Chagas Disease More Prevalent in US Than Thought
In south Texas, wild and domesticated animals carrying Chagas disease point to higher-than-expected risk of infection for humans.
This story was originally published in NOVA Next.
Edward Wozniak was sitting on his porch in Uvalde, Texas, one day in 2010 when a dog lying nearby stood up and a nickel-sized insect fell from its belly. Wozniak recognized the insect as a triatomine bug — the vector that carries the parasite Trypanosoma cruzi — and rushed to capture it. When the insect tested positive for the parasite, Wozniak launched a public effort to collect the bugs in Texas. “I had no problem getting almost 400 of them from in and around houses over a three-year period,” Wozniak said, “which blew me away.”
The T. cruzi parasite causes Chagas disease, which is designated a “Neglected Tropical Disease” by the World Health Organization. Chagas is most prevalent in Central and South America, where experts estimate it afflicts some 6 to 8 million people, and has only recently gotten attention in the United States. Now, a new study has found the parasite that causes Chagas in overlapping populations of humans, dogs, coyotes, and insects in southern Texas, adding a new dimension to the evidence that the potentially fatal disease can be acquired locally in the U.S.
T. cruzi lives in the feces of triatomine bugs. Nicknamed “kissing bugs,” these nocturnal insects bite people (often near the mouth) while they’re sleeping and feed on their blood. The bugs defecate while feeding, and if the feces are rubbed into the person’s bite wound, mouth, or eyes, they can contract the disease.
Because Chagas victims are often symptom-free or experience only generic flu-like symptoms in the first weeks or months of infection, the disease often goes unnoticed. But some 30% of infected people will develop severe cardiac disease up to 30 years later. In Latin America, Chagas is a leading cause of cardiac complications, causing about 12,000 deaths per year. Because kissing bugs thrive in mud walls and poorly constructed shelters, poor communities are often hit the hardest.
The researchers deemed the south Texas border area to be at high risk for Chagas partly because of its high poverty rate. The study focused on nine south Texas counties near the Mexican border to get a sense of the parasite’s prevalence across species. They tested samples of human blood as well as blood serum from shelter dogs and coyotes that had been collected during overlapping periods from 2005 to 2009. Additionally, they tested over 100 kissing bugs that had been collected near people’s homes in six of the nine counties from 2012 to 2013. They found T. cruzi in 56% of the kissing bugs, 8% of the coyotes and 3.8% of the dogs. Of the three people who tested positive for Chagas, they believe there is evidence that one of them contracted it locally.
Based on these numbers, the researchers estimate that the Chagas disease burden in the Rio Grande Valley could be as much as 23 times higher than they had previously thought, which would mean 4,600 people in the region are currently infected.
In Hidalgo County, both coyotes and kissing bugs tested positive for T. cruzi. Steven Hinojosa, lead epidemiologist at the Hidalgo County Health Department, said those study results were something he would “definitely expect to see.” He said he believes the disease is underdiagnosed, but it’s hard to know by how much since they only have three full years of data. Chagas disease only recently became a “notifiable condition,” meaning that doctors are required to report positive cases to government health officials.
When a case is reported, treatment must be coordinated between the physician and the Centers for Disease Control and Prevention (CDC). This is because the two drugs used to treat the disease are not FDA regulated, said Melissa Garcia, an instructor at Baylor College of Medicine and an author of the study. Although the drugs are decades old, safe, and widely available in Latin America, they aren’t licensed in the United States because there is no perceived demand for them, she said.
Before patients can get medication, they have to get tested for the disease. Everyone contacted for this article said that a primary obstacle to addressing Chagas in the United States is the fact that physicians are either unfamiliar with the disease or refuse to believe that it is present in this country. Although records of T. cruzi-infected kissing bugs in Texas date back to the 1930s and the first confirmed case of locally acquired Chagas was in 1955, many physicians consider the disease to be limited to immigrants who contracted it in Latin America.
Wozniak, a zoonosis control veterinarian with the Texas Department of State Health Services, has seen physician pushback time and again. People still send him kissing bugs they find in their homes, which frequently test positive for both T. cruzi and human blood. When positive results are returned, he advises people to get tested themselves. “That’s where we hit a brick wall,” Wozniak said. They will sometimes go from doctor to doctor, only to be turned away, he added.
Candace Stark of LaGrange, Texas, ran up against similar challenges. Stark, 52, donated blood in 2013 and was later notified that her blood had tested positive for T. cruzi. She went to her doctor, and he sent her to an infectious disease expert who said he had never treated a patient with Chagas. The CDC later confirmed her diagnosis, but when she asked her doctor if she should warn her neighbors about the disease, he advised her to keep quiet unless she wanted to be treated like Typhoid Mary. Stark eventually did receive an antiparastic drug to treat Chagas, but once treatment was complete, no follow-up plan was established.
“I don’t know if [the drug] worked,” she said.
By including both dog and coyote populations in their study, Garcia and her colleagues shed light on different transmission cycles of T. cruzi. “We can learn a lot by looking at wildlife because what they’re carrying can predict risk of human disease,” said Sarah Hamer, an assistant professor at the College of Veterinary Medicine and Biomedical Sciences at Texas A&M University, who was not involved with the study. The parasite is strongly associated with wild animals, but domestic dogs may bridge the gap between wild animals and humans by serving as a host to kissing bugs and a “reservoir” of the parasite near human habitations.
Garcia said that in Texas, veterinarians are “absolutely” more on top of Chagas than physicians. “I get many more vets that tell me they’re aware of [Chagas],” she said. She suggests it could be because dogs present with Chagas sooner, developing heart failure within a matter of months rather than decades. They are also at risk of eating the kissing bugs, which could explain why there is a higher rate of Chagas among animals than among people, she said.
Despite the obstacles, Garcia feels that health experts and researchers are making progress in tackling Chagas in Texas. In 2015, the CDC awarded a $544,000 grant to a researcher at the University of Texas Health Science Center for Chagas outreach and education efforts.
“I think in Texas we’re doing a decent job of getting the policies up to date,” Garcia said. “It’s now a mandatory reportable condition so at least it’s somewhat on people’s radar. However, in other states, like Louisiana, there’s not really any policy.”
Meanwhile, Wozniak continues his efforts to educate the public about Chagas disease. “It’s something that’s here, it’s something that needs to be recognized, and people should be tested for it,” he said.
Photo credits: Jim Gathany/CDC, Dr. Edward J. Wozniak.
