New Equine Herpes Virus Cases in California Traced to Bishop Mule Days

Two horses euthanized after contact with horses and mules that had been at event
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California EHV barn equine herpes virus

Show management for the 47th Annual Bishop Mule Days Celebration, held over Memorial Day in Bishop, California, had an important message for their exhibitors last week. 

More than three weeks after the show had ended, horses and mules that were on the grounds of the event have scattered throughout the country. Show management, however, wants their owners to know that two horses on properties in California located hundreds of miles apart have been euthanized after contact with horses and mules returning from Bishop.

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"Bishop Mule Days Celebration was recently informed of three isolated cases of the EHV-1 virus. All three cases were animals owned by competitors that attended the 2015 event.The Mule Days bio security team has been working closely with those affected and the State of California Veterinarian’s office.

"Mule Days would like you to know that protecting the health of our competitors’ animals is of the utmost importance. Mule Days follows animal health and bio-security guidelines established by the California Department of Food and Agriculture (CDAF) and California State University Davis." (Note: the show is probably referring to the University of California at Davis School of Veterinary Medicine.)

On June 16, CDAF reported on the first two cases: 

"A 12-year-old Quarter Horse (QH) gelding and a 12-year-old mule, originating from Riverside County, attended Mule Days in Bishop, CA, from May 17-26, 2015. After returning home, the QH gelding spiked a fever of 106 F on May 30th and exhibited neurologic signs on June 4th and confirmed positive for the non-neuropathogenic strain of EHV-1.

"The 12-year-old mule never spiked a fever and began coughing on June 2nd but showed no other clinical signs.

"An 8 year old QH gelding who did not attend Mule Days but was a cohort to the 12-year-old QH and mule became ill on June 4th exhibiting a high fever and severe incoordination with his hind limbs. His condition deteriorated and was euthanized on June 10th. He was affected with the neuropathogenic strain of EHV-1.

"The 12-year-old QH gelding and mule are recovering with treatment provided by the owner’s private veterinarian. The affected premises is home to 19 horses and mules and at this time there are no other affected equids on this property. The owner has been monitoring temperatures 2X/day on all of the horses and mules for the past two weeks. This premises is under CDFA quarantine."

Note: Riverside County is east of the metropolitan Los Angeles region.

CDFA learned on June 18th about another case with links to Mule Days:

"A 13-year-old Quarter Horse mare residing in San Joaquin County was confirmed positive for Equine Herpes Myeloencephalopathy (EHM). This mare did not attend Mule Days in Bishop, CA from May 17-26, 2015 but was exposed to two cohort mules after they arrived home from Mule Days. The mules were asymptomatic for EHV-1.

"The QH mare exhibited symptoms compatible with EHV-1 beginning on June 5th including lethargy, fever, stocking up of her hind limbs and severe incoordination in her hind limbs. The mare was euthanized on June 14th. She did test positive for the neuropathogenic strain of EHV-1.

"The affected premises is home to 10 horses and mules and at this time there are no other affected equids on this property. The owner has been monitoring temperatures 2X/day on all of the horses and mules. This mare had not received any EHV-1 vaccinations in the past two years. This premises is under CDFA quarantine."

Note: San Joaquin County is located east of the San Francisco-Oakland metropolitan area.

These are the first cases of EHV in California reported by CDFA since March. 

What CDFA doesn't mention is that some animals present at this particular event come from very remote sections of mountainous areas where they work in pack trains. Getting word to their keepers will be difficult. Accessing veterinary care for a sick animal in remote areas would also be difficult.

CDFA is advising all horses to use caution when traveling with horses and to practice biosecurity measures to protect their horses.

Primary recommendations include:

  • Limit horse-to-horse contact.
  • Limit horse-to-human-to-horse contact.
  • Avoid use of communal water sources.
  • Avoid sharing of equipment unless thoroughly cleaned and disinfected between uses.
  • Monitor your horse for clinical signs of disease and report any temperature over 102°F to a veterinarian.