Susceptibility of Anopheles maculatus and An. minimus to Synthetic Pyrethroid by WHO Test and Biochemical Assay Technique

Abstract

Abstract

Malaria is an important epidemic arthropod-borne disease, recognized as a public-health problem by the Thai Ministry of Public Health (MOPH). Vector control using insecticides is considered an effective tool in the Thai Malaria Control Program. Since 1996, the Thai MOPH has been using pyrethroids, ie, deltamethrin and permethrin, rather than organochlorines to control anopheline mosquitoes . The Bureau of Vector-borne Disease, MOPH, has routinely used a WHO test kit to assess the insecticide susceptibility of anophelines. This experimental comparative study of the WHO test kit and biochemical assay test was conducted to ascertain the susceptibility of major malaria vectors to synthetic pyrethroid. The two mosquito species used were wild Anopheles maculatus collected from Uthai Thani Province, and An. minimus collected from Tak, Chumphon, and Surat Thani provinces during the period May-July 2005. The study aimed to assess the distribution of field populations of An. minimus and An. maculatus and their insecticide susceptibility using the WHO test kit and the biochemical assay test, and to evaluate the potential usefulness of the biochemical assay test compared with the WHO test kit, as a potential monitoring tool in vector-control programs.

The results of testing An. maculatus from Uthai Thani and An. minimus from Tak and Chumphon showed up to 98% mortality by WHO test kit, and thus no resistance according to WHO standards. The results of the biochemical assay testing of An. maculatus from Uthai Thani and An. minimus from Surat Thani, Chumphon, and Tak were compared with those for two laboratory colonies, both MOPH and AFRIMS. It was interpreted that the An. maculatus from Uthai Thani and An. minimus from Chumphon and Tak had the same susceptibility to the pyrethroid as found with the WHO test kit. The biochemical assay is a promising new technique for detection and assessment. However, in this study, only a small number of mosquitoes were tested. Continuous large-scale studies should be conducted to determine provisional susceptibility thresholds for use in monitoring the effects of control strategies on vector mosquito resistance.

Keywords : Anopheles maculatus, An. minimus, pyrethroid, WHO, biochemical assay technique, Thailand