Susceptibility of Simulium damnosum complex larvae to temephos in the Tukuyu onchocerciasis focus; southwest Tanzania

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

Impact of ivermectin mass distribution for onchocerciasis control on Ascaris lumbricoides among schoolchildren in Rungwe and Kyela Districts; southwest Tanzania

Across-sectional survey on the impact of ivermectin treatment for onchocerciasis control; on Ascaris lumbricoides infections was conducted in 1994; before the first treatment cycle was implemented in the Tukuyu focus in Tanzania. A total of 560 pupils were randomly selected for stool samples before; 7 days and 3 months after treatment. Modified Kato Katz technique was used to prepare slides; and a dissection microscope for examination. Results showed pre-treatment A. lumbricoides prevalence ranging from 4.2(Lutete) to 34.0(Lufilyo). At day seven post-treatment; samples were devoid of Ascaris eggs; except at Lufilyo with 2.9prevalence. Three months post treatment showed 34 (8.2) out of 213 pupils had patent infections and 24 (5.8) re-infections. Mean infection intensities were significantly higher at pretreatment than three months post-treatment. A. lumbricoides adult worm expulsion was self-reported in the first week of treatment; especially 2-3 days after; by 21.9participants. Ivermectin treatment was effective against adult A. lumbricoides and cleared egg excretion by day seven; but re-infection occurred within three months. Visible worm excretion wasappreciated as potency of treatment. Long term mass treatment with ivermectin proposed for onchocerciasis control can be used to reduce A. lumbircoides infections. To benefit optimally from this programme; additional inputs should be availed to reduce re-infection between consecutive annual cycles. Appreciation of visible worm expulsion enhanced acceptance and compliance of onchocerciasis control campaign using ivermectin. Follow-up surveys are recommended