Malaria mosquito fights back

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.