Chicken Pox

Introduction 
Chicken Pox is an ubiquitous and extremely contagious viral illness. The primary illness, characterised by a generalised skin rash, is caused by the Varicella Zoster virus. Recurrence of the infection results in a localised skin rash, otherwise known as shingles or Herpes Zoster. Chicken Pox, often confused with Small Pox in earlier times, occurs seasonally and in epidemics the world over. Humans are the only known reservoir. The virus is spread by the respiratory route and is a common infection in children.

Cause and Pathogenesis 
Varicella Zoster virus is an enveloped virus of the herpes family. Chicken Pox occurs in susceptible individuals who are exposed to the virus after intimate contact. After entry through the respiratory route, the virus replicates, reaches the lymphatic system and then the blood stream. Roughly two weeks after the virus entry, a diffuse vesicular skin rash is seen. It is believed that the virus lodges in the sensory nerves after the rash clears only to reactivate at a later date, several years later, to cause herpes zoster.

Symptoms and Signs 
Chicken Pox presents with a low-grade fever and malaise, followed by a diffuse skin rash. This is associated with itching, loss of appetite and listlessness. The blisters are initially small and discrete with clear fluid, but gradually become cloudy and scab over. The rash is often referred to as "dew drop" during the early stages. The rash starts on the trunk and rapidly spreads to involve other areas of the body over 2 to 4 days. The crusts formed completely fall off in 1 to 2 weeks. Children with impaired immunity (decreased resistance) have numerous lesions that often bleed. Secondary bacterial infections can occur.
Chicken Pox can also cause encephalitis (brain fever) and cerebellar symptoms. A serious and life threatening complication is Chicken Pox Pneumonia, especially in adults and immunocompromised individuals. Chicken Pox affecting pregnant women just before delivery can cause fetal death. If the infection occurs earlier in pregnancy, the baby may be born malformed.

Investigations and Diagnosis 
History and physical examination usually aid the diagnosis of Chicken Pox. The characteristic skin rash with itching and low grade fever help to make the diagnosis.
Small Pox, earlier confused with chicken pox, has now been eradicated. Sometimes other viral infections or impetigo may resemble chicken pox. Herpes Zoster or Shingles is suspected if a localised rash is seen on one half of the body.
Confirmation of the diagnosis is possible by examining the direct scraping of the skin lesion under a microscope, viral cultures or a rising antibody level in convalescing blood samples.

Treatment and Prognosis 
The medical management of Chicken Pox and Shingles in a healthy host is directed towards reduction of the risks of complications, as the disease is essentially self-limited. Hygiene is very important, including bathing, astringent soaks and closely cropped fingernails to avoid secondary bacterial infections. Paracetamol should be used to reduce fever. Acyclovir is the drug of choice for both Chicken Pox and Herpes Zoster. The therapy should be started within 24 hours of the onset of the rash.
In children 2 to 16 years of age, the oral dosage is 20 mg/kg, 4 times a day for 5 days (maximum of 800 mg 4 times a day). Adolescents and adults can receive up to 800 mg 5 times a day. For Chicken Pox Pneumonia, intravenous Acyclovir or Vidarabine is of value, though excellent supportive nursing care is mandatory. In children, Chicken Pox has a very good prognosis.

Prevention 
Since Chicken Pox has a high secondary attack rate, people susceptible to Chicken Pox should avoid coming into contact with patients suffering from the infection. Prophylaxis for children is of little relevance as Chicken Pox is usually a benign disease.
However, vaccination is available for the prevention of Chicken Pox and is generally recommended between 10 - 12 years of age for children who have not had Chicken Pox before. This is also advised for immunocompromised patients who have not been previously exposed to Chicken Pox. Varicella Zoster Immuno Globulin (VZIG) and Varicella Zoster Immune Plasma (VZIP) are useful in preventing or ameliorating symptomatic Chicken Pox in high-risk individuals.