The presumptive treatment of all school-aged children is the least costly strategy for schistosomiasis control in Plateau and Nasarawa states, Nigeria.

The results of previous studies in Nigeria indicate that 81% of the villages in Plateau and Nasarawa states probably qualify for the mass administration of praziquantel (PZQ) because of Schistosoma haematobium (SH) and/or S. mansoni (SM) infection. To determine the best strategy, relative costs were modelled for four different programmatic approaches to mass drug administration (MDA) at village level. The approaches considered were (1) village-by-village screening for SH (using dipsticks to test for haematuria), with MDA confined to those villages where at least 20% of school-aged children were found infected; (2) screening for both SM (using Kato-Katz smears) and SH, with MDA confined to those villages where at least 20% of school-aged children were found infected with SH or at least 10% of such children were found SM-positive; (3) the presumptive annual treatment of all school-aged children with PZQ (without village-by-village screening); and (4) the presumptive annual treatment of all eligible adults and children with PZQ. In the MDA in models 1 and 2, treatment is only given to children unless the prevalence of schistosome infection is >or=50%, when adults are also treated. As first-year 'assessment' costs were particularly high for the models that included screening, costs were projected over 5 years for all four models. The total 5-year costs, to cover a population of 30,000, were U.S.$18,673 for the model with screening only for SH, U.S.$36,816 for the model with screening for both SH and SM, U.S. $15,510 for the treatment of all school-aged children, and U.S.$68,610 for the treatment of the entire population. Although the presumptive treatment of school-aged children appeared to be the cheapest approach, it would exclude the community-wide treatment of highly endemic communities, the importance of which needs further study.

Significant decrease in the prevalence of Wuchereria bancrofti infection in anopheline mosquitoes following the addition of albendazole to annual, ivermectin-based, mass treatments in Nigeria.

A prospective entomological survey was conducted in four sentinel villages in central Nigeria from 1999-2002, to assess the impact of annual, single-dose, mass drug administrations (MDA), with a combination of ivermectin and albendazole, on the transmission of Wuchereria bancrofti. As they were also endemic for human onchocerciasis, the four villages had received annual MDA based on ivermectin alone for 7 years prior to the addition of albendazole. Resting Anophelines gambiae s. l., An. funestus and Culex species were collected from 92 sequentially sampled households and dissected. Mosquitoes harbouring any larval stage of W. bancrofti were classified as 'infected', and those containing the third-stage larvae of the parasite were classified as 'infective'. Over the 41-month observation period, 4407 mosquitoes were captured and dissected, of which 64% were An. gambiae s. l., 34% An. funestus, and 1% Culex species. The baseline data, from dissections performed before the addition of albendazole to the MDA, showed high prevalences of mosquito infection (8.9%) and infectivity (2.9%), despite apparently good treatment coverages during the years of annual ivermectin monotherapy. Only the anopheline mosquitoes were found to harbour W. bancrofti larvae. After the third round of MDA with the ivermectin-albendazole combination, statistically significant decreases in the prevalences of mosquito infection (down to 0.6%) and infectivity (down to 0.4%) were observed (P<0.0001 for each). The combination of albendazole and ivermectin appears to be superior to ivermectin alone for reducing the frequency of W. bancrofti infection in mosquitoes.