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A Tropical Disease Hits the Road

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Science  19 Aug 2011:
Vol. 333, Issue 6045, pp. 934
DOI: 10.1126/science.333.6045.934

Generally considered one of the many neglected tropical diseases, Chagas disease has been drawing increased attention, which some attribute to its growth outside of Latin America.

Generally considered one of the many neglected tropical diseases, Chagas disease has been drawing increased attention (see main text), which some attribute to its growth outside of Latin America. Spain and the United States are seeing the highest incidence among developed countries, but there have been cases as far afield as Switzerland and Japan. The main reason for this rise isn't the spread of insects carrying Trypanosoma cruzi but rather emigration from Latin America of large numbers of people who are already infected.

SOUCRE: CDC

Because no one has performed comprehensive testing, the number of infected people living in the United States remains unknown, says medical epidemiologist Caryn Bern of the U.S. Centers for Disease Control and Prevention in Atlanta. To improve on previous projections, she and her colleague Susan Montgomery combined new figures on the prevalence of the disease in different Latin American countries with data on immigration into the United States from those nations. Their results, which they published in 2009 in Clinical Infectious Diseases, suggested that about 300,000 immigrants in the United States are likely infected. “It's very much an estimate. We have almost nothing in the way of direct data,” Bern says.

Some small-scale surveys have gathered direct data, however, and they point to a fairly high prevalence in areas with large expatriate populations. Cardiologist Sheba Meymandi of the University of California, Los Angeles, School of Medicine and colleagues have run blood tests on patients with heart failure and other cardiac problems, and on Latin American parishioners from several Los Angeles–area churches. The researchers found that about 1% of the approximately 2000 people they tested harbor T. cruzi. “One in 100, that's pretty substantial,” Meymandi says. Similarly, earlier this year in PLoS Neglected Tropical Diseases, a Spanish group testing Latin American immigrants at a clinic in Barcelona reported that 3% were positive for the Chagas parasite.

An unknown is how many infections in the United States result from native assassin bugs. They live from coast to coast, ranging as far north as Illinois and Pennsylvania, and T. cruzi is prevalent in them. One study found that more than 40% of the assassin bugs in Tucson, Arizona, harbored the parasite. However, since the 1950s, the United States has recorded only a few definite cases of parasite transmission. Most researchers think that the risk from these insects is low, in part because homes in the United States are typically not congenial to the bugs. However, Hotez and some other researchers suspect that such transmission is more common than generally accepted. Meymandi notes that she recently diagnosed two teenage patients who were infected in Los Angeles. “It is here; people do acquire it,” she says.

Whatever its source, the rising incidence of Chagas disease has already required action by health officials in the United States and other developed nations. Although T. cruzi is usually bug-borne, it can also spread through blood transfusions and organ transplants. U.S. blood banks began voluntary testing for the parasite in 2007, and facilities in France and Spain have done the same. And developed countries can expect that the illness's toll will rise. Bern and Montgomery calculated, for example, that if their estimate of the number of infected people in the United States is close to the mark, undiagnosed Chagas disease is responsible for 30,000 to 45,000 cases of cardiomyopathy, or severe heart damage.

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