An international team of researchers has found two different compounds that can block malaria transmission when added to pre-existing treatment regimes.
One of the compounds is primaquine, an older malaria drug that is used to treat a strain of the disease called P.vivax. The second is a laboratory dye called methylene blue, which is typically used to distinguish dead cells from living ones and is known to have antimalarial properties. Both methylene blue and primaquine have been in use for many years.
Researchers found that when added to malaria treatments, the compounds prevented the P.falciparum parasite’s gametocytes from passing between humans and the mosquitoes that bit them. The study has been published in The Lancet Infectious Diseases.
“The results are very promising,” said Radboud Institute for Health Sciences associate professor Dr Teun Bousema. “We found that adding either of these drugs to antimalarial medicines already in use ensured that patients were no longer able to pass the disease back on to mosquitoes.”
The researchers said the findings could help rapidly reduce population-level transmission of P. falciparum, the most common form of malaria in Africa. They also said the new combinations could target the disease’s drug-resistant forms and thus accelerate the process of eliminating it.
A Phase II trial, funded by the Bill & Melinda Gates Foundation, was conducted comparing the effectiveness of the two compounds in preventing gametocyte transmission. The researchers chose 80 boys and men to participate in the trial, all from Mali and with asymptomatic malaria.
The findings revealed that adding a single dose of primaquine to sulfadoxine-pyrimethamine and amodiaquine treatment, or adding three doses of methylene blue to dihydroartemisinin-piperaquine treatment, resulted in the near-complete blockage of transmission within 48 hours. Comparatively, patients who were not given the added combination were able to infect mosquitoes for at least one week after treatment.
Professor of epidemiology and biostatistics at UC San Francisco (UCSF) Dr Roly Gosling said: “Although these two drugs have been around for more than half a century, this is the first time that the exciting and impressive effects…on malaria transmission have been so clearly demonstrated…now we can say that the effectiveness of common malaria drugs used for seasonal malaria chemoprevention can be improved, with the potential of removing the threat of malaria to many millions of people across West Africa.”
However, formal trials are still needed to build on these results and identify the optimal cases in which these treatments can be used. More research is also needed to investigate how new treatments can be incorporated into other antimalarial strategies and tools.