Alternative insecticide dramatically reduces malaria transmission
Baku, January 26 (AZERTAC). Indoor spraying with the insecticide bendiocarb has dramatically decreased malaria transmission in many parts of Benin, new evidence that insecticides remain a potent weapon for fighting malaria in Africa despite the rapid rise of resistance to an entire class of mosquito-killing compounds, according to a study published in The American Journal of Tropical Medicine and Hygiene.
Scientists with Benin's Entomologic Research Center in Cotonou evaluated the effects of two applications of bendiocarb in homes throughout the West African country over an eight-month period in 2009. They found that after "indoor residual spraying" or IRS, which involves applying insecticide on walls where mosquitoes are likely to land, none of the 350,000 household members living in the treated homes "received infected bites" from the malaria-carrying mosquito Anopheles gambiae.
Moreover, none of the mosquitoes collected from the treated homes tested positive for the Plasmodium falciparum—the world's most deadly malaria parasite. The absence of infected bites and parasites was seen as evidence that malaria transmission had fallen precipitously in an area where mosquitoes have developed resistance to permethrin and other members of a popular class of insecticides known as pyrethroids.
The successful lifecycle of the malaria parasite depends on constantly moving from mosquitoes to humans and from humans back to the mosquito. Indoor spraying and bednets disrupt this lifecycle by broadly preventing mosquitoes from an opportunity to feed on infected blood and thus obtain and transmit the malaria parasite. The researchers believe that where there was indoor spraying, malaria transmission likely continued at a very low level difficult to detect. They conclude that it would have required analyzing "thousands of mosquitoes to find any positive for malaria parasites."
Bendiocarb has been deployed in the fight against malaria despite the fact that it has been voluntarily withdrawn from the U.S. market due to safety concerns. The World Health Organization has approved its use - with strict safety protocols - for indoor spraying programs to combat malaria. Padonou said investigators in Benin monitored for both human and environmental exposures and found no evidence of any adverse events.
The indoor spraying campaign in Benin was conducted by the country's National Malaria Control Program, with support from the U.S. through the President's Malaria Initiative. This is part of a broad effort to find alternatives to pyrethroids, the mainstay of public health campaigns against malaria, chiefly through the distribution of insecticide-treated bednets (ITNs) and indoor spraying campaigns. Malaria experts point to wider use of both interventions—coupled with greater access to malaria medicines and diagnostics—as a key reason why malaria deaths in Africa have dropped by more than a third over the last decade, which represents about 1.1 million lives saved.
Indoor spraying was tested in homes in what is known as the plateau region of Benin, which alternates between wet and dry seasons. But in swampy, frequently flooded areas of Benin, there was concern that indoor spraying with any malaria-killing insecticides could produce toxic runoff into local waterways. Therefore, public health officials opted for increased distribution of ITNs as the primary tool for reducing transmission
The study reports that both indoor spraying and treated bednets demonstrated a capacity to significantly decrease malaria transmission. For the areas that received indoor spraying, infected bites declined by 94 percent overall during the eight-month study, though in some villages scientists believe infected bites stopped altogether. No one living in a treated home received an infected bite. Bites from infectious mosquitoes also declined substantially in areas where there was increased distribution of ITNs, though the drop was about 5 percent less than what was achieved via indoor spraying.
In contrast, in an area of Benin that received neither indoor spraying nor increased access to treated nets, each resident received an average of 120 infected bites over the same period.
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