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Act now on growing insecticide resistance, says malaria expert

Dr Vincent Corbel, malaria expert and WHO advisor, addresses a symposium on mosquito resistance to pyrethroids at a Nairobi hotel on 23 April 2009 Georgina Goodwin/IRIN
Mosquitoes in east Africa have developed resistance to some of the insecticides used to impregnate bed nets, according to a leading malaria scientist.

"Studies have indicated that two species of malaria-transmitting mosquitoes found in Kenya have developed resistance to permethrin and DDT," Vincent Corbel, a malaria specialist with the World Health Organization, told a symposium held in Nairobi on 23 April.

Corbel presented findings of studies carried out in several African countries showing an increase in mosquito resistance to not only synthetic pyrethroids but also to DDT, which was mostly used in Europe and the US to eradicate malaria there until its prohibition.

"Insecticide resistance is not new but it has received much more attention in the last 10 years because of the lack of alternatives to mosquito nets; WHO recommends use of long-lasting insecticide-treated nets as well as indoor residual spraying for effective malaria control," Corbel said.

Corbel added: "Since resistance is developing, the time to develop preventive measures is now; we need to implement a management strategy, an integrated approach, in order to contain this resistance."

The symposium was organised by Kenya’s Ministry of Public Health and Sanitation in the run up to World Malaria Day on 25 April.

Pyrethroid insecticides still effective?

Malaria mosquito. 20039105
Photo: Swiss Radio
A malaria-transmitting mosquito
The ministry’s director of malaria control, Elizabeth Juma, told the symposium that the pyrethroid insecticides used in Kenya remained effective.

"Although the gene [that confers resistance] has been detected in western Kenya, tests on mosquitoes have found that the knock-down time is still within one hour, meaning that the mosquitoes are still vulnerable to insecticide-treated nets."

"As far as the ministry is concerned, information gathered by various researchers shows that there is a difference between the gene that confers resistance being discovered and the mosquitoes themselves developing resistance," she said.

Juma said that even in west Africa - where studies have found resistance to be higher - public health services still used insecticide-treated nets.

"The objective of malaria control is to reduce the disease's burden in the population...; hence vector control; why continue to try and reduce human-vector contact? That is why we also undertake larviciding [spraying of mosquito breeding grounds]," she said.

The ministry is to study the impact of this resistance in three western Kenyan districts - Bondo, Rachuonyo and Nyando, according to Nabie Bayoh of the Kenya Medical Research Institute's Centre for Disease Control.

"The significance of the finding of these genes should be assessed in terms of the impact of resistance in malaria control measures," he told the symposium.

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