Studies on Dengue in Vellore, South India

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Abstract
Summary During the past several years, 137 group B arthropod-borne-virus infections have been detected among persons with dengue-like illnesses at Vellore, South India. From these cases 104 strains of dengue have been isolated. Most of these strains have been recovered from the sera of ill staff and students at the Christian Medical College Hospital. Dengue types 1, 2 and 4 have been identified. During 1961 and 1962 dengue type 1 isolates predominated. Dengue 2 virus, last isolated in 1959, reappeared in 1963. Patients yielding dengue virus or developing group B antibody in the absence of a virus isolation had clinical courses predominantly resembling classical dengue. A study that included collection of pre- and post-dengue season sera from 61 student nurses during 1961 showed that there was little if any subclinical dengue infection in this group. Eleven infections were detected serologically or by virus isolation, and all but one of these were associated with dengue-like illnesses occurring during the dengue season. The eleventh student developing antibody had an illness compatible with dengue but at a time when no other cases were recognized. Cases and virus isolations have shown a bimodal distribution, with peaks in March and September corresponding with periods of rising and falling ambient temperatures. Antibody responses were marked by their height and their broadness. Dengue virus was isolated both from sera containing group B complement-fixing and/or hemagglutination-inhibiting antibody and from sera with no detectable antibody. Factors important in the isolation of dengue virus have included inoculation of very young mice with patient's serum obtained early in the illness, careful daily checking of each mouse and passage at the first signs of illness in any of the mice.

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