Influence of temperature on development of Schistosoma mansoni female cercariae in Biomphalaria glabrata

Nestes experimentos a relacao de larvas de Schistosoma mansoni, macho e femea, em Biomphalaria glabrata de Belo Horizonte e de Ribeirao das Neves, MG, Brasil, criada no laboratorio ou capturada no campo variou de 1:1 a 1:1,3 ou 1,4:1...

Transmission of intestinal schistosomiasis in Bahir Dar, northwest Ethiopia.

Parasitological, malacological and transmission studies were made for a period of one year in the town of Bahir Dar, northwest Ethiopia. The overall prevalence of schistosomiasis mansoni in residents of Kebeles 8, 9 and 10 was 12%. The prevalence in Sertse Dengel school children was 45% and that in Dil Chibo school children was 32%. The peak prevalence in both sexes in school and non-school populations occurred in the age group 10-14 years. Intensity of infection showed a similar pattern of age variation as prevalence. Biomphalaria pfeifferi snail density peaked towards the end of the rainy season (September) in Lake Tana and around the middle of the dry season (January) on the shore of the River Abay. In September, infected snails were recovered from all collection sites. Of mice immersed in four water contact sites in September, schistosome infections developed in those immersed in three sites. Parasitological findings suggested that schistosomiasis infection rates depended on age and sex of individuals and geographical location of the place from the potentially infective water bodies. Snail population density and associated schistosomal infection in a human population depended on rainfall and associated ecological changes such as fluctuation in water level and vegetation density. As malacological findings and sentinel mouse immersion results indicated, it appeared that the main transmission season in Lake Tana region is towards the end of the rainy season although low level intermittent transmission may take place throughout the year.

Potential schistosome-vector snails and associated trematodes in ricefields of Corrients province, Argentina. Preliminary results.

Considering the possibility of introduction of schistosomiasis mansoni into Argentina as a consequence of dam construction on the Rio De La Plata basin, preliminary studies have been carried out on agrosystems such as ricefields in Corrientes province with the following purposes: 1) to survey and estimate the relative abundance of planorbids and identify potential vector species; 2) to identify environmental factors capable of influencing Biomphalaria population dynamics; and 3) to find out snail-parasite associations and estimate snail infection rates in order to detect possible competitive interactions between larval stages of native trematodes that could be used in biological control of Schistosoma mansoni. Three potential schistosome vectors were detected in ricefields, namely Biomphalaria straminea, B. tenagophila and B. peregrina, although B. orbignyi, a species refractory to infection with S. mansoni, proved the most frequent and abundant. Positive correlations (P less than 0.05) were found between Biomphalaria abundance and some environmental parameters: conductivity, hardness, calcium, nitrites plus nitrates, ammonium and bicarbonates. Water temperature correlation was negative (P less than 0.05). No correlation (P less than 0.05) was found in total iron, phosphates (SRP), pH and soil granulometry.

[French Guiana and bilharziasis]. / Guyane et bilharziose

The authors discuss about the lack of bilharziasis in French Guyana and report the experimental infestation of Biomphalaria glabrata coming from Cayenne with a porto-rican strain of Schistosoma mansoni.

The influence of stream geology on the distribution of the bilharzia host snails, Biomphalaria pfeifferi and Bulinus (physopsis) sp.

The Gladdespruit and Komati River surveys have shown that similar environmental conditions have developed where the watercourses flowed over particular rock types. In these watercourses a potentially useful association was found between the occurrence of permanent, lentic habitats produced by the weathering of bedrock with a hardness above 5 in Mohs' Scale of Hardness and the longitudinal distribution of persistent populations of the bilharzia intermediate host snails Biomphalaria pfeifferi and Bulinus (Physopsis) sp. Bilharzia transmission follows this pattern in these waterways. Weathering of bedrock with hardness below 5 in Mohs' scale, and/or flow over beds of alluvial sand, produced perpetually lotic (flowing) environments without persistent host snail populations because of the snail's inability to tolerate high current speeds. However a few temporary populations survived in temporarily lentic habitats during the dry winter season.