The association of Ehrlichia canis infection with myocardial injury in canine populations is still unclear. Highly sensitive and specific cardiac biomarkers, such as cardiac troponin I (cTnI), may help elucidate this association. This study evaluated blood analyses, electrocardiograms (ECGs), ultrasounds, and cTnI values from dogs with natural tick exposure in a Brazilian population. A total of 194 dogs were evaluated for clinical illness. Study exclusions were trauma, previous cardiac disease, or antirickettsial treatment. Clinically healthy dogs (n = 24) were selected as controls. Groups were defined on the basis of E canis positivity, antibody testing, and polymerase chain reaction (PCR). Systemic inflammatory response syndrome (SIRS) was defined on the basis of clinical criteria. Higher cTnI concentrations were detected in E canis–infected dogs than in control dogs. Myocardial injury was associated with acute E canis infection, and risk for myocardial injury was associated with decreased packed cell volume. The packed cell volume was significantly lower in E canis–infected dogs, suggesting that anemia severity was associated with an increased risk for cardiomyocyte damage due to myocardial injury. Median cTnI concentrations in dogs with SIRS were higher than in those without SIRS, and greater risk for myocardial injury was identified in dogs with SIRS. Dogs with severe ECG abnormalities had higher cTnI concentrations than dogs with less severe changes, and all dogs with severe ECG changes were infected with E canis. These results suggested that acute E canis infection was a risk factor for myocardial damage in this population. SIRS and anemia were additional morbidity factors contributing to myocardial injury and damage. Study supported in part by the Waltham Foundation and IDEXX Laboratories.

COMMENTARY:
Any study with naturally infected animals inherently has issues with uncontrolled factors, but it is clear that being infected with Ehrlichia caused dogs to have myocardial damage—detected in most cases not only with elevations in cTnI but also with ECG changes. The damage appears to be caused early in the disease because the highest cTnI values were in dogs infected with E canis that had not yet seroconverted. Studies such as this cannot confirm causal relationships and thus should be interpreted with caution and confirmed with other experimental designs. However, myocardial damage should be considered in dogs infected with E canis.—Patricia Thomblison, DVM, MS

Serum cardiac troponin I concentration in dogs with ehrlichiosis. Diniz PPVP, de Morais HSA, Breitschwerdt EB, Schwartz DS. J VET INTERN MED 22:1136-1143, 2008.