Adrian C. Sleigh

Comparison of filtration staining (Bell) and thick smear (Kato) for the detection and quantitation of Schistosoma mansoni eggs in faeces

We compare results of one Bell and one Kato-Katz examination performed on each of 315 stool specimens from residents in an area in north-eastern Brazil endemic for schistosomiasis mansoni. The prevalence of Schistosome infection detected by the Bell technique was 76% and by the Kato-Katz technique was 63%. 81% (44/54) of the infections missed by a Kato-Katz smear were light infections (one of 50 epg range by Bell examination). Over, all, 55% (44/80) of stools in this egg count range by the Bell technique were negative on a single Kato-Katz smear. This implies that five Kato-Katz smears per stool would ensure a 95% probability (0.55(5) X 100) of detecting such light infections. However, a single Kato-Katz smear detected eggs in 97% (124/128) of stools with a Bell count greater than 100 epg. For stools positive by both methods the egg counts per gram of stool were higher (p less than 0.001) by Kato-Katz examination. Geometric mean egg counts for the infected population were 199 epg by the Kato-Katz and 92 epg by the Bell methods. 64% (59 v. 36) more persons were classified as heavily infected (greater than 400 epg) by the Kato-Katz method than by the Bell method. The differing measurements of schistosome infection obtained with the Bell and Kato-Katz methods must be considered when comparing data on morbidity-infection relationships.

Manson's schistosomiasis in Brazil: 11-year evaluation of successful disease control with oxamniquine.

This prospective study has shown that oxamniquine treatment controlled endemic schistosomiasis mansoni in a defined rural population in Castro Alves, north-east Brazil. Data before and after treatment spanning 11 years were collected for a cohort of 191 residents. Before treatment (1974-77), the cohort was heavily infected and the prevalence of associated hepatomegaly (greater than 86%) and splenomegaly (greater than 17%) was stable. The cohort was treated when oxamniquine became available in 1977; during the next 8 years, over 80% received further treatments from the Brazilian programme for the control of schistosomiasis. With treatment, the incidence of splenomegaly fell (10% to 2%) and the splenomegaly regression rate increased (43% to 91%). Declining disease rates were coincident with substantial falls in the prevalence and intensity of Schistosoma mansoni infections. The final prevalence rates for hepatomegaly (31%) and splenomegaly (3%) in Castro Alves approached the corresponding rates of 10% and 1% in a comparable uninfected control population.

A three year follow-up of chemotherapy with oxamniquine in a Brazilian community with endemic schistosomiasis mansoni

Oral oxamniquine was tested as a control strategy for endemic schistosomiasis in a rural area of Bahia, Brazil. Adults were treated with a single dose (12.5 to 15 mg per kg) and children (less than 12 years old) with a total of 20 mg per kg in two doses. The 191 (infected) persons treated represented 69% of the infected population in the study area. Follow-up stool examinations (Kato-Katz method) at one, 3, 6, 13, 25 and 33 months showed the cure rate declining from 80% at three months to 46% at 33 months. Over one half of those not cured showed a decrease in egg counts throughout the follow-up which, after 33 months, remained 66% below the pre-treatment levels. Stool examinations conducted on all study area residents during three years before chemotherapy showed the prevalence and intensity of Schistosoma mansoni infection to be high and stable. 33 months after the chemotherapy the prevalence was 41% and for infected individuals the geometric mean egg count was 121 epg, a decline of respectively 35% and 40% from pre-treatment levels for each index. Chemotherapy of infected persons with oxamniquine protected the community as a whole from high worm burdens for almost three years, although at this point the prevalence began to rise towards pretreatment levels.

THREE-YEAR PROSPECTIVE STUDY OF THE EVOLUTION OF MANSON'S SCHISTOSOMIASIS IN NORTH-EAST BRAZIL

A cross-sectional study of morbidity associated with Schistosoma mansoni infection in an area in North-East Brazil where the disease is endemic was carried out in 1974. The survey was repeated in 1977, before mass treatment with oxamniquine, providing a cohort of 210 individuals who had both examinations. The high prevalence of hepatomegaly (over 80%) and of splenomegaly (over 15%) contrasted with rates of 10% and 1%, respectively, in a non-endemic area. Over the 3-year period hepatomegaly spontaneously regressed in 13% of patients, and splenomegaly regressed in 56%, a phenomenon most common in older individuals with light infections. Those with heavy infections--ie, 500 or more eggs per g faeces, had an excess risk of splenomegaly of 19.6% and, of its persistence, of 61.5%. Thus, intensity of infection was a critical factor in liver and spleen involvement, and programmes of chemotherapy that reduce infection should mitigate the risk of schistosomal morbidity.

Water-contact patterns and schistosoma mansoni infection in a rural community in northeast Brazil

Este estudo analisa a relacao entre as ca racteristicas da infeccao por S. mansoni e o padrao de contato com agua, os habitos de higiene, a localizacao do domicilio, o nivel educacional e as condicoes socio-economicas, em uma populacao definida residente na zona endemica de Castro Alves, Bahia, Brasil. A area de estudo e tipica de zonas rurais do Nordes te, com relevo acidentado e sua populacao dedica-se a lavoura nao irrigada de fumo e mandioca. Apos o mapeamento da area e um inquerito malacologico completo, foi aplicado um questionario para cada familia com questoes referentes as atividades de contato com agua, tempo de exposicao, condicoes de habitacao e caracteristicas socio-economicas. A prevalencia e a intensidade de infeccao por S. mansoni foram obtidas usando-se a tecnica de Bell para a contagem de ovos nas fezes. A analise dos dados incluiu o calculo de um indice de infeccao da familia utilizando-se a contagem de ovos por grama de fezes de cada individuo. Poucas casas tinham instalacoes sanitarias ou fonte de agua para uso domestico, entretanto, os habitos de defecacao e de contato com agua nao eram indiscriminados, observando-se que os individuos dispendiam esforco consideravel em busca de agua mais limpa para beber e para tomar banho, evitando defecar proximo as fontes de agua. A propriedade da terra e o nivel educacional nao mostraram-se correlacionados com o indice de infeccao. O fator que pareceu influenciar a maior ou menor prevalencia de infeccao por S. mansoni foi a localizacao das casas em relacao a distância de uma fonte de agua nao colonizada por Biomphalaria glabrata.