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Delayed Hypersensitivity in Ugandan Schistosomiasis

I. Sensitivity, Specificity, and Immunological Features of Intradermal Responses^*

Pamela L. Moriearty AND Robert M. Lewert

Immediate hypersensitivity (IHS) and delayed hypersensitivity (DHS) responses to intradermal injection of Schistosoma mansoni adult worm and cercarial antigens were evaluated for over 700 African residents of Uganda, an area endemic for schistosomiasis mansoni. Current and former residents of areas of high and low endemicity were tested. Biopsies from 6 individuals with DHS and 2 with IHS but no DHS were examined histologically. The sensitivity of the IHS test with adult worm antigen was high (87–95%), and this antigen showed higher sensitivity than cercarial antigen in infected women and children. Specificity of the IHS test, defined as the per cent of IHS responders with S. mansoni eggs in a single stool examination, was low, ranging from 38% in children to 48% in adults for adult worm antigen. Histology and time course of appearance of DHS reactions were similar to reactions of cellular hypersensitivity to other antigens. Biopsies from DHS reactions showed perivascular infiltration of mononuclear cells which increased in intensity from 24 to 48 hours. DHS responses were less frequently encountered than IHS responses; though most subjects with DHS also had IHS, DHS was present alone in 12% of late responders. Size distribution of DHS response areas approximated log normal distribution; mean log₁₀ response areas of adult males were significantly larger than corresponding reactions in females or children. An area of 0.6 cm² was accepted as an adequate criterion of positive DHS response; selection of smaller areas to distinguish negative from positive reactions caused some increase in sensitivity, but in most cases a drop in specificity. The DHS test was not an indicator of the number of eggs in the stool at the time of testing. The sensitivity of the DHS test was low, ranging from 29% in infected adult females to 59% in adult males. Combined use of the IHS and DHS tests improved specificity of the intradermal test markedly in children but only slightly in adults. The utility of the DHS intradermal test in diagnosis of schistosomiasis seems limited. Other possible uses of DHS testing in schistosomiasis are mentioned.

Accepted for publication August 18, 1973.

^* These investigations have been supported in major part by United States Public Health Service-National Institute of Infectious Diseases Grant No. AI 00884 and in part by the United States-Japan Cooperative Medical Science Program Grant AI 07724, and by a travel grant from the Rockefeller Foundation: Biomedical Sciences Grant No. GA MNS 6952.

Address reprint requests to: Dr. Robert M. Lewert, Department of Microbiology, University of Chicago, Cummings Life Sciences Center, 920 East 58th Street, Chicago, Illinois 60637.

Trainee, United States Public Health Service Training Grant No. AI 00331.