MIAMI—Malaria continues to be a global scourge, sickening some 300 million to 500 million people annually. Most of the resulting one million to three million malaria deaths occur in regions where it is highly endemic, such as sub-Saharan Africa and parts of south Asia. 

Some parts of the world where malaria was once rampant, however—such as Central and South America—have seen morbidity and mortality rates of the disease cut in half in the past decade, reported specialists here Wednesday at the 14th annual International Congress on Infectious Diseases in Miami. And areas where it is currently common, including many African countries, might expect eradication in the next decade, according to a report released Monday by the Global Fund, an organization that addresses infectious diseases. New malaria treatment guidelines, published Tuesday by the World Health Organization (WHO), could help achieve that goal by advocating for universal testing of all suspected cases and treatment of confirmed patients with artemisinin-based combination therapy (ACT), which has gained prominence since the guidelines were first published four years ago.

The Americas appear on their way to becoming a success story in the global battle against the mosquito-borne illness. Twelve years ago, the Roll Back Malaria partnership was launched by several international organizations, including the WHO, with the goal of reducing incidence of the disease 50 percent from 2000 levels (more than one million cases and 300 deaths) by 2010. By 2008, the numbers from Central and South America were already showing a victory, noted Keith Carter, of the Pan-American Health Organization, with a 52 percent drop in the number of cases and 57 percent decrease in deaths.

Despite these promising figures, however, malaria transmission is ongoing in 21 countries in the Americas, he noted. And not all areas have seen a uniform decrease—or a decrease at all. Cases in the Dominican Republic, Haiti and Venezuela have actually increased in the same time span.

Even those who live in countries that currently do not have sustained malaria transmission, such as the U.S., are often faced with a health dilemma when traveling abroad. In regions of the world such as sub-Saharan Africa where the dominant malaria parasite is Plasmodium falciparum (considered the most deadly form), travelers often take preventative medication to keep from getting infected in the event they are bitten by a disease-carrying mosquito. But for areas of the world, such as Central and South America, where the more prevalent form is P. vivax (and even that is relatively rare), many experts are hesitant to recommend anti-malarials that might be costly, cumbersome or have unpleasant side effects. 

Marcos Boulos, of the University of Sao Paulo in Brazil, argued that these doctors might be on the right track, noting that foreigners usually stick to cities and are more likely to have better housing and protection from mosquitoes than locals. As he pointed out, even though Brazil has areas of moderate transmission in the Amazon, visitors to Sao Paulo are probably just as likely to catch malaria as they would in New York—that is to say the risk is slim to none.

"There just isn’t much malaria" in the Americas, said Alan Magill, of the Walter Reed Army Institute of Research in Silver Spring, Md. But, he noted, "unfortunately, that risk is not zero."

Because of that risk—small though it may be in many parts of the world like Central and South America—other experts prefer to err on the side of safety. "It is much better to prevent cases than wait for them to appear," concluded Paul Arguin, of the U.S. Centers for Disease Control and Prevention. He cited a number of instances of travelers who returned from trips abroad only to develop malaria (which can have an incubation period of weeks or months) in the U.S. where doctors might not be so quick to recognize it. Some 1,400 people in the U.S. are diagnosed with malaria each year (and about five die from it), Arguin noted. About 82 percent of the cases are caused P. vivax, which is not as widely feared as P. falciparum, but, said Arguin, "I wouldn’t characterize it as a totally benign disease."

Image of P. vivax courtesy of Wikimedia Commons/CDC/Steven Glenn