Pyrethroid resistance in southern African Anopheles funestus extends to Likoma Island in Lake Malawi
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RESEARCH
Open Access
Pyrethroid resistance in southern African Anopheles funestus extends to Likoma Island in Lake Malawi RH Hunt1,2, M Edwardes3, M Coetzee1,2*
Abstract Background: A mosquito survey was carried out on the island of Likoma in Lake Malawi with a view to collecting baseline data to determine the feasibility of implementing an integrated malaria vector control programme. No vector control interventions are currently being applied on the island apart from the sporadic use of treated and untreated bed nets. Results: Large numbers of Anopheles funestus were found resting inside houses. WHO susceptibility tests were carried out on wild caught females and 1-5 day old F-1 female progeny. Wild caught females were tested on deltamethrin (77.8% mortality) and bendiocarb (56.4% mortality). Female progeny were tested on deltamethrin (41.4% mortality), permethrin (40.4%), bendiocarb (52.5%), propoxur (7.4%), malathion, fenitrothion, DDT, dieldrin (all 100%) and pirimiphos-methyl (98.9%). The malaria parasite rate was 4.9%. A small number of Anopheles arabiensis were also collected. Conclusion: This locality is 1,500 km north of the currently known distribution of pyrethroid resistant An. funestus in southern Africa. The susceptibility results mirror those found in southern Mozambique and South African populations, but are markedly different to An. funestus populations in Uganda, indicating that the Malawi resistance has spread from the south.
Background Anopheles funestus is the major malaria vector in southern Africa. Early records of its involvement in malaria transmission give Plasmodium falciparum parasite rates as high as 22% in South Africa [1]. More recently, in Tanzania 11% infection rate was recorded [2] and 5% in southern Mozambique [3]. South Africa eradicated An. funestus in the 1950’s when an extensive indoor residual spraying (IRS) campaign using DDT was rolled out. In the next 50 years, this vector species was recorded only once during a small malaria outbreak in the northern part of the country [4]. In 1999/ 2000, however, South Africa experienced its worst malaria outbreak since the introduction of IRS in the 1950’s and An. funestus was found once again in northern KwaZulu/ Natal, just south of Mozambique [5,6]. The P. falciparum
parasite rate in An. funestus was 5.4% and the mosquitoes were found to be resistant to both pyrethroids and carbamates. Subsequent research in southern Mozambique showed that the insecticide resistant population of An. funestus extended north of the capital, Maputo [7-9]. Most recently, resistance was found in An. funestus from Chokwe [10], approximately 200 km north of the capital, where previously this population was found to be susceptible [8]. The present study provides evidence of insecticide resistance in An. funestus from an island in Lake Malawi that is considerably further north than any previous records of resistance.
Materials and methods Study site
* Correspondence: [email protected] 1 Malaria Entomology Research Unit, School of Pathology, Faculty o
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