Partner study description
Tanzanian samples were collected from four distinct locations. Moshi samples came from lower Mabogini (-3.400, 37.350), rice fields near lower Moshi on the southern slope of Mount Kilimanjaro, a region shown to have increasing resistance to pyrethroids (1). Mosquitoes were collected as larvae, during the rice growing season in August-September 2012, raised to adults and females bioassayed in WHO tubes for one hour with 0.05% lambda cyhalothrin. Alive and dead mosquitoes were preserved over silica. In Tanzanian samples screened in Kabula et al. (2), Moshi was the most pyrethroid resistant population, they were found to be completely DDT susceptible, only in one out of 642 mosquitoes assayed by (1) was found to carry a kdr resistance mutation (Vgsc-995F).
Tarime collections took place in the village of Komaswa (-1.417, 34.183) about 410km north west of Moshi, during August 2012. Mosquito larvae were collected, raised to adults and females bioassayed with a range of insecticides in WHO tubes for one hour finding almost complete multi-insecticide susceptibility: permethrin (100% mortality), lambda cyhalothrin (97%), fenitrothion (100%), DDT (100%) and bendiocarb (100%) (3).
Muheza samples were collected from Zeneti village (-5.217, 38.650), northeast Tanzania. Malaria is intense and perennial with transmission peaking after the rainy season in May and June (2). Mosquitoes were sampled between November 2012 and May 2013. Indoor resting collections were used to obtain live females for deltamethrin susceptibility testing and pyrethrum spray catches were used for mosquitoes that were collected for blood meal analysis. Collections were conducted between 06:00 and 09:00 from randomly selected houses. Live mosquitoes collected for susceptibility testing were provided with 10% glucose solution and transported to the field insectary. Mosquitoes were sorted and morphologically identified to species, carcasses were stored individually over desiccant for laboratory processing.
Muleba (1.750, 31.667), the final collection region, is in the North-western part of Tanzania. The district is known to be a malaria epidemic prone area with unstable transmission of varying seasonality. The highest peak of malaria transmission is usually reached between May-July and November-January, which results from proceeding rain seasons. There have been malaria vector control efforts since 2007 when indoor residual spraying using lambda cyhalothrin was introduced. Insecticide resistance in this district is coupled with high frequency of kdr pyrethroid target site mutations in the An. gambiae s.s. population (2, 4). Sampling was conducted over six months, which include both dry and rainy season and covers 6 villages selected to represent all major ecological systems in the district.
1. Johnson Matowo, Christopher M Jones, Bilali Kabula, Hilary Ranson, Keith Steen, Franklin Mosha, Mark Rowland, and David Weetman. Genetic basis of pyrethroid resistance in a population of anopheles arabiensis, the primary malaria vector in Lower Moshi, north-eastern Tanzania. Parasites & Vectors, 7:274, 2014. https://doi.org/10.1186/1756-3305-7-274
2. Bilali Kabula, Patrick Tungu, Johnson Matowo, Jovin Kitau, Clement Mweya, Basiliana Emidi, Denis Masue, Calvin Sindato, Robert Malima, Jubilate Minja, Shandala Msangi, Ritha Njau, Franklin Mosha, Stephen Magesa, and William Kisinza. Susceptibility status of malaria vectors to insecticides commonly used for malaria control in Tanzania. Tropical Medicine & International Health, 17:742–750, April 2012. https://doi.org/10.1111/j.1365-3156.2012.02986.x
3. Deokary Joseph Matiya, Anitha B. Philbert, Winifrida Kidima, and Johnson J. Matowo. Dynamics and monitoring of insecticide resistance in malaria vectors across mainland Tanzania from 1997 to 2017: a systematic review. Malaria J, March 2019. https://doi.org/10.1186/s12936-019-2738-6
4. Natacha Protopopoff, Johnson Matowo, Robert Malima, Reginald Kavishe, Robert Kaaya, Alexandra Wright, Philippa A West, Immo Kleinschmidt, William Kisinza, Franklin W Mosha, and Mark Rowland. High level of resistance in the mosquito anopheles gambiae to pyrethroid insecticides and reduced susceptibility to bendiocarb in north-western Tanzania. Malaria J, May 2013. https://doi.org/10.1186/1475-2875-12-149
Bilali Kabula (Bika72 [at] gmail.com) National Institute for Medical Research (NIMR), Dar es Salaam, Tanzania.
Johnson Matowo Kilimanjaro Christian Medical University College, Tumaini University, Makumira, Tanzania.
David Weetman (david.weetman [at] lstmed.ac.uk) Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
Martin J. Donnelly (Martin.Donnelly [at] lstmed.ac.uk) Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
Parasites and Microbes Programme, Wellcome Sanger Institute, Hinxton, Cambridge CB10 1SA, UK.