The following are general questions and answers commonly asked about canine Chagas disease.
Chagas disease is a potentially fatal disease caused by the protozoan parasite Trypanosoma cruzi. Humans, dogs, and other mammals can get infected with the parasite. While the parasite can infect many tissues in the body, the heart is the predominant area of damage in dogs. Some infected dogs develop clinical disease due to inflammation and scarring of the heart that leads to irregular heartbeats, weakening of the heart muscle, heart failure, and sudden death.
The parasite (Trypanosoma cruzi) is located in the gut of the kissing bug insect and is passed through the kissing bug’s fecal contents or when a dog eats an infected bug. It is NOT spread to a host through the kissing bug’s bite or saliva, but infected feces can enter through the bite site or mucus membranes and infect a host. Kissing bugs become infected after feeding on an infected animal. Wildlife species such as raccoons, armadillos, and coyotes, as well as dogs and humans, can play a role in transmission to kissing bugs.
Dogs that encounter an infected kissing bug can become infected. Kissing bugs are present in the United States and Latin America and are most active during the warmer months (April – October). Risk factors include dogs that:
- Live in, travel to, or originated from areas with infected insect vectors
- Live, work, or spend a lot of time outdoors
- Live in multidog kennel environments or have an infected littermate or housemate
- Regularly eat insects
Because Chagas disease primarily affects the cardiovascular system, the most common clinical manifestations involve abnormalities of the heart’s electrical system and heart muscle. These may include arrhythmias and conduction disturbances (abnormal heart rate and rhythm) as well as cardiomyopathy, or weakening of the heart muscle. As the disease progresses, affected dogs may develop weakness, exercise intolerance, fainting or collapse, congestive heart failure (including labored breathing and/or abdominal enlargement due to fluid accumulation), or sudden death. Other nonspecific signs may include lethargy, decreased appetite, coughing, and difficulty breathing.
Several testing options are available to evaluate dogs for Trypanosoma cruzi (T. cruzi) infection, and these tests generally fall into two categories: (1) serologic testing and (2) PCR testing.
- Serologic testing detects antibodies produced against T. cruzi. Common examples include IFA (indirect fluorescent antibody testing) and ELISA testing. A positive serology result indicates exposure to the parasite and suggests infection. However, interpretation of serologic testing can sometimes be challenging, particularly with low-positive antibody results or potential cross-reactivity with antibodies against other parasites that may occasionally occur with some tests.
- PCR testing detects the DNA of the parasite in the dog’s bloodstream. A positive PCR result confirms that the parasite is present and actively circulating in the blood at the time of testing. However, because the parasite can reside within tissues and may not always be present in detectable numbers in the bloodstream, a negative PCR result does not definitively rule out infection.
Unfortunately, no single test is perfect, and results can occasionally be inconsistent between different testing methods performed on the same sample. For this reason, confirmation with multiple tests is recommended whenever possible. Interpretation of results should also take into account the dog’s clinical signs, cardiac findings, geographic exposure risk, and overall likelihood of infection.
No test is perfect, and unfortunately test results can be positive when an animal is actually negative (false positive) or negative when an animal is truly infected (false negative). There are a variety of reasons related to the specific test being used, sample quality, how the test is performed and interpreted, and the dog’s immune response.
Test Performance and Interpretation
- Geographic variations and parasite genetic diversity
- Test is for specific parasite strain type
- Test was evaluated in lab animals not in the field with natural infections
- Use of antigen from Latin America that is not representative of parasite in the US
- Challenges with interpreting faint bands or fluorescence
- Not adhering to the test kit guidelines (over processing)
- Poor sample quality
Patient Response
- Poor antibody response by an individual
- Other protozoal infection that is cross reacting with T. cruzi (example: Leishmania)
- Resolution of infection – transient infection cleared without treatment but the immune system maintains memory
When there is an increased risk of infection. This includes animals with:
- Any of the risk factors listed above
- A dam, littermate, or housemate (dog, cat, or human) had a positive test and were diagnosed with Chagas disease
- A dog with any of the above risk factors is experiencing clinical signs of heart disease (abnormal heart beats, weak heart, or heart failure) or other nonspecific symptoms like weakness, collapse, breathing difficulty, or abdominal distension from fluid accumulation that are not explained by underlying conditions.
Trypanosoma cruzi primarily affects the heart, and cardiac arrhythmias are among the most common abnormalities identified in infected dogs. A cardiac evaluation is recommended to assess the presence and severity of heart disease.
- An electrocardiogram (ECG) records the heart’s electrical activity and can identify conduction disturbances (interruptions in normal electrical signaling) as well as arrhythmias (abnormal heart rhythms). Evaluation may include a standard ECG rhythm strip performed in the hospital and/or a 24-hour ambulatory Holter monitor, which records the heart rhythm continuously over an extended period to detect intermittent abnormalities.
- An echocardiogram (cardiac ultrasound) is used to evaluate heart structure and function and to assess for evidence of cardiomyopathy or risk of congestive heart failure.
- In addition, measurement of the cardiac biomarker cardiac troponin I can provide information about ongoing heart muscle injury, as elevated levels are associated with damage to cardiac cells.
Approximately 20–30% of people with antibodies against Trypanosoma cruzi develop clinical heart disease, known as Chagas cardiomyopathy. The percentage of infected dogs that will develop Chagas cardiomyopathy is not currently known but may be similar to humans. Most but not all infected dogs have evidence of cardiac abnormalities on a comprehensive cardiac evaluation; however, many infected dogs remain clinically normal throughout their lives and never develop significant health problems. Dogs with more severe or life-threatening arrhythmias (i.e., ventricular tachycardia, third-degree AV block), impaired heart muscle function, or congestive heart failure are more likely to develop clinical signs and may have a shorter survival time despite antiparasitic therapy and cardiac medications. In some dogs, the disease progresses slowly over time, while in others it may cause sudden and severe illness. Acute cardiac decompensation and sudden death are recognized complications of infection and are reported most commonly in younger dogs (less than 2 years of age) or dogs newly introduced to environments where kissing bugs are present. As a result, the prognosis for Chagas disease in dogs is highly variable.
Treatment in humans and animals has remained challenging for many reasons. The antiparasitic medicines can be difficult to obtain, cause side effects, and may not change the disease process or reverse clinical signs if significant heart damage has already occurred. An additional challenge is the lack of a reliable test of cure after treatment. Our research team is actively working on testing and treatment for canine Chagas disease.
Discuss your pet’s clinical condition and risk factors for infection with your veterinarian. A cardiac evaluation can help determine whether there is evidence of heart involvement associated with Trypanosoma cruzi infection. Because arrhythmias are among the most common manifestations of Chagas disease, routine ECG monitoring every 6–12 months is recommended to screen for cardiac abnormalities.
If your dog has clinical signs or if cardiac abnormalities are identified, additional diagnostic testing—such as an ECG and/or 24-hour Holter monitor, echocardiogram, and measurement of cardiac troponin I—may be advised to further assess heart structure, function, and rhythm disturbances. Depending on the findings, medications such as antiarrhythmics or treatments for congestive heart failure may also be recommended to help manage cardiac disease. In households with multiple pets, testing of other animals may also be worth considering after discussion with your veterinarian.
Any mammal (including cats, rodents, etc.) is at risk of acquiring Chagas disease, but clinical disease appears to be much less common and less severe in species other than dogs. Birds, reptiles, and amphibians cannot get this disease. A positive dog is unlikely to give the parasite to another animal in the home. However, if an animal was infected while living in a home, kissing bugs are nearby and may pose a risk to others in that area.
No; there are no known cases where a human has become infected by a dog. You cannot get Chagas disease from petting your dog, getting licked by your dog, or from your dog’s feces. However, care should be taken to avoid your dog’s blood as this could contain the infective organism if they were recently infected.
Cows, and other farm animals, seem to be unpopular hosts for kissing bugs to feed on. There is currently no scientific evidence to support disease transmission through eating properly prepared meats and animal products. Wildlife can be infected with the parasite, so there is likley some risk of exposure to T. cruzi when dressing an animal in the field. However, well-cooked meat is safe to handle and eat.
Many wild mammals (like raccoons, opossums, woodrats, etc.) can be infected with the Chagas disease parasite and serve as a reservoir to infect other kissing bugs. Your dog is not likely to get infected from direct contact with a wild mammal unless your dog is eating them. Birds, reptiles, and amphibians cannot carry this disease.
The best way to prevent Chagas disease is to prevent exposure to infected kissing bugs. This includes a combination of environmental control: turning off outdoor lights especially at dawn/night/dusk, cleaning up brush and wood piles near where dogs spend time that serve as breeding areas for insects, shoring up any cracks/gaps in the integrity of your house including doors and windows, housing animals inside, and using pet-safe insecticides. There is not currently a vaccine or monthly preventative available for Chagas Disease.
