Sensitivity and Specificity of Three Onchocerca volvulus Cloned Antigens in the Diagnosis of Onchocerciasis

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Elmakki, Miskelyemen Abdelatti Abdalla
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University of Khartoum
Human Onchocerciasis is endemic in three geographic regions in the Sudan and is presented with variable clinical reactions. The current diagnosis of onchocerciasis is based on demonstration of live microfilariae in skin snips in addition to clinical signs and history of living in an endemic region. Different serological diagnostic trials using crude soluble antigen of Onchocerca volvulus have shown variable degrees of cross-reaction with other nematodes co-endemic in the same area. In this study, sensitivity and specificity of three O. volvulus recombinant antigens (RAL-2, Mwt.57, Calreticulin, Mwt. 87, PDI (protein disulphide isomerase), Mwt. 95) were determined using ELISA techniques. Eighty serum samples of onchocerciasis patients, 20 non-endemic normal controls and 42 samples of patients of other endemic diseases including leishmaniasis, malaria, tuberculosis and schistosomiasis were tested. RAL-2 detected the highest IgG response, with sensitivity of 83.75% and specificity of 91.66%. PDI sensitivity was 20% and its specificity was 91.66%, while Calreticulin showed sensitivity of 37.5% and specificity of 73.30%. The level of IgG3 subclass was not significantly different in patients and controls, while IgG4 was significantly higher in the patients. The sensitivity of RAL-2 for IgG4 was 90% with a specificity of 100%. For PDI, sensitivity was 25% and specificity of 100%, while Calreticulin had a sensitivity of 75% and specificity of 100%. Low levels of circulating IgE to RAL-2 antigen were detected. For all antigens, there was no significant correlation between IgG, IgG subclasses or IgE with gender, age, microflarial load or presence of nodules.
Human Onchocerciasis; Sudan; Leishmaniasis; malaria