Comparison of three larviciding options for malaria vector control.

A field study was carried out over 27 weeks in the south Batinah region of Oman to assess the efficiency and cost-effectiveness of different strategies for vector control of malaria. Three larviciding strategies for Anopheles spp. were applied to intervention areas and compared with a control area, with over 2000 breeding sites monitored for 6 months. The normal method of spraying 1 ppm temephos larvicide fortnightly was found to be less efficient and less cost-effective than using 0.5 ppm temephos applied weekly. A third, more environmentally favourable method, to search for vector larvae and treat only those breeding places, was more effective than fortnightly spraying but less effective than the weekly half dose and was the most expensive strategy.

Comparison of three larviciding options for malaria vector control

A field study was carried out over 27 weeks in the south Batinah region of Oman to assess the efficiency and cost-effectiveness of different strategies for vector control of malaria. Three larviciding strategies for Anopheles spp. were applied to intervention areas and compared with a control area, with over 2000 breeding sites monitored for 6 months. The normal method of spraying 1 ppm temephos larvicide fortnightly was found to be less efficient and less cost-effective than using 0.5 ppm temephos applied weekly. A third, more environmentally favourable method, to search for vector larvae and treat only those breeding places, was more effective than fortnightly spraying but less effective than the weekly half dose and was the most expensive strategy

Rapid decomposition of permethrin in the outer fly of an experimental tent in Pakistan.

The residual activity of permethrin on the canvas of an experimental tent, used by nomadic refugees in a malarious area in northern Pakistan, was assessed. A permethrin emulsion sprayed on the inner sheet of a pitched double-fly tent (0.5 g/m2) had an effective residue for at least 6 months in bioassays using the local malaria vectors, Anopheles stephensi and Anopheles culcifacies. However, a high concentration of permethrin (2 g/m2) sprayed on the inner surface of the outer tent, simulating single-fly tents, decomposed within 2 months. These findings were confirmed with chromatographic analysis. Under the conditions found in the study area, the shortened residual effect most likely resulted from photodecomposition, not previously reported to affect operational performance of this insecticide.

Malaria control using permethrin applied to tents of nomadic Afghan refugees in northern Pakistan.

Malaria control among nomadic populations has, in the past, posed serious logistic difficulties. Presented in this article are the results of a pilot study in which permethrin was sprayed on the tents of over 26000 nomadic Afghan refugees in an area of Pakistan where seasonal malaria outbreaks occur. In this area Anopheles culicifacies and A. stephensi are the malaria vectors. Population surveys in the year of the study, before and at the end of the transmission season, showed that the increase in the Plasmodium falciparum prevalence among the Afghan nomads was on average significantly less (increase from 6.4% to 15.3%) than that among the resident Pakistani population (from 3.2% to 45.6%). Surveys at the end of the transmission season among primary schoolchildren the year before and the year of the permethrin trial showed that the P. falciparum prevalence among nomadic children decreased significantly (from 46.9% to 16.3%), whereas an increase was observed among the local Pakistani children. The results show that spraying tents with permethrin was a safe and culturally acceptable intervention for the Afghan refugees and that the findings warrant further investigation.

PIP: During 1989-90, in the North-West Frontier Province of Pakistan, a pilot study was conducted in the remote and politically unstable area of South Waziristan Agency (altitude, 1300-1750 m) to determine the feasibility of spraying about 5600 tents (used by more than 26,000 nomadic Afghan refugees) with permethrin and its effect on malaria prevalence. The researchers compared baseline data on the refugees and data from Pakistani schoolchildren with follow-up data on the nomadic Afghan refugees. The mosquito species harboring malaria parasites in the area were Anopheles culicifacies and A. stephensi. An effective permethrin residue persisted for at least 6 months after spraying. Between seasons, the prevalence of Plasmodium falciparum increased at a significantly lower rate among the Afghan nomads (6.4-15.3%) than the resident Pakistan population (3.2-45.6%). Prevalence decreased significantly among nomadic Afghan children after the permethrin intervention (46.9-16.3%; p 0.002). On the other hand, it increased significantly among the local Pakistani children (11.6-40.7%; p 0.001). There were no reports of adverse effects from permethrin spraying operations. The absence of toxic effects, the immediate impact on flies, and the lack of smell or color of the permethrin emulsion made the spraying operation acceptable among the nomads. These findings suggest that spraying tents with permethrin was a safe and culturally acceptable intervention.

Two new mutations and a linkage map of Anopheles stephensi.

Genetic analyses of two new mutations in Anopheles stephensi are presented. Spotless wings (sl) and 2nd-3rd costal spots fused (2-3f) have been mapped on chromosome 2, approximately 79.5 map units apart. A preliminary linkage map for this species also is presented.