Principal Investigator(s): Sarah Hamer, DVM, Ph.D., M.S.
There is currently no available, approved treatment for canine Chagas disease in the U.S nor is there a vaccine to protect against the parasite. Diagnosis of canine Chagas disease most commonly happens during the chronic phase when heart damage may be irreversible. Thus, prevention of infection is the main approach for disease management. The mechanisms by which border patrol dogs are becoming infected must be identified to facilitate the development of effective disease management strategies.
This epidemiological investigation of Chagas disease in canines within a network of the Department of Homeland Security (DHS) working dogs populations across the U.S will help determine when and where dogs are becoming exposed, and quantify the prevalence of exposure. This information is prerequisite for an effective disease management program. The study aims include elucidating the geographic patterns of canine seropositivity and parasitemia through sampling of working dogs along the border and across the U.S.; identifying risk factors for infection; determining infection prevalence in kissing bugs collected by dog handlers and border patrol officers from areas frequented by border patrol dogs; identifying the parasite genotypes that infect dogs and local kissing bugs in relation to those implicated in human disease; and determining the clinical outcomes in T. cruzi infected canines.
Phase I (2015-2016):
The distribution of working dogs along the U.S.-Mexico border in Texas – a presumed high-risk zone – allowed the opportunity for to determine spatial patterns of infection. In 2015-2016, 528 government working dogs across five management areas plus a training center in Texas were tested and kissing bugs were collected from canine environments. Dogs were tested for antibodies to the Chagas parasite. Additionally, both dogs and kissing bugs were tested for parasite DNA as a marker of infection. Overall, between 7.4 and 18.9% of dogs had antibodies; the wide range represents discordant results using different testing methods. Exposed dogs occurred across all management regions along the border, and were also found at the training center in Texas. Nine of 20 (45%) kissing bugs of two different species were found to be infected. Both dogs and kissing bugs were infected with two different genetic strains of the parasite, one of which has previously been implicated in human disease in the US. We were able to determine the hosts upon which some of the kissing bugs previously fed, and most of the bugs were found to have canine bloodmeals in their abdomen. These findings were published in PLoS Neglected Tropical Diseases in 2017. Additionally, wetransmission potential.
Phase II (2016-2017):
Texas has been the focus of U.S. Chagas disease studies, but triaomine vectors, including many infected with T. cruzi, have been reported from 25 states. During Phase II, sampling and testing for T. cruzi was extend to a larger network to include DHS working dogs for across the U.S. in all canine divisions (TSA, Border Patrol, Secret Service, Federal Protective Service, Coast Guard and Port of Entry). Additionally, we aimed to characterize cardiac rate and rhythm abnormalities associated with T. cruzi infection, and hypothesized that ECG abnormalities would be more common in T. cruzi seropositive than seronegative dogs. In 2015-17, we sampled 1,484 working dogs from 43 states and found an overall seroprevalence of 7.3% based on immunochromatographic tests and indirect fluorescent antibody testing. We applied a 24-hour, ECG Holter monitors to 41 dogs including 24 seropositive and 17 dogs seronegative dogs. Additionally, we measured serum concentrations of cardiac Troponin I (cTnI), a biomarker of cardiac injury. Overall, we found that 75.0% (18/24) of the seropositive dogs had one or more EGG abnormality, which was significantly higher (p<0.001) then the 5.9% (1/17) of seronegative dogs with ECG abnormalities. Similarly, 29.2% (7/24) of seroprositive dogs had elevated (>0.07 ng/mL) cTnI levels; whereas none of the seronegative dogs had elevated cTnI levels. Understanding the epidemiology and clinical impacts of T. cruzi infection is critical for implementing disease control measures and managing the health of these high-value working dogs.