Chagas disease, also known as American trypanosomiasis or Chagasic myocarditis, is a disease that can occur in dogs due to the protozoan parasite Trypanosoma cruzi (T. cruzi). Chagas disease was named after Carlos Chagas, a Brazilian physician who discovered T.cruzi in 1908. It was first diagnosed in the United States since 1916.
Protozoans are basic one-celled organisms that can cause a range of medical problems and symptoms including diarrhea, dehydration, weakness, weight loss, and eventually death. Two of the most common protozoan infections in dogs are Coccidia and Giardia. Protozoan infections are most common in young puppies and those with immature or weak immune systems. Infection is more common in crowding situations such as pet shops, boarding kennels, and breeder facilities.
Chagas disease is caused by the protozoan parasite T. cruzi. The kissing bug (Triatominae or Triatoma) carries T. cruzi and is named such because it often bites people and pets around their mouths.
The following are ways dogs can be infected with T. cruzi and acquire Chagas disease:
- Dogs can be born with the disease receiving it from the mother.
- Ingestion of a kissing bug.
- Ingestion of the feces of an infected kissing bug.
- A bite from the kissing bug that subsequently infects the bite with its own feces. Note: The kissing bug commonly defecates during feeding. The natural instinct after a bite is to rub or scratch at the area which can contaminate the wound with the kissing bug feces.
- Ingestion of a rodent infected with T. cruzi.
- Blood transfusion from a donor dog infected with T. cruzi.
- Eating food infected with the feces of the kissing bug.
After exposure and infection with T. cruzi, the parasite multiplies and eventually invades the dogs cardiac (heart) cells which cause the infected cells to rupture. Chagas disease is common in Central and South American and becoming more common in the United States. Historically Chagas disease has been focused in the warmer Southern states including Texas, Arizona, Oklahoma, Louisiana, South Carolina, Georgia, North Carolina, New Mexico, California, Florida, and Virginia but is expanding as the kissing bug spreads throughout the country. Most recently it has been found in 28 states including Ohio and Maryland.
There are many estimates as to the number of humans infected in the United States that range from 350,000 to over a million. Most infected humans live in the Southern United States with many being immigrants from South and Central America.
The kissing bug likes to bite (feed) at night and lives in crevices such as wood piles. Chagas disease is most common in dogs less than one year of age and common in dogs that are strays, feral, or abandoned dogs and infection rates may be as high as 9%. In the United States, infection rates in dogs are highest in dogs kenneled and those outdoors/free to roam. The infection rates in Mexico are estimated to be 17 to 22%, almost double the % in the US.
Symptoms of Chagas Disease in Dogs
There are typically three phases of the infection in dogs that cause different clinical signs. When the infection is new (acute) dogs will experience some very general symptoms that occur from day zero to 4 weeks and then often appear asymptomatic for months to years.
The severity of signs is believed to relate to the age and activity of the dog as well as the specific strain of the T. Cruzi.
Top Signs of Acute Chagas Disease in Dogs
The acute signs of disease occur from 0 to 4 weeks.
- Decreased or loss of appetite
- Enlarged liver and/or spleen
- Lymph node enlargement
- Seizures or disorientation
- Sudden death
Top Signs of Chronic Chagas Disease in Dogs
- Abnormal heart arrhythmias (arrhythmias)
- Difficulty breathing
- Fluid accumulation in the abdomen (ascites)
- Fluid accumulation in the lungs (pulmonary edema)
- Inability to exercise or “exercise intolerance”
- Increased heart rates
- Pale mucous membranes
- Weight loss
Diagnosis of Chagas Disease in Dogs
The diagnosis of Chagas disease in dogs can be a challenge. T. Cruzi can be found in the lymph nodes and bloodstream during the acute phase of the disease, but there has been no reliable way to see these organisms. They can sometimes be seen in the blood or lymph node samples but the numbers can be low and they can be hard to visualize.
There are serologic tests that evaluate antibody levels but those can take three to four weeks to become detectable. These serologic tests can be expensive and are not always reliable. Sometimes the patient is somewhat better by this time and those diagnostics are not completed.
Most dogs are not diagnosed with Chagas disease during the acute phase but rather in the chronic phase when the signs of heart failure are evident.
Baseline tests include a complete blood count (CBC), biochemical profile, fecal evaluation, and urinalysis. Changes are variable, depending on the organ system(s) involved.
Additional tests include:
- Echocardiogram in Dogs (Cardiac Ultrasound)
- Chest and abdominal radiographs (X-rays)
- Serologic testing to confirm antibody levels to T. Cruzi. is available through the Texas Veterinary Medical Diagnostic Laboratory. A positive titer indicates that the dog has been exposed to T. Cruzi. at some previous time.
- Blood troponin I blood levels may be elevated indicating inflammation of the myocardium.
Treatment of Chagas Disease in Dogs
Chagas disease can be very difficult to treat when the infection is advanced. There has been no medication proven to treat T. cruzi. Medications such as Albaconazole, Benznidazole, and Ravuconazole, can be used in the acute phase of infection but the treatment success rates are variable.
Once the disease is in the chronic phase, the treatment is focused on treating the underlying symptoms. For example:
- Fluid therapy for dehydration
- Anti-nausea medications for vomiting
- Diuretics to treat abnormal fluids accumulations resulting from heart failure
- Heart medications to treat arrhythmias and abnormal heart muscle function
Home Care For Dogs with Chagas Disease
Administer all medication as directed by your veterinarian. Contact your veterinarian at once if your dog is not responding to therapy and/or getting worse. Return for follow up examination and testing as recommended by your veterinarian.
Prevention of Chagas Disease in Dogs
There is no vaccine to prevent Chagas disease. The best way to prevent Chagas disease is to prevent exposure and bites from the kissing bug. Learn more about some important ways to prevent your dog from getting bit by a kissing bug in this article: 5 Common Questions About Kissing Bugs. This article includes excellent suggestions on keeping your dog in at night and recommendations to seal cracks to prevent the kissing bug from getting indoors.
For those of you in the veterinary field, it is important to understand that needle sticks or sharp objects contaminated with blood from an infected dog could be an important hazard and possible method to acquire Chagas disease. Treat any possible contamination as important and call your physician.
People do get Chagas disease but it is not believed that dogs can spread Chagas disease to people. Just like dogs, humans are infected if they are exposed to and bit by the infected insect. However, dogs and other animals can become a reservoir for T. curi. This means that a kissing bug could acquire the infection from a dog to later transmit it to a person. For this reason, some veterinarians recommend dogs that are infected with T. cuzi be euthanized.
Prognosis for Dogs with Chagas Disease
The prognosis in dogs with Chagas disease is poor to grave.