Chagas disease, also called American trypanosomiasis, is caused by infection with Trypanosoma cruzi, a single-celled parasite naturally transmitted by several species of triatomine bugs (“kissing bugs,” “cone-nose bug,” “vinchuca”). Humans, dogs, and many other species of domestic and wild animals are susceptible to infection. The parasite and its vector are naturally present in the Americas, from most of South America to the southern half of the United States (U.S.), including all regions of Texas. Human infection occurs commonly in some parts of Latin America, but relatively rarely within the U.S., mainly due to improved housing conditions.
The Pan American Health Organization estimates that approximately 8 million people in Latin America are infected, resulting in about 12,000 deaths per year. The U.S. Centers for Disease Control and Prevention (CDC) estimates that approximately 300,000 people within the U.S.—predominantly immigrants from high-risk areas of Latin America—are infected. Human cases acquired in Texas are uncommon.
The T. cruzi parasite is naturally transmitted in the feces of blood-feeding triatomine bugs (also called reduviid bugs, kissing bugs, or cone-nosed bugs). The triatomine bug vectors usually become infected after feeding on an infected animal or, more rarely, a person. After the organism reproduces in the bug, it can spread to people if the infected bug defecates while feeding on them, usually while the person is sleeping at night, and the person accidently rubs the feces into the bite wound, an open cut, or a mucous membrane.
People also can become infected through:
- congenital transmission (from a pregnant woman to her baby)
- blood transfusion
- organ transplantation
- consumption of beverages or uncooked food contaminated with feces from infected bugs
- accidental laboratory exposure
Chagas disease is not transmitted from person to person like a cold or the flu or through casual contact with infected people or animals.
There are two phases of Chagas disease: acute and chronic. Both phases can be symptom-free or life-threatening.
The acute phase of disease occurs during approximately the first 8 weeks of infection. Symptoms, if present, may include:
- body aches
- loss of appetite
- a localized swelling (“chagoma”) where the parasite entered the body
People with acute illness may also have mild enlargement of the liver or spleen and swollen lymph nodes, among other less-common findings. The most recognized marker of acute Chagas disease is called Romaña's sign, a swelling of the eyelids on the side of the face near the bite wound or where bug feces were deposited into the eye or accidentally rubbed into the eye. Symptoms of acute illness can last weeks to months and then disappear, even with out treatment. The acute phase of disease may go unnoticed because it often causes no symptoms or only mild symptoms.
The chronic phase of disease follows the acute phase and includes an asymptomatic form (“indeterminate” or “latent” infection) and a symptomatic form. The majority of people in the chronic phase will remain symptom-free for life, but 20-30% will develop symptomatic illness, including:
- an enlarged heart (cardiomyopathy), heart failure, altered heart rate or rhythm, or sudden death
- an enlarged esophagus (megaesophagus) or enlarged colon(megacolon), which can cause difficulties eating or having bowel movements
Medical Evaluation and Treatment
If you think you have Chagas disease, have been exposed to a triatomine bug, or share risk factors with a family member who has Chagas disease, contact your medical provider. Your medical provider will conduct a thorough physical exam, ask you about risk factors for infection, especially travel to areas where Chagas disease is common, evaluate your heart rhythm, and order blood tests to determine if you have been infected. If tests show that you are infected, drugs are available for treatment, however a cure is not always possible. These drugs may cause significant side effects that some people may not tolerate.
Blood Donor Testing
Blood banks screen first-time blood donors for evidence of T. cruzi infection. Donors testing positive are notified by the blood bank and are advised to consult their medical provider for evaluation and additional laboratory testing. Potential blood donors found to be infected with T. cruzi should not donate blood or tissues for the remainder of their lifetime.
T. cruzi Infection in Dogs and Cats
T. cruzi infection has been reported in dogs in Texas and several other states, including Louisiana and Oklahoma. Infections in domestic cats have been reported in South America, but not in the U.S. Although dogs may become infected anywhere in the state, infection most commonly occurs in Central and South Texas. Outdoor dogs are at much higher risk due to their outdoor exposure, the likelihood of infestation of outdoor kennel areas, and the tendency for some dogs to eat triatomine bugs. Studies conducted in South Texas in 1999 found that 7.5% of the stray dogs tested were positive for the parasite and infection in coyotes has also been reported. If you think your dog may have been infected, contact your veterinarian. Your veterinarian will be able to examine your dog and collect blood samples for laboratory testing. Currently, there are no drugs available in the U.S. to treat dogs infected with T.cruzi.
Preventing Chagas Disease
Preventive measures while traveling to endemic areas include using bed nets treated with long-lasting insecticides, wearing protective clothing, and applying insect repellent to exposed skin. In addition, travelers should be aware of other possible routes of transmission, including blood-borne (i.e. blood transfusion) and food-borne (ingestion of food and/or drink contaminated with infected bug feces) transmission.
Recommendations for reducing the risk of transmission to animals and humans in the U.S. include:
- keep yard and kennel areas clean to eliminate habitat for the bugs; remove brush piles, rock piles, excessive buildup of leaf litter, etc.
- control rodents to remove a potential food source that may sustain populations of bugs in the yard
- turn off outdoor lights at night so that bugs aren’t attracted to the house and yard
- identify and seal entry points for the bugs into the home and consider the appropriate use of a long-lasting insecticide
- keep pet food and water bowls inside to prevent contamination with feces from the infected bugs
- keep dog houses and poultry coops clean, fill in crevices where the bugs might hide, and consider the appropriate use of long-lasting pesticides in and around these structures