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).
What happens next here matters for the entire world; malaria remains one of the biggest killers in low-income countries. Estimates of the number of deaths each year range from 450,000 to 720,000 — and ACT pills keep that toll from being much higher. And although southeast Asia accounts for just 7% of malaria cases worldwide, it has a notorious history as the breeding ground for strains of malaria parasites that resist every drug thrown at them and then spread to other regions.
In 2015, reports of drug resistance prompted the governments of five countries in the Greater Mekong Subregion — Cambodia, Thailand, Vietnam, Laos and Myanmar — to pledge to banish P. falciparum from the region by 2025. Together with the World Health Organization (WHO), the countries drew up plans and budgets. This year, the nations’ governments have committed US$41 million towards the effort; the Global Fund to Fight AIDS, Tuberculosis and Malaria also backed elimination efforts in the region, with a 3-year, $243-million grant. Donors such as the Bill & Melinda Gates Foundation and the Asian Development Bank will add more than $20 million to the fight this year.
But the rise of cases in northeastern Cambodia shows how difficult getting to zero will be — and how crucial. As long as P. falciparum exists, it can resurge. And the last parasites remaining are the hardest to find. They reside in the hinterlands, borderlands and war zones — and in people who show no signs of the disease. “Malaria is very clever — it hides out where you don’t know and comes back when you aren’t ready,” says Ladda Kajeechiwa, a malaria-programme manager at a branch of the Mahidol Oxford Tropical Medicine Research Unit (MORU) in Mae Sot, Thailand.
“Malaria is very clever — it hides out where you don’t know and comes back when you aren’t ready.”
To eliminate malaria, public-health officials are trying to cover the region with volunteers and health workers who can dispense malaria drugs promptly, and report any signs of an upsurge. They are also looking to researchers for tools that can forestall drug resistance, technologies that improve detection of the parasite, and evidence on strategies for rooting it out. The pressure is on. “Everybody has fears of malaria resurgence,” says Myaing Nyunt, a malaria researcher at Duke Global Health Institute in Durham, North Carolina. She worries that donors will tire of the cause, and that the people in the Greater Mekong region will grow to resent the obsession with malaria when they have more pressing needs. Yet if the effort lets up, malaria will roar back.“That is why it is so important to eliminate it as quickly as possible,” Myaing Nyunt says.