Echocardiographic evaluation of horses challenged with African horse sickness virus

Abstract

African horse sickness (AHS) is an infectious, often fatal viral disease of equids with a severe impact on the equine industry in sub-Saharan Africa. Clinicopathological mechanisms are poorly understood, and there is limited information on the degree and type of cardiac involvement. This study followed four horses experimentally infected with African horse sickness virus (AHSV) as part of a vaccine trial to describe echocardiographic changes during the course of the disease. Echocardiography was performed once prior to infection, and daily from infection to humane euthanasia of each subject. Both objective and subjective (eFoCUS) evaluations of all appropriate echocardiographic variables were performed. An increase in diastolic myocardial thickness and a decrease in the size of the left cardiac chambers during diastole and systole were consistent findings on the last day of evaluation of each subject and suggestive of hypovolaemia. The cause of the suspected hypovolaemia was not investigated, but increased vascular permeability causing third space volume loss was considered the most likely cause, as this is associated with the disease process. During the eFoCUS evaluation substantial and perfect interobserver agreement were found for an increase in myocardial thickness and diminution of the left ventricle, respectively, suggesting that these variables could be used to subjectively evaluate intravascular volume in clinical cases in an emergency setting. In addition, perfect interobserver agreement for impaired diastolic dysfunction, and almost perfect agreement for pericardial effusion, was found during the eFoCUS evaluation of the final data sets for each subject. Further studies are needed to objectively define the presence, quantify the severity, identify the cause and significance of these findings.