Pathology of fatal natural African horsesickness virus infection in dogs

Abstract

African horsesickness (AHS) is a highly fatal arthropod-transmitted viral disease affecting mainly equids. Dogs are known to contract fatal AHS by ingestion to AHS-infected horse meat. At the Section of Pathology, Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria a number of canine mortalities with no history of horse meat consumption have been diagnosed since 2006. Limited published information describing the pathological findings in AHSV-infected dogs however exists. This study is a retrospective survey focussing on providing a full macroscopic, histologic (including immunohistochemistry) and ultrastructural description of the pathological changes observed in dogs naturally infected by AHS virus. Clinically most dogs presented with severe dyspnoea that deteriorated rapidly and terminated in respiratory failure and death. Some of the dogs had a history of lethargy and anorexia of less than 24 hours. Macroscopically the most significant lesions were observed in the thoracic cavity and characteristically included severe acute interstitial pneumonia associated with mild serofibrinous pleuritis and moderate mediastinal oedema. Histopathologically the pulmonary findings included severe protein rich alveolar and septal oedema with randomly scattered areas of haemorrhage. In addition, acute inflammatory changes were present, characterised by mononuclear interstitial pneumonia and alveolar exudation, with hyperactivation of the alveolar capillary endothelial cells, alveolar macrophage proliferation and moderate diffuse hyperaemia. Immunohistochemical labelling revealed AHSV-specific positive labelling of the microvascular endothelial cells as well as scattered mononuclear leukocytes (monocytes and macrophages). The ultrastructural changes observed were supportive of vascular injury similar to those observed in horses infected by AHSV. The pathological findings observed in all cases were indicative of acute pulmonary inflammation of haematogenous origin, resulting in fatal immune- and pathogen induced vascular injury.