Friday, April 24, 2009

Killing River Blindness and Malaria With the Same Drug

Researchers ponder whether a common drug that kills parasitic worms (helminths) might also prevent mosquitoes from transmitting malaria. The work is more preliminary than most in the field of malaria research, so don’t expect it to save any lives any time soon—if ever. But it is an interesting application of the old adage about trying “to kill two birds with one stone.”

In anticipation of World Malaria Day (which is tomorrow), the Bill and Melinda Gates Foundation held its first telephone briefing for bloggers who cover global health.

There were three researchers on the line—each of whom had won a $100,000 grant to explore an idea for fighting malaria that was a little unorthodox or “out of the box.” These are part of the Grand Challenges Exploration grants that the Gates Foundation has championed in recent years. Depending on the results, grantees are eligible for $1 million grants to further prove their concepts.

I focused most of my attention on Brian Foy, an assistant professor at Colorado State University.

Foy, who has previously done some work on malaria vaccines, started thinking about the life cycle of the malaria parasite inside the mosquito as an under-explored route of attack. It takes 10 to 14 days for the malaria parasite to mature in a mosquito’s body--from the time a mosquito bites an infected person (what entomologists call “taking a blood meal”) to the time that same mosquito can transmit the parasite to a different person. “If you could just make one of those blood meals toxic to the mosquito, you would basically kill it before it could transmit the parasite,” Foy says.

Enter ivermectin, a drug that targets parasitic worms, like heartworms in dogs or the worms that cause river blindness in people in West Africa. Ivermectin works by targeting certain neurotransmission channels in worms. It turns out those same channels exist in other invertebrates like mosquitoes.

So the idea is to give ivermectin to people, who then pass the drug along with their blood to the mosquito that bites them. To be most effective, the drug should kill only those mosquitoes infected with the parasite before it has a chance to fully mature. As an added bonus, you minimize the risk of resistance because you’re not killing all the mosquitoes, just the infected ones, so there is no selection pressure against the mosquitoes—at least in theory.

So far, the evidence from the field is encouraging. Foy reported data from Senegal that showed that mosquitoes died for up to a week after ivermectin was given in an anti-river blindness campaign. Now he is trying to determine if the effect is large enough so that if you expanded ivermectin treatment you could actually change the transmission of malaria.

You see, ivermectin is normally given only once or twice a year for the treatment of river blindness. To have any effect on mosquitoes, you would probably have to give ivermectin once a month.

But this is just a pilot test—a chance to see if the idea is worth pursuing further.

You’re talking about four very complicated organisms—humans, mosquitoes, malaria parasites and helminths. In 2007, there was a research paper that suggested that infection with helminths actually made malaria symptoms less severe and that treating the parasitic worms could actually make a co-infection with malaria worse. (TW Mwangi, et al. Annals of Tropical Medical Parasitology.)

So for now, the idea that ivermectin could make a dent in both river blindness and malaria at the same time is still just an intriguing idea that is being tested further.

The other two presenters on the Gates telebriefing were Szabolcs Marka, assistant professor at Columbia University and Pradipsinh Rathod, professor at University of Washington.

Marka is looking at the possibility of using laser light to interfere with a mosquito’s ability to find and bite people. Rathod is trying to see if genetic differences between Plasmodium falciparum parasites found in Asia and those in Africa might help develop more effective treatments.

You can hear a recording of the full teleconference until April 30th by calling (800) 475-6701 and entering access code # 997326.

Full disclosure: my 2008 Nieman Fellowship in Global Health Reporting was supported by a grant from the Gates Foundation. I believe I have no conflict of interest in this story because the Gates Foundation did not play an active role in my choice of study or of my field project on nurses in Malawi.

1 comment:

naman said...

Thanks for posting the disclosure - not many folks do that. Like Dr Rabinovich said on the call - it is high risk, high reward research but I think we need to consider risks beyond the purely technical. Even if the idea works, mass drug administration on a monthly basis and achieving a high coverage of the population is difficult. In fact, we have trouble doing it once or twice a year for deworming or against lymphatic filariasis.