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EHV-1 Warning: 2 Cases Reported in California

Two cases of equine herpes myeloencephalopathy (EHM) have been confirmed in California, June 2015. EHM is a neurological disease that is caused by an infection of the equine herpes virus (EHV-1). The infections have been traced back to the Bishop Mule Days celebration in Bishop, California. Both infected horses have since been euthanized and their respective counties, Riverside and San Joaquin, have been placed under state-ordered quarantine, restricting the transportation of horses within them.

Though these cases occurred a safe distance from Alberta, the EHV-1 virus has appeared in our province several times before. These cases should serve as a reminder of the importance of adhering to standard equine biosecurity principles in order to reduce the risk of infection and contain its spread, should the need arise. EHV-1 is not federally controlled and can therefore cross borders via infected horses and spread without warning. While some treatments may protect from the viral infection, there is no vaccine available for the neurological form of the disease

Possible visible symptoms of an EHV-1 infection are listed below. If any of your horses are displaying a combination of the following symptoms, quarantine the animal and contact your veterinarian immediately:

  • fever
  • weakness
  • incoordination
  • urine dribbling
  • inability to urinate


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Equine Canada (details of last outbreak in Alberta, spring 2011)