Clinical signs and clinical pathology findings in horses with equine encephalosis at the Onderstepoort Veterinary Academic Hospital, South Africa

Abstract

Introduction: Equine encephalosis is a systemic disease of horses caused by equine encephalosis virus. This virus is an Orbivirus that is transmitted by biting midges (Culicoides species). Equine encephalosis is often reported as a subclinical infection with a relatively limited number of clinical cases showing predominantly fever, with minimal morbidity and mortality. Rare instances of neurological disease have also been associated with the virus. Clinical relevance: Information regarding the clinical presentation of equine encephalosis is underrepresented in current scientific literature. This study aims to contribute to a more detailed conceptualization of the significance of the disease and its clinical impact. Method: A retrospective, descriptive, observational study was performed on data obtained from the University of Pretoria’s clinical database for cases identified with equine encephalosis over the period 2013-2023. Data from the history, clinical signs and clinicopathological findings were analysed. The clinical presentation and clinicopathological findings are reported. Results: A total of 28 horses conformed to the study parameters as having clinical infection with equine encephalosis virus. Pyrexia was apparent in 89.2% of these cases. Other clinical findings included tachycardia (64.3%), tachypnoea (46.4%), colic (39.3%), neurological signs (21.4%), peripheral oedema (14.3%), and icterus (10.7%). Evaluation of the clinicopathological findings identified lymphopenia (86.7%), thrombocytopenia (76.0%), leukopenia (48.0%), immature neutrophilia (31.8%), and mature neutropenia (27.3%). Conclusion: Equine encephalosis can result in a wide variety of clinical signs in horses and is associated with changes in haematology variables. These haematological changes suggest a systemic response to the viral infection. Further research into the pathophysiology of equine encephalosis is required to better understand the disease and its clinical relevance.