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Less May Be More When Treating Malaria

For centuries, malaria was a fact of life in the tropics and anywhere else the parasite-carrying mosquito could live and breed.

But during the middle of the 20th century, health officials started to bring the disease under control, using pesticides and medications. Rates of malaria in many countries dropped, and in some places, public health experts began to talk about eradicating the disease altogether.

Unfortunately, in the last two to three decades, malaria has gotten out of control again.

According to Andrew Read, an entomology professor at Pennsylvania State University, the problem is actually worse now than it was at the beginning of the 20th century.

Read says one could argue that a large part of the reason malaria is still with us is drug resistance. That's because many of the different species of malaria parasite have evolved to become resistant to anti-malarial drugs. More virulent strains seem especially unaffected by inexpensive drugs, such as chloroquine, which is now useless against malaria in many parts of the world. And often, when someone gets the disease, they're actually infected with more than one strain. Read wondered if part of the problem of drug resistance had to do with how those different strains of malaria compete inside of a host.

To test his idea, Read infected mice with two different strains of malaria: one that was somewhat resistant to medications and another that wasn't. Then he gave the mice anti-malarial drugs.

"If you take away the susceptible strain by killing it with drugs, then all of a sudden the resistant strain is able to grow up and become a much more successful parasite," Read reports. "In other words, the removal of the competitor has made a drug-resistant strain do much, much better."

Read realized that the common medical practice of flooding a patient's body with anti-malarial drugs might actually have the paradoxical effect of making drug resistance worse. He explains that what may be happening is that drug resistant malaria is able to grow without any competition once the medicine has killed drug sensitive strains. And then… it's the drug resistant strain that's more likely to get spread from person to person.

"Our results suggest that it might be that the best thing to do would be to use the drugs only to keep the patient healthy," Read says. "Beyond that, let the parasites grow, let the drug sensitive parasite grow because it suppresses the resistant parasite."

Read believes that suppressing the resistant parasite means that the resistance will transmit less well from person to person. He says that could slow the spread of resistance within a population.

Read says his results are still too preliminary to suggest that patients stop taking their malaria drugs. But he says that these ideas might be important in re-thinking how we treat malaria. And, as new anti-malaria drugs come onto the market, this approach might be used to prevent the development of resistance against these newer medications.

Read's results are published online in the Proceedings of the National Academy of Sciences.