Zecca Jr., Italo Balbo (2019-07). A ONE HEALTH APPROACH TO STUDY THE EPIDEMIOLOGY OF TRYPANOSOMA CRUZI IN HUMANS, DOMESTIC ANIMALS, AND WILDLIFE IN THE RIO GRANDE VALLEY OF TEXAS ALONG THE UNITED STATES-MEXICO BORDER. Doctoral Dissertation.
Thesis
This dissertation focused on a One Health approach to assess the prevalence of Trypanosoma cruzi in south Texas. We sampled from humans, domestic animal, and wildlife populations of south Texas to understand the seroprevalence and the ecology of parasite transmission in an area where infected vectors are present. In 2015 we conducted a cross- sectional prevalence study in indigent, medically underserved human and cohabiting canine populations of seven south Texas border communities, known as colonias. Defining positivity as those samples that were positive on two or more independent tests, we found 1.3% seroprevalence in 233 humans, including one child born in the United States with only short-duration travel to Mexico. Among 209 dogs, seroprevalence was 19.6%, but adjusted to 31.6% when including those dogs positive on only one test and extrapolating potential false negatives. Parasite DNA was detected in five dogs, indicating potential parasitemia. In 2016-2019, a cross-sectional study was conducted to quantify the prevalence of T. cruzi in owned dogs, including both measures of anti-T. cruzi antibodies and parasite DNA circulating in the blood. Through serological testing of 340 dogs using three different tests, we identified 110 (32.4%) dogs that showed positivity on at least two independent antibody tests. Using PCR assays, 10 of 300 (3.3%) dogs showed parasite DNA in their blood. In 2017, we collected samples from 100 wild opossums and 167 cats across three seasons that were euthanized in a south Texas animal shelter for reasons unrelated to our study. Samples were screened for T. cruzi DNA using qPCR to amplify the 166-bp gene region with confirmation of positive status achieved through one or more additional PCR assays, including a qPCR to determine the parasite discrete typing unit (DTU). Of 100 opossums, parasite DNA was found in blood clot (9%), heart tissue (10%), and anal gland secretions (12%). The 43 of these opossums with expanded sample collection showed infection in 16.3% of intercostal muscle and 11.6% of anal gland tissue. In total, 15 (15%) opossums had at least 1 infected tissue type, of which 9 (9%) had two or more different tissue types that tested positive. Through serological testing of 167 cats from 14 south Texas regions that arrived to a large shelter, 19 cats (11.4%) were seropositive on at least two independent tests. Three cats- of which two were seropositivehad at least one PCR-positive tissue (1.8%); infected tissues included heart, bicep femoris muscle, sciatic nerve, mesentery, and esophagus. Histopathology identified pathology, like lymphoplasmacytic inflammation, consistent with T. cruzi infection. In 2018 and 2019, we received ocelot tissues from salvaged animals that were installed in the Biodiversity Research & Teaching Collections at Texas A&M University and Gladys Porter Zoo; carcasses were collected following death primarily by vehicle collision from 2010-2017 around Laguna Atascosa National Wildlife Refuge in South Texas. T. cruzi DNA was detected in samples of two different ocelots (9.5%) with infection found in skeletal muscle and blood clot. Samples where the parasite discrete typing unit (DTU) was successfully ascertained showed exclusively 'TcI', the T. cruzi strain associated with autochthonous human disease in the US. Under a one-health framework, the identification of infection in humans, domestic animals, and wildlife is a critical prerequisite to developing public health interventions in south Texas and underserved border communities.
