Chagas disease, a condition caused by infection with the protozoal parasite Trypanosoma cruzi, has always been a big problem for our neighbors to the south. The U.S. Centers for Disease Control (CDC) says that it is “endemic throughout much of Mexico, Central America, and South America, where an estimated 8 million people are infected.”
The United States has not been immune to Chagas disease, however. The CDC “estimates that more than 300,000 persons with Trypanosoma cruzi infection live in the United States” but that most of these people “acquired their infections in endemic countries.”
Chagas disease is becoming increasingly important in our country right now for two reasons:
- The range of the disease appears to be moving farther northward into the United States (can anybody say “climate change?”)
- The disease affects many different species — most notably dogs and people.
The parasite that causes Chagas disease is transmitted by triatomine bugs, more commonly called kissing bugs. Unlike many other types of vector-borne diseases, the bite of a kissing bug is not responsible by itself for transmission. The true story is a bit grosser. When a kissing bug bites a person, dog, or other mammal, it tends to defecate (poop) more or less at the same time. The bite causes the victim to scratch, and that activity is likely to push the nearby feces and the parasites it contains into the small wound caused by the bite. Dogs can also become infected with T. cruzi by eating infected bugs or prey, or the disease can be passed congenitally from a mother to her offspring.
The symptoms of Chagas disease in dogs vary with the duration of infection:
- Acutely infected dogs typically have a fever, loss of appetite, lethargy, swollen lymph nodes, and an enlarged liver and/or spleen. This phase may go unnoticed by owners, particularly since the clinical signs tend to resolve with time.
- Dogs have no symptoms at all in the latent phase, which may last for several years.
- With chronic infection, however, dogs can develop a type of heart disease called dilated cardiomyopathy. This may result in congestive heart failure or more shockingly, affected dogs may drop dead before developing any symptoms of heart disease.
Unfortunately, no medications have been found that effectively treat Chagas disease in dogs. Symptomatic treatment for dilated cardiomyopathy and congestive heart failure can help dogs feel better and live longer than they would otherwise, but the underlying problem remains. A vaccine is also not available, so prevention is limited to practices that limit a dog’s exposure to kissing bugs and other sources of infection with T. cruzi. The Veterinary Medicine and Biomedical Sciences program at Texas A&M (Texas is a Chagas disease hotspot) makes the following recommendations:
- Prevent dogs from eating bugs
- House dogs indoors at night
- Prevent dogs from eating potentially infected animals (mice, rats, etc.)
- Test breeding females to prevent congenital transmission
They also state that “although direct transmission from dogs to humans has not been reported, infection in dogs indicates the local presence of infected vectors, which may present an increased risk of vector borne transmission to humans.” See the CDC’s website for more information on Chagas disease in people.
Dr. Jennifer Coates