Chagas disease is an infection caused by a microscopic parasite called Trypanosoma cruzi, spread primarily through the feces of triatomine insects, commonly known as “kissing bugs.” An estimated 6 to 7 million people worldwide carry the infection, most of them in Latin America, though roughly 288,000 infected people currently live in the United States. The disease progresses in two phases: an early phase that often goes unnoticed and a chronic phase that can silently damage the heart and digestive system over decades.
How the Infection Spreads
The primary route of transmission is surprisingly indirect. Triatomine bugs feed on blood at night, often biting people on the face (hence “kissing bugs”). The parasite isn’t injected through the bite itself. Instead, the bug defecates near the bite wound, and the parasites in those droppings enter the body when a person instinctively scratches or rubs the area. The parasites can also slip in through mucous membranes like the eyes or mouth.
Several other transmission routes matter, especially outside the regions where kissing bugs live. Congenital transmission, from mother to baby during pregnancy or birth, has become the leading route of new infections globally, accounting for over 10,000 new cases each year. The parasite can also spread through blood transfusions, organ transplants, and contaminated food or drinks. Foodborne outbreaks happen when beverages like fruit juice become contaminated with crushed bugs or their droppings during preparation.
Since 2007, U.S. blood banks have screened donations for T. cruzi using an antibody test. Donors who test positive are permanently deferred from future donations, and previous recipients of their blood are traced and tested.
Acute Phase: The First Weeks
The acute phase begins in the first weeks to months after infection. Most people have mild symptoms or none at all, which is a major reason Chagas disease goes undiagnosed so often. When symptoms do appear, they resemble a generic viral illness: fever, fatigue, body aches, headache, rash, loss of appetite, diarrhea, and vomiting.
One distinctive sign is Romaña’s sign, a painless swelling of one eyelid. This happens when the parasite enters through the eye, typically because a person rubbed bug feces into their eye or into a bite wound near it. Romaña’s sign is a telltale marker of acute Chagas disease, but it only appears in a fraction of cases. Without treatment, the acute phase resolves on its own within a few weeks as the immune system pushes parasite levels in the blood down to nearly undetectable levels. The infection, however, persists.
Chronic Phase: Heart and Digestive Damage
After the acute phase, most people enter a long silent period called the indeterminate form. About 60% of infected people stay in this stage for the rest of their lives, carrying the parasite without ever developing symptoms. The other 40% eventually develop serious complications, sometimes 10 to 30 years after the initial infection.
The heart is the most common target. Chronic Chagas cardiomyopathy involves persistent inflammation and scarring of heart muscle, which disrupts the heart’s electrical system and weakens its ability to pump. This can lead to irregular heartbeats, blood clots, and progressive heart failure. In Latin America, Chagas disease is one of the leading causes of heart failure in younger adults. An estimated 57,000 people in the U.S. have Chagas-related heart disease.
The digestive system is the second major target. The parasite destroys nerve cells in the walls of the esophagus or colon, impairing the muscle contractions that move food through. Over time, the affected organ stretches and dilates. When this happens in the esophagus (megaesophagus), swallowing becomes progressively difficult. When it happens in the colon (megacolon), severe chronic constipation and bowel obstruction can result. Some patients develop both heart and digestive complications simultaneously.
How Chagas Disease Is Diagnosed
Diagnosis depends on the stage of infection. During the acute phase, parasite levels in the blood are high enough to see under a microscope. A clinician prepares a blood smear, stains it, and looks for the parasites directly. This method only works in the early weeks, because parasite numbers in the bloodstream drop rapidly.
In the chronic phase, the standard approach is blood testing for antibodies against the parasite. No single antibody test is accurate enough on its own, so diagnosis requires at least two different tests that look for antibodies to different parts of the parasite. If both come back positive, the infection is confirmed. If results conflict, additional testing is needed. This two-test requirement is one reason chronic Chagas disease remains underdiagnosed, particularly in countries where awareness is low and testing infrastructure is limited.
Treatment Options
Two antiparasitic medications are available. Both work best when given early, ideally during the acute phase or in childhood, when cure rates are highest. Treatment becomes less effective the longer the infection has been present, and its benefit in adults with established chronic disease is less clear.
The treatment course is demanding: 60 days of medication taken multiple times daily. Side effects can be significant and include skin reactions, digestive symptoms, and effects on the nervous system. Because of these side effects, some patients have difficulty completing the full course. For people who have already developed heart failure or severe digestive complications, treatment focuses on managing those specific problems rather than eliminating the parasite.
Who Is at Risk in the United States
Most of the estimated 288,000 people living with Chagas disease in the U.S. are immigrants from Latin American countries where the infection is common, particularly Mexico, Central America, and parts of South America. An additional 10,000 cases are thought to have been acquired locally. Triatomine bugs capable of carrying the parasite live across the southern United States from coast to coast, and natural transmission cycles between the bugs and wild animals (like raccoons, opossums, and dogs) are well established.
An estimated 43,000 infected women of reproductive age live in the U.S., which matters because congenital transmission can occur even in areas with no kissing bugs. A woman infected decades ago in another country can still pass the parasite to her baby during pregnancy. Screening programs for at-risk pregnant women remain inconsistent across states.
Prevention and Vector Control
In regions where kissing bugs are common, the most effective prevention strategies target the bugs’ habitat. Triatomine bugs hide during the day in cracks and crevices in walls, roofs, and floors, particularly in homes made of adobe, mud, or thatch. Housing improvements like sealing wall cracks, fitting ceilings, and screening windows and doors significantly reduce transmission. Insecticide spraying of homes and surrounding areas complements these structural changes.
If you live in or travel to areas where kissing bugs are present, sleeping under bed nets, keeping sleeping areas away from walls, and checking for bugs in bedding can reduce your exposure. For travelers, the risk is generally low in well-constructed hotels and urban areas. The greater concern is for people living in rural housing conditions in endemic regions over extended periods.