Meyers, Alyssa Catherine (2019-07). DOG-VECTOR-PARASITE INTERACTIONS IN THE CHAGAS DISEASE SYSTEM: CARDIAC CLINIC STATUS OF NATURALLY-INFECTED DOGS ACROSS THE US. Doctoral Dissertation.
Thesis
In the southern U.S., triatomine vectors maintain Trypanosoma cruzi- the protozoan parasite that causes Chagas disease in humans and animals- in sylvatic cycles. Infection with T. cruzi may be asymptomatic or lead to heart disease and death. Using dogs as a model host system, our objectives were to improve the ecological and clinical understanding of Chagas disease in the U.S. We collected 461 triatomines from Big Bend National Park from 2015- 2017 and found an overall infection prevalence of 23.1%. Blood meal analysis on 42 triatomines showed DNA evidence of humans, domestic animals, wild birds and mammalian wildlife. In 2015-17, we sampled 1,660 working dogs from 43 states using three independent serology assays to detect a seroprevalence of 7.3% (CI: 6.1-8.6%). To better characterize the cardiac outcomes in T. cruzi-infected dogs we applied a 24-hour Holter monitor to 17 T. cruzi-infected, 18 uninfected dogs and 4 dogs with discordant serology results. The presence of ECG abnormalities varied by T. cruzi infection status (p<0.001) and positive dogs had higher serum concentrations of cardiac troponin I (cTnI), a biomarker for cardiac injury, than both negative dogs (p=0.044) and discordant dogs (p=0.06). Finally, we performed a retrospective study looking at 375 dogs presented to a teaching hospital in Texas. T. cruzi-infected dogs (N=63, 16.8%) were significantly younger than negative dogs (N=312) (mean 5.9 vs. 7.4 yr old respectively; p=0.0069) with no difference in infections by sex or breed. Infected dogs were more likely to have ventricular arrhythmias (28.6%), combinations of ECG abnormalities, and cTnI greater than 0.129 ng/mL (ADVIA assay). Combining ecological and clinical approaches to enhance our understanding of Chagas disease should provide insight for vector control and measures to protect veterinary and public health.
