In the fight against malaria, there is good news and awful news. First, the good news: malaria infection rates are on the decline. Now, the awful news: many of the new malaria cases that do occur are resistant to drugs.
In December, the World Health Organization (WHO) announced that global malaria deaths fell from 839,000 in 2000 to 438,000 in 2015. But the disease still strikes 200 million people a year, often killing children.
A recent study published in The Lancet Infectious Diseases Journal found that in areas of Cambodia, malaria-carrying parasites, including mosquitoes, have developed resistance to piperaquine, a major drug used in combination with the drug artemisinin to fight malaria in that country since 2008. 
Artemisinin was developed by Chinese scientists to treat North Vietnamese soldiers during the Vietnam War. The drug can wipe out malaria quickly, doesn’t cause many side effects, can be administered easily, and only requires 3 doses over 3 days.
Unfortunately, artemisinin is taking longer and longer to treat malaria.
The piperaquine-artemisinin combination is also one of the last remaining therapies that effectively treat multi drug-resistant malaria which has emerged in Southeast Asia in recent years. Experts are deeply concerned that this drug resistance could spread to other parts of the world.
“(Treatment) failures are caused by both artemisinin and piperaquine resistance, and commonly occur in places where dihydroartemisinin-piperaquine has been used in the private sector,” researchers said.
Each time the parasite that causes malaria mutates and kills millions globally, it starts in Southeast Asia. 
And in this case, fewer cases of the disease don’t comfort health experts; it only makes them worry that a new, deadlier wave is brewing.
“When no one is worried, that’s when we have to worry,” said Professor Francois Nosten, director of the Shoklo Malaria Research Unit, which includes Wang Pha and four other clinics along the Thai-Myanmar border.
“Of course, if you go to a place, and you see nobody in the hospital with malaria, then of course it’s difficult to worry about. It doesn’t mean everything is settled and solved,” Nosten said. “We know from the past that it’s not going to stay that way.”
Parasites resistant to artemisinin have been found in Cambodia, Laos, Myanmar, Thailand, and Vietnam. Resistance to both drugs has emerged in sections of Cambodia and Thailand.
A worst-case scenario would be for artemisinin-resistant parasites to spread to sub-Saharan Africa, where approximately 90% of malaria cases and deaths occur. It’s much easier for malaria to be transmitted there because the mosquitoes are more aggressive, have longer life spans, and bite more people. 
“Because few other artemisinin combination therapies are available, and because artemisinin resistance will probably accelerate resistance to any partner drug, investigations of alternative treatment approaches are urgently needed,” the researchers said.
In the past, when malaria-transmitting parasites grew resistant to one drug, there was always another one waiting in the wings. Now experts fear artemisinin combination therapies could become useless before a new drug is developed.
“This time, we don’t have a backup,” Nosten said.
Julie Fidler is a freelance writer, legal blogger, and the author of Adventures in Holy Matrimony: For Better or the Absolute Worst. She lives in Pennsylvania with her husband and two ridiculously spoiled cats. She occasionally pontificates on her blog.