Chagas disease is a parasitic infection caused by a single-celled organism that spreads primarily through the feces of triatomine bugs, commonly called “kissing bugs.” An estimated 10.5 million people worldwide are living with the infection, and roughly 8,400 die from it each year. Most cases occur in Latin America, but the disease is increasingly recognized in the United States and other non-endemic countries due to migration and, less commonly, local bug exposure.
How Chagas Disease Spreads
The parasite behind Chagas disease is carried by triatomine bugs, blood-feeding insects that typically bite people at night around the face and lips. After feeding, the bug defecates near the bite wound. When a person scratches or rubs the area, they push the parasite-laden feces into the wound or into mucous membranes like the eyes or mouth. The parasite then enters the bloodstream and begins multiplying inside cells.
Bug-to-human contact is the most common route, but it’s not the only one. A mother with Chagas disease has an estimated 1 to 5 percent chance of passing the infection to her baby during pregnancy or delivery. The parasite can also spread through blood transfusions, organ transplants, and contaminated food or drink. In the United States, the FDA requires a one-time screening of every blood donor for antibodies to the parasite. Donors who test positive are permanently deferred from giving blood, and any previously donated units within a lookback period are quarantined or destroyed.
The Acute Phase: Early Weeks and Months
The first stage of infection begins within the initial weeks or months after exposure. Most people have no symptoms at all, or symptoms so mild they’re mistaken for a common virus. When signs do appear, they can include fever, fatigue, body aches, headache, rash, loss of appetite, diarrhea, and vomiting.
One distinctive clue is called Romaña’s sign: noticeable swelling of one eyelid, which happens when the parasite enters through the eye’s mucous membrane. It’s not present in every case, but when it shows up, it’s a strong indicator. During this stage, the parasite is actively circulating in the blood, which means a doctor can sometimes spot it directly under a microscope using a simple blood smear. Without treatment, the acute phase resolves on its own in most people within a few weeks, but the parasite doesn’t leave the body. It retreats into tissues and enters a quiet, long-term phase.
The Chronic Phase: What Happens Over Years
After the acute phase, Chagas disease enters a prolonged period that can last the rest of a person’s life. For the majority of people, this chronic phase is completely silent. They feel healthy, have no symptoms, and may never know they’re infected. But in roughly 30 to 40 percent of cases, the parasite slowly damages internal organs over years or even decades.
The chronic symptomatic stage breaks down into three patterns. The most common is cardiac involvement, affecting 20 to 30 percent of chronically infected people. The parasite damages the heart muscle, leading to an enlarged, weakened heart that struggles to pump blood effectively. This carries a real risk of heart failure and dangerous irregular heart rhythms. Chagas-related heart disease is, in fact, one of the leading causes of heart failure in Latin America.
Digestive complications develop in 10 to 20 percent of chronic cases. The parasite destroys nerve cells in the walls of the esophagus or colon, causing these organs to gradually stretch and lose their ability to move food along. In the esophagus, this leads to difficulty swallowing, chest pain, and weight loss. In the colon, it causes severe chronic constipation that can progress to dangerous blockages. Another 5 to 10 percent of patients develop both cardiac and digestive problems simultaneously.
How Chagas Disease Is Diagnosed
Testing depends on the stage of infection. In the acute phase, when the parasite is actively multiplying in the bloodstream, a doctor can detect it by examining a blood sample under a microscope. This direct approach works well early on because parasite levels are relatively high.
In the chronic phase, the parasite retreats into tissues and becomes much harder to find in the blood. Diagnosis shifts to blood tests that look for antibodies your immune system has built against the parasite. Two common laboratory methods are used, and doctors typically require positive results on both before confirming a chronic infection. This two-test approach reduces the chance of a false positive.
Treatment Options and What to Expect
Two antiparasitic medications are available to treat Chagas disease. Both work best when given early, ideally during the acute phase or in younger patients with chronic infection. Treatment is a 60-day course taken by mouth. The goal is to kill the parasite and prevent the long-term organ damage that develops in chronic disease.
The medications are effective but come with significant side effects that can make the full course difficult to complete. In studies of one of the two drugs, half of patients experienced nausea, nearly half lost their appetite, about a third lost weight, a third had headaches, and roughly a quarter reported abdominal pain. Doctors sometimes reduce the dose or temporarily pause treatment to help patients get through the full 60 days. For people who already have advanced heart or digestive damage, antiparasitic treatment may not reverse the harm, and care focuses on managing symptoms, such as medications for heart failure or surgical procedures for severe digestive complications.
Where Chagas Disease Is Found
Chagas disease is concentrated in rural areas of Mexico, Central America, and South America, where triatomine bugs live in the cracks and crevices of mud-brick and thatched-roof homes. Globally, there were an estimated 352,000 new infections in 2023, though that number has dropped 55 percent since 1990, largely thanks to insecticide spraying programs and improved housing in endemic regions.
In the United States, triatomine bugs are found across the southern half of the country, from California to the Carolinas. Most U.S. cases, however, are in people who were infected before immigrating. The CDC recommends screening women from endemic regions before or during pregnancy, since early detection allows treatment of infected newborns when the drugs are most effective.
Preventing Kissing Bug Exposure
If you live in an area where triatomine bugs are present, practical steps can reduce your risk. Seal cracks and gaps in walls, doors, and windows, and keep window screens in good repair. These bugs are drawn to light at night, so replacing standard white outdoor bulbs with yellow or orange-hued bulbs (sodium vapor) on porches and near entryways makes your home less attractive to them.
Clearing clutter, woodpiles, and brush from around your house helps too. Rodents and other small mammals are the bugs’ primary blood source, and moving potential nesting material at least 400 to 500 feet from your home reduces the number of animals, and therefore bugs, in your immediate area. For homes with known infestations, residual insecticides applied to cracks, crevices, baseboards, and spaces under cabinets can target the bugs where they hide during the day.