What if a deadly epidemic was burgeoning and almost nobody noticed?
In the latest issue of PLoS Neglected Tropical Diseases, a distinguished group of virologists, epidemiologists and infectious-disease specialists say that’s not a hypothetical question. They argue that Chagas disease, a parasitic infection transmitted by blood-sucking insects, has become so widespread and serious — while remaining largely unrecognized — that it deserves to be considered a public health emergency. Extending the metaphor, they liken Chagas’ stealth spread to the early days of AIDS:
Both diseases are health disparities, disproportionately affecting people living in poverty. Both are chronic conditions requiring prolonged treatment courses… As with patients in the first two decades of the HIV/AIDS epidemic, most patients with Chagas disease do not have access to health care facilities. Both diseases are also highly stigmatizing, a feature that for Chagas disease further complicates access to … essential medicines, as well as access to serodiagnosis and medical counseling.
That sounds like rhetoric — after all, what disease expert doesn’t think his or her disease is vitally important — but the numbers the experts bring to the argument are stunning. Overall, there are believed to be 10 million people living with Chagas infection; most of them are in Central and South America, but there are an estimated 1 million in the United States. Up to one-third of those infected, 3 million, are at risk of Chagas’ worst complications, enlarged heart and heart failure. And wherever blood donations are not tested for the protozoan, the blood supply — as well as organ transplants — are at risk.
Chagas transmission is squick-making. The disease originates with the protozoan Trypanosoma cruzi, harbored in the guts of long-beaked Triatoma bugs such as the one above. The insects live in wall crevices and thatched roofs; at night, they crawl out and drop onto people sleeping below. They prefer to bite at the lip margin, which earned them the name “kissing bugs.” After they ingest blood, they defecate, pooping out copies of the parasite at the same time. The person wakes up, feels the itch where they were bitten, scratches or rubs the bite, and rubs the parasite-containing feces into the wound. Voila, Chagas infection.
The bugs that transmit Chagas are tropical, and the poor housing conditions that allow them access to victims are pretty much limited to poverty. Combine those two, and you’d think that Chagas’ home range would be fairly limited. But immigration has brought people who are unknowingly infected with Chagas into areas where doctors are unfamiliar with the disease. A separate editorial on Chagas, published last year in the same journal, notes:
Immigration from endemic regions is widespread; for example, there are Brazilian immigrants in Portugal and Bolivian immigrants in Spain, and currently, there are an estimated 100,000 or more Latin American immigrants living in France… Chagasic heart disease has been reported in Brazilian immigrants of Japanese origin in Japan, and the seroprevalence of Chagas disease among Bolivian women in Barcelona has been determined to be 3.4 percent.
The issue with Chagas isn’t only that its primary victims represent an undetected public health and healthcare burden; when they do not know they are infected, they can become a source of infection as well. The protozoan can pass from mother to child during pregnancy, causing congenital Chagas; and when infected people donate blood or become organ donors, the protozoan hitches a ride. The earliest cases of Chagas in New York City, back in the 1980s, were transmitted by transfusion. There’s been an FDA-approved test for Chagas in donated blood for just two years. The latest map from AABB (formerly the American Association of Blood Banks), showing where positive donations have been identified, vividly demonstrates how the disease has spread.
As I type that I can almost feel the default anti-immigrant response: “They” pose a risk to us, so if we only kept “them” on the other side of our borders, we’d be safe. The problem, of course, is that diseases and their vectors have no concept of borders — and thanks in part to climate change, there is now a competent Chagas vector on our side of the border, in Texas. A third paper, published two years ago in PLoS NTD, argues that Chagas is now endemic in Texas, traveling from Triatoma species through dogs and into people — and is going undetected because blood-donation screening is not mandatory in the state and physicians are not required to report the disease’s occurrence to health authorities. (Chagas in fact is only reportable in a handful of states.) Here’s that group’s map of relative risk of Chagas in Texas; the higher-risk areas cover about a third of the state and include Houston, San Antonio and Dallas-Fort Worth.
So, solutions? This may be yet another public-health story that turns into a plea for more money and more research. The authors of the new editorial argue that tackling Chagas requires both finding new drugs and achieving a vaccine. But the first step in addressing a burgeoning epidemic is recognizing that it exists, and these papers might at least ring that warning bell.
- Hotez PJ, Dumonteil E, Woc-Colburn L, et al. (2012) Chagas Disease: “The New HIV/AIDS of the Americas”. PLoS Negl Trop Dis 6(5): e1498. doi:10.1371/journal.pntd.0001498
- Tanowitz HB, Weiss LM, Montgomery SP (2011) Chagas Disease Has Now Gone Global. PLoS Negl Trop Dis 5(4): e1136. doi:10.1371/journal.pntd.0001136
- Sarkar S, Strutz SE, Frank DM, et al. (2010) Chagas Disease Risk in Texas. PLoS Negl Trop Dis 4(10): e836. doi:10.1371/journal.pntd.0000836
Image: Triatoma infestans, PHIL, CDC