Kiehl, Whitney (2021-01). Horizontal and Vertical Transmission Excluded as Primary Causes of Trypanosoma cruzi in Rhesus Macaques (Macaca mulatta) Housed Within a Texas Breeding Colony. Master's Thesis.
Thesis
Trypanosoma cruzi (T. cruzi) is a kinetoplasid protozoan parasite that infects both invertebrates and vertebrate hosts during its life cycle and is the causative agent for Chagas disease. Triatomine insects (kissing bugs) serve as vectors of T. cruzi and are distributed across the Americas including the southern United States. Kissing bugs feed on diverse wild animals, domestic animals, and humans, and hundreds of wild mammals serve as reservoirs of T. cruzi in nature. Across the southern US in regions where kissing bugs occur, biomedical research facilities housing non-human primates (NHPs) have increasingly been faced with T. cruzi infections among the NHPs, presenting major concerns for both the integrity of the animal models and for animal welfare. For this project, we tracked a population of T. cruzi seropositive rhesus macaques (Macaca mulatta) housed in an outdoor breeding colony in Texas to determine the potential for horizontal and vertical transmission. We determined the physical location of each seropositive animal within the colony at the time of their infection and also identified all animals housed with seropositive animals, including any offspring of seropositive dams. The animals housed with seropositive animals were deemed to be T. cruzi-associated monkeys (TAMs). The serostatus of all TAMs was determined through medical records or from the testing of archived banked serum samples. These serological data, along with spatial analyses of the seropositive and seronegative animals over time, were used to look for associations between animals that could support horizontal transfer, vertical transfer, or implicate environmental factors in the transmission of T. cruzi with the colony. A total of 80 breeding colony animals housed between 1999 and 2018 were identified to be seropositive for T. cruzi antibodies. From these 80 animals, 688 individual TAMs were identified to have interacted in a total of 925 animal-to-animal association events during the period covered in this study. These events were explored through the use of husbandry records, PCR, and identification of different discrete typing units (DTUs) to look for the potential of vertical and horizontal transmission within the colony. In review of the data related to the possibility of vertical transmission, there were 54 breeding-age, seropositive females identified in the colony that collectively produced 196 offspring. None of the offspring from these dams were found to be seropositive suggesting that vertical transmission either does not occur or is a rare event within this colony. In review of the data related to the possibility of horizontal transmission, it was found that horizontal transmission of T. cruzi may have occurred in as many as 25 of the 925 (2.70%) associations between na?ve and seropositive animals, and that horizontal transmission may be the route of infection for as many as 25 of the 80 (31.25%) seropositive animals within the colony. These last two values are interpreted to represent the maximum number of horizontal transmission events that could have possibly occurred within the colony between 1999 and 2018, as these data are the result of a study-design that favored sensitivity over specificity, with regard to its inclusion of animals that were suspected to have become infected through horizontal transmission. Despite the fact that these values are likely overestimates of horizontal transmission within the colony, it is notable that even these data suggest horizontal transmission accounts for less than one-third of all T. cruzi infections and that horizontal transmission appears to be a very inefficient means of T. cruzi infection. Spatial analysis using the location of the T. cruzi seropositive animals at the time of their seroconversion was undertaken to identify potential spatial clusters (hot spots) of infections within the colony and to determine if there were aspects of the environment that influenced the incidence of infection
