ABSTRACT
In 1926, Blacklock first described onchocerciasis (OV) transmission by black fly, Simulium damnosum in Sierra Leone. In the 1950-1960's, high OV prevalence was demonstrated along the rivers and the existence of black flies nationwide except around the capital and the coastal plain of Bonthe. In 1957, control efforts started with insecticides along the river breeding sites. In 1974, the Onchocerciasis Control Programme focusing on vector control was launched, extending to Sierra Leone in the 1980s. From 1995, the African Programme for Onchocerciasis Control commenced community-directed treatment with ivermectin (CDTI) in hyper- [microfilaridermia (mf) prevalence≥40%] and meso- (nodule prevalence 20%-39%) sites. To be effective programme, coverage among the eligible population over five years of age needed be at least 80%. In the mid-1990s, the rebel war stopped vector control and effective CDTI was not established until 2006. Baseline data using skin snips from 39 sentinel villages found the average OV mf prevalence was 53.1% (28.9 mf/snip). From October 2008, albendazole was added in phases to CDTI for all communities in all 14 districts for lymphatic filariasis (LF) elimination. In 2010, after five rounds of effective MDA, OV mf prevalence was 21.1% (8.29 mf/snip). Males had higher prevalence and density than females in both studies. Since then, OV control (acknowledging transmission continues) has transitioned to OV elimination assuming transmission can be interrupted once mf prevalence is less than 5%. In 2017, a rapid assessment was integrated into LF-Transmission Assessment Survey and independently in 8 and 4 districts respectively, designed by the Survey Sample Builder. Children aged 5-9 years were randomly selected from 177 clusters and tested by OV-16 (Rapid Diagnostic Tests, SD BIOLINE) using finger-prick blood samples. Overall, 17 441 children participated and 347 (2.0%) were positive (M: 2.4% versus F: 1.6%) (P10%). The LF- Transmission Assessment Survey sampling methodology does not take cognizance of black fly breeding sites, but did demonstrate ongoing transmission and another 4-5 rounds were advisable. A technical advisory committee has been established with representation from international experts to help plan for accreditation of onchocerciasis elimination around 2025.
ABSTRACT
Background and Objectives: Onchocerciasis is a parasitic filarial disease of the tropics, having serious effects on global public health and the economy of endemic countries. Nigeria is among the most endemic countries, necessitating much research and control program interests. This study determined the rate of transmission of onchocerciasis in Oji-River and Ezeagu Local Government Areas of Enugu State, Nigeria. Methodology: Human landing sampling method was used to collect black flies. Parity assessment was conducted to determine the age of fly populations. Parous flies were further dissected to detect the presence or absence of Onchocerca larvae. Biting rates and transmission potentials were calculated using standard methods. The principal vector groups in the study area were identified morphologically. Results: A total of 352 adult female flies were collected during the study period. These were identified as members of the forest species of the S. damnosum complex. There were significant differences between monthly abundances of black flies caught during the entire study period (P < 0.04). Comparison of the monthly biting rates (MBRs) showed a significant difference in (P < 0.02). The MBR was lowest in February but highest in October. Generally, parity rate of over 50 % was observed throughout the period except for November. None of the flies dissected was infective. Diurnal biting activities of black flies between the months were significantly different from each other (P < 0.01). Conclusions: Onchocerciasis transmission is low in the studied area, and is largely by means of the forest black flies as these were the only observed group. None of the dissected flies was found to be infective. The findings of this study will be of tremendous benefit to policy makers in the National Onchocerciasis Elimination Programme. It calls for a continuous monitoring of onchocerciasis disease conditions in the study area.
ABSTRACT
Tukuyu onchocerciasis focus was earmarked for vector control using insecticide against larval stages.Susceptibility tests of mature larvae of Simulium damnosum s.l. vectors to temephos insecticide were carried out before and after two years of insecticide treatment of rivers within Tukuyu onchocerciasis focus, south-western Tanzania. The tests were done in 1999/2000 and 2004 using WHO standard methods. Mature larvae were exposed to 9 concentrations of temephos active ingredient, from the weakest 0.00975mg/litre to the strongest of 2.5mg/l. Each test concentration and control was run in duplicates of 25 larvae each, set for three hours in a cool temperature. After incubation, test solution was discarded and larval condition checked. Numbers of larvae in each category were recorded and used to determine mortality rate for each concentration as well as for the LC50 and LC95. A total of 1,666 larvae were tested, 942 during the pre- and 724 post-treatment. Results showed that both pre and post-treatment samples were susceptible, attaining 100% mortality at the diagnostic dose of 1.25mg/l, and LC50 between 0.129-0.34mg/l pre - and 0.144-0.211 mg/l (95% CI, P<0.05) post- treatment. These values fall within the standard diagnostic dose of ≤0.4mg/l for susceptible S. damnosum s.l populations. It was concluded that the endemic S. damnosum population was susceptible to temephos before and after two years of intermittent field application. Temephos was thus recommended for continued use in onchocerciasis vector control in the Tukuyu focus, to complement Community Directed Treatment with Ivermectin, but close monitoring of vector susceptibility should be done