A study conducted in Kenya shows that taking high doses of an anti-parasitic drug called ivermectin may kill mosquitos who feed on your blood up to 28 days later.
This is big news for the field of tropical medicine, because the single-celled microorganism that causes malaria is infamously adept at developing resistance to anti-malaria agents and hiding from the immune system during dormant lifecycle phases.
Despite our best efforts to combat the Plasmodium protozoa, millions of people suffer from infections each year, of which an estimated 500,000 people die.
Thus, public health officials focus on preventing transmission by reducing mosquito populations in affected regions. Following previous reports that ivermectin – developed to wipe out parasitic worm infection – makes human blood toxic to mosquitos, the multinational team of researchers sought to determine exactly how much of the drug was required to achieve this effect, and whether or not it would last long enough to actually impact nearby mosquitos.
They recruited 128 patients who were already being treated for malaria infections and randomly assigned them to take 300 mcg/kg or 600 mcg/kg (micrograms per kilogram of body weight) of ivermectin, or placebo, alongside a standard three-day course of the malaria drug combination DHA/PPQ.
Over the next 28 days, blood samples were periodically taken from the patients and fed to captive Anopheles gambiae mosquitos, a subtype of the insect species known to spread the most dangerous strain of the malaria parasite.
Remarkably, 97 percent of mosquitos died within two weeks of ingesting blood taken from patients who had started the 600 mcg/kg ivermectin regimen seven days previously. The complete results, published in The Lancet, indicate that blood from patients taking the 300 mcg/kg dose was also impressively fatal to mosquitos (93 percent).
Better yet, average mosquito survival time remained below 14 days even after they consumed blood taken 28 days after patients started the 600 or 300 mcg/kg course of ivermectin plus DHA/PPQ – a much longer duration of effect than the researchers anticipated.
“The combination of an artemisinin-based combination therapy and ivermectin targets both the malaria parasite and its vector," they wrote, "a unique property among malaria interventions that has the potential to reduce onward transmission of antimalarial drug-resistant parasites.”
Effectiveness aside, because ivermectin is typically taken as a single dose of 200 mcg/kg or less, the researchers needed to demonstrate that three days of 600 mcg/kg is actually tolerable. Fortunately, although patients did experience some drug reactions, the symptoms were mild in everyone except three patients with pre-existing liver conditions.
Now, as promising as this data sounds, the authors concede that more clinical trials will be needed before this treatment protocol can be accepted as safe.
"The patients may have noticed less side effects because they were already feeling sick," study lead Menno Smit told NPR. "We have yet to see if the excellent tolerance we saw would be just as good in healthy individuals."
It's also possible the mosquitos will eventually build resistance to the drug. Nevertheless, if ivermectin does get the green light for malaria, the team calculates that giving infected individuals 600 mcg/kg of ivermectin could reduce the current rate of new cases by 61 percent in high-risk areas.