The epidemiology and control of schistosomiasis mansoni where Biomphalaria tenagophila is the snail host

Abstract

The epidemiology and control of schistosomiasis mansoni in the Municipality of Pedro de Toledo (State of S. Paulo, Brazil) since 1980, has been studied. In 1980 the prevalence evaluated by stool exams (Kato-Katz method) was 22.8% and no statistical difference at 5.0% level was observed between rural and urban zones. The intensity of infection was low (58.5 eggs/g of faeces); the highest prevalence and intensity of infection rates were observed within the group of from 5 to 29 years of age, respectively. The transmission of schistosomiasis usually occurred during leisure time. The majority of the carriers of the parasite were asymptomatic. Of the B. tenagophila examined only 0.4% were found to be infected. The control programme has been intensified from 1981 on resulting in a sharp decrease in the prevalence from 22.8% in 1980 to 6% at the present time. This result shows that, in spite of the control programme there is a residual human prevalence. A beginning has been made on the investigation into the possible causes of this residual prevalence (6.0% was maintained through out 1987).

Genetic differences between strains of Biomphalaria glabrata (Planorbidae) that are susceptible and unsusceptible to schistosomiasis

“…Today, it is one of the most serious public health problems, especially in third world countries (Mott, 1989), where it is closely associated with irrigation projects and with migratory movements (Dias et al, 1988;World Health Organization, 1993).…”

“…This species also has a considerable degree of intraspecific polymorphism . Therefore, it is important to investigate the genetic variability related to the susceptibility to S. mansoni infection of mollusks, which are vectors of the genus Biomphalaria, both for a better understanding of the epidemiology of schistosomiasis (Paraense an Correa, 1978) and for the understanding of the parasite pathogenesis to its vertebrate host (Dias et al, 1988;ZanottiMagalhães et al, 1991ZanottiMagalhães et al, , 1993ZanottiMagalhães et al, , 1997. Richards and Merritt Jr. (1972) used classical methods of genetic analysis, on the basis of which they proposed that the susceptibility of B. glabrata to S. mansoni infection may be regulated by at least four genes or, as defined by Larson et al (1996), may be a polygenic trait.…”

Schistosomiasis mansoni in Bananal (State of São Paulo, Brazil): III. Seroepidemiological studies in the Palha District

“…Most (75%) of the infected inhabitants of the Palha district were aged 34 or under. According to Dias et al (1988), people aged from 5 to 29 years are at the greatest risk. More recent serologic surveys often include only subjects aged under 17 (Camargo-Neves et al 1998, Lima et al 1998, Kamura et al 1998.…”

Epidemiologia da esquistossomose mansônica em área de baixa endemicidade

“…De todas as regiões de ocorrência de focos ativos de esquistossomose em São Paulo, a área dos municípios de Pedro de Toledo e Itariri, no vale do rio Ribeira de Iguape, está sendo uma das mais pesquisadas por nós, desde 1980 (Dias et al, 1988). Nesse ano, como contraposição ao aumento do índice de prevalência humana em Pedro de Toledo, de 4%, em 1970, para 12%, em 1978, intensificou-se o programa de controle no município, com a inclusão de estudos parasitológicos, epidemiológicos e imunológi-cos, educação sanitária e manejo do ambiente, por meio de obras de saneamento básico (Dias et al, 1988).…”

“…Nesse ano, como contraposição ao aumento do índice de prevalência humana em Pedro de Toledo, de 4%, em 1970, para 12%, em 1978, intensificou-se o programa de controle no município, com a inclusão de estudos parasitológicos, epidemiológicos e imunológi-cos, educação sanitária e manejo do ambiente, por meio de obras de saneamento básico (Dias et al, 1988). Segundo esses autores, todos os portadores da endemia eram assintomáticos.…”