Varicella (Chickenpox)

Bacteriology at UW-Madison

The Microbial World

Lectures in Microbiology by Kenneth Todar PhD University of Wisconsin-Madison Department of Bacteriology

Varicella (Chickenpox)

Varicella (chickenpox)

Chickenpox is a common, highly contagious disease of children. It involves a slight fever and cutaneous lesions characterized by crops of blister-like vesicles. The exudates and scabs of these pock-like lesions transmit the disease by the respiratory route.

Chickenpox is caused by the Varicella zoster virus (VZV), an icosahedral, enveloped, DNA virus in the Herpes family. It is related to Herpes simplex viruses and to the Epstein-Barr virus.

The rash associated with chickenpox. Some of the lesions are red spots and some are blisters. The red spots will become blisters and new red spots will appear. The rash appears on the trunk and face, but can spread over the entire body causing between 250 and 500 blisters. Most cases of chickenpox occur in persons less than 15 years of age. Prior to the use of varicella vaccine, the disease had annual cycles, peaking in the spring of each year. CDC.

Chickenpox generally is a mild disease with rare mortality in children or adults suffering no other diseases. However, according to CDC, about half of all children with chickenpox visit a health care provider due to symptoms of their illness, such as fever, severe itching, an uncomfortable rash, dehydration, or headache. In addition, about one child in ten that visits a health-care provider has a complication from chickenpox, including infected skin lesions, other infections, dehydration from vomiting and diarrhea, exacerbation of asthma, or pneumonia. Many people are not aware that before a vaccine was available, there were approximately 11,000 hospitalizations and 100 deaths from chickenpox every year in the United States.

Treatment

Scratching is discouraged because it may cause the blisters to become infected. Calamine lotion or Aveeno (oatmeal) baths may be used to relieve itching. Aspirin should not be used to relieve a child's fever. Aspirin has been associated with the development of Reye syndrome. Non aspirin medications, such as acetaminophen, may be used.

Acyclovir, an antiviral drug, is recommended for individuals who are more likely to develop serious disease, including persons with weakened immune systems from either illness or from medications such as steroids.

Varicella zoster immune serum (VZIG) can prevent or modify the disease after exposure, but it is only recommended for persons who are at high risk of developing severe disease.

Prevention

Varicella vaccine is a live attenuated virus vaccine that is administered subcutaneously. For children under 12 years of age it is administered as a single dose. Persons 13 years and older should receive two doses 4-8 weeks apart. Preliminary studies showed the vaccine to be 70-90% effective in preventing disease and more than 95% effective in protecting against severe disease. The duration of protective immunity is not known since the vaccine is relatively new. However, data from pre-licensure clinical trials indicates that immunity lasts from 14 to 25 years, and there is no recommendation at this time for a booster dose.

Congential Varicella Complications

If infection by the varicella virus occurs in utero during the first trimester of pregnancy, congenital varicella syndrome may result in the newborn, as evidenced by scarring of the skin of the limbs, damage to the lens, retina and brain, and microphthalmia.

Infection of a mother at around the time of birth can lead to the infection of the infant. Since the infant will not have maternal antibodies against varicella and has immature cell-mediated immunity, it may succumb to the disease with a mortality rate of up to 35%. If the mother becomes infected near to term, both she (before delivery) and her infant (immediately after delivery) should be treated with varicella immune globulin. Most infants, however, get maternal antibodies trans-placentally and are protected from the disease.

Shingles

The Varicella zoster virus that causes chickenpox also causes shingles or herpes zoster in individuals who have recovered from chickenpox. After a case of chickenpox, the virus may migrate to nervous ganglia associated with areas of viral replication and remain latent. The virus may then be reactivated under stress or with immune suppression later in life. The recurrence of varicella replication is accompanied by severe radicular pain in areas innervated by the nerve in which latent infection has occurred. A few days later chicken pox-like lesions occur in restricted areas (dermatome) that are innervated by a single ganglion. New lesions may appear in adjacent dermatomes and even further afield. Reactivation can affect the eye via the trigeminal nerve (uveitis, keratitis, conjunctivitis, ophthalmoplegia, iritis) and the brain via the cranial nerve VII and VIII (Bell's Palsy and Ramsay-Hunt syndrome). Reactivation can lead to chronic burning or itching pain called post-herpetic neuralgia. The pain may last well after the rash has healed (even months or years). Often associated with post-herpetic neuralgia, is increased sensitivity to touch (hyperesthesia). Patients with AIDS often exhibit multi-dermatomal recurrence of varicella infection.

More about Chickenpox and other Varicella Diseases
CDC - Chickenpox vs Smallpox Poster.pdf
University of South Carolina School of Medicine: Herpes Viruses
CDC: Varicella Zoster Infection
CDC National Immunization Program: Varicella Disease (Chickenpox)