Ka Lar Nar caught malaria for the sixth time when he was working on his small farm in the jungle of southeastern Myanmar, but this time it was a lot harder to get rid of it.

He got a three-day course of drugs from a health volunteer in his village, but even though his fever subsided he continued to be plagued by headaches, and another test still showed positive results.

Experts say his case could be an indication of drug resistance to the mosquito-borne disease, which has been spreading in Myanmar and other countries in the Mekong River basin in what threatens to become the next big global health emergency if it marches on to India and Africa.

"This was a missed opportunity," said Eisa Hamid, an epidemiologist working with the United Nations in Myanmar, who specializes in monitoring and evaluating malaria programs.

Normally, after three days of treatment the farmer's blood should have been clear of malaria-transmitting parasites.

"With any patient showing positive test results after three days of treatment, we have to suspect drug resistance, and more sophisticated blood testing should have been done as he could still carry the parasites that cause malaria in his blood."

Malaria death rates dropped by 47 percent between 2000 and 2014 worldwide, but the disease still killed 584,000 people in 2013, most of them in sub-Saharan Africa, according to the World Health Organization.