Malaria mosquito fights back

The malaria transmitting mosquito has built resistance against popular insecticides used for indoor spraying and to treat bed nets, effectively removing one of the most important weapons used to fight the disease in Kenya.

In a study published online recently in the Genome Research journal and carried out by the Liverpool School of Tropical Medicine in the UK, researchers have confirmed suspicions that mosquitoes have evolved to overcome the effects of pyrethroids, a chemical derived from pyrethrum.

Gene responsible

“This might mean that these insecticides can no longer be used to control malaria causing mosquitoes,’’ scientists say in the study, adding that they have discovered the gene responsible for resistance in the insects.

Studying the anopheles mosquito, the vector responsible for transmitting malaria, the scientists found a family of genes that code for enzymes known as cytochrome P450s, which can soak up the pyrethroids, making them ineffective.

This study could strengthen the case for a return to DDT as a preventive tool. The new development comes barely a week after a study published in the New England Journal claimed that the malaria parasite is building resistance against the new and very effective artemisinin medicines which are the first-line treatments in Kenya.

The cases of resistance in plasmodium falciparum were detected on the Thailand-Cambodia border, in the same area that drug-resistant strains of the malaria parasite have developed in the past, most notably to chloroquine in the 1950s.

The reports of resistance confirm fears that artemisinin — extracted from a plant used in traditional Chinese medicine — is losing its effectiveness in some parts of Asia.

Although Kenya has adopted a malaria policy requiring that any anti-malarial be combined with another molecule to protect against building resistance, monotherapies are still widely used in the private sector.

Medical experts say if artemisinin resistance spreads quickly, there are no drugs in the pipeline to replace its combinations.

In Kenya, use of combined therapy or ACT as a first-line treatment, distribution of bed nets and indoor spraying with pyrethroids has been credited with helping reduce malaria mortality for children under five years by half, from about 35,000 deaths per year to less than 15,000.

Experts say a combination of factors, especially misuse by patients, the illegal manufacture of counterfeits with low levels of the active ingredients and failure to finish prescribed doses were responsible for the development of resistance by the malaria parasite to both chloroquine and suphadoxine-pyrimethamine (SP). The same factors, they say, could herald the end for artemisinin-combination drugs.