Designing of a laboratory model for evaluation of the residual effects of deltamethrin (K-othrine WP 5%) on different surfaces against malaria vector, Anopheles stephensi (Diptera: Culicidae).

Background & objectives: Deltamethrin plays an important role in controlling malaria vectors, and is used in indoor residual spraying and manufacture of long-lasting insecticidal mosquito nets. The residual activity of deltamethrin (K-othrine WP 5%) @ 25 mg/m2 was studied in laboratory conditions on different surfaces. Methods: The surfaces were made artificially with different building materials such as mud, plaster, cement and wood in the laboratory. The surfaces were mounted inside petri-dishes (diam: 20 cm) and wood surface was prepared separately. The prepared surfaces were attached to the walls and deltamethrin was applied using standard Hudson pump sprayer with a discharge rate of 757 ml/ min or 0.2 gal/min. The spraying was conducted at standard rhythm as recommended by WHO. After application all the sprayed surfaces were transferred into the special wooden boxes designed for this purpose. The surfaces were maintained at laboratory conditions. The WHO’s recommended bioassay kit and method was used during this study. Results: Bioassays on Anopheles stephensi Liston showed that the persistence of deltamethrin on different surfaces (>70% mortality) was around 4 months on plaster (Mortality = 77±6.2%), 2 months on mud (76.9±6.8%), 4.5 months on cement (79±3.2%), 4 months on wood (71.7±6.8%) and 4 months on filter papers (82.3±5.4%). Interpretation & conclusion: The results of this study on residual effects of deltamethrin WP 5% (25 mg/m2) are highly concordant with two field bioassays carried out in a malarious area at south-eastern Iran. This method can be replaced by the field bioassay tests which are time consuming and costlier.

Comparative performance of imagicides on Anopheles stephensi, main malaria vector in a malarious area, southern Iran.

BACKGROUND & OBJECTIVES: Jiroft district has subtropical climate and prone to seasonal malaria transmission with annual parasite index (API) 4.2 per 1000 in 2006. Anopheles stephensi Liston is a dominant malaria vector. The monitoring of insecticide susceptibility and irritability was conducted using discriminative dose as described by WHO. METHODS: The IV instar larvae were collected from different larval breeding places and transported to the temporary insectary, fed with Bemax and then 2-3 days-old emerged and sugar-fed adults were used for susceptibility and irritability tests employing WHO methods and kits to organochlorine (OC) and pyrethroid (PY) insecticides. RESULTS: Mortality rates of field strain of An. stephensi were 91.3 +/- 0.14 and 90 +/- 0.47% to DDT and dieldrin, respectively at one hour exposure time but was susceptible to all pyrethroids tested. The average number of take-offs per min per adult was 2.09 +/- 0.13 for DDT, 0.581 +/- 0.05 for dieldrin, 1.85 +/- 0.08 for permethrin, 1.87 +/- 0.21 for lambda-cyhalothrin, 1.53 +/- 0.13 for cyfluthrin, and 1.23 +/- 0.1 for deltamethrin. INTERPRETATION & CONCLUSION: Currently, deltamethrin is being used for indoor residual spraying against malaria vectors in the endemic areas of Iran. The findings revealed that the main malaria species is susceptible to all pyrethroids including deltamethrin, permethrin, cyfluthrin and lambda-cyhalothrin but was tolerant to DDT and dieldrin. This report and the finding are coincided with results of previous studies carried out during 1957-61 in the same area. Irritability tests to OC and PY insecticides revealed the moderate level of irritability to DDT compared to pyrethroids and dieldrin. Monitoring for possible cross-resistance between OC and PY insecticides should come into consideration for malaria control programme.

Effect of washing on the bioefficacy of insecticide-treated nets (ITNs) and long-lasting insecticidal nets (LLINs) against main malaria vector Anopheles stephensi by three bioassay methods.

BACKGROUND & OBJECTIVES: The use of pyrethoid impregnated bednets is one of the main malaria vector control strategies worldwide. The objective of the present study was to evaluate the bioefficacy of bednets impregnated with various pyrethroids after repeated washings. METHODS: The effectiveness of bednets impregnated with permethrin, deltamethrin, bifenthrin, etofenprox and long-lasting bednets like OlysetNet and PermaNet which were provided by WHOPES was evaluated. The tests were carried out according to the WHO-recommended methods. Malaria vector, Anopheles stephensi was exposed to impregnated bednets for 3 min and the mortality was measured after 24 h recovery period. Knockdown was measured as well. RESULTS: Results of three methods of bioassay tests showed that between two LLINs, PermaNet was more efficient than OlysetNet. Results of ITNs exhibited that deltamethrin and permethrin were more effective than etofenprox and bifenthrin as impregnants. INTERPRETATION & CONCLUSION: Findings of this study will be useful for WHO, local authorities and people who wish to use different pyrethroid-impregnated bednets for malaria vector control.

Larval habitats of main malaria vectors in Hormozgan province and their susceptibility to different larvicides.

Hormozgan Province is located in the south of Iran bordering the Persian Gulf. In this area, malaria is still considered a major health problem. In the province, eleven species of Anopheles were identified: An. pulcherrimus, An. sergenti, An. apoci, An. multicolor, An. subpictus, An. turkhudi, An. fluviatilis, An. stephensi, An. d'thali, An. superpictus, and An. culicifacies, among which only the last five species play an important role in malaria transmission. Larval habitats of malaria vectors varied from clean to brackish water, as well as sewage water, under palm trees, marshland, pools, pounds, drainage, irrigation canals, wells, and water containers. Malathion, fenitrothion, chlorpyrifos, and temephos were tested against An. stephensi, An. fluviatilis and An. d' thali larvae at diagnostic doses recommended by WHO. The results showed susceptibility to malathion, chlorpyrifos and temephos, but fenitrothion was not able to yield 100% mortality.

Factors involved in the re-emergence of malaria in borderline of Iran, Armenia, Azerbaijan and Turkey.

The borderline of Iran with Azerbaijan, Armenia and Turkey had been considered a malaria free region. However, in 1991, after the independence of the southern countries of the former Soviet Union, a new threat of malaria importation emerged from those countries into Iran, which was affected by serious epidemics of Plasmodium vivax malaria. Various factors can affect malaria resurgence in this region, such as socioeconomic conditions, especially the displacement of massive populations from war-stricken zones in the Republic of Azerbaijan. Accordingly, in some parts of West-Azerbaijan, East-Azerbaijan, Ardebile and Gilan provinces of Iran, several malaria foci were observed. Construction of dams, people traveling from neighboring countries to Iran, urbanization, irrigation projects, lack of malaria vector control, shortage of drug supplies are also major factors in malaria outbreaks in the region. An investigation was carried out on the bionomics of the main malaria vectors in the region. The result showed that Anopheles sacharovi plays an important role in malaria transmission and An. maculipennis and An. superpictus can be secondary vectors. Larvae were found in slow flowing water and channels with water plants. They were more abundant in June. The parity rate of blood-fed females was high in May. An. sacharovi is active from May to October with two peaks of activity, which occur in August and October. The population of this species is higher in animal shelters with a zoophicity of 95%. About 90% of bites took place in the second half of the night. A CDC light trap can also catch this species. Susceptibility testing using the WHO-recommended diagnostic doses of insecticides, revealed that this species is resistant to DDT and dieldrin, but susceptible to malathion, fenitrothion, propoxur, bendiocarb, lambdacyhalothrin, permethrin, cyfluthrin, etofenprox and deltamethrin.