From protecting our borders to patrolling our airports, the U.S. Department of Homeland Security (DHS) manages more than 3,000 working dogs in various capacities. These specialized dogs are highly valuable and an integral part of both search and rescue functions and detection of concealed persons, narcotics or explosives – meaning that keeping them healthy is of upmost importance. The Institute for Infectious Animal Diseases (IIAD), DHS Office of Health Affairs and Texas A&M University College of Veterinary Medicine and Biomedical Sciences (TAMU CVM) are working together to better understand the impact and spread of Trypanosoma cruzi (T.cruzi) – the parasite that causes Chagas disease – in DHS working dogs.
“Recent studies have shown Chagas disease in dogs and humans in the Southern U.S. and along the [Texas-Mexico] border, right where these dogs are working,” said Sarah Hamer, DVM, Ph.D., MS, TAMU CVM Associate Professor. “So, it became a priority to begin testing these highly-valued dogs to determine the impact Chagas disease is having.”
Infection with T. cruzi can cause Chagas disease in people, dogs or other mammals when it is transmitted by a “kissing bug,” a nocturnal, blood-feeding insect of the Reduviidae family. The T. cruzi parasite isn’t new to Texas – the first case was reported in an infected dog in 1972 while the first human case was reported in the 1950s. Dogs can serve as a sentinel of human risk as they share the same environment as their human handlers and reflect potential exposure to kissing bugs.
“Though Chagas is an emerging disease that we know is in Texas and know can infect dogs and people – but we don’t know the full extent the impact or spread of the disease,” said Melissa Berquist, Ph.D., IIAD director. “By gaining a better understanding of the geographic areas dogs are becoming exposed in and the prevalence of exposure, we are gaining critical information for canine management and vector control programs in order to decrease transmission to these high-value dogs. And, because these dogs are potentially exposed in the same working environments as their human handlers, this work will also inform human health protection strategies.”
The team tested 528 DHS working dogs along the Texas-Mexico border – finding that 7.4-18.9% of dogs were positive for T. cruzi antibodies reflecting current infections and a small number had the parasite in their blood. The team also collected two species of kissing bugs from areas where the dogs work and sleep – and found that 45% of those tested positive for T. cruzi and had recently bitten a canine.
“Many studies have found that stray or shelter dogs seem to be highly infected with vector-borne diseases, due not only to prolonged outdoor exposure where vectors occur but also perhaps related to reduced health and veterinary care,” said Alyssa Meyers, a Ph.D. student working in Hamer’s lab. “What was surprising is that these very high-value DHS working dogs receive the highest quality of food, shelter and veterinary care – but they are still infected at a prevalence equal to that of stray or shelter dogs.”
Chagas disease isn’t always obvious – some dogs may exhibit no symptoms while some dogs may show acute symptoms that range from fever and lethargy to swollen lymph nodes and sudden death. Some dogs may also progress into a chronic stage and suffer from weakness, exercise intolerance, cardiac disease, tachycardia and fluid accumulation.
“As you can imagine, if a working dog develops these symptoms it could cause them to be unable to perform their duties and be retired early,” Hamer said. “However, we do know many dogs can be asymptomatic and live a healthy life after exposure – most of the working dogs that tested positive for exposure are still actively working.”
Though Chagas is not a new disease, there is relatively little research or common, public knowledge surrounding it.
“We are also trying to determine, if a dog is infected, what is the clinical outcome?” said Meyers. “We know in humans that about 30% of people infected develop chronic Chagas disease. We also know that takes 10-30 years to develop. We don’t know what percentage of infected dogs develop the disease or on what timeline – this is a problem for dog owners and veterinarians because we don’t know what a diagnosis of Chagas disease actually means.”
The team is next working with all types of DHS working dogs across the nation to test for T. cruzi infection. Hamer said that, unfortunately, their research is finding some infection in dogs that work in northern regions that are well outside of the kissing bug vector’s range – most likely the result of an infection that occurred when the dog was being trained in the southern U.S.
“In regions outside of the bug’s range, there is even less medical/veterinary awareness for Chagas disease,” Hamer said. “Chagas disease is yet one more example of how there are not firm geographic restrictions on areas of disease risk given the movement of infected people, animals and vectors. We feel it is important to conduct this surveillance and share findings with dog handlers and the veterinary community.”
The team’s research article, Widespread Trypanosoma cruzi infection in government working dogs along the Texas-Mexico border: Discordant serology, parasite genotyping and associated vectors, can be viewed here as featured in the Public Library of Science Neglected Tropical Diseases Journal. For more information on Hamer’s lab and this project, click here.
The Institute for Infectious Animal Diseases focuses on research, education and outreach to prevent, detect, mitigate and recover from transboundary, emerging and/or zoonotic diseases, which may be introduced intentionally or through natural processes. IIAD is a member of the Texas A&M University System, a World Organisation for Animal Health Collaborating Centre in the specialty of biological threat reduction and a Department of Homeland Security Science and Technology Emeritus Center of Excellence. For more information about the Institute, visit iiad.tamu.edu.