Chagas Disease in Dogs: Is It Transmissible to Humans?

Chagas disease (also known as American trypanosomiasis) is a parasitic vector-borne disease. This disease is found mainly in Central and South America and in the southern United States. The parasite is a flagellated protozoan named Trypanosoma cruzi (T. cruzi) that can infect over 100 species of mammals and cause heart disease. The vector is a reduviid or Triatominae insect also known as a "kissing bug" or "assassin bug." About 300,000 people are diagnosed in the U.S. with Chagas disease; most are due to infections acquired outside of the United States (immigrants and travelers). Worldwide estimates range from about 7.5 to 15 million infected individuals.

The parasites are often referred to as "viruses," but this is incorrect. The parasites are flagellated protozoans (T. cruzi) that have a complicated life cycle (see for example, reference one) and are transmitted to mammals and humans by the bite of the vector, the "kissing bug."

The development of Chagas disease in dogs is similar to the development of Chagas disease in humans. Some dogs may not develop any clinical symptoms until entering a chronic phase of the disease, which may be several years after initial infection. The clinical signs in dogs during the acute phase are:

• fever,
• anorexia,
• lethargy,
• swollen lymph nodes,
• an enlarged liver, or
• enlarged spleen.

After the acute phase, there may be a latent phase that is asymptomatic and may last for several years. The chronic phase usually begins with right-sided heart failure that may develop into chronic myocarditis. Arrhythmias of the heart may develop and result in sudden death of the dog.

There are reports that dogs, especially in the southern U.S. and in particular, Texas, may be infected with these parasites and some reports imply there is a danger for humans to become infected because the vectors now reside in the southern U.S. However, the percentage of dogs found to be infected with the parasites is relatively low (about 8.8%) and it is often associated with dogs that are feral, strays, or abandoned. In Mexico, the infection rate of dogs is higher (about 17%-21%). However, all dogs are at some risk to become infected if they are bitten by the vector. Dogs housed outside are at higher risk than "indoor" dogs. Because of the life cycle of T. cruzi, it is possible to become infected if an infected dog is bitten by a reduviid bug, and then that same reduviid bug bites a human. In central and South America, individuals are exposed more often to reduviid bugs because these vectors of disease like to live in thatching used to make roofing over huts where people live. Consequently, the likelihood of getting bitten by reduviid bug is high in these poor housing areas with thatched roofing.

Studies have shown that more modern housing can drastically reduce the incidence of Chagas disease in humans because the vectors, reduviid bugs, do not live in most modern dwellings. Consequently, in the U.S., the chance of your dog getting Chagas disease is relatively low and the chance you will get Chagas disease transmitted from your dog to you is extremely low (unless, of course, you live in a dwelling with a thatched roof that is a great environment for reduviid bugs!). If your dog exhibits symptoms of Chagas disease, your dog's vet can send blood tests that can be examined to diagnose the disease. Treatment of Chagas disease in dogs is mainly symptomatic. There is no vaccine currently available for dogs. To date, in the United States, there have been no reports of dog to vector (reduviid bug) and then to human transmission of Chagas disease.