Throngs of men and women ventured into the forests of northeastern Cambodia in April, lured by a bumper crop of a rare tropical treat called samrong. After days of hiking through the wilderness, some of the travellers returned to their homes with a bounty of the wrinkled seeds, which fetch a high price as a special dessert or an ingredient in traditional Chinese medicine. But many soon fell ill. Khong Chhoem, a 56-year-old rice farmer, says the fevers hit him a few days after the expedition. His muscles hurt. His eyes hurt. He had unbearable nightmares. A health worker told Chhoem that he had tested positive for Plasmodium falciparum, the deadliest kind of malaria-causing parasite. But because a wave of malaria was sweeping through the region, medicine was in short supply. Chhoem eventually found a shop that carried the drugs he needed, and he recovered. But in the intervening days, mosquitoes probably sucked up the parasites in his blood and spread them to other people.
After years in decline, malaria infection rates seem to be on the rise in northeastern Cambodia, where people are moving deeper into lush, mosquito-ridden territories in search of timber and seasonal goods such as samrong (Scaphium affine). Their movements provide opportunities for P. falciparum — which requires both human and insect hosts — to thrive. There are other contributors as well, such as treatment delays that allow the parasites to linger and spread, and an alarming decline in the potency of gold-standard malaria drugs called artemisinin-based combination therapies (ACTs).