Horse News & Views - October 2004

Ministry of Agriculture, Food and Rural Affairs

Ontario Association of Equine Practitioners

• Eastern equine encephalitis (EEE) and West Nile virus (WNV) infections can both cause neurological disease in humans and horses. Both viruses are spread by mosquitoes. Horses serve as a sentinel for these diseases since they are often exposed 12 to 24 hours per day and are highly susceptible to these diseases. Clinically, it is difficult to differentiate between the two viral infections. An Ontario government surveillance project is currently underway to increase the reporting and testing of horses with neurological signs. As of September 13th, six cases of WNV were diagnosed. Four cases occurred in the North Bay-Sudbury area, one in the Bracebridge area and one is possibly an imported case. No cases of EEE have been found.
  
  
• Potomac horse fever (PHF) causes severe illness (diarrhea and colic) and death in approximately 30% of infected horses. Potomac horse fever is caused by the rickettsial agent Ehrlichia risticii and is maintained in nature in a complex aquatic ecosystem involving immature and adult caddisflies. These caddisflies spend part of their life cycle in water and then hatch and fly onto pastures. Transmission to horses is thought to occur through accidental ingestion of these insects while grazing pastures. The disease is observed more commonly in some geographic areas than others; it occurs in Eastern Ontario (Brighton to Kemptville) and just below Lake Simcoe (Keswick) more than other areas of the province. However, cases have recently been diagnosed in the Ancaster area of the province.
  
  

• Studies have shown that heating and molding of hay during storage is decreased with the use of buffered acid preservatives. When given the choice of dry hay or preservative-treated hay, horses preferred the dry hay. However, when only given treated hay, daily consumption did not decrease. The preservatives, when used properly, allow the storage of hay at a moisture content level of up to 30%.

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