Equine encephalitis caused by snowshoe hare (California serogroup) virus.

The study aims to report the observation of a clinical case of equine encephalitis caused by the snowshoe hare virus (SSH) in Western Canada and describes the disease progression.

Background

• The SSH virus, a mosquito-borne Qbunyavirus of the California-serogroup, is found all over Canada.
• Serological studies revealed various exposure rates in horses towards the California serogroup antibodies.
• Despite high levels of seroprevalence, only one report was produced in association with clinical disease caused by the SSH virus before this study.
• This study thus reports a second case of the clinical infection and the seroconversion to the SSH virus which was found in an eleven-month-old Quarter Horse filly.

Clinical history of the horse

• The horse was bought by its current owners at an auction two months prior to it showing symptoms of the disease.
• The filly shared a pasture with healthy horses, had access to water from a slough and was fed a diet of brome and alfalfa hay.
• The filly’s illness started the day before the owners brought it to the Western College of Veterinary Medicine (WCVM).
• Initial symptoms included losing balance, falling multiple times, nodding off and overreaching her muzzle when offered water. It deteriorated until after 36 hours, the horse was brought in for professional medical attention.

Clinical Findings

• Upon presentation, the filly weighed 338 kg and was reported to be in poor to moderate condition.
• It was found to be tense and anxious, with frequent muscle spasms in groups. The muscles of the head and neck were most affected.
• Generalized hyperesthesia was prevalent, and the horse seemed to have difficulty moving.
• Hopping on both forelimbs and hindlimbs was delayed. Raising the horse’s head did not affect its balance but turning the head often led to a wide-based stance.
• Mild leukocytosis was observed, with significant lymphocytes found in the CSF. The CSF protein level was slightly elevated.

Assessment

• The horse was determined to have multifocal or diffuse lesions in the central nervous system, affecting the cerebellar and cerebral cortices, brain stem, and cranial nerve nuclei possible.
• Nonsuppurative inflammation and neuronal necrosis consistent with viral encephalitis was found through the clinicopathological analysis.
• Preliminary treatment with antibiotics and tetanus antitoxin was carried out.
• A potential diagnosis of Rabies was ruled out due to the absence of obscuring clinical signs by corticosteroids.