Selected cardiac abnormalities in Trypanosoma cruzi serologically positive, discordant, and negative working dogs along the Texas-Mexico border.

BACKGROUND: Chagas disease is increasingly recognized in the southern U.S., where triatomine vectors transmit Trypanosoma cruzi among wildlife and domestic dogs with occasional vector spillover to humans. As in humans, clinical outcome in dogs is variable, ranging from acute death to asymptomatic infections or chronic heart disease. In order to characterize cardiac manifestations of T. cruzi infections, we tracked a cohort of naturally-infected dogs and a matched cohort of uninfected dogs. We hypothesized that selected measures of cardiac disease (abnormal rate, abnormal rhythm, and elevated cardiac troponin I (cTnI; a biomarker of cardiac injury)) would occur more commonly in infected than uninfected dogs matched by age, breed, sex and location. In addition to the clearly positive and negative dogs, we specifically tracked dogs with discordant test results across three independent serological assays to gather clinical data that might elucidate the infection status of these animals and inform the utility of the different testing approaches. RESULTS: We placed an ambulatory ECG monitor (Holter) on 48 government working dogs and analyzed 39 successful recordings that met length and quality criteria from 17 T. cruzi-infected, 18 uninfected dogs and 4 dogs with discordant results. Overall, 76.5% of positive, 100.0% of discordant, and 11.1% of negative dogs showed > 1 ECG abnormality (p < 0.0001), and positive and discordant dogs had a higher mean number of different types of ECG abnormalities than negative dogs (p < 0.001-0.014). The most common cardiac abnormalities included supraventricular and ventricular arrhythmias and atrioventricular block. Positive dogs had higher serum concentrations of cTnI than both negative dogs (p = 0.044) and discordant dogs (p = 0.06). Based on dog handler reports, nearly all (4/5; 80%) dogs with reported performance decline or fatigue were T. cruzi-infected dogs. CONCLUSIONS: Further understanding cardiac manifestations in dogs naturally infected with T. cruzi is critical for prognostication, establishing a baseline for drug and vaccine studies, and better understanding of zoonotic risk.

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.

Cardiac diagnostic test results and outcomes in 44 dogs naturally infected with Trypanosoma cruzi.

BACKGROUND: The protozoal parasite Trypanosoma cruzi causes myocarditis in dogs. OBJECTIVES: To describe the cardiac diagnostic test results and outcomes of dogs naturally infected with T. cruzi. ANIMALS: Forty-four client-owned dogs. METHODS: Medical records were retrospectively reviewed to identify dogs with an indirect fluorescent antibody test result for T. cruzi ≥1 : 80. Data collected included signalment, cardiac diagnostic test results (ECG, echocardiography, cardiac troponin I) and outcome. Outcomes were categorized as alive, dead (cardiac or noncardiac) or lost to follow up. RESULTS: ECG abnormalities were present in 41 dogs with ventricular arrhythmias (n = 28) and atrioventricular block (AVB) (n = 15) most commonly identified. Echocardiographic chamber enlargement was present in 28 dogs and most often included the right ventricle (RV) (n = 15) and left atrium (n = 12). Troponin was ≥2 times the reference range in 20/36 (56%) dogs. In univariate analysis using nonparametric Kaplan-Meier, ventricular arrhythmias with a modified Lown score ≥2 (P = .02), presence of AVB (P = .04), and RV enlargement (P = .006) were associated with decreased survival times. Right ventricular enlargement (HR 3.6; 95% confidence interval [CI] 1.4-9.3; P = .007) and higher body weight at presentation (HR 1.0; 95% CI 1.0-1.1; P = .04) were associated with decreased time to death in the final explanatory multivariable model. CONCLUSIONS AND CLINICAL IMPORTANCE: Cardiac abnormalities were common and variable, and RV enlargement was associated with shorter survival time. A diagnostic evaluation that includes screening for arrhythmias, echocardiography, and cTnI can provide useful information related to the characterization of heart disease in dogs seropositive for T. cruzi.

High incidence of Trypanosoma cruzi infections in dogs directly detected through longitudinal tracking at 10 multi-dog kennels, Texas, USA.

Canine Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is increasingly recognized as a health concern for dogs in the USA, and infected dogs may signal geographic regions of risk for human disease. Dogs living in multi-dog kennel environments (kennels with more than one dog) where triatomine vectors are endemic may be at high risk for infection. We monitored a cohort of 64 T. cruzi-infected and uninfected dogs across 10 kennels in Texas, USA, to characterize changes in infection status over one year. We used robust diagnostic criteria in which reactivity on multiple independent platforms was required to be considered positive. Among the 30 dogs enrolled as serologically- and/or PCR-positive, all but one dog showed sustained positive T. cruzi diagnostic results over time. Among the 34 dogs enrolled as serologically- and PCR-negative, 10 new T. cruzi infections were recorded over a 12-month period. The resulting incidence rate for dogs initially enrolled as T. cruzi-negative was 30.7 T. cruzi infections per 100 dogs per year. This study highlights the risk of T. cruzi infection to dogs in kennel environments. To protect both dog and human health, there is an urgent need to develop more integrated vector control methods as well as prophylactic and curative antiparasitic treatment options for T. cruzi infection in dogs.

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.

Nationwide Exposure of U.S. Working Dogs to the Chagas Disease Parasite, Trypanosoma cruzi.

Trypanosoma cruzi is a zoonotic protozoan parasite vectored by triatomine insects that are endemic to the Americas, including the southern United States. Surveillance of domestic dogs for T. cruzi exposure allows for the determination of geographic regions of transmission that are relevant for human and animal health. The U.S. Department of Homeland Security (DHS) working dogs provide critical security and detection services across the country, and many train or work in the southern United States, where they are at risk for T. cruzi exposure. We sampled blood from 1,610 working dogs (predominantly Belgian Malinois, German shepherds, and Labrador retrievers) from six task forces (including the Transportation Security Administration, Customs and Border Protection, Secret Service, and more) and two canine training centers across 41 states from 2015 to 2018. Canine sera that were reactive on at least two independent serological assays were considered positive for anti-T.-cruzi antibodies. In addition, up to three independent polymerase chain reaction (PCR) assays were used to detect and type T. cruzi DNA. Overall seroprevalence was 7.5%, and four dogs (0.25%, n = 1,610) had detectable parasite DNA in the blood, comprising parasite discrete taxonomic units (DTUs) TcIV and a coinfection of TcI/TcIV. Dogs that worked within versus outside of the geographic range of established triatomines showed comparable seroprevalence (7.3% and 9.2%, respectively; P = 0.61). Determining the prevalence of T. cruzi in these working dogs and looking at spatially associated risk factors have practical implications for disease risk management and could assist with improved control measures to protect both animal and human health.

Risk factors and select cardiac characteristics in dogs naturally infected with Trypanosoma cruzi presenting to a teaching hospital in Texas.

BACKGROUND: Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, causes sudden death and chronic heart disease with no currently approved treatment. OBJECTIVE: To report epidemiologic and select cardiac characteristics associated with T. cruzi infection in dogs presenting to a teaching hospital in Texas. ANIMALS: Three hundred seventy-five client-owned dogs. METHODS: A retrospective search of medical records identified dogs tested for T. cruzi antibodies or with histologic T. cruzi parasites. Data retrieved included signalment, location of residence, reported reason for testing, cardiac troponin I (cTnI) concentration, and ECG abnormalities. RESULTS: Trypanosoma cruzi-infected dogs (N = 63, 16.8%) were significantly younger than negative dogs (N = 312) (mean, 5.9 ± 3.8 versus 7.4 ± 4.0 years; P = .007) with no difference by sex or breed. Ninety-one breeds were tested; the highest percent infected were non-sporting (10/35; 29%) and toy breed (10/42; 24%) groups. The odds of infection were 13 times greater among dogs with an infected housemate or littermate (95% confidence interval [CI], 3.94-50.45; P < .001). Infected dogs were more likely to have ventricular arrhythmias (odds ratio [OR], 2.19; 95% CI, 1.15-4.33, P = .02), combinations of ECG abnormalities (OR, 2.91; 95% CI, 1.37-5.99; P = .004), and cTnI >0.129 ng/mL (ADVIA; OR, 10.71; 95% CI, 1.60-212.21; P = .035). CONCLUSIONS AND CLINICAL IMPORTANCE: Dogs infected with T. cruzi were identified in Texas in many breed groups including breeds affected by well-described heart diseases that mimic Chagas disease suggesting a need for increased awareness, including knowledge of when to consider testing.

Parasitic interactions among Trypanosoma cruzi, triatomine vectors, domestic animals, and wildlife in Big Bend National Park along the Texas-Mexico border.

National parks attract millions of visitors each year. Park visitors, employees, and pets are at risk of infection with various zoonotic pathogens, including Trypanosoma cruzi, causative agent of Chagas disease. Big Bend National Park is located along the Texas-Mexico border in a region with endemic triatomine insects- vectors of T. cruzi- yet the degree to which the parasite is transmitted in this region is unknown. We collected triatomines for T. cruzi detection and discrete typing unit (DTU) determination, and conducted blood meal analyses to determine recent hosts. As an index of domestic/peridomestic transmission, we tested residential dogs in the Park for exposure to T. cruzi. From 2015 to 2017, 461 triatomines of three species-Triatoma rubida, Triatoma gerstaeckeri, and Triatoma protracta-were collected in and around the Park. Adult triatomine encounters peaked in June of each year (52.8% of collections). We detected an overall infection prevalence of 23.1% in adult triatomines (n = 320) and 4.2% in nymph triatomines (n = 24). DTU TcI was the only T. cruzi strain detected. Of 89 triatomines subjected to blood meal analyses, vertebrate host DNA was successfully amplified from 42 (47.2%); blood meal sources included humans, domestic animals, and avian and mammalian wildlife species. Tested dogs were considered positive if reactive on at least two independent serologic assays; we found 28.6% seroprevalence in 14 dogs. These findings reveal interactions between infected triatomines, humans, dogs, and wildlife in and around Big Bend National Park, with potential risk of human disease.

Daily activity patterns of movement and refuge use in Triatoma gerstaeckeri and Rhodnius prolixus (Hemiptera: Reduviidae), vectors of the Chagas disease parasite.

Transmission risk for vector borne disease is greatest during periods of heightened vector activity. Triatomine bugs (Hemiptera: Reduviidae), which transmit Trypanosoma cruzi, the causative agent of Chagas disease, are generally considered nocturnal, but their patterns of activity in controlled settings have rarely been studied. We quantified activity patterns across a 24-hour period in nymphs of two triatomine species: (1) Triatoma gerstaeckeri Stål, a North American triatomine which is closely associated with sylvatic and peridomestic hosts, and (2) Rhodnius prolixus Stål, a Central and South American triatomine that thrives in the domestic environment. T. gerstaeckeri showed activity throughout the night, with peaks around midnight, 3:00, and again around dawn. Refuge use was highest in the pre-dawn hours then again after the dawn activity peak. We hypothesize that the dawn activity peak may represent a period of host seeking for this sylvatic species that targets nocturnal hosts returning to their home at dawn. In contrast, R. prolixus displayed high activity near 23:00 and again around noon. This study provides a baseline understanding of diel activity for future behavioral experiments and identifies periods of time that may represent the greatest risk of host exposure to triatomines and T. cruzi.

Maintenance of Trypanosoma cruzi, T. evansi and Leishmania spp. by domestic dogs and wild mammals in a rural settlement in Brazil-Bolivian border.

Domestic dogs are considered reservoirs hosts for several vector-borne parasites. This study aimed to evaluate the role of domestic dogs as hosts for Trypanosoma cruzi, Trypanosoma evansi and Leishmania spp. in single and co-infections in the Urucum settlement, near the Brazil-Bolivian border. Additionally, we evaluated the involvement of wild mammals' in the maintenance of these parasites in the study area. Blood samples of dogs (n = 62) and six species of wild mammals (n = 36) were collected in July and August of 2015. The infections were assessed using parasitological, serological and molecular tests. Clinical examination of dogs was performed and their feeding habits were noted. Overall, 87% (54/62) of sampled dogs were positive for at least one trypanosomatid species, in single (n = 9) and co-infections (n = 45). We found that 76% of dogs were positive for T. cruzi, four of them displayed high parasitemias demonstrated by hemoculture, including one strain types TcI, two TcIII and one TcIII/TcV. Around 73% (45/62) of dogs were positive to T. evansi, three with high parasitemias as seen by positive microhematocrit centrifuge technique. Of dogs sampled, 50% (31/62) were positive for Leishmania spp. by PCR or serology. We found a positive influence of (i) T. evansi on mucous pallor, (ii) co-infection by T. cruzi and Leishmania with onychogryphosis, and (iii) all parasites to skin lesions of sampled dogs. Finally, feeding on wild mammals had a positive influence in the Leishmania spp. infection in dogs. We found that 28% (5/18) coati Nasua nasua was co-infected for all three trypanosamatids, demonstrating that it might play a key role in maintenance of these parasites. Our results showed the importance of Urucum region as a hotspot for T. cruzi, T. evansi and Leishmania spp. and demonstrated that dogs can be considered as incidental hosts.

Widespread Trypanosoma cruzi infection in government working dogs along the Texas-Mexico border: Discordant serology, parasite genotyping and associated vectors.

BACKGROUND: Chagas disease, caused by the vector-borne protozoan Trypanosoma cruzi, is increasingly recognized in the southern U.S. Government-owned working dogs along the Texas-Mexico border could be at heightened risk due to prolonged exposure outdoors in habitats with high densities of vectors. We quantified working dog exposure to T. cruzi, characterized parasite strains, and analyzed associated triatomine vectors along the Texas-Mexico border. METHODOLOGY/PRINCIPLE FINDINGS: In 2015-2016, we sampled government working dogs in five management areas plus a training center in Texas and collected triatomine vectors from canine environments. Canine serum was tested for anti-T. cruzi antibodies with up to three serological tests including two immunochromatographic assays (Stat-Pak and Trypanosoma Detect) and indirect fluorescent antibody (IFA) test. The buffy coat fraction of blood and vector hindguts were tested for T. cruzi DNA and parasite discrete typing unit was determined. Overall seroprevalence was 7.4 and 18.9% (n = 528) in a conservative versus inclusive analysis, respectively, based on classifying weakly reactive samples as negative versus positive. Canines in two western management areas had 2.6-2.8 (95% CI: 1.0-6.8 p = 0.02-0.04) times greater odds of seropositivity compared to the training center. Parasite DNA was detected in three dogs (0.6%), including TcI and TcI/TcIV mix. Nine of 20 (45%) T. gerstaeckeri and T. rubida were infected with TcI and TcIV; insects analyzed for bloodmeals (n = 11) fed primarily on canine (54.5%). CONCLUSIONS/SIGNIFICANCE: Government working dogs have widespread exposure to T. cruzi across the Texas-Mexico border. Interpretation of sample serostatus was challenged by discordant results across testing platforms and very faint serological bands. In the absence of gold standard methodologies, epidemiological studies will benefit from presenting a range of results based on different tests/interpretation criteria to encompass uncertainty. Working dogs are highly trained in security functions and potential loss of duty from the clinical outcomes of infection could affect the work force and have broad consequences.