Health experts seek more awareness about Chagas
■ Detection and treatment of this disease spread by a Latin American parasite are difficult because those infected are often asymptomatic when therapies are most effective.
By Victoria Stagg Elliott — Posted Jan. 7, 2008
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A parasite that is the leading cause of heart failure in Latin American countries appears to be far more common here than previously thought. Public health officials and physicians are now struggling to devise strategies for detecting, treating and preventing transmission, according to a series of papers published over the past year and symposiums at recent infectious disease meetings.
"This is really a neglected disease, but Chagas is more and more on the radar screen in the U.S.," said Caryn Bern, MD, MPH, medical epidemiologist at the Centers for Disease Control and Prevention's division of parasitic diseases.
Chagas disease, caused by the Trypanosoma cruzi parasite and carried by the triatomine or "kissing bug," has always been here in a very limited way. Many mammals are infected. The first indigenous human case was noted more than a half century ago in the Oct. 15, 1955, Journal of the American Medical Association, but its incidence in humans has been considered rare.
Widespread testing of the blood supply as of January 2007 triggered by cases of transmission through transplanted organs and transfused blood -- in some cases causing death -- has enabled the detection of many more infections. Most are in people who have spent significant time in Latin America or, because this parasite can be transmitted to a fetus, are children of immigrants from endemic regions. A handful of cases, though, seem to have been contracted on this side of the border.
Data from the American Red Cross presented at the American Society of Tropical Medicine and Hygiene meeting in Philadelphia in November 2007 show that one in 30,000 donors tested positive for the parasite. This number is much higher in some regions of the country with large numbers of Latin American immigrants.
Not everyone who tests positive on the initial screen will actually carry it, but at least 317 people in 30 states were confirmed as infected last year by AABB, an association which represents organizations that collect about 65% of the U.S. blood supply. Experts say more than 100,000 people may have Chagas without knowing it.
"We're just seeing the tip of the iceberg," said Patricia Dorn, PhD, associate professor of biological sciences at Loyola University New Orleans. She was the lead author on a paper in the April 2007 Emerging Infectious Diseases that documented the first locally acquired case of Chagas in Louisiana.
In order to facilitate treatment, JAMA published a review of data by leading experts in this field. In addition, the first U.S. clinic devoted to it, the Center of Excellence for the Diagnosis and Treatment of Chagas Disease at Olive View-UCLA Medical Center in Los Angeles, opened last month.
"We want to treat these patients, and we want to follow them long term because this has not been looked at before in the U.S.," said Sheba Meymandi, MD, center director and associate professor of medicine at UCLA.
But with all this activity comes a growing awareness of the complexity of dealing with Chagas.
Experts urge physicians to test those who may be infected, but determining who that may be is difficult. Dr. Meymandi is running a trial to evaluate the effectiveness of screening all Latin American patients with heart conduction abnormalities and unexplained cardiomyopathy. She is also testing close relatives of those known to carry the parasite.
Until the results are available, the categories of those who potentially carry this -- including those who have spent significant time in Latin America -- are too broad to allow targeted testing. This infection is also, for the most part, asymptomatic for decades until heart or gastrointestinal trouble appears.
"The most important thing for physicians is to keep Chagas disease on the differential," said Dr. Bern.
There's also not yet an easy way to detect this parasite. Two different tests, at minimum, are needed, and even those whose results are negative may still be infected.
"There is not one single test that is considered the gold standard, and we may be missing some people," Dr. Bern said.
And then there's the question of what to do with a positive result. Drug treatment is most effective in those who are newly infected and those who are younger than 18.
Limited evidence suggests that treating those who are older can have some benefit, and one of the more contentious debates is whether adults should be given these medications. They can be hard to take, and they're not always effective.
Moreover, the majority of those infected will never develop the major heart or gastrointestinal problems that drug treatment seeks to prevent. The estimated 20% to 30% of patients who do can be monitored and managed symptomatically.
"The bottom line is that there are no properly structured, double-blinded trials that demonstrate that giving a full course of the drug to those with long-standing infection is beneficial," said Louis V. Kirchhoff, MD, MPH, professor in the division of infectious diseases at the University of Iowa. Dr. Kirchhoff has been studying Chagas disease for more than 20 years.
A randomized clinical trial that may answer this question of drug treatment for long-term infections is under way, but there is also the challenge of getting patients access to treatment. The drugs are not approved by the Food and Drug Administration, even though they have been used in Latin America for decades. They are only available in the United States from the CDC, which provides them at no charge.
Despite these challenges, experts hope that all this testing will not only protect the blood and organ supply, but also ensure that more babies who contract the parasite congenitally will be treated.
Not all infants born to mothers who are infected will acquire Chagas. But some will -- and treatment is most effective in this group soon after birth.