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| VARICELLA |
Disease and occurence
The causative pathogen is the varicella zoster virus (VZV). Varicella (chickenpox) is an acute, highly contagious disease with worldwide distribution. In temperate climates most cases occur before the age of 10 years. The epidemiology is less well understood in tropical areas, where a relatively large proportion of adults in some countries are seronegative.
Transmission is via droplets, aerosol or direct contact, and patients are usually contagious from a few days before rash onset until the rash has crusted over. While mostly a mild disorder in childhood, varicella tends to be more severe in adults. It is characterized by an itchy, vesicular rash, usually starting on the scalp and face, and initially accompanied by fever and malaise. As the rash gradually spreads to the trunk and extremities, the first vesicles dry out. It normally takes about 7–10 days for all crusts to disappear. The disease may be fatal, especially in neonates and immunocompromised persons. Complications include VZV- induced pneumonitis or encephalitis and invasive group A streptococcal infections. Following infection, the virus remains latent in neural ganglia; upon subsequent reactivation, VZV may cause zoster (shingles), a disease affecting mainly immunocompromised persons and the elderly.
Risk for travellers
In several industrialized countries, varicella vaccines have been introduced into the childhood immunization programmes. Most adult travellers from temperate climates are immune (as a result of either natural disease or immunization). Adult travellers without a history of varicella who travel from tropical countries to temperate climates may be at increased risk.
Vaccine
Varicella-zoster vaccine
Varicella-zoster vaccine (live) is licensed for immunisation against varicella in seronegative individuals. It is not recommended for routine use in children but can be given to seronegative healthy children over 1 year who come into close contact with individuals at high risk of severe varicella infections. Two types of vaccine are used for prevention of VZV infection. First a live attenuated varicella vaccine (oka) is recommended for all children of more than 1 year of age (upto 12 years of age) who did not have chicken pox or for adults known to be seronegative for VZV infection.
Live attenuated vaccine is given as single dose in children, while 2 doses, 4–8 weeks apart, are recommended for adolescents and adults.
Second inactivated virus vaccine which contains 18 times of the viral content of the Oka vaccine is being administered to immunocompromised persons with success. It is being recommended for individuals of more than 60 years of age. Live Varicella-zoster vaccine is contra-indicated in pregnancy (avoid pregnancy for 3 months after vaccination). It must not be given to individuals with primary or acquired immunodeficiency or to individuals receiving immunosuppressive therapy.
Rarely, the varicella-zoster vaccine virus has been transmitted from the vaccinated individual to close contacts. Therefore, contact with the following should be avoided if a vaccine-related cutaneous rash develops within 4--6 weeks of the first or second dose:
- varicella-susceptible pregnant women;
- individuals at high risk of severe varicella, including those with immunodeficiency or those receiving immunosuppressive therapy.
Vaccines for Travellers: Vaccines in this section need be offered only to travellers who are going to certain specific destinations. The decision to recommend a vaccine will depend on a travel risk assessment for the individual. |
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