In the industrialized countries of the West, varicella is largely a childhood disease, whereas reports from tropical countries indicate a significant incidence of varicella among adults. High ambient temperature, epidemiologic interference from other viruses, and race have been blamed. We tested our hypothesis that less exposure to varicella-zoster virus (VZV) during childhood in rural areas accounts for the reported greater frequency of varicella in adults in tropical climates by comparing rates of VZV seropositivity among urban and rural adult Bengalee populations living in identical climatic conditions in India. Only 5 (3.4%) of 153 urban adults were seronegative compared with 74 (31.1%) of 246 rural adults. Ninety-six percent of urban adults were immune by the age of 25, compared with 42% in the rural group. The results suggest that higher adult susceptibility to varicella is seen only in rural areas of the Tropics and is due to reduced transmission of VZV. for the contrasting epidemiologic scenes between the industrialized countries of the temperate north and the developing coun-ú90% of adults are immune to infection with VZV. However, numerous reports point to a different age-distribution pattern tries of the warmer south. It has been suggested that the high ambient temperature of the Tropics inactivates VZV in cutafor VZV infection in developing countries in the Tropics. Some reports are based on surveys of antibody to varicella. neous lesions thereby lessening its transmission potential [8]. Sinha [15] postulated the concept of epidemiologic interference Sera from an age-stratified sample of 1810 people on the Caribbean island of St. Lucia showed that õ10% of the populaby the high prevalence of certain childhood viruses in the developing countries; the interference postponed the age of tion had experienced VZV infection before the age of 15 years, and the proportion rose to ú70% by the age of 40 [8]. In a varicella infection. Dworkin [19] felt that race could be a possible factor; he referred to four studies, involving US Army seroepidemiologic survey in Singapore conducted during [1989][1990], 40% of persons in the 15-to 24-year-old age group (samand Navy personnel, the results of which suggested that black persons were more susceptible than white persons to varicella ple size 100) and ú80% in the 25-to 34-year-old age group (sample size 50) had evidence of past infection [9]. Only 30% in adulthood [20 -23]. CurrentlyIn the current study, we looked at an alternative hypothesis, of student nurses who were 17 to 20 years old possessed complement-fixing antibodies to VZV antigen in Vellore, India [10].postulating that the higher adult susceptibility observed in tropical countries is a rural phenomenon and results from a lack In a serologic survey of pregnant women, the proportion with VZV antibodies was 84% for 51 women born in the Tropics of exposure to VZV because of rural living conditions in the Tropics where VZV circulates poorly. Most reports of higher and 95% for 88 women in the United States [11]...

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