Evaluation of microscopical and serological techniques in the diagnosis of Schistosoma mansoni infection at Sennar State, Central Sudan

Abstract

ObjectiveTo determine the prevalence of Schistosoma mansoni (S. mansoni) infection among schoolchildren and to evaluate the sero-diagnostic techniques of indirect-haemagglutination (IHA) and enzyme-linked immunosorbent assay (ELISA) in comparison with Kato-Katz smear examination. MethodsA descriptive cross-sectional study was conducted from August, 2011 to January, 2012 at Sennar State, central of Sudan. Stool and blood samples were collected from schoolchildren (n=214) those with age groups from 6 to 16 years old. Kato-Katz smear was used for the detection of S. mansoni eggs and then the intensity of infection was determined as per standard procedure. IHA and ELISA assays were applied to detect S. mansoni antibodies. Considering the Kato-Katz as a reference method, the sensitivity, specificity, positive predictive values (PPV) and negative predictive values of serological methods were evaluated. ResultsOut of 214 schoolchildren enrolled, 45 (21%) were found to be positive for infections using Kato-Katz technique. Of these, 84.4% were having light infections, 6.7% with moderate infections and 8.9%with heavy infections. Shistosomiasis was significantly higher (P=0.007) among boys (33/124; 26.6%) than girls (12/90; 13.3%). In comparison between the applied methods, the majority of the positive cases were detected by ELISA (56.1%; 120/214) followed by IHA (33.2%; 71/214) and Kato-Katz (21%; 45/214). The sensitivity of the ELISA was 93.3% compared to 84.4% given by IHA. Furthermore, the specificity was reduced to 53.8% in ELISA compared to the 80% detected by IHA. The PPV was increased in IHA (53.3%) than that of in ELISA (35%). The combination use of the ELISA and IHA were yielded good sensitivity (93.3%), increased the rates of specificity to 85.8% and PPV to 55.1%. ConclusionsIn the settings where the prevalence of S. mansoni infection was high with a low infection intensity, performing of serodiagnostic methods together with a microscopical examination are required to detect more positive cases.