Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, continues to make inroads in the United States and physicians are both unprepared to diagnose and under equipped to treat cases of the disease in their patients. Chagas is a rare disease in the United States and has typically been associated with immigration from Central and South America, where the disease is endemic. The dynamics of the disease are changing, however, and strong evidence continues to emerge indicating that local infection is occurring among the American population, particularly in the southern states.
Research performed over the past years has consistently shown that the parasite is embedded in the ecology and landscape of the south: its vector, the blood-feeding triatomine insect known as the “kissing bug” for its proclivity to feed near the mouth, resides in a swath of states including Texas, Oklahoma, Louisiana, Mississippi, and Arkansas. Studies of these same bugs show that they not only carry the parasite that causes Chagas disease, but also that they are coming into uncomfortably close contact with humans, with genetic studies indicating bloody feasts of human origin. Most recently, a study this year found that many canines in shelters carry T. cruzi, serving as a reservoir that brings the disease into even closer contact with humans.
Stages of the triatomine insect or "kissing bug," the vector of Chagas disease. Image: Thierry Heger According to the latest research presented this month at the annual gathering of the American Society of Tropical Medicine and Hygiene
, rates of Chagas infection among Americans are on the rise and are presenting a growing yet unappreciated public health threat to the United States. Researchers at Baylor University presented the results of a study of the emergence of Chagas disease in Texas which demonstrate not only a surprisingly high incidence of the parasite in the state of Texas, but also showing elevated rates of associated heart disease in afflicted individuals. The researchers found that one in every 6,500 blood donors in Texas tested positive for the parasite, a finding that grossly undermines the CDC’s national estimate that one in every 300,000 people may be infected with Chagas in this country.
The Baylor team has monitored a group of 17 people who tested positive for Chagas after donating blood in order to track their clinical outcomes. Of those patients, over 40% went on to develop manifestations of severe Chagas disease, which included flabby, weakened hearts and abnormal heart rhythms such as arrhythmias. "We're the first to actively follow up with positive blood donors to assess their cardiac outcomes and to determine where southeastern Texas donors may have been exposed to Chagas," says Melissa Nolan Garcia, the epidemiologist who led the Baylor team. Their research finds that Chagas is a significant risk factor for life-threatening forms of cardiac disease and highlights the serious need for closer monitoring of transmission in Texas.
Many of the cases were diagnosed in people with no history of significant international travel to endemic areas, strongly suggesting that their infections are homegrown. Several individuals lived in rural areas or reported frequently engaging in outdoor activity, greatly increasing their exposure to triatomine bugs. The Baylor research suggests that those living in rural regions of Texas may be at the greatest risk of contracting Chagas, a disease of which the public is barely aware, if at all.
Though Chagas is making its presence known in this country, American physicians are unprepared to meet the challenges of the disease in their patients. Chagas is still considered an exotic, foreign disease and, as such, the parasite is rarely considered as a viable diagnosis in a patient presenting with heart disease of idiopathic, or unknown, origin. This is especially true in those patients that present without the requisite risk factors like obesity, high blood pressure, and diabetes. In short, a lack of awareness of Chagas among American physicians stymies diagnosis in those that are infected.
Triatomine insect occurrence by state. Image: CDC. Click for source.
Even if physicians were to suspect Chagas in their patients, they are hampered in their ability to effectively detect the parasite using available diagnostic assays - there are only three assays available; of these, only one has FDA approval, and all available assays have poor sensitivity in correctly classifying an individual with the disease.
To compound matters, there are no established systematic treatment plans in the United States for patients who eventually obtain a definitive diagnosis. Of the drugs available to treat infection, only two exist and they both must be ordered from the CDC. “A lack of infrastructure for diagnosis and a systemized treatment plan just do not exist for Chagas” says Dr. Jennifer Manne-Goehler, a clinical fellow at Harvard Medical School and Beth Israel Deaconess Medical Center. She presented research to the American Society of Tropical Medicine and Hygiene showing “an enormous treatment gap” between those individuals that tested positive for Chagas after blood donation and those that receive treatment. Of the nearly 2,000 people that tested positive through the blood banking system from 2007 to 2013, only 422 doses of medication were administered by the CDC.
Dr. Manne-Goehler reports that many physicians devise their own treatment plans for lack of a systemic and approved way to approach the disease. Her group is calling for the formation of an expert panel to draft guidelines for Chagas treatment and to call for the developmentof more robust diagnostic tools. “There’s a lot of hand-waving in the community,” when it comes to how the public health community should tackle the emergence of Chagas in the United States, says Manne-Goehler, but with the formation of an expert panel her group hopes that headway can be made in constructing a structured response to the threat of Chagas disease in America.
What we know now is that Chagas is no longer an exotic affliction from abroad, affecting only immigrants and globetrotters. Recent research provesthat the disease is being acquired domestically and is slowly percolating into the American population from infected bugs within our borders. A lack of awareness of Chagas, subpar diagnostic tests, and insufficient standardized guidelines are hindering our ability to mount an effective response to the disease and to prevent the continued emergence of this parasite. Without these targeted initiatives, Chagas disease will continue to spread, knowing no borders.
Previously on Body HorrorsCrying Wolf: Texan Dogs Used as Sentinels for Chagas Disease