Chicken pox or Varicella in children

Chickenpox is a rather common infectious illness among children, particularly those under the age of 12 years. The maximum incidence of the disease is in those aged 1-6 years while children older than 14 years account for only about 10% of cases. Annual global incidence is estimated to be around 80-90 million cases. It is a highly contagious illness caused by primary infection with varicella zoster virus (VZV). Chickenpox has an incubation period of 10 to 14 days typically but this may be extended up to 21 days. It spreads easily through coughs or sneezes of ill individuals or through direct contact with secretions from the rash. Spread by droplet infection through the air is the commonest mode of spread. A person with chickenpox is infectious from one to five days before the rash appears. The contagious period continues until all blisters have formed scabs, which may take 5 to 10 days. It is not always necessary to have intimate contact with the infected person for the disease to spread. Chickenpox has also been observed in non-human primates, including chimpanzees and gorillas.

The illness starts with high fever, like any other viral illness. This is followed within one to two days by the appearance of the characteristic rash. An itchy rash of spots that later develop into blisters can appear all over the body. The temperature tends to settle down from the time of appearance of the rash. The skin rash tends to appear in several waves up to about the fifth day of the illness, tends to be centred around the chest and abdomen and only a few lesions may occur over the peripheries of arms and legs. The chicken pox lesions or blisters start as a two to four millimetre red area which develops an irregular outline like a rose petal. A thin-walled, clear blister resembling a dew drop develops on top of the area of redness. This "dew drop on a rose petal" lesion is very characteristic of chickenpox. After about 8 to 12 hours the fluid in the vesicle becomes cloudy and the vesicle breaks leaving a crust. The fluid is highly contagious, but once the lesion crusts over, it is not considered contagious. The crust usually falls off after seven days sometimes leaves a crater-like scar. Although one lesion goes through this complete cycle in about seven days, another hallmark of chickenpox is that new lesions crop up every day for several days. Therefore it may be a week before new lesions stop appearing and existing lesions crust over.

The severity of the illness is quite unpredictable in children. Even in the same family, one child may get a rather severe attack while the others may have milder illnesses. The disease tends to be more severe in the first month of life. In addition, in certain states of immune compromisation as seen in some inherited disorders, those on chemotherapy, acquired immune deficiencies and with long-term steroid therapy, the disease tends to be more severe. In them disseminated varicella and haemorrhagic complications pose significant problems. All children with cancer have an increased risk for severe varicella. The risk is highest for children with leukemia.

Even in normal children, it may not always be an entirely benign disease. One study suggested that nearly 1 in 50 cases are associated with some complications. The majority of these complications are due to secondary bacterial infection of the skin lesions. This is not serious and could be easily dealt with. Among the more serious complications are varicella pneumonia affecting the lung and encephalitis involving the brain. These two complications are associated with a significant mortality rate but it must be stressed that they are quite rare in normal children. A serious complication known as malignant chickenpox with a severe haemorrhagic rash is a grave clinical condition that has a mortality rate of greater than 70%. The exact cause of the hemorrhagic chickenpox syndromes is not known. In general and in otherwise healthy children aged 1-14 years, the mortality rate is estimated at 2 deaths per 100,000 cases.

In pregnant women, antibodies produced as a result of immunisation or previous infection with chicken pox are transferred via the placenta to the fetus. Women who are immune to chickenpox cannot become infected and do not need to be concerned about it for themselves or their infant during pregnancy. However, it could be a problem in those wwho have not had the disease or been vaccinated against it. Varicella infection in pregnant women can lead to viral transmission via the placenta and infection of the fetus. If infection occurs during the first 28 weeks of gestation, this can lead to fetal varicella syndrome, also known as congenital varicella syndrome. Effects on the fetus can range in severity from underdeveloped toes and fingers to severe anal and bladder malformation. Possible problems include damage to the brain, eye problems, neurological disorders with damage to the spinal cord, disturbances in development of limbs, ayal region and the urinary bladder and skin disorders with marked scar formation.

Infection late in gestation or immediately following birth is referred to as neonatal varicella. Maternal infection may be associated with complications for the mother and also lead to premature delivery. The risk of the baby developing the disease is greatest following exposure to infection in the period 7 days prior to delivery and up to 7 days following the birth. The baby may also be exposed to the virus via infectious siblings or other contacts, but this is of less concern if the mother is immune. Newborns that develop symptoms are at a high risk of pneumonia and other serious complications of the disease.

The word "pox" means a curse. Many people in this country, especially in the villages, refer to chicken pox as a "God given illness" or Deviyange leda. This notion has led to various types of dietary restrictions, especially a complete embargo on all types of meat and fish together with various types of semi-religious rituals for the disease. There is no scientific evidence that any dietary article has further deleterious effects on the disease. There is also no evidence to support the effectiveness of topical application of calamine lotion, in spite of its wide usage and excellent safety profile. It is important to maintain good hygiene and daily cleaning of skin with warm water to avoid secondary bacterial infection. To relieve the symptoms of chicken pox, many parents commonly use anti-itching creams and lotions. As long as these are bland preparations, no serious problem would be caused. However, no steroid containing creams should be used on the skin lesions.

There is a specific anti-viral drug that is effective in chicken pox. If started within the first 24 hours of the appearance of the rash it decreases symptoms quite noticeably. However, it does not seem to have any effect on the complication rates. If the general manifestations are quite severe, then there may be a place for this drug but general blanket use of this drug is not currently recommended. If exposure to varicella in certain ‘high risk’ populations such as immune suppressed children and pregnant mothers is confirmed, anti-varicella-zoster immunoglobulin may be given prior to onset of disease symptoms. This may not always be 100 per cent effective.

A person usually gets only one episode of chickenpox but the virus can lie dormant within the body and cause a different type of skin eruption later in life called shingles or herpes zoster. Varicella is associated with humoral and cell-mediated immune responses. These responses induce long-lasting immunity. Repeat sub-clinical infection can occur in these persons but second attacks of chickenpox are extremely rare in immunocompetent persons. One of the associated problems of the disease is that children with varicella expose adult contacts in households, schools, day-care centres and public places to the risk of severe, even fatal, disease.

A real problem with the disease occurring in children and adolescents is that they may catch it during important and most inconvenient times such as prior to examinations, crucial sporting events and social occasions such as weddings.

A vaccine against chicken pox was first developed by Michiaki Takahashi in 1974. It has been available in the Western countries from the mid nineties. The United States of America adopted universal vaccination against varicella in 1995 and this manoeuvre reduced the morbidity and mortality rates of this disease. Protection is not life-long and further vaccination is necessary five years after the initial immunization. In Sri Lanka, the vaccine is available in the private sector. Some countries require the varicella vaccination or an exemption before entering elementary school. Most developing countries have low immunization rates because of the cost involved and varicella disease is a risk for travelers to such countries.

The writer would appreciate some feed-back from the readers. Please e-mail him at bjcp@sltnet.lk or write to him at the following address :-

Dr, B.J.C.Perera, Consultant Paediatrician, Asiri Medical Hospital, 181, Kirula Road,
Colombo 5.

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