RESUMEN
Recently, our group determined the relationship between serum CAA levels and fecal egg counts in two foci very intense Schistosoma mansoni transmission: Maniema (Zaire), an area endemic for S. mansoni since several decades, and Ndombo (Senegal), where transmission has only been established since a few years. The objetive was to study and compare age-related worm load and worm fecundity patterns in these two different endemic settings. Here, we will summarize the most important findings and conclusions of this study.
Asunto(s)
Animales , Antígenos Helmínticos , Enterobius/fisiología , Schistosoma mansoni/parasitología , República Democrática del Congo/epidemiología , Esquistosomiasis , SenegalRESUMEN
Recently, our group determined the relationship between serum CAA levels and fecal egg counts in two foci with very intense Schistosoma mansoni transmission: Maniema (Zaire), an area endemic for S. mansoni since several decades, and Ndombo (Senegal), where transmission has only been established since a few years. The objective was to study and compare age-related worm load and worm fecundity patterns in these two different endemic settings. Here, we will summarize the most important findings and conclusions of this study.
Asunto(s)
Antígenos Helmínticos/sangre , Enfermedades Endémicas , Recuento de Huevos de Parásitos , Esquistosomiasis mansoni/parasitología , África , Factores de Edad , Animales , Fertilidad , Humanos , Esquistosomiasis mansoni/epidemiología , Esquistosomiasis mansoni/inmunologíaRESUMEN
Schistosoma mansoni egg counts by faecal examination vary considerably and are not very sensitive, so prevalences are underestimated. The distribution of egg counts can adequately be described by a stochastic model which distinguishes variation in counts between persons and variation in repeated counts within a person. Based on this model a pocket chart has been developed which predicts the proportion of individuals harbouring at least 1 S. mansoni worm pair-the 'true prevalence'-from a simple single survey prevalence and geometric mean egg count (using common duplicate 25 mg Kato-Katz smears). The current paper describes the validation of this chart by comparing predicted true prevalences with prevalences observed after 5-7 repeated Kato-Katz faecal examinations (Burundi), by examination of a large quantity of stool using the Visser filter (Brazil) or a selective sedimentation-filtration method (Surinam). Because 5-7 repeated examinations do not suffice to measure all infections, predictions have been made of the cumulative proportion positives over 5-7 surveys-the 'approximate true prevalence'-as well. After dividing the data into age groups, 12 different subsets were considered for validation. In all 12 cases, predicted true prevalences (or approximate true prevalences for the Burundi data) agree well with those observed. The overall agreement depends only slightly on the assumed relationship between worm numbers and mean egg counts, with a good fit for a productivity between 0.8 and 4.4 eggs per gramme faeces (EPG) per worm pair (WP). This interval includes the most plausible value from the literature, i.e. 1.0 EPG/WP, which has been applied in the initial pocket chart. These findings support the validity of the chart to predict true prevalences for a wide range of productivity assumptions, and reinforces the applicability of its underlying stochastic model to describe egg count variation. However, as predictions appear to vary importantly when using only part of the data, it is also concluded that the pocket chart never compensates for limited validity of initial single survey prevalences and geometric means in consequence of small sample sizes.
Asunto(s)
Heces/parasitología , Recuento de Huevos de Parásitos , Schistosoma mansoni/aislamiento & purificación , Esquistosomiasis mansoni/diagnóstico , Esquistosomiasis mansoni/epidemiología , Adolescente , Adulto , Factores de Edad , Animales , Brasil/epidemiología , Burundi/epidemiología , Niño , Preescolar , Métodos Epidemiológicos , Humanos , Prevalencia , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Procesos Estocásticos , Suriname/epidemiologíaRESUMEN
We evaluated the applicability of circulating antigen detection in serum and urine for the diagnosis of Schistosoma infections in a low endemic area. In total 389 individuals from Saramacca (Surinam) participated in the survey. Stool samples were examined using the Kato method, while circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) were determined by highly specific monoclonal antibody-based ELISA's. Also schistosome specific IgM antibodies were measured by the indirect immunofluorescence assay, but the diagnostic performance of this test was found to be poor in this population. S. mansoni eggs were found in 29% of the examined cases, while CAA and CCA could be demonstrated in 23% and 17% of the serum samples and in 3% and 28% of the urine samples, respectively. Forty three percent of the study population was positive in at least one of these diagnostic assays, indicating that each individual test misses a substantial part of the subjects with an active infection. In most positive cases, intensities of infection were very low. As 204 individuals participated in all screening assays, diagnostic performance of each test was evaluated in this sub-population. The highest sensitivities were achieved with the urine-CCA assay and the parasitological examination, detecting 59 and 58 out of the 107 cases with an active infection, respectively. The serum-CAA assay detected 47 positive cases. Our results demonstrate that determination of circulating antigens, especially CCA in urine and CAA in serum, provides information additional to the parasitological examination, for the assessment of prevalence and intensity of Schistosoma infection in low endemic areas.
Asunto(s)
Antígenos Helmínticos/análisis , Glicoproteínas/sangre , Glicoproteínas/orina , Proteínas del Helminto/sangre , Proteínas del Helminto/orina , Esquistosomiasis mansoni/diagnóstico , Adolescente , Adulto , Factores de Edad , Anciano , Anciano de 80 o más Años , Animales , Anticuerpos Antihelmínticos/aislamiento & purificación , Antígenos Helmínticos/sangre , Antígenos Helmínticos/orina , Niño , Preescolar , Heces/parasitología , Femenino , Humanos , Pruebas Inmunológicas , Lactante , Masculino , Persona de Mediana Edad , Recuento de Huevos de Parásitos , Prevalencia , Schistosoma mansoni/inmunología , Esquistosomiasis mansoni/sangre , Esquistosomiasis mansoni/epidemiología , Esquistosomiasis mansoni/orina , Sensibilidad y Especificidad , Suriname/epidemiologíaRESUMEN
An epidemiological survey for infection with Schistosoma mansoni was carried out in the community of Catharina Sophia in northern Surinam. The merits of a more sensitive diagnostic system, the Sedimentation-Selective-Sieving (SSF) method, were evaluated; the results were compared with those obtained with the standard Kato-Katz thick smear technique. Examination of a duplicate Kato smear (2 x 25 mg) resulted in a prevalence of 22% while the real prevalence was shown to be more than 42%. The SSF procedure was shown to have a comparatively high sensitivity although the egg counts per gram (calculated on the basis of examining samples of 2-3 g) were considerably lower than those derived from Kato smears. The implications for epidemiological surveillance of communities with excretion of low numbers of S. mansoni eggs are discussed and the observations are compared with those one might expect on the basis of mathematical modelling (De Vlas et al., 1992).