Epidemiology of poly-parasitism. III. Effects on the diagnostic capacity of immunological tests

Abstract

The paper describes some effects of interaction between different types of parasitic infections on the diagnostic capacity of immunological tests for parasitic diseases. Examples shown include an analysis of association for anergy to tuberculin in skin tests of individuals with and without skin manifestations of onchocerciasis; skin tests with P. westermani and C. sinensis antigens to detect double infections in patients harbouring both trematodes; geographical evaluation of the sensitivity of the complement fixation (CF) test for schistosomiasis with S. mansoni antigen between different communities in Chad; reduced sensitivity of the CF test for schistosomiasis in patients with confirmed schistosomiasis who have also onchocerciasis; studies on the specificity of the slide flocculation (SF) test for schistosomiasis in relation to specified intestinal parasites and to the presence of antibodies to E. granulosus and T. spiralis in villages of Afghanistan; and a study of association between poly-parasitism and anticomplementary activity in the sera of population samples from the African Savannah. The combined investigations indicate that there are large dissimilarities in test performance between communities with different disease spectra and nutritional status. The findings suggest that polyparasitism interferes with immunodiagnostic tests both directly through cross-reactions with antigens and antibodies and indirectly through its effects on nutrition and on mechanisms affecting the complement system. Large scale screening for parasitic diseases with immunodiagnostic tests in areas in which the medical problems are not well-known should be prededed by a small, well-planned pilot study in which the relative sensitivity and specificity of the test can be determined before its use in extensive population studies.