A drug used to rid people of worms is a new weapon against malaria IVERMECTIN, a drug employed for the treatment of worm infections, has a side effect. It has been known since the 1980s that it kills arthropods (lice, mites, insects and so on) foolish enough to bite someone treated with it. That has led some researchers to wonder if it might be deployed deliberately against the mosquitoes which transmit malaria. Preliminary studies suggested so. Mosquitoes do, indeed, get poisoned when they bite people who have taken the drug. Moreover, even if a mosquito does not succumb, ivermectin imbibed this way is often enough to kill any malarial parasites it is carrying. And, since ivermectin is routinely deployed en masse to deal with lymphatic filariasis (a nasty disease that can lead to extreme swelling of limbs and genitalia), river blindness and so on, it might already be expected to be having an effect. What no one had measured, though, was the size of that effect.A paper presented by Brian Foy of Colorado State University, to this year meeting of the American Society of Tropical Medicine and Hygiene, in Philadelphia, has changed that. Dr Foy and his colleagues ran a small clinical trial in Burkina Faso that is the first to measure the effect of the drug on rates of malaria. In four villages included in the trial everyone except pregnant women and young children received five doses of ivermectin, at three-week intervals. People in a comparison group of villages got just the first dose”which is the routine annual mass-treatment for worm diseases. The extra rounds of ivermectin, Dr Foy found, cut the number of malarial episodes among children under five by 16%”even though these children were not, themselves, receiving the drug. That equates to about one episode per child being averted over the course of two years.A second study presented to the meeting, which was conducted in Thailand by Kevin Kobylinski of the United States Walter Reed Army Institute of Research, brought further good news. It was the first to test the effect of ivermectin on Plasmodium vivax, the predominant parasite in Asia (the African parasite is called Plasmodium falciparum). Dr Kobylinski and his colleagues fed mosquitoes malaria-infected human blood mixed with the drug. They found that a dose of ivermectin which killed 25% of mosquitoes also cleared the parasite in 45% of their surviving sisters. And even in those surviving insects that remained infected, the drug cut the number of parasites in half.In Thailand, a country well on its way to eliminating the scourge of malaria, one line of attack is mass-treatment with drugs that can clear the parasite from its human hosts. Unfortunately, those infected with P. vivax often have no symptoms. Convincing the asymptomatic to take antimalarial drugs can be tricky. Indeed, they may not even realise they are infected. But the task may be easier if the mix includes ivermectin, since this is already a familiar treatment for common problems like scabies.The discoverers of ivermectin predecessor, avermectin, were among the winners of this year Nobel prize for medicine. By an odd coincidence, the third winner was the inventor of artemisinin, which is now the most effective antimalarial drug around. If ivermectin can be pressed into service as an antimalarial agent, too, it will increase the chance that the disease can be knocked on the head once and for all.