Abstract
Studies of the urine-based point-of-contact cathodic circulating antigen test (POC-CCA) in Schistosoma mansoni-endemic settings in Africa indicate it has good sensitivity in detecting infections, but in areas of low prevalence, the POC-CCA can be positive for persons who are egg-negative by Kato-Katz stool assays. We examined the POC-CCA assay for: (a) batch-to-batch stability; (b) intra-reader and inter-reader variability; (c) day-to-day variability compared to Kato-Katz stool assays, and (d) to see if praziquantel (PZQ) treatment converted Kato-Katz-negative/POC-CCA positive individuals to POC-CCA negativity. We found essentially no batch-to-batch variation, negligible intra-reader variability (2%), and substantial agreement for inter-reader reliability. Some day-to-day variation was observed over 5 days of urine collection, but less than the variation in Kato-Katz stool assays over 3 days. To evaluate the effect of treatment on Kato-Katz(−)/POC-CCA(+) children, 149 children in an area of 10–15% prevalence who were Kato-Katz(−) based on 3 stool samples but POC-CCA(+) were enrolled. Seven days after treatment (PZQ 40 mg/kg) samples were again collected and tested. Almost half (47%) POC-CCA positive children turned negative. Those still POC-CCA positive received a second treatment, and 34% of them turned POC-CCA negative upon this second treatment. Most who remained POC-CCA positive shifted each time to a “lesser” POC-CCA “level of positivity.” The data suggest that most Kato-Katz-negative/POC-CCA positive individuals harbor low-intensity infections, and each treatment kills all or some of their adult worms. The data also suggest that when evaluated by a more sensitive assay, the effective cure rates for PZQ are significantly less than those inferred from fecal testing. These findings have public health significance for the mapping and monitoring of Schistosoma infections and in planning the transition from schistosomiasis morbidity control to elimination of transmission.
Highlights
WHO guidelines for control and elimination of schistosomiasis involve pre-treatment and periodic post-treatment evaluations of the prevalence of Schistosoma infections to inform programmatic decisions on whom, and how often to treat within endemic areas [1]
This assay worked very well for control programs in areas of high intensity and corresponding high prevalence. It was used extensively and became established as part of WHO guidelines for morbidity control programs, with prevalence estimates usually based on examination of one stool per subject, using two separate Kato-Katz slides
ETHICS STATEMENT AND PARTICIPANT SELECTION The study protocol was approved by the scientific steering committee (SSC) of the Kenya Medical Research Institute (KEMRI, SSC number 1820), the Ethical Review Committee (ERC) of KEMRI, the Institutional Review Boards (IRB) of the Centers for Disease Control and Prevention (CDC), the Pontificia Universidad Catolica del Ecuador, Quito, Ecuador, the Aklilu Lemma Institute of Pathobiology, Addis Ababa University of Ethiopia and of the University of Georgia
Summary
WHO guidelines for control and elimination of schistosomiasis involve pre-treatment and periodic post-treatment evaluations of the prevalence of Schistosoma infections to inform programmatic decisions on whom, and how often to treat within endemic areas [1]. By making stool exams more feasible on a population level, the Kato-Katz technique revolutionized the process of obtaining intensity and prevalence data from large numbers of people. This assay worked very well for control programs in areas of high intensity and corresponding high prevalence. It was used extensively and became established as part of WHO guidelines for morbidity control programs, with prevalence estimates usually based on examination of one stool per subject, using two separate Kato-Katz slides. Over the course of a control program, the ability of the KatoKatz assay to provide true prevalence estimates will become less and less as the population mean intensity of infection decreases www.frontiersin.org
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