(NEXSTAR) – Right now in some areas the southern U.S, a significant percentage of dogs are infected with a potentially life-threatening disease — and many of their owners are likely not even aware.
Canine Chagas disease, which is caused by the parasite Trypanosoma cruzi (or T. cruzi), is estimated to be present in 2% to 6% of dogs in the southern U.S. But in more rural areas, or among working dogs housed in communal kennels or dogs who spend most of their day outside, the rate of infection is closer to 20%, and could be as high as 30% in some parts of the South, according to an expert who spoke with Nexstar.
“Currently, there might be three-quarters of a million, or a million dogs across the U.S., infected,” estimated Rick Tarleton, a regents professor and distinguished research professor at the University of Georgia’s Department of Cellular Biology.
The parasites that cause the disease, Tarleton said, are more commonly found in temperate climates in the Americas, though primarily in Latin America. In the U.S. the T. cruzi parasite is more often infecting canines in the Southern part of the country, where its insect hosts are more likely to thrive.
Chagas disease, meanwhile, doesn’t just infect dogs. The World Health Organization estimates that between 6 and 7 million people are infected with the T. cruzi parasite throughout the Americas (mostly in endemic areas of Latin American countries), and chronic cases can result in cardiac disorders later in life.
But dogs are of particular concern in the U.S., Tarleton said, because of their lifestyle and potential interactions with the bugs — known as triatomines or reduviid bugs — that spread T. cruzi infection.
“Dogs tend to get much higher level initial infections, because they’re eating the bugs, for example. They have acute symptoms because they have a much bigger load, initially, orally,” Tarleton said.
T. cruzi parasites are also often passed through the feces of these insect species, which they leave on their host after bites. Infection can occur if the feces is then smeared into a break in the skin, or rubbed into a cut or a bite.
“Dogs are more likely [than humans] to eat these bugs, or clean themselves where bugs have been or left droppings,” Tarleton explains.
Infected dogs, meanwhile, do not pose high risks of transmitting the infection to humans, according to Tarleton.
“It couldn’t do it through infected feces … it would have to be blood-blood contact. If your dog had a wound, and you had a wound on your hand, and the dog’s blood mixed with yours, for example,” Tarleton said. “It’s not an easy infection to get that way.”
Perhaps frustratingly, the symptoms of T. cruzi infection in dogs may not appear conspicuous at first. Symptoms can include lethargy, weight loss, or a lack of appetite, according to VCA Animal Hospitals. Continued damage to a dog’s cardiac tissue can result in progressed heart issues, and sometimes result in sudden death.
“The ultimate result is, in most dogs, they will develop chronic disease and will die from that disease,” Tarleton said.
In addition to presenting subtle symptoms, T. cruzi infection in dogs isn’t something most veterinarians routinely test for. When dogs are tested for T. cruzi infection, most diagnostics are conducted off-site at a veterinary college or a university-operated diagnostic lab.
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“The problem is not considered large enough to direct any resources to developing a common-use test and also to promote the treatments that can be used,” Tarleton said.
But Tarleton doesn’t recommend dog owners just start bringing in any of their lethargic dogs for testing without any other factors. If these factors are present, though — and the dogs are known to have prolonged, repeated exposure to the outdoor environment where T. cruzi infection is suspected or is known to have been transmitted — “seeking such a test would be reasonable/advisable,” Tarleton said.
Treatment for positive cases of T. cruzi infection in dogs is implemented much in the same way that humans can be cured of the disease, such as with the use of an antiparasitic medication like benznidazole, albeit in different dosages over longer courses, Tarleton said.
Such medications have been shown to be effective in treating dogs during the initial acute phases of infection, but not as much in chronic cases, at which point treatment usually shifts to “managing the heart failure and arrhythmias that may occur” throughout the rest of the animal’s life, according to VCA Animal Hospitals.
Further complicating things is that benznidazole is only approved for humans in the U.S., and must be prescribed off-label for dogs, Tarleton said. That’s why he’s pushing to develop a commercial version for dogs, but there just isn’t as much interest on the part of pharmaceutical companies, he claims.
In the meantime, dog owners can try to prevent infection — but that’s also not as straightforward as it sounds.
“It’s not an easy thing to prevent unless you want to keep your dog inside, and a lot of people do. A lot of dogs that are only occasionally outside on a leash are not at high risk of developing or contracting this disease,” Tarleton tells Nexstar. “But there are a lot of dogs that spend a lot of time outdoors, and It is not an uncommon thing to hear that they may be infected.”
People who manage or own dogs in higher-risk areas or environments — like hunting dogs or working dogs who spend lots of time outdoors and live in large kennels — can also use insecticides to limit the dogs’ contact with the triatomine bugs that spread infection, as noted in a 2021 study by Texas A&M researchers published in the peer-reviewed PLOS Neglected Tropical Diseases journal.
No method, though, appears to be completely effective in preventing infection.
Because of this, Tarleton is advocating for more interest from the pharmaceutical industry. Failing that, he’s hoping for more money to develop common-use diagnostics, and to further test and illustrate the safety and effectiveness of available drug treatments to those pharmaceutical companies.
“It’s just such a reasonably solvable problem that could be largely avoided,” Tarleton said. “If you have a dog that is at risk, you do a yearly test. These dogs could be treated and severe side effects and result from long-term infection could be prevented.”