New tactic to tame killer mosquitoes

Scientists are trialling a new type of antimalarial that kills mosquitoes, in a bid to tame the leading killer of children.

Traditionally, treatment for malaria involves administration of drugs targeting plasmodium, the malaria-causing parasite transmitted through the bite of female anopheles mosquitoes.

CHANGING TACK

However, researchers from the Kenya Medical Research Institute (KEMRI), and the US Centres for Disease Control and Prevention (CDC), are changing tack. Preliminary research on patients with symptomatic and uncomplicated malaria, aged 18 to 50 years, being treated at the Jaramogi Oginga Odinga Teaching and Referral Hospital where adults aged 18–50 years, are promising.

Over 741 adults were enrolled in the study between July 2015 and May 2016. Of these, 141 were randomly assigned to receive 600 µg/kg of ivermectin, or 300 µg/kg of ivermectin per day, or a placebo.

Mosquitoes that fed on blood drawn from patients who had been treated with ivermectin, after seven days, were more likely to die 14 days later, compared with those who fed on blood of patients who took the placebo.

Higher doses of ivermectin were associated with a higher mortality rate. A mathematical model by researchers from the Imperial College London, predicted that a higher dose of ivermectin would reduce malaria cases by up to 61 per cent.

“This is an entirely novel type of intervention which could be added to community-wide campaigns with antimalarial drugs, such as mass drug administration and seasonal malaria chemoprevention, to kill both mosquitoes and parasites,” said Dr Menno Smit, one of the study authors.

Ivermectin is an antiparasitic drug, widely used in the treatment of other tropical diseases, in lower doses. It has safely been used in doses of up to 10 times the standard dose.

THREE-DAY COURSE

The research team experimented with drug levels that were two and four times higher than the standard dose. They combined ivermectin with DP, a malaria drug that is routinely used in mass drug administration in many malaria-endemic countries.

Three-day courses of ivermectin 300 and 600 were found to be safe, well-tolerated and routinely killed mosquitoes feeding on the blood of the treated individuals for at least 28 days post-treatment.

Particularly, Ivermectin 300 µg/kg per day for three days, provided a good balance between efficacy and tolerability, and this drug shows promise as a potential new tool for malaria elimination. It could also be used in the fight against other mosquito-borne diseases such as dengue fever and chikungunya.

 “The drug’s impact on mosquito mortality, long effect-duration, and tolerability make it a promising new tool in malaria control. It has a different mode of action from other insecticides, meaning that it could also be effective against mosquitos that rest and feed outdoors, as well as mosquitoes that are resistant to the standard insecticides used on bed nets and indoor spraying,” said Professor Feiko ter Kuile, a senior author of the paper.

The study was funded by the Malaria Eradication Scientific Alliance (MESA), and findings were published in The Lancet Infectious Diseases.

Life without mosquitoes?

There are over 3,500 species of mosquito, but only 200 blood-sucking mosquitoes feed on human blood. According to Prof Grayson Brown, a public health entomologist, killing mosquitoes wholesale would upset the balance of nature.

“Mosquito larvae are very important in aquatic ecology. Many other insects and small fish feed on them and the loss of that food source would cause their numbers to decline as well. Anything that feeds on them, such as game fish and birds would also suffer,” said Prof Brown in an interview on io9.com.

“Wiping out a species of mosquito could leave a predator without prey, or a plant without a pollinator,” says aquatic entomologist Richard Merritt. In the absence of mosquito larvae, hundreds of species of insects would have to change their diet to survive.

“This may sound simple, but traits such as feeding behaviour are deeply imprinted. The loss could have major effects up and down the food chain,” he said.

Additional reporting by Aggrey Omboki