Describe the epidemiology, pathogenesis and control of chickenpox.

Outline:

·        Epidemiology:

- childhood disease

- spread by respiratory secretions

·        Pathogenesis:

- vesicular rash

- complications: encephalitis & Reye’s syndrome

·        Control:

- isolation

- acyclovir

- vaccine & immunoglobulins

Suggested Answer:

            Chickenpox, or varicella, is the manifestation of primary varicella-zoster virus infection. Varicella-zoster virus belongs to the family of herpesvirus. It has a linear double-stranded DNA genome and a lipoprotein envelope. There is only one serotype.

Varicella is a highly contagious disease of childhood. The spread of varicella-zoster virus depends upon airborne droplet transmission from a person who is shedding virus to a susceptible host. By adulthood, as many as 90 to 95 per cent of individuals have serologic evidence of infection with varicella-zoster virus. Rarely, it spreads perinatally. Humans are natural hosts of the virus. A primary attack of varicella is followed by solid and long-lasting immunity to varicella, but not to zoster, a disease caused by reactivation of the latent varicella infection.

            Varicella virus infects mucosa of the upper respiratory tract from which it spreads via blood to the skin, causing a vesicular rash. Multinucleated giant cells are found at the base of the lesions. After primary infection, the virus becomes latent in the dorsal and cervical ganglia.

             Varicella infection occurs most commonly in young children of preschool age and has a characteristic disseminated vesicular rash which appears after an incubation period of 14 to 17 days. Fever and malaise are common in the prodrome phase. The rash begins on the face and trunk and spreads to the extremities. The lesions of chickenpox are initially vesicles which become pustular, crusted, and then scabbed prior to healing. The average duration of lesion formation is three to five days in the normal child; however, it is usually longer in adolescents and adults and certainly in the immunocompromised.

            Complications of varicella are rare and they include post-infectious encephalitis and hemorrhage, pneumonia, which is common in adults and Reye’s syndrome. Adults and immunocompromised children have a higher incidence of visceral disease. Immunocompromised children, particularly those with acute lymphoblastic leukemia, are at increased risk for progressive disease, specifically resulting in pneumonitis and/or hepatitis.

            Maternal varicella during the first two trimesters of pregnancy may cause the congenital varicella syndrome (CVS). After infection in the first 20 weeks' gestation, the incidence is estimated to be about 2%. The characteristic symptoms consist of skin lesions in dermatomal distribution (76%), neurologic defects (60%), eye diseases (51%), and skeletal anomalies (49%). About 30% of infants born with these lesions died in the first months of life. The diagnosis of CVS should be established by the appearance of maternal varicella, the presence of typical clinical symptoms as well as the laboratory evidence of in utero varicella-zoster virus (VZV) infection. In the reviewed infants, intrauterine VZV-infection has been proved in about 60%. Passive immunization may reduce the risk of fetal infection but there is no evidence to prevent fetal viremia. Up to now, there are no controlled studies concerning antiviral chemotherapy in preventing CVS.

            Varicella in normal health individuals in a self-limiting disease with recovery complete in one to three weeks. During this period of time, the person with chickenpox is infectious and should be segregated from members of the family and the community to prevent further spread of the disease. A varicella vaccine containing the live attenuated virus is now available to prevent varicella. Acyclovir may be used in severe disease and immunocompromised patients; they accelerate the healing of lesions. Varicella-zoster immunoglobulin contains high titer of antibody to the virus and reduces the severity of varicella in contacts of the virus. It is commonly used amongst immunosuppressed children or adults, or neonates born to mothers with varicella and pregnant women exposed to the virus.

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