Many tropical diseases are co-endemic in a given country and environment. Therefore, it only makes sense to learn whether there can be common strategies and synergies in disease control and elimination efforts. Onchocerciasis or River Blindness is carried by the black fly (simulium damnosum) that breeds along the banks of fast flowing rivers and malaria are examples.
Onchocerciasis was eliminated in many settings in the Sahel through the process or aerial spraying of these riverbanks to kill the black fly larvae. Though the insecticide used was often the same as used for malaria larviciding, the habitats differed and no synergies were achieved then.
Through subsequent programs using community directed treatment with ivermectin (Mectizan ®) interventions sponsored by the African Program for Onchocerciasis Control (APOC) it was learned that ivermectin also had beneficial effects on malaria transmission.
Ivermectin had been used in agriculture not only for internal parasites of animals. The agricultural community has long known that ivermectin kills both internal parasites (worms) but is also effective against some external parasites (lice and ticks).
Around 2010 scientists began to consider the anti-mosquito effects ivermectin might have when humans consumed it. It turns out that after a mass distribution in a community of ivermectin for onchocerciasis that mosquitoes feeding on people who had recently swallowed ivermectin would die. This was demonstrated when mosquitoes bit volunteers who took ivermectin of the first few days after consumption died there was no effect in the group not taking the drug.
Of particular interest was the fact that people who had consumed ivermectin would contribute to mosquito mortality even when they were outdoors. While the effect was not long lasting, the onchocerciasis control programs in the Americas have shown that it is safe to administer the drug two or four times a year.
Research that looks at the malaria parasite concluded that, “it is likely that ivermectin treatment is arresting parasite growth.” The researchers note that, “given the prior use of ivermectin and its safety record in humans and animals, it can be considered in combination therapy with other antimalarials.” The issue of dosage would need to be tested further. Ivermectin at sub-lethal concentrations even inhibits the sporogony of P. falciparum in An. Gambiae.
Because of the need to find new and complementary tools to eliminate malaria the Malaria Policy Advisory Committee (MPAC) of the World Health Organization’s Global Malaria Program considered at its recent meeting the role of endectocides including ivermectin in the future of malaria control and elimination and the importance of further research.
The future of malaria elimination requires finding new tools to integrate with and the strengthening of existing tools. If these efforts also benefit the control and elimination of other diseases, the public’s health will benefit.