Varicella zoster virus

Varicella zoster virus (VZV) is one of eight herpesviruses (HHV 3) and is known to only infect humans. It causes varicella (chickenpox) upon initial infection, and can reactivate to cause herpes zoster (shingles). After initial infection, VZV establishes a latent infection in the body.

Initial infection
Varicella, or more commonly referred to as chickenpox, usually lasts 5-7 days. Typical signs and symptoms include: People who have been vaccinated against varicella can still get the disease, but it is usually a milder form. Complications can occur, but are not common in healthy, vaccinated people who get the disease. People who are at risk for complications include infants, adolescents, adults, pregnant women, and people with weakened immune systems. Complications include:
 * A rash that turns into itchy, fluid-filled blisters (turn into scabs after a week)
 * Fever
 * Tiredness
 * Loss of appetite
 * Headache
 * Bacterial infections of the skin and soft tissues
 * Pneumonia
 * infection/inflammation of the brain
 * Bleeding problems
 * Sepsis
 * Dehydration

Age of infection
Similar to Epstein-Barr virus, the age of initial infection affects the severity of the infection. In childhood (except for in infants), varicella is usually significantly less severe than in adolescence and adulthood. As a result, adolescents and adults are at risk for complications. Reactivation (zoster/shingles) also continues this pattern; older adults are more likely to have complications, with longer lasting and more severe pain.

Reactivation: Zoster/Shingles
About 1 in 3 people in the U.S. will develop zoster/shingles in their lifetime. Anybody who has had varicella/chickenpox may develop zoster (including children). People who have weakened immune systems or use immunosuppressive drugs (e.g., steroids) are at higher risk to develop zoster. Most people only have one episode of zoster, but multiple reactivations may occur. Zoster causes a painful rash on one side of the face or body. The rash consists of blisters that are accompanied by pain, itching, or tingling. Other symptoms can include fever, headache, chills, and an upset stomach.

Transmission of VZV
VZV is a highly contagious virus that spreads through touching or breathing in the virus particles that come from the chickenpox blisters. VZV can also be spread from people with zoster/shingles via the same methods of transmission, resulting in varicella/chickenpox. For most people, getting varicella/chickenpox once provides immunity for life, meaning they will not get chickenpox twice.

The best method of prevention is the chickenpox vaccine.

Latency and reactivation
After initial infection, VZV establishes a latent infection in the trigeminal nerve and dorsal root ganglia, most predominantly in 87% of the nuclei of neurons of the trigeminal ganglia, as VZV is neurotropic (preferentially targets neural tissue). VZV infects less than 0.1% of non-neuronal cells. It is present in the ganglia of more than 90% of adults.

Virus gene transcription during latency is epigenetically regulated by at least 6 genes. The expression of gene 63 is the indicator of VZV latency. Thus, reactivation can occur either spontaneously or following a triggering factor.

The latency burden of VZV seems to correlate with the severity of the primary illness.

Complications
Neurological complications may follow reactivation (zoster/shingles), especially in immunocompromised individuals. These complications include:
 * Encephalitis
 * Segmental motor weakness
 * Myelitis
 * Asteritis
 * postherpetic neuralgia
 * Vasculopathy
 * Viral infection of cerebral arteries
 * Vision loss
 * Hearing problems

Treatment
Antiviral treatment can be curative, even after weeks to months of chronic VZV infection.

VZV in ME/CFS
Other herpesviruses have been linked to ME.

One medical hypothesis states that for some patients, CFS is a result of infection by a neurotropic virus, particularly VZV. Shapiro argues that virtually all CFS symptoms could be produced by infection of the peripheral ganglia. He further argues that the chronic course of CFS could be explained by how infections of the peripheral ganglia can cause long-term nerve dysfunction.

Studies
A population cohort study followed a group of VZV-infected and non-infected individuals, and found that the incidence of CFS was higher among the VZV-infected cohort. The authors report that the VZV-infected patients that used antiviral treatment had a 15% reduced risk of CFS compared to patients without antiviral treatment. Overall they concluded that VZV infection may be associated with the risk of CFS, even without a comorbidity.

Lyme Disease
Several herpesviruses including varicella-zoster virus may cause false positives on Lyme Disease tests.

Prevalence

 * 2001, In a Belgian study, 26.8% of patients meeting the Fukuda criteria and 30.7% of patients meeting the Holmes criteria, in a cohort of 2073 CFS patients, reported cold sores and /or shingles.

Learn more

 * Wikipedia - Varicella zoster virus