Increased detection of schistosomiasis with Kato-Katz and SWAP-IgG-ELISA in a Northeastern Brazil low-intensity transmission area

Abstract

Introduction:The laboratory diagnosis of schistosomiasis is based mainly on the detection of parasite eggs in stool samples through the Kato-Katz (KK) technique, reading one slide by test. However, a widely known limitation of parasitological methods is reduced sensitivity, particularly in low endemic areas. Methods: To increase sensitivity, we conducted further slide readings from the same stool sample using the parasitological method associated with a serological test. We used the KK method (three slides) and the IgG anti-Schistosoma mansonienzyme-linked immunosorbent assay (ELISA) technique to diagnose schistosomiasis in low endemic areas in the Brazilian State of Ceará. Fecal samples and sera from 250 individuals were analyzed. Results: Sixteen percent and 47.2% of samples were positive in parasitological tests and serological tests, respectively. Parasitological methods showed that 32 (80%) individuals tested positive on the first slide, 6 (15%) on the second slide, and 2 (5%) on the third. The performance of the ELISA test in the diagnosis, using the KK method as diagnostic reference, showed a negative predictive value of 100%, with specificity and positive predictive values of 62.8% and 33.9%, respectively. Conclusions: In this study, the increase from one to three slides analyzed per sample using the KK technique was shown to be a useful procedure for increasing the diagnostic sensitivity of this technique.

High Schistosoma mansoni Disease Burden in a Rural District of Western Zambia

“…19,40 Sensitivity can be enhanced by examining multiple stool samples and smears. [40][41][42][43][44] In a study by Enk and others, 40 S. mansoni prevalence increased from 13.8% with 1 smear to 27.2% with 10 smears. Additional increase was observed when three samples were examined.…”

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

“…Therefore, microscopical method is not satisfied, especially when the number of worms is low or the test is done after the eggs were eliminated from the body [6] . In such cases, we should increase the number Kato-Katz smear per sample or run multiple Kato-Katz tests in interval days [5,26] .…”

“…In our study, since we examined a single Kato-Katz slide from each patient sample, the false positive results which detected by the serological tests should be followed up and confirmed by increasing the number of Kato-Katz smears per sample or repeating the stool sample in interval of days. However, these cases could be due to previous infections [11] , or due to the cross reactions with other parasites [5] . Also it could be useful to determine whether there is cross-reactivity with antibodies against other helminthes infections [7] .…”

“…In addition, the semi-quantitative egg counts can be performed by this method to determine the intensity of the infection [5] . Despite the specificity is very high, the sensitivity of Kato-Katz in single stool sample examination is becoming not satisfied, especially when the number of worms is low or the test is done after the eggs were eliminated from the body [1,6] , which leads to measurement error in estimating the presence of infection [1] .…”

“…Despite the specificity is very high, the sensitivity of Kato-Katz in single stool sample examination is becoming not satisfied, especially when the number of worms is low or the test is done after the eggs were eliminated from the body [1,6] , which leads to measurement error in estimating the presence of infection [1] . Nevertheless, there is a possibility to increase the sensitivity of Kato-Katz smear through examination of multiple samples [5] , but this is a limiting procedure for field study [7] . Moreover, this microscopic method is unsufficient in the areas of low endemicity, in post-treatment situations, and in the control of transmission [8,9] .…”