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Demise of Malaria Drug Started with Travelers

By Kate Ruder

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Over the last decade or so, some people traveling from Asia to Africa unknowingly brought with them the parasite that causes malaria, including some strains that are highly-resistant to a drug commonly used to treat the disease. These parasites are today so widespread in Africa that the drug, fansidar, is no longer effective across much of the continent.

Two groups of American and British scientists made the discovery by analyzing the DNA of the parasite in malaria patients in Thailand and South Africa. Many patients had been infected by parasites that had nearly identical mutations in a gene that confers resistance to the drug.

The new findings don’t offer an immediate solution to the problem of drug resistance, but they are proof that travelers can spread drug-resistant parasites to different parts of the world. The scientists recommend that more rigorous screening of travelers be put in place in the future, although they admit this will be logistically difficult.

“We suggest that careful thought be given to preventing further import of resistant parasites, perhaps by screening and treatment of passengers traveling from southeast Asia or South America to Africa,” the researchers write in a paper published today in Science.

“The study comes as a surprise,” says Xinzhuan Su at the National Institutes of Health in Bethesda, Maryland, who is an expert in drug resistance in malaria and was not involved in the study.

“Part of the surprise is the implication that drug resistance is spread through traveling,” says Su. “People move around so much that if we don’t have a good monitoring system, in one or two years, resistance to new malaria drugs could occur.”

One of the key’s to the research was the genome sequence of the malaria parasite—which was sequenced in 2002. It allowed them to zero-in on specific mutations in a gene that makes the parasite resistant to fansidar.

“The work would not have been possible without the sequence of the malaria parasite genome,” says Tim Anderson of Southwest Foundation for Biomedical Research in San Antonio, Texas, who was a member of the research team.

This is actually the second time that the spread of resistant parasites from Asia to Africa has made an affordable, commonly used drug useless. The drug chloroquine is no longer effective in many parts of the world. It was the spread of drug-resistant parasites from Asia to Africa that made chloriquine an ineffective treatment in much of Africa.

“Import of southeast Asian parasites has thus led to the demise of the two affordable drugs that have been the mainstay of malaria treatment in Africa,” the researchers conclude in the paper.

Roper, C. et al. Intercontinental spread of pyrimethamine-resistant malaria. Science 305, 1124 (August 20, 2004).

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