Chagas Disease (American Trypanosomiasis) in Dogs

What is Chagas disease?

Chagas disease, also known as American trypanosomiasis, is an infection caused by Trypanosoma cruzi (T. cruzi), a blood-borne protozoal parasite. It is primarily observed in Latin America, but in recent years, it has been observed at various sites in the southern United States, including Texas, Louisiana, South Carolina, Virginia, Georgia, Tennessee, and Oklahoma. 

How is Chagas disease spread?

Chagas disease is spread mostly by insects in the subfamily Triatominae, known as "kissing bugs." These beetles lie in the bedding of dogs and other animals, feeding on the animals' blood as they sleep. The insects become infected with the T. cruzi parasite when they feed on an infected dog, and then they transmit the parasite to uninfected dogs.

As the insects feed, they release an infective form of the parasite in their feces, laid close to the bite wound. The parasite makes its way into the dog’s bloodstream through the bite wound or may penetrate mucous membranes, such as the gums or inside the lips. Dogs can also become infected by eating infected insects, which excrete the parasite into the dog’s mouth. It also may rarely be transmitted through an infected blood transfusion or through the placenta to the developing puppy.

Once inside the dog, the parasite enters several types of cells, including the cells lining the blood vessels, the heart muscle cells, and other cells, including those in the liver, spleen, kidneys, skeletal muscle, and the central nervous system. The parasite reproduces within these cells until the cells explode and release large numbers of T. cruzi into the bloodstream. This cell rupture and death cause the effects seen with Chagas disease.

What are the clinical signs of Chagas disease?

The clinical signs of Chagas disease vary and are often non-specific. Some infected dogs have no signs, while others become seriously ill. Signs seen in dogs with Chagas disease include:

• Lethargy (tiredness)
• Fever
• Decreased appetite
• Weight loss
• Enlargement of the lymph nodes and spleen (due to the body's immune system attempting to fight off the infection)
• Pale gums (due to poor circulation) 
• Fainting, collapse, syncope
• Cardiac arrhythmia or murmur
• Hindlimb ataxia, weakness or paralysis
• Coughing
• Exercise intolerance
• Difficulty breathing
• Distended abdomen caused by fluid buildup
• Sudden death

The disease has three recognized phases:

Acute phase: The first 30 days of infection. The parasite is invading and destroying cells, causing a widespread inflammatory response. It often attacks heart muscle cells and, less commonly, cells in the central nervous system. Milder cases may experience lethargy, fever, and lymph node enlargement, while severe cases can have signs of heart disease or paralysis. Some dogs die during the acute phase.

Latent or indeterminate phase: Most dogs that survive the acute phase will develop chronic disease. However, there is a long window of time, from months to years, in which a dog will not have clinical signs. This is often referred to as the latent phase but may be included in the chronic phase.

Chronic phase: Dogs develop chronic disease when the ongoing inflammatory effects have caused enough scarring (fibrosis) to result in dysfunction of the target organ – often the heart. Dogs generally develop signs of heart failure, such as difficulty breathing, exercise intolerance, or a distended abdomen. Sudden death may occur because of a severe arrhythmia (irregular heartbeat).

How is Chagas disease diagnosed?

Diagnosis of Chagas disease during the acute phase is difficult. The infectious organism may be found in the blood or lymph nodes, but there are often so few organisms that this technique is not reliable for diagnosis. About three weeks after infection, antibody levels may be detectable on laboratory tests, but false positives may occur. 

In the chronic phase, Chagas disease is primarily diagnosed based on the presence of clinical signs. If a dog dies from the condition, heart tissue samples often reveal characteristic changes consistent with T. cruzi.

If a dog shows signs of Chagas disease, tests may include a complete blood count (CBC), radiographs (X-rays) of the chest and abdomen, electrocardiogram (to detect heart malfunction or damage), cardiac ultrasound, blood cultures (looking for the T. cruzi organism), and PCR tests to detect T. cruzi genetic material.

How is Chagas disease treated?

There is currently no agreed-upon treatment for Chagas disease. In the acute phase, several medications have been used with varying success, including benznidazole, itraconazole, and amiodarone. Once infection reaches the chronic phase, these medications have little effect, so treatment focuses on managing heart failure and arrhythmias.

Can Chagas disease be prevented?

There is currently no vaccine for Chagas disease, although research is underway. The most effective way to prevent infection is to limit contact with the insects that spread the disease. 

• Keep your pet away from areas where kissing bugs prefer to live, like piles of brush and wood piles. 
• Turn off outdoor lights at night to avoid attracting kissing buts to your property.
• Keep your pets inside, when possible, to minimize exposure. 
• Talk to your vet about appropriate preventives for your dog. Certain tick preventive medications and collars can be used to kill the vector insects (T. infestans) before they can transmit the disease.  

Does Chagas disease affect humans?

Chagas disease can affect humans if they encounter infected insects. However, there have not been any reported cases of dog-to-insect-to-human transmission of Chagas disease in the United States. All individuals living in areas affected by Chagas disease are at risk of the condition, but having an infected dog is unlikely to significantly increase that risk.