Field trial of permethrin impregnated sisal curtains in malaria control in western Kenya.

A trial to determine the effectiveness of sisal eaves-curtains impregnated with permethrin for malaria control was conducted in the malaria holoendemic western Kenya between 1991 and 1993. Indoor resting densities of Anopheles gambiae s.l. and Anopheles funestus were reduced by 90.9% and 93.8% respectively in protected houses. The entomological inoculation rate (EIR) was reduced by 72% in the intervention village. There was no significant reduction in vector longevity or survival as shown by the sustained high sporozoite rates. Monthly bioassays for retained insecticidal potency of permethrin on the fibre indicated vector mortality rates above 95% over the period. Of 283 and 240 children followed up from the intervention and control villages, a mean malaria prevalence of 43.2% and 52.2% respectively was observed over the trial period (p < 0.01). The prevalence rose to 73.5% and 75.7% (p = 0.541) respectively after the removal of the curtains. No significant differences were observed in the mean parasite density between the groups or between the proportions with parasite density exceeding 2,500 per microliter and with or without fever. The prevalence of splenomegaly was significantly lower in the intervention group compared to the control, both during (p = 0.005) and after the intervention (p < 0.001). There was no significant difference in the mean change in haematocrit at the end of the intervention. We observe that permethrin impregnated sisal curtains effectively retain permethrin, alter favourably the indoor vector density and EIR, and could provide a reduction in malaria prevalence.

Knowledge and attitudes to malaria control and acceptability of permethrin impregnated sisal curtains.

OBJECTIVES: The objectives of this study were to conduct a survey on the knowledge and practices relating to malaria prevention and treatment in two rural communities in Western Kenya, and to determine the acceptability of specially designed permethrin impregnated sisal strands curtains previously introduced into one of the study communities as barriers to mosquito biting. DESIGN: A knowledge, attitudes and practices (KAP) survey was conducted by pre-trained interviewers using a pre-tested questionnaire. SETTING: The study was conducted in two communities located 15 km northwest of Kisumu town, and next to the swamps bordering Lake Victoria in Kisumu District, Western Kenya. PARTICIPANTS: Adult individuals from 50 houses selected from the intervention, and 50 houses from the control sites were included in the study. RESULTS: Both communities had a clear conception of malaria and its symptoms, and of the mosquito as its vector. Malaria was recognised as a potential cause of death by 44% and 72% of the participants in the intervention and control sites respectively. Sixty two per cent to 74% of the people interviewed in both sites named mosquitoes as the causative agents of malaria. Chloroquine was still the drug of choice for malaria treatment, with over 70% usage among the study population. Mention of pyrimethamine/sulfadoxine and pyrimethamine/sulfalene as alternative therapy was below five per cent. Despite a high level (86%) of awareness of bednets as effective barriers to mosquito biting, they were reported in use by less than 35% in both communities. Sisal strand curtains were considered effective and acceptable to more than 80% of the community. CONCLUSIONS: The results of this study underscore the existing need for affordable means of mosquito control, such as sisal strand curtains, for such rural communities which may be acutely aware of the problems associated with malaria, but are constrained from taking any action by lack of resources.

Some observations on the biting behavior of Anopheles gambiae s.s., Anopheles arabiensis, and Anopheles funestus and their implications for malaria control.

Studies were carried out in three villages in western Kenya on the biting behavior of Anopheles gambiae s.s., Anopheles arabiensis, and Anopheles funestus. Blood feeding behavior and departure from houses were studied under the impact of permethrin-impregnated eaves-sisal curtains. Only 2-13% of the female vector population was collected biting before 2200 hr. Over 90% of the villagers went to bed by 2100 hr. An. funestus was 6.6-8.2 times more likely to bite people indoors than outdoors, while An. gambiae s.l. females were only 2 times as likely. Under the influence of permethrin-impregnated sisal curtains placed under the eaves of village houses, there was a marked egress of blood-fed An. funestus and An. gambiae s.s. Permethrin seems to have induced exophily of half-gravid female An. gambiae s.s. While An. gambiae s.s. remained highly anthropophagic under the impact of permethrin, An. funestus shifted to feeding more on cattle. An arabiensis were largely zoophilic. Our results underline the difficulties of controlling An. gambiae s.s., the principal African malaria vector. New strategies must be found to control this vector.