Chagas disease spreads primarily through the feces of triatomine bugs, commonly called kissing bugs, which deposit the parasite Trypanosoma cruzi on the skin while feeding on blood. But vector transmission is only one of several routes. The disease also passes through contaminated food, from mother to child during pregnancy, and through blood transfusions or organ transplants. Globally, an estimated 10.5 million people are living with Chagas disease.
The Kissing Bug: Primary Route of Infection
Triatomine bugs pick up the parasite by feeding on infected animals or people. After a blood meal, the bug defecates near the bite wound. The parasite lives in those feces, not in the bug’s saliva, which makes Chagas transmission unusual compared to mosquito-borne diseases. Infection happens when the feces enter your body through a break in the skin, the bite wound itself, or mucous membranes like the eyes or mouth.
Most people don’t feel the bug bite because triatomines feed at night while their hosts sleep. The natural response, scratching or rubbing the area, is exactly what pushes the contaminated feces into the wound. Rubbing your eyes after contact with the feces is another common entry point. This is why one of the classic early signs of Chagas disease is swelling around one eye, known as Romaña’s sign.
After exposure through a bug bite, the incubation period is typically one to two weeks before the acute phase begins. Many people have mild or no symptoms during this stage, which is part of what makes the disease so difficult to catch early.
Oral Transmission Through Food
In parts of the Amazon basin, the most common route of new infections isn’t the bug bite itself but contaminated food and drinks. When triatomine bugs or their feces end up in freshly prepared fruit juices or other uncooked foods, anyone who consumes them can become infected. The parasite enters through the lining of the mouth and digestive tract.
Açaí berry juice has been a major suspected source in Brazilian outbreaks. The berries are harvested, blended into pulp, and consumed widely as a drink. Triatomine bugs living near the palm trees can contaminate the fruit during harvesting or processing. Research published in the CDC’s Emerging Infectious Diseases journal found that the parasite can survive in açaí juice for extended periods, likely because the fatty content of the juice acts as a natural preservative, especially when frozen. Other locally produced fruit juices have been implicated in similar outbreaks.
Oral transmission is particularly concerning because it tends to deliver a larger dose of the parasite at once, which can lead to more severe acute illness compared to a single bug bite.
Mother-to-Child Transmission
A pregnant woman with Chagas disease can pass the parasite to her baby during pregnancy or delivery. The risk is relatively low: an estimated 1 to 5 percent of infants born to infected mothers in the United States acquire the infection. But because Chagas disease is often undiagnosed in the mother, many of these cases go undetected in the newborn as well.
Congenital Chagas can occur regardless of whether the mother is in the acute or chronic phase of her infection. This means a woman infected decades earlier, who may have no symptoms at all, can still transmit the parasite. Early detection in newborns matters because treatment is most effective in infancy.
Blood Transfusions and Organ Transplants
Before routine screening was introduced, blood transfusions were a significant transmission route in both endemic and non-endemic countries. The risk of acquiring the infection from a single transfusion with seropositive blood is about 0.8 percent. That number is low per transfusion, but it adds up across blood supply systems serving millions of people.
In the United States, the FDA now requires one-time screening of every blood donor for Chagas antibodies. Donors who test negative are cleared for future donations without repeated testing. Those who test positive are permanently deferred. Organ transplant recipients face similar risks and undergo screening protocols as well.
When transmission does occur through transfusion or transplant, the incubation period is longer than with a bug bite, sometimes stretching up to 120 days before symptoms appear. This longer window can delay diagnosis.
Laboratory and Accidental Exposure
Researchers and healthcare workers who handle blood samples or cultures containing T. cruzi face a small but real occupational risk. Several documented cases of laboratory-acquired Chagas disease have followed needlestick injuries. The CDC considers needle-stick prevention a serious priority in any lab working with the parasite, and molecular testing is used to monitor workers after suspected exposures.
Where Transmission Happens, Including the U.S.
Chagas disease has historically been associated with rural Latin America, where mud-and-thatch housing gives triatomine bugs easy access to cracks, crevices, and indoor hiding spots. But the geographic picture is broader than many people realize.
Locally acquired human infections have been documented in eight U.S. states: California, Arizona, Texas, Tennessee, Louisiana, Missouri, Mississippi, and Arkansas. A review of cases from 2000 to 2018 found 29 confirmed and 47 suspected locally acquired infections. Common risk factors included rural residence, outdoor work, and activities like hunting or camping. Dogs are frequently infected in these regions and serve as reservoirs, maintaining the parasite in the local environment. Communities along the Rio Grande in Texas have documented both infected dogs and infected people, raising concerns about ongoing domestic transmission cycles.
Triatomine bugs are increasingly encountered in and around homes in the southern United States. While the risk of transmission remains far lower than in Latin America, where housing conditions and bug behavior differ, it is not zero.
Reducing Your Risk
The most effective prevention targets the bug’s access to living spaces. The World Health Organization identifies poor-quality housing as a primary risk factor and recommends screening windows and doors, fitting ceilings, and sealing cracks in walls, floors, and roofs. These structural improvements eliminate the hiding places triatomine bugs rely on.
If you live in or travel to areas where kissing bugs are present, sleeping under bed nets and checking bedding before sleep can reduce nighttime exposure. Keeping dogs from sleeping indoors in endemic areas also limits the reservoir cycle. For food-borne risk, avoiding unpasteurized fruit juices from informal vendors in endemic regions is the most practical step.
Age-standardized mortality from Chagas disease has dropped 72.5 percent globally since 1990, driven largely by vector control programs, housing improvements, and blood supply screening. The disease remains most lethal in tropical Latin America, where mortality runs about 2.2 per 100,000 people, but the overall trend reflects real progress in cutting off the routes through which the parasite reaches new hosts.