Scientists have been working for decades to develop a vaccine against malaria but the Plasmodium parasite is a formidable enemy. Although a promising vaccine finally reached clinical trials terminal, it provides only partial protection against the disease, which kills up to one million people per year. Now a team of scientists came to what might be relatively simple alternative: two antibiotics widely used already can act as a kind of vaccine against malaria in mice. If the discovery holds in humans, it could be a low-cost and relatively safe tool to help control the disease, they say.
people living in areas where malaria is common to develop a natural immunity, and many scientists have tried to mimic this effect by creating a vaccine using whole parasites, or damaged or killed. Although small human trials have shown good results, production and delivery of such a vaccine will not be cheap. Steffen Borrmann from the School of the University of Heidelberg Medical in Germany and the Kenya Medical Research Institute in Kilifi and his colleagues wondered whether the administration of certain antimalarial drugs to people at high risk of infection could a similar effect.
Drugs scientists had studied are antibiotics that attack a subunit of the malaria parasite called apicoplast, which has some similarities with bacteria. Previous studies had shown that apicoplast-targeting drugs have a delayed death effect: They enable the parasite to grow and replicate in the liver, where the immune system can develop antibodies against invaders. But they block the multiplication of the parasite in the bloodstream, which is where Plasmodium causes symptoms of malaria, including anemia, high fever, and convulsions. The researchers wondered if the treatment of the aggressive malaria with such drugs could be a safe way to allow people to develop a natural immunity. (The drugs are not yet widely used against malaria.)
The researchers tested two of these antibiotics clindamycin and azithromycin, which are used against a range of bacterial infections, a model mouse malaria. They gave the mice a dose of one of the drugs at the same time as they are inoculated with malaria parasites. Parasites infected livers of animals, but none of the mice developed symptoms of malaria. A month later, after all traces of the drug have disappeared from the flow of blood of animals, the animals were still free from the disease: They showed no symptoms after receiving a dose of parasites gave control animals cerebral malaria the most deadly form of the disease. As controls, mice that received only the drug but not parasites in the original protocol also got sick of the challenge dose of Plasmodium , the team announced today online science Translational Medicine .
Azithromycin has a particularly secure balance in infants and pregnant women, the two most vulnerable groups, Borrmann note. He said the combination of azithromycin and chloroquine (a drug against the common malaria), currently approved to treat pregnant women in areas at high risk of malaria would be easy enough to test in an initial human trial. The idea will not work in all areas prone to malaria, he warns. A fairly heavy dose of parasites seems to be necessary to ask a strong immunity, so he said the areas where malaria hits hard during one season would be the best places to try the approach. People could receive a drug dose at the start of the rainy season, which would not prevent infection, but prevent them from developing malaria symptoms. Asymptomatic infection and allow them to develop immunity to the rest of the malaria season. Although the general treatment still carries a risk of emerging resistance to drugs, Borrmann said azithromycin was used in mass campaigns against trachoma without losing its power.
The studies support the idea of using natural exposure in combination with drugs against malaria fighting to help people build up protection against the disease, said the vaccine against malaria researcher Robert Sauerwein medical Center Radboud University Nijmegen in the Netherlands. "It leaves the natural route of infection intact, and may also neutralize the immune evasion strategies used by the parasite."
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