Assessment of immediate and delayed hypersensitivity skin tests with Schistosoma mansoni adult worm antigen in a rural Egyptian population.

Immediate and delayed hypersensitivity responses to schistosome adult worm skin test antigen were assessed in 418 farmers in Dakahlia Governorate, Egypt. All were from a population frame being epidemiologically evaluated for bilharzial urinary bladder cancer and thus were all 20 years old or older. A control, group of 108 adult urban dwellers without antecedent or current history of schistosomiasis were also tested. Ninety eight percent (411/418) of farmers and 35% (38/108) of controls showed reaginic hypersensitivity to 20 micrograms protein antigen. While 43% (180/418) of farmers and 4.6% (5/108) of controls showed positive delayed responses. Schistosoma haematobium eggs were found in 6% on urine cytology smears (Papanicolaou) and in 5% by Nuclepore filtration. A subsample of 97 individuals showed 21% to have S. haematobium eggs in urine by a traditional sedimentation technique. Immediate skin tests were equally positive in egg positive or egg negative farmers but delayed responses were 55% positive in the former and 26% in the latter. It is suggested that the delayed hypersensitivity skin test may be more specific and useful in epidemiologic surveys. The changing prevalence of S. haematobium infections in the Nile Delta is briefly discussed.