Trypanosoma cruzi infection in dogs along the US-Mexico border: R0 changes with vector species composition.

Infection with Trypanosoma cruzi, etiological agent of Chagas disease, is common in US government working dogs along the US-Mexico border. This 3145 km long border comprises four states: Texas (TX), New Mexico (NM), Arizona (AZ) and California (CA) with diverse ecosystems and several triatomine (a.k.a., kissing bug) species, primary vectors of T. cruzi in this region. The kissing bug (Heteroptera: Reduviidae) community ranging from CA to TX includes Triatoma protracta (Uhler), Triatoma recurva (Stål) and Triatoma rubida (Uhler) and becomes dominated by Triatoma gerstaeckeri Stål in TX. Here, we ask if T. cruzi infection dynamics in dogs varies along this border region, potentially reflecting changes in vector species and their vectorial capacity. Using reversible catalytic models of infection, where seropositivity can be lost, we estimated an R0 (Estimate ± S.E.) of 1.192 ± 0.084 for TX and NM. In contrast, seropositivity decayed to zero as dogs aged in AZ and CA. These results suggest that dogs are likely infected by T. cruzi during their training in western TX, with a force of infection large enough for keeping R0 above 1, i.e., the disease endemically established, in TX and NM. In AZ and CA, a lower force of infection, probably associated with different vector species communities and associated vectorial capacity and/or different lineages of T. cruzi, results in dogs decreasing their seropositivity with age.

Fatal Chagas myocarditis in government working dogs in the southern United States: Cross-reactivity and differential diagnoses in five cases across six months.

We describe the diagnostics surrounding the deaths of five working dogs over six-months to provide an enhanced clinical and diagnostic understanding of canine Chagas disease. Cases were five dogs with antibodies to Trypanosoma cruzi. Medical records were reviewed for diagnostic history. Testing was performed from samples collected before or immediately after death, including measurement of cardiac troponin I, histology, PCR and serology for Leishmania spp. and T. cruzi. Four dogs had a 2 to 7-year history of T. cruzi antibodies, while one positive dog had an unknown duration of exposure. Age at death ranged from 2 to 11 years and four dogs were actively working. The cardiac troponin I was elevated in all four dogs for which it was measured, although postmortem reference ranges are not established. Histopathologic diagnoses included mild to severe, chronic, lymphoplasmacytic to histiocytic myocarditis with variable fibrosis. Notably, only one dog had T. cruzi amastigotes observed in the heart histologically. T. cruzi DNA was detected in three other hearts. Although all five dogs tested antibody-positive for T. cruzi using three independent tests, all were also indirect fluorescent antibody-positive for Leishmania spp., interpreted as cross-reaction. Chagas disease in dogs is a diagnostic challenge owing to cross-reactions and variable clinical, histologic and molecular presentations. The use and interpretation of multiple diagnostic strategies is useful in diagnosis. This study demonstrates techniques used to diagnose and characterize Chagas disease in an at-risk dog population.

Epidemiology of Vector-Borne Pathogens Among U.S. Government Working Dogs.

Surveillance of U.S. domestic dogs for exposure to vector-borne pathogens can identify regions of transmission that are relevant for human and animal health. Working dogs with high levels of outdoor exposure may be sensitive indicators of local risk, owing to increased contact with vectors. We randomly selected 476 high-value government working dogs from 40 states to determine the prevalence of infection with Dirofilaria immitis and Rickettsia spp., and exposure to Ehrlichia spp., Anaplasma spp., and Borrelia burgdorferi, and identify risk factors for positivity. Additionally, we tested 100 of these dogs from Texas for Leishmania spp. where sand fly vectors occur. Previously published Trypanosoma cruzi infection data on these dogs were used to identify coinfection or co-exposures. Infection prevalence was 0.84% for D. immitis, and all dogs were negative for Rickettsia spp. DNA. Seroprevalence of each pathogen was: B. burgdorferi 0.84%, Ehrlichia spp. 1.3%, Anaplasma spp. 1.5%, Leishmania spp. 2.0%, and T. cruzi 12.2%. Coinfection or co-exposure took place in four (0.84%) dogs. In bivariable analysis, we found that D. immitis-positive and Ehrlichia-seropositive dogs were significantly older than negative dogs (p < 0.05). Furthermore, seroprevalence of Anaplasma spp. was significantly higher among dogs in the Northeast United States relative to other areas of the country (4.7% vs. ≤1.4%; p = 0.041). Although autochthonous Leishmania infections have been described in the United States, the cases reported herein may represent imported Leishmania infection. Most federal working dogs are bred in Europe, where the parasite is endemic and congenitally transmitted. Serological cross-reaction between T. cruzi and Leishmania spp. complicates diagnosis. In this study, the use of multiple testing strategies in a comparative complementary manner provided evidence for these dogs' true exposures. Comprehensive surveillance for vector-borne pathogens in dogs can improve clinician awareness and target prevention and treatment in a One Health manner.