Biomphalaria snails are instrumental in transmission of the human blood fluke Schistosoma mansoni. With the World Health Organization's goal to eliminate schistosomiasis as a global health problem by 2025, there is now renewed emphasis on snail control. Here, we characterize the genome of Biomphalaria glabrata, a lophotrochozoan protostome, and provide timely and important information on snail biology. We describe aspects of phero-perception, stress responses, immune function and regulation of gene expression that support the persistence of B. glabrata in the field and may define this species as a suitable snail host for S. mansoni. We identify several potential targets for developing novel control measures aimed at reducing snail-mediated transmission of schistosomiasis.

The prevalence, virological and epidemilogical aspects of the hepatitis C virus (HCV)

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BackgroundSchistosomiasis has a considerable impact on public health in many tropical and subtropical areas. In the new world, schistosomiasis is caused by the digenetic trematode Schistosoma mansoni. Chemotherapy is the main measure for controlling schistosomiasis, and the current drug of choice for treatment is praziquantel (PZQ). Although PZQ is efficient and safe, its repetitive large-scale use in endemic areas may lead to the selection of resistant strains. Isolates less susceptible to PZQ have been found in the field and selected for in the laboratory. The impact of selecting strains with a decreased susceptibility phenotype on disease dynamics and parasite population genetics is not fully understood. This study addresses the impact of PZQ pressure on the genetics of a laboratory population by analyzing frequency variations of polymorphic genetic markers.MethodologyInfected mice were treated with increasing PZQ doses until the highest dose of 3×300 mg/Kg was reached. The effect of PZQ treatment on the parasite population was assessed using five polymorphic microsatellite markers. Parasitological and genetic data were compared with those of the untreated control. After six parasite generations submitted to treatment, it was possible to obtain a S. mansoni population with decreased susceptibility to PZQ. In our experiments we also observed that female worms were more susceptible to PZQ than male worms.ConclusionsThe selective pressure exerted by PZQ led to decreased genetic variability in S. mansoni and increased endogamy. The understanding of how S. mansoni populations respond to successive drug pressure has important implications on the appearance and maintenance of a PZQ resistance phenotype in endemic regions.

5 patients with visceral leishmaniasis were treated with sodium stibogluconate (2 patients) or meglumine antimoniate (3 patients) given intramuscularly at a dose of 10 mg antimony (Sb) per kg body weight daily for 30 d. Blood samples were obtained at intervals during treatment and blood Sb concentrations measured by anodic stripping voltametry. The pharmacokinetics of both drugs were remarkably similar, with peak concentrations of approximately 10 mg/litre occurring 2 h after the initial dose. Most of the Sb was eliminated rapidly, but nadir Sb concentrations increased gradually during treatment from 0.04-0.08 mg/litre 24 h after the first dose to 0.19-0.33 mg/litre 24 h after the 30th dose. For both drugs, the data were best described by a two compartment, three term pharmacokinetic model representing an initial absorption phase with a mean half-life of 0.85 h, a rapid elimination phase with a mean half-life of 2.02 h, and a slow elimination phase with a mean half-life of 76 h. The slow terminal elimination phase may be related to in vivo conversion of pentavalent Sb to trivalent Sb, which could contribute to the toxicity associated with long-term high dose therapy.