Infection with the vector-borne parasite Trypanosoma cruzi, the pathologic agent of canine Chagas disease, has remained a significant concern to dog owners for decades. Infections with T. cruzi are highly problematic for three reasons: 1) a significant percentage of dogs infected with T. cruzi will develop Chagas disease and eventually die of heart failure; 2) there is currently no validated treatment for Chagas disease in dogs; and 3) despite decades of research there is currently no definitive data to explain why some T. cruzi-infected individuals develop Chagas disease while others remain asymptomatic for life. Vector-borne pathogen coinfections have routinely been identified in animals. Recently there has been increased appreciation as to the role that pathogen coinfections play in altering the clinical outcomes of other well-recognized diseases/syndromes (e.g., Lyme disease). Interestingly, despite the immensity of the research into Chagas disease progression, there has been essentially no focus on the possibility that differences in Chagas disease manifestation between individual patients could be the result of coinfections. This research study will try and ascertain if the clinical manifestation of disease for individual T. cruzi-infected dogs is affected by coinfections with other vector-borne pathogens. To investigate this possibility, investigators will utilize an archived set of longitudinally-collected biological samples and heart-health data obtained from a previous study (CHF grant No. 02448) in which 40 T. cruzi-infected dogs and 24 T. cruzi-uninfected dogs in 10 Texas kennels were observed over a one-year period. If vector-borne pathogen coinfections are a key factor in disease progression, then it may be possible to treat T. cruzi-infected dogs with inexpensive and readily available antibiotics/antiparasitic drugs to prevent the lethal manifestations of Chagas disease.