Seroepidemiology and serodiagnosis of schistosomiasis in Kenya using crude and purified egg antigens of Schistosoma mansoni in ELISA

Abstract
The performance of antibody detection for the diagnosis of schistosomiasis has been evaluated in Kenya. Approximately 1500 blood samples from 3 areas with endemic schistosomiasis (Schistosoma mansoni only, S. haematobium only, and a mixed infection area), and from a non-endemic control area, were tested for their antibody reactivity in an enzyme-linked immunosorbent assay (ELISA). The results were compared with infection status determined by parasitological examination. Two test antigens were used: unfractionated S. mansoni egg homogenate (SEA), and CEF6, a previously described, partially purified fraction of SEA containing 2 cationic antigens. The antigens prepared from eggs of Kenya and Puerto Rico S. mansoni isolates gave very similar results. Bloods from patients with S. haematobium infection cross-reacted significantly with the two S. mansoni antigen preparations, but reactivity against CEF6 appeared more specifically indicative of S. mansoni infection. Of 254 blood samples from schoolchildren in the non-endemic area, 100% gave ELISA optical density readings at 492 nm (OD492) < 0.20 against SEA, and 98% were < 0.20 against CEF6. With 887 blood samples from subjects of all ages in the area endemic for S. mansoni alone, using an ELISA OD492 cut-off point of 0.20, SEA and CEF6 had sensitivities of 94% and 97% respectively, and specificities of 64% and 59% respectively. Increasing the OD492 cut-off value reduced the sensitivity and increased the specificity of both test antigens. Specificity of both antigens was poor with samples from 234 children in an area endemic for both S. mansoni and S. haematobium (< 20% for both antigens at an OD492 cut-off value of 0.20).(ABSTRACT TRUNCATED AT 250 WORDS)

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