Chagas disease and your dog

What is Chagas disease, and should you worry about your dog? It depends on where you live.

You may or may not have heard of Chagas disease, depending on where you live. This serious and frustrating disease affects both dogs and humans and is caused by a one-celled microorganism called Trypanosoma cruzi. It’s spread by kissing bugs, though thankfully, dogs and people can’t spread it among others of their kind. Chagas disease is especially common in South America, but is also found in the US — states with the highest incidence are Texas, Oklahoma, Louisiana and Georgia, though some cases have also occurred in Virginia, South Carolina and Tennessee. If you live in one of the affected states, it’s important to understand something about Chagas disease, including its symptoms, diagnosis and treatment.

How does a dog get Chagas disease?

Trypanosoma cruzi lives in the digestive tract of the kissing bug and is found in their feces. Kissing bugs are insects that feed on blood; they’re found in the southern and western US as well as Mexico and parts of Central and South America. Most kissing bugs are harmless, but in the states mentioned above, they can carry Chagas disease.

After an infected kissing bug bites a dog (or person), it turns around and defecates on the bite. The trypanosomes then enter the body through the bite. Infection can also occur when dogs eat an infected kissing bug. The trypanosomes multiply in the dog’s tissue for three days and then enter the bloodstream. From there, they travel to various parts of the body. In dogs, the primary area to be infected is the heart, but sometimes the nervous system is also involved. The trypanosomes cause a high level of inflammation by destroying the cells of the heart, and by giving off chemicals that cause inflammation. Although the immune system eventually produces antibodies, they are not very effective against Chagas disease because the trypanosomes can hide from the immune system.

Signs and symptoms

Signs of infection start appearing about 14 days after the dog is bitten.

  • Most dogs in the early acute phase of Chagas disease have a fever and are weak and lethargic. They can also show sudden signs of heart disease, such as difficulty breathing and abnormal heart rhythms. They may additionally develop anemia (which will cause pale gums), swollen lymph nodes, and sometimes swelling of the lower legs. If the trypanosomes enter the nervous system, dogs will show signs of weakness in the back legs, and problems swallowing and defecating. Some dogs die during the acute phase.
  • In the chronic phase of Chagas disease, the heart problems (and nervous system signs, if affected) gradually worsen. Dogs can develop a cough, and the abdomen may fill with fluid and become swollen. Since the heart is the main target in dogs, Chagas disease is one of the major causes of myocarditis, conduction disturbances, arrhythmias and heart failure from cardiomyopathy in regions where the disease is common. Nervous system signs in the chronic phase include weakness of the hind legs, megaesophagus and megacolon. Some dogs may suddenly die.

Diagnosis can be difficult

A definite diagnosis of Chagas disease can be difficult, because the signs and lab tests are so variable. In fact, not all infected dogs show signs of illness, which means the disease may only be diagnosed by a blood test or blood smear done for other reasons.

Your veterinarian might see increased spleen and liver size when doing an x-ray or ultrasound. Lab tests might show anemia, and elevated liver enzymes. At other times, all tests can look normal. Trypanosomes might be seen in a blood smear or in the fluid from a swollen abdomen, but they may not be easy to find.

The best method of diagnosing Chagas disease is with a PCR test. A blood test for antibodies can also help, but it can be negative in a dog with the disease. False positives can also occur.

The best method of diagnosing Chagas disease is with a PCR test.

Treatment requires an integrative approach

The most important part of treating Chagas disease is to support the dog’s heart (and nervous system, if that is also affected), whether or not the disease has been definitely diagnosed. It is also crucial to decrease the massive inflammation in the heart and other parts of the body.

Since this disease can progress rapidly, fast-acting drugs that are commonly used to help the heart should be utilized, especially when coughing or abdominal swelling is present. Sometimes the heart beats so slowly that a pacemaker is needed. High doses of vitamins E and C, along with blackberry leaf extract, can be used together and in conjunction with the medication, and will not interfere with the drugs’ action.  If the dog’s liver is affected, milk thistle is useful as well. Acupuncture can be helpful for hind leg weakness.

Acupuncture can be helpful for hind leg weakness.

Unfortunately, no herb can completely get rid of the trypanosomes in a dog’s body. The drug Benznidazole can kill them, but is not always effective. If the dog has no symptoms, even though he has tested positive for the disease, the general consensus is not to treat. But if he is positive and showing symptoms, it is worth trying the drug. In the early phase of the disease (when it is hardest to diagnose), treatment is effective in just under 70% of patients, but in the chronic phase, only about 30% respond. The most common side effect of Benznidazole is vomiting, sometimes severe enough that the drug must be discontinued. However, ginger can help with the vomiting, and Chinese herbs can sometimes work too – just be sure to work with a veterinarian who is knowledgeable in the use of Chinese herbs before trying any on your dog.

Even if the trypanosomes are completely destroyed, the heart may continue to worsen due to the damage and inflammation that has occurred and the dog may end up with cardiomyopathy.

It’s true that Chagas disease is serious, but to date, most of the US, as well as Canada, are free of the disease. This may change in the future, but for now, if you happen to live in an affected state, the best thing you can do is be aware of Chagas disease and its symptoms in both dogs and humans, and take steps to help prevent infection (see sidebar above). And as always, be sure to maintain a healthy lifestyle for both of you!