A worsening epidemic of sophisticated antimalarial drug counterfeiting in Southeast Asia and Africa is increasing the likelihood of drug-resistant parasites, which yield false-positive results on screening tests and risk the lives of hundreds of thousands of malaria patients—mostly children—researchers say. Malaria is a widespread international problem, primarily in poor and developing countries in the tropics—though some cases have been reported in Florida in the United States. The disease is transmitted by mosquitoes infected with the parasite Plasmodium falciparum and infects 300 to 500 million people every year. Although genuine antimalarial drugs are quite effective, about 1.5 million of infected people, mostly children, die each year. One of the most efficacious drugs is artesunate, derived from the Artemisia annua plant native to China.

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