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.

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.

Evaluation of the QBC method to detect malaria infections in field surveys.

The conventional peripheral blood film method used to diagnose malaria is characterized by low sensitivity in scanty parasitaemia and can be time consuming when required to rule out infection. The Quantitative Buffy Coat (QBC) method has been proposed to be quicker and more sensitive. We conducted a malaria survey in April 1992 among school-children in Kisumu (holoendemic) and Webuye (hypoendemic) areas of Western Kenya. Peripheral blood samples were examined by thick blood smear (TBS) stained with Giemsa solution, and by the QBC method. A total of 360 paired samples were analyzed. There were 175 (49%) positive TBS and 201 (56%) positive QBC. Of the 185 TBS classified as negative, 30 (16%) were positive by QBC. When parasite density by TBS was > or = 100/300 WBCs, the sensitivity of QBC was 100%. Overall sensitivity for QBC was 98%, with a specificity of 84%. Negative predictive value for the QBC was 98%, and had a calculated accuracy of 92%. It took an average of 44 minutes to process a TBS and a further average of 2.6 minutes to examine a negative TBS. For the QBC the mean time to process and to examine was 7.09 and 1.04 minutes respectively. We conclude that the QBC is quicker, with high sensitivity, and will prove useful in clinical and epidemiological screening, especially when parasitaemia is low.

The effect of permethrin impregnated sisal curtains on vector density and malaria incidence: a pilot study.

Impregnation of bednets and curtains with suitable pyrethroids may reduce entomological inoculation rates (EIR) and malaria incidence. We conducted a quasi-experimental pilot study over 3 months in Western Kenya on 20 houses with 54 children. Ten houses in the experimental site received sisal curtains treated with permethrin at either 0.5g/m2 or 0.1g/m2. Control houses had untreated curtains or none. Mosquito vector density (MVD), man biting rates (MBR), and residual insecticidal effects (RIE) of permethrin were determined every two weeks. MVD was reduced by 97.7% and 98.7% in houses from the 2 experimental groups with a 60% reduction with unimpregnated curtains. MBR varied from 6.4 (no curtains), 1.7 (unimpregnated), 0.7 (0.5g/m2 curtains) to 0.4 (1.0g/m2 curtains). RIE begun to decline after the fourth month. Malaria incidence remained similar at the two sites. We conclude that covering of eaves and windows with permethrin impregnated sisal curtains can reduce MVD and the number of mosquito bites to individuals sleeping in protected houses.

The effect of permethrin impregnated sisal curtains on vector densities and malaria incidence: a pilot study

Malaria is a major public health problem in the tropics and sub-tropics and has been shown to be a major cause of days of healthy life lost. Impregnation of bednets and curtains has been reported to reduce vector inoculation rates and malaria incidence. We conducted a qausi-exiperimental pilot study for three months in western Kenya on 20 houses with 54 children. 10 houses in the control area received either no sisal curtains or unimpregnated curtains while 10 others in the experimental site received impregnated curtains but at different concentration levels viz:0.5 g/m2 and 1.0 g/m2). Vector densities and man biting rates were monitored once every two weeks using the spray sheet collection and the human bait catches. Bioassays using the standard WHO cone-method were done fortnightly. Malaria morbidity was monitored among the 54 children (22 in control and 32 in experimental) fortnightly by taking blood smears and temperature. In houses with impregnated curtains at 0.5 g/m2 vector densities were reduced by 97.7 while in the houses with 1.0 g/m2 the density reduction was 98.7. A 50 reduction was also observed in houses with unimpregnated curtains. On average man biting rates in houses with no curtains were 6.4 bites per man per night. In the houses with curtains the average bites per man per night were 1.7 (unimpregnated); 0.7 (0.5 g/m2curtains) and 0.4 (1.0 g/m2curtains). All mosquitoes exposed toimpregnated curtains (at both concentration levels) died; up to the fourth month;aftre which therewas decline in residual effect. There was no significant difference in malaria incidence at the two sites. We conclude that covering for eaves and windows with permethrin impregnated sisal curtains can reduce mosquito densities in the houses as well as the number of mosquito bites to individuals sleeping in those houses

Intestinal parasitoses and other infections in a college community.

In order to assess the health status of students doing their teaching diploma course at the Siriba Teachers College, Maseno, a study of their blood slides, their stools for ova and cysts and their urine samples for urinary tract infection was carried out. A total of 298 students were investigated: 27 (6%) had intestinal parasites, 96 (32.2%) had urinary tract infection, i.e., pyuria, bacteria and epithelial cells in their urines, most of them being females (55/96 or 57.3%). The peak occurrence of urinary tract infections was in the 22-23 year age group. There were four female students who were found to have Trichomonas vaginalis giving a prevalence rate of 1.3%.