A drug-resistant strain of the disease malaria - first detected about 18 months ago near the Thailand-Cambodia border - is now showing up again along Thailand's border with Myanmar.
Many patients in the region taking anti-malarial drugs are now taking much longer to respond to treatment.
Medics fear the resistant strain could eventually spread to Africa, where most of the world's malaria cases and deaths occur.
Aela Callan reports from a clinic near the Thai town of Mae Sot on the border with Myanmar.
Source: Al Jazeera