Seasonal biting pattern of Simulium damnosum s.l and its implications on onchocerciasis treatment with ivermectin.

BACKGROUND: The current control strategy adopted by African Programme for Onchocerciasis Control (APOC) is the mass distribution of ivermectin in all endemic areas for between 12-15 years. One of the major obstacles of the strategy, is the ability of the fly to migrate long distances and this brings about the possibility of flies migrating from uncontrolled areas to controlled areas. OBJECTIVE: To assess the impact of annual ivermectin treatment of onchocerciasis and to ascertain the seasonality of transmission and its impact on the current control strategy in the forest zone around a dam in Southern Nigeria. METHODS: A 36 x 11-hour entomological survey was carried out in the study area. Simulium damnosum s.l were caught using two human baits from 07.00 hours-18.00 hours, three days of every month for 12 months according to the method of Walsh et al. The head, thorax and abdomen of each insect were dissected separately. Catches were made from dawn to dusk. RESULTS: Catches yielded a total of 2,807 female S. damnosum s.l. Higher mean biting rates (2,486 flies/man/year) occurred during the dry season. The mean monthly distribution of parous flies also showed distinct seasonality with preponderance of parous flies during the dry season (61.8%) as compared to the rainy season (38.6%). Flies harbouring developing and infective larvae were observed during the dry season in October and December when the monthly transmission potential recorded was 31 larvae/man/month. This dropped to 28 larvae/man/month and 25 larvae/man/month in January and February respectively. An annual transmission potential of 115 larvae/man/year was recorded. CONCLUSION: In spite of the ivermectin treatment in the area at the time of study, the transmission of Onchocerca volvulus continued unabated in the area with a higher transmission in the dry season than the rainy season. The distribution of ivermectin should be intensified through improved coverage while other control measures may be necessary during the dry season which is the peak of transmission in the area.

Identification of the forest strain of Onchocerca volvulus using the polymerase chain reaction technique.

Annual mass treatment with ivermectin for 12-15 years in endemic communities is the control strategy adopted by the African Programme for Onchocerciasis Control (APOC) for the control of onchocerciasis in Nigeria. This long-term treatment necessitates the use of Polymerase Chain Reaction (PCR) for the proper identification of the Onchocerca species and strains in endemic areas and also for monitoring recrudescence of infection in areas where infection has been controlled. This study, which forms part of a larger study on transmission of onchocerciasis identifies the Onchocerca volvulus strain in Ondo state using the Polymerase Chain Reaction (PCR) technique. Deoxyribonucleic acid (DNA) was extracted from the adult worm of Onchocerca parasite using the glass bead method of extraction. The repeated sequence family present in the genome of the parasite designated as 0-150bp was amplified by the polymerase chain reaction (PCR). The amplified parasites produced significant products visible as bands in a 2% agarose gel stained with ethidium bromide. Hybridization of the PCR products with specific DNA probe identified the products as forest strain of Onchocerca volvulus. The epidemiological implication of this is that there would be more of the skin lesions and low blindness rate in the area.

Effect of aestivation of Biomphalaria pfeifferi on the survival and infectivity of Schistosoma mansoni cercariae.

Schistosoma mansoni cercariae from post-aestivated Biomphalaria pfeifferi remain motile for 20 hours after release. Thereafter, their activity decreases with age. The difference in mortality rate of cercariae from aestivated and non-aestivated B. pfeifferi studied here proved to be statistically significant (P < 0.05) within the first 10 hours of the experimental period. Results of the percentage recovery of worms from different mouse organs infected with cercariae from aestivated and non-aestivated snails varied. The two main organs infected were the liver and intestine. In conclusion, the penetration, migration and maturation of cercariae into adult worms were not affected by the aestivation of B. pfeifferi.

Faecal contamination level; survival of salmonella typhi and pH changes in 'Gari' and its potential public health hazard in Lagos

The pH changes; faecal contamination level; survival of nalidixic-acid resistant salmonella typhi in 'gari' soaked in water was examined. The pH values showed that 'gari' had a range of pH 3.76 to pH 6.24. The mean pH values showed that there were no appreciable change for gari types from various sources within the studied time period of 120 minutes. Faecal coliform contamination of 4 to 2;400/g using the MPN technique were recorded in 33of the 36 'gari' samples. This high faecal coliform contamination rate of gari; a popular fermented cassava food is unacceptable and it is of public health importance. Our survival experiment showed that the seeded enteric pathogen slightly decreased in colony-forming unit (cfu) with log(0.3 10) 0.3 within the studied 120 minutes. It is concluded that our local foods should be monitored regularly for public health safety; and improved hygienic practices should be emphasized as an intervention for diarrhoeal diseases in developing countries