U.S. experts are raising the alarm over the spread of drug-resistant malaria in several Southeast Asian countries, endangering major global gains in fighting the mosquito-borne disease that kills more than 600,000 people annually.

While the communicable disease wreaks its heaviest toll in Africa, it's in nations along the Mekong River where the most serious threat to treating it has emerged.

The availability of therapies using the drug artemisinin has helped cut global malaria deaths by a quarter in the past decade. But resistance to it emerged on the Thai-Cambodia border in 2003, and has since been confirmed in Vietnam and Myanmar too. It has also been detected in southwest China and suspected as far away as Guyana and Suriname, according to a new report by the Center for Strategic and International Studies think tank.

The report warns that could be a health catastrophe in the making, as no alternative anti-malarial drug is on the horizon. The U.N. World Health Organization, or WHO, is warning that what seems to be a localized threat could easily get out of control and have serious implications for global health.

"Absent elimination of the malaria parasite in the Mekong, it is only a matter of time before artemisinin resistance becomes the global norm, reversing the recent gains," writes Dr. Christopher Daniel, former commander of the U.S. Naval Medical Research Center, in the report for a conference at the Washington think tank Tuesday.

Mosquitoes have developed resistance to antimalarial drugs before.

The same happened with the drug chloroquine, which helped eliminate malaria from Europe, North America, the Caribbean and parts of Asia and South-Central America during the 1950s. Resistance first began appearing on the Thai-Cambodia border, and by the early 1990s it was virtually useless as an antimalarial in much of the world.

Nowhere are the challenges in countering the threat to drug-resistance greater than in Myanmar, also known as Burma. Some 70 percent of its 55 million people live in malaria-endemic areas, and as a nation, it accounts for about three-quarters of malaria infections and deaths in the Mekong region, the report says.

Myanmar's public health system is ill-equipped to cope, as government spending on health dwindled to the equivalent of just 60 U.S. cents per person under military rule, although it has been increased significantly under the quasi-civilian administration that took power in 2011. In a third of townships, there been virtually no public health presence for years.

It's an issue of regional concern as Myanmar has large transient populations in its border regions, including ethnic minorities displaced by fighting and migrant workers who cross borders.

"It is clear that this country with its chronically under-resourced health system needs urgent additional attention," Daniel said.

Resistance to artemisinin can be driven by various factors: delays in giving treatment, use of counterfeit or substandard drugs, and prescribing artemisinin on its own rather than in combination with another longer-acting drug to ensure that all malaria-carrying parasites in a patient's bloodstream are killed off.

Cambodia and Laos have banned the use of such monotherapies, and Myanmar's military, which manufactures pharmaceuticals, announced in June it would cease production of them by early 2014. That comports with the global push by the U.N. for proper testing, treating and tracking of malaria cases to prevent the disease spreading.

The Center for Strategic and International Studies is advocating greater U.S. involvement and aid for health and fighting malaria in the Mekong region, particularly in Myanmar, where Washington has been in the vanguard of ramping up international aid, as sanctions have been eased to reward it for democratic reforms.

The centrist think tank argues that can increase America's profile in Southeast Asia in a way that will benefit needy people and not be viewed as threatening to strategic rival, China.

But securing more funds won't be easy at a time when Washington is cutting back on programs for its own poor. The U.S. is already a major contributor to international anti-malaria efforts, and in Myanmar, is promising $20 million per year in health assistance under its recently resumed bilateral aid program.