West Nile virus encephalomyelitis in horses: 46 cases (2001).

This research study examined the signs, diagnosis results, treatment options, and outcomes of horses with West Nile virus (WNV) encephalomyelitis. From the findings, it was observed that more male horses were affected than females and that despite treatment, most of the horses had residual problems up to a year after release from the hospital.

Objective of the Study and Methods Used

• The main goal of this research was to study the symptoms, diagnostic test results, treatment approach, outcome, and postmortem findings in horses infected with the West Nile virus (WNV) leading to encephalomyelitis (a neurological condition that involves inflammation of the brain and spinal cord).
• The research was conducted retrospectively on 46 horses that had been diagnosed with WNV encephalomyelitis.
• Information related to each case was extracted from medical records of the respective horses.

Results and Findings

• Out of 56 horses with clinical signs pointing towards Central Nervous System (CNS) issues, 46 were diagnosed with WNV encephalomyelitis. More males were affected than females.
• The most common symptoms noted among the affected horses were raised rectal temperature, muscle weakness or lack of coordination (ataxia), and muscle spasms (fasciculations).
• It was observed that partial paralysis (paresis) was more common than ataxia, and both of them could have varying severity and distribution across the body.
• For treatment, the veterinarians primarily administered anti-inflammatory medications and fluids, prescribed antimicrobial medications, and used slings to support horses unable to stand on their own.
• IgM capture Enzyme-Linked Immunosorbent Assay (ELISA) and Plaque reduction neutralization tests were used for diagnosis. Of the 46 horses, 43 were diagnosed via both tests, while 3 were diagnosed solely through the plaque reduction neutralization test.

Outcome and Post-Treatment

• The mortality rate was dishearteningly high at 30%, and 71% of those unable to stand were euthanized. Worryingly, a horse previously vaccinated against WNV still contracted the disease and had to be euthanized.
• Follow-up communication with owners showed that most of the horses exhibited lingering health issues a month after being released from the hospital. However, these issues had resolved in all but two horses one year after release.

Conclusions

• The findings of this study corroborate previous research on WNV encephalomyelitis outbreaks in horses but contribute additional details about the clinical course of treated, hospitalized patients.
• The study emphasizes the importance of proper diagnostic testing for identifying affected horses.
• It was observed that treatment is mainly supportive and does not ensure full recovery, as evident from the lingering deficits observed in discharged horses.