Chickenpox (varicella) is a generalised infection caused by the virus Herpes zoster.
Infection occurs when the virus passes to another person from the fluid-filled blisters that cover the body of patients, or in their breath and saliva.
Patients are infectious for a day or two before the spots appear, and remain infectious for about eight days. The incubation period is 10 to 21 days.
Early symptoms are similar to those of a cold, with a vague feeling of being unwell, headache, fever and sore throat. The rash usually starts on the head or chest as red pimples, then spreads onto the legs and arms, and develops into blisters before drying up and scabbing over. New spots may develop for three to five days, and it may be two weeks or more before the last spot disappears.
The diagnosis can be confirmed by varicella antibody blood tests, but none are usually necessary.
Treatment involves bed and home rest until the patient feels well, and medications to relieve the itch (e.g. calamine lotion, antihistamines), fever and headache. Children must be excluded from school for at least five days from the appearance of the first blisters and until all blisters have developed a dry scab.
There is a vaccine has been available since 2000 to prevent the disease, and as a result chickenpox is now rarely seen in Australian general practice. One injection is necessary if given between 12 months and 12 years of age, but two injections six weeks apart in older children and adults.
Complications are more common in adults, and include chest infections and a type of meningitis. It is unusual for the pockmarks to scar unless a secondary bacterial infection occurs.
Complete recovery within ten days is normal. Once a person has had chickenpox, it is unlikely (but not impossible) that they will ever catch it again.
Once a patient has had chickenpox, the virus never leaves their body but migrates to the nerves along the spinal cord where it remains forever. The virus may be reactivated years later at times of stress to give the patient the painful rash of shingles.