus lead to chicken pox.

Prevention 

There is a live attenuated (weakened) varicella vaccine which is highly effective at preventing chicken pox. There is also a zoster vaccine that is recommended for person over 50 years old.

Diagnosis 

A person who has been infected with VZV will develop antibodies to the virus that will stay in the body for the rest of that person’s life. A blood test for these antibodies can tell whether a person has been infected sometime in the past with VZV. VZV can be detected in lesions by direct fluorescent antibodies and fluorescent microscopy or by polymerase chain reaction (PCR).

Treatment

There's no cure for VZV, and treatment for the virus generally is not recommended for healthy patients. Patients with encephalitis, newborns, and people with compromised immune systems do need treatment for VZV infection. Antiviral drugs such as acyclovir and are available that slow down the virus reproduction and reduce symptoms, but cannot eliminate the virus.

Recommended Reading 

http://www.cdc.gov/chickenpox/index.html http://www.nlm.nih.gov/medlineplus/chickenpox.html

Herpes zoster: diagnostic, therapeutic, and preventive approaches. Postgrad Med. 2013 Sept; 125(5):78-91.