Washington ? Blood banks turn away up to 150,000 would-be donors each year on the slight chance they picked up malaria while traveling to any of dozens of countries.

At the same time, concern is growing that a second parasitic infection from abroad – the Chagas disease rampant in parts of Latin America – increasingly threatens donated blood.

Both infections are rare here, but there’s no way to test donated blood for either one. Now blood banks are pushing for better safeguards that also could help stretch the nation’s tight supply.

First up, malaria: Next week, the Food and Drug Administration opens debate on how to balance the need for blood with Americans’ increasing travel to malaria hot spots, and to urge manufacturers to develop a malaria test to solve the problem.

The vast majority of U.S. travelers return healthy, and there have been only one or two cases of transfusion-spread malaria in five years. But without a blood test, there’s no way to tell who might be unknowingly incubating the mosquito-borne disease.

So FDA requires blood banks to ask about would-be donors’ travels. No donating for a year after a short trip to a malaria-prone country; for three years for anyone who spent more than a year in a malaria-prone country or suffered malaria symptoms.

It doesn’t matter if you faithfully took anti-malaria medicine; you could have forgotten a missed pill or be one of the unlucky few infected anyway. Staying in a cruise ship or large resort is OK in some countries, unless you took even one trip inland, even during daytime hours when mosquitoes seldom fly.

Some 34,000 pints of blood are needed every day, yet only about 5 percent of the Americans eligible to donate do so, and increasing foreign travel is further shrinking that donor pool. The American Red Cross, which collects half the nation’s blood, last year estimated that some of its regions were losing 150 to 200 donations a month because of the malaria risk.

One U.S. manufacturer, Abbott Laboratories, is in the initial stages of designing a malaria test for donated blood.

Britain and parts of Europe already allow travelers to donate if blood tests show they’re free of malaria antibodies, immune cells that attack the parasite. Those tests aren’t used here because they detect just two of the four malaria species, albeit those that cause most disease. Next Tuesday, FDA will ask specialists if that’s still good policy.

“We may have to be open-minded about that,” says Dr. Hira Nakhasi, FDA’s director of emerging transfusion-related diseases.

For Chagas, a test for donated blood could arrive by year’s end, one blood banks anxiously await as they seek more donors from a growing Hispanic population.

Chagas infects up to 18 million people in parts of rural Mexico, Central and South America and kills 50,000 of them yearly. Most don’t know they’re infected: The parasite can lie silent for decades, until one day erupting inside the heart, esophagus or intestine.

It’s spread mostly by “kissing bugs” that live in the cracks of thatch-roofed, mud-walled homes, crawling out at night to bite sleepers. But it’s also spread from mothers to their unborn children, and through blood transfusions.

FDA’s Nakhasi says the agency will mandate a Chagas test for every blood donation as soon as it’s convinced there’s a good method. First in line may be a test developed by Ortho-Clinical Diagnostics, currently under FDA review; competitor Abbott is researching another version.