Characterization of arrhythmias, evaluation of cardiac biomarkers and their association with survival in calves suffering from foot-and-mouth disease

Introduction: Foot-and-mouth disease (FMD) causes mortality in calves due to myocarditis; however, the effects of FMD virus on cardiac arrhythmogenesis and Purkinje cells are unknown. Identifying diagnostic and prognostic markers in FMD-affected calves may be useful in disease management in the endemic countries.

Materials and methods: A total of 81 FMD-affected calves were prospectively monitored till death or recovery. Foot-and-mouth disease was diagnosed by serology and reverse transcriptase-polymerase chain reaction (RT-PCR). Electrocardiography was recorded and serum cardiac biomarkers were measured. Histopathological examination of the ventricular myocardium was carried out in the calves that died of FMD (n = 33). Apparently healthy calves (n = 15) served as control.

Results: Serology and RT-PCR consistently revealed that the FMD was caused by serotype O virus. Arrhythmias occurred in 62 of 81 (76.5%) FMD-affected calves, of which, ventricular premature complexes (VPCs) were the most common type (22%). The combined mortality rate due to ventricular tachycardia, polymorphic VPCs, and atrial fibrillation was 27.6%. Receiver operating characteristic curve analysis revealed that cardiac troponin I (cTnI) concentrations of ≥1.3 ng/mL were diagnostic of myocarditis with a sensitivity and specificity of 90% and 100%, respectively. Similarly, serum cTnI concentrations of <6.4 ng/mL were a good predictor of survival [odds ratio of 263; 95% confidence interval: 29-2371]. Histopathology of the myocardium revealed hyaline degeneration, necrosis, edema, mononuclear cell infiltration, and disruption by fibroblasts. Atrophy of the Purkinje cells was also present.

Conclusions: FMD induces cardiac arrhythmias and Purkinje cell pathology in the calf. Portable ECG coupled with assay of serum cTnI would help in predicting survival in FMD-affected calves.