Chagas disease is a vector-borne parasitic disease, endemic to the Americas, that remains as little recognized by U.S. patients and practitioners as the obscure winged insects that transmit it.
Transmission occurs when triatomine bugs, commonly called “kissing bugs,” pierce the skin to feed and leave behind parasite-infected feces that can enter the bloodstream; pregnant women can also transmit Chagas to their newborns.
About a third of patients infected with Trypanosoma cruzi, the protozoan parasite that causes Chagas, will develop cardiac abnormalities such as cardiomyopathy, arrhythmias, and heart failure – often decades after becoming infected. In the United States, where blood banks began screening for Chagas in 2007, patients without symptoms are likely to learn they are positive only after donating blood.
Conventional wisdom has long maintained that Chagas is limited to Central and South America. But immigration from Chagas-endemic countries, such as El Salvador, Mexico, and Bolivia, means more people are living with the disease in the United States.
“One percent of the Latin American immigrant population we screen [in Los Angeles] has Chagas,” said Dr. Sheba K. Meymandi, cardiologist and director of Center of Excellence for Chagas Disease at Olive View–UCLA Medical Center in Los Angeles, who also works with the city’s health department to detect Chagas. “That’s huge.”
Meanwhile, blood banks are discovering more cases among people without ties to Latin America, and species of kissing bugs native to the southern United States are increasingly recognized as a non-negligible source of Chagas transmission. Of 39 Chagas cases reported to Texas health authorities in 2013 and 2014, 12 were thought to be locally acquired.
Dr. Heather Yun, an infectious disease specialist at the San Antonio Military Medical Center, said risk factors for local transmission are not well established, but “we think people who are living in poverty in substandard housing, people who spend a lot of time outdoors, especially at night, and people involved with direct blood contact with wild game in Southern parts of the United States” may be at higher risk.
A U.S. disease
Evidence is amassing quickly that Chagas is a U.S. disease. But U.S. clinicians still lag in their knowledge of it, say physicians treating Chagas cases. “In medical school we get a 2-hour lecture on it, and it’s always been presented as an exotic disease and one you don’t treat,” Dr. Meymandi said.
The persistent perception of Chagas as a foreign disease means clinicians are inclined to dismiss positive results from a blood screening, particularly from someone who is not from Latin America. Yet cardiologists, ID practitioners, obstetricians, and primary care physicians all need to be aware that cases do occur in the United States and are potentially treatable.
Dr. Laila Woc-Colburn, an infectious disease and tropical medicine specialist at Baylor College of Medicine in Houston, said many people with Chagas never make it to an infectious disease specialist or cardiologist for a work-up. “When you test positive on serology [after a blood donation], you get a letter recommending you consult your physician. Most will go to their primary care doctors, who might say ‘this isn’t a disease in the United States.’ In Houston, that is often the case.”
Dr. Meymandi, who has treated hundreds of patients with Chagas with and without cardiac involvement, said any physician with a potential Chagas case must act. “If you get someone that’s positive, it’s your duty as a physician to confirm the positivity with CDC,” she said.
Dr. Yun concurred. “The most important message is, do something,” she said. “Don’t just assume it’s a false positive.”
Diagnosis is not simple and requires testing beyond the initial ELISA assay used in blood-bank screening. Confirmatory tests must be carried out in coordination with the Centers for Disease Control and Prevention. Also, with no agents approved by the Food and Drug Administration to treat Chagas, treatment is available only through the CDC’s investigational drugs protocol. Both drugs used in Chagas, benznidazole and nifurtimox, come with serious adverse effects that must be closely monitored.
“It’s time consuming, filling out the forms, getting the consent, tracking and sending back lab results to CDC in order to get drugs – it’s not like you can just write a prescription,” Dr. Meymandi said. But, “if you don’t know how to treat the patient or don’t have time, find someone like me,” she noted, adding that she is available to counsel any physician daunted by a potential Chagas case.
No formal clinical algorithm exists for Chagas, but Dr. Meymandi, Dr. Yun, and Dr. Woc-Colburn all pointed to a 2007 JAMA article, which describes diagnosis and treatment protocols, as an important reference for clinicians to start with. It’s “the best approximation of a clinical guideline we have,” Dr. Yun said (JAMA. 2007;298:2171-81. doi:10.1001/jama.298.18.2171).