Varicella (Chickenpox)

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Organism, Causative Agent, or Etiologic Agent
Chicken pox is caused by the varicella-zoster virus, VZV, a member of the Herpesvirus group. 

The virus spreads easily from people with chickenpox to others who have never had the disease or been vaccinated. The virus spreads mainly by touching or breathing in the virus particles that come from chickenpox blisters, and possibly through tiny droplets from infected people that get into the air after they breathe or talk, for example.

The Varicella-zoster virus also causes shingles. Chickenpox can be spread from people with shingles to others who have never had chickenpox or received the chickenpox vaccine. This can happen if a person touches or breathes in virus from shingles blisters. In these cases, a person might develop chickenpox, not shingles.

Symptoms (Clinical Illness)
A skin rash of itchy, blister-like lesions that eventually turns into scabs. The rash may first show up on the face, scalp, and trunk and then spread to the rest of the body. It usually takes about one week for all the blisters to become scabs.

Other typical symptoms that may begin to appear 1-2 days before rash include:

  • Fever
  • Tiredness
  • Loss of appetite
  • Headache

People who have been vaccinated against chickenpox can still get the disease. However, the symptoms are usually milder (sometimes involving only a few red bumps that look similar to insect bites and mild or no fever).  Adolescents and adults are more at risk for severe disease. Women infected during pregnancy may pass the disease on to their baby. People with weakened immune systems are also at risk for complications.

Incubation Period
The incubation period is usually 14-16 days with a range of 10-21 days.

Varicella is most infectious 5 days before rash onset (especially 1-2 days before rash onset) and for up to 5 days after onset of lesions (until crusting). Communicability may be prolonged in those who have altered immunity.

Prevention and Vaccination
Varicella vaccine can prevent this disease. Currently, two doses of vaccine are recommended for children, adolescents, and adults. Children should receive two doses of vaccine—the first dose at 12 through 15 months and a second dose at 4 through 6 years old.

School Exclusion Policy
Children with suspected or confirmed chickenpox (varicella) should be kept out of school or childcare until the lesions are dry (scabbed) or if lesions are not vesicular (blister-like), until 24 hours have passed with no new lesions. Rules for exclusion of sick children from school and childcare are outlined in the Texas Administrative Code, specifically Rule 97.7 for schools.

Recent Texas Trends
Texas’s varicella incidence dropped dramatically in 1999, as vaccination coverage rose across the state due to school vaccine requirements. Varicella infections have continued to decline through 2018 reaching 972 cases of varicella in Texas, the lowest annual case count since reporting began. Cases increased to 1,291 the following year in 2019, with a drop in 2020 to 348 cases. Overall, the biggest decrease has been seen in the age group most heavily affected by varicella, five to nine-year olds.
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