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Update on EHV-1 Situation in Maine

May 11, 2007

Contact: Donald E. Hoenig, VMD
207-287-3701, 207-624-5044

Quarantine restrictions, which had been placed on the horses at a Rome, Maine stable due to infection with equine herpes virus type 1, neuropathogenic strain (EHV-1), have been lifted on nine of 10 horses. The 10th horse remains in isolation pending the results of further testing to be performed on or after May 17, 2007. Since the outbreak of EHV-1 in mid-March at the Rome stable and another stable in Wales, no further cases of the disease have been reported to the Maine Department of Agriculture.

I’m continuing to strongly recommend that tracks, agricultural fairs and equine training facilities in Maine require that all horses entering their facilities be vaccinated for EHV (rhinopneumonitis) and equine influenza, not more than six months or less than 14 days before entry. Proof of vaccination should be listed on the Certificate of Veterinary Inspection (required for all horses entering the State of Maine) or on a certificate of vaccination signed by the owner’s practicing veterinarian. (Please remember that any horse entering the State also needs to have a negative Coggins test within the previous 12 months). Although at this time there is no EHV-1 vaccine that has a label claim for protection against the neurologic strain of EHV-1, the rationale for vaccinating is to reduce viral shedding in the event that a horse is exposed to the virus. According to an April 2, 2007 article in The Horse Report, a publication of the Center for Equine Health at the University of California, Davis, School of Veterinary Medicine, “While this approach [vaccination] does not guarantee protection of individual horses against the potentially fatal neurological form of EHV-1, the hope is that reduced nasal shedding of infectious EHV-1 by vaccinated horses will indirectly help protect other horses by reducing the dose of virus to which they are exposed”. This may also help in minimizing the spread of the disease in an exposed population. This article also goes on to stress the importance of strict biosecurity in the prevention and control of this disease.

This outbreak of EHV-1 affected two stables in Maine and killed three of four horses that were infected with the virus and exposed 18 other horses at those stables, all of whom have remained healthy. For those individuals whose animals and livelihoods were affected by this disease, this has been an extremely stressful and upsetting time. For everyone involved in the equine industry in Maine, this situation has also created much anxiety, many questions and a thirst for accurate, timely information.

A question that has emerged this week now that most restrictions have been lifted from both farms concerns the status of exposed or previously infected animals. An article written by Dr. George Allen of the Gluck Equine Research Center at the University of Kentucky which appeared in Equine Veterinary Education in 2002 addresses this question. Quoting Dr. Allen, “There are no available data to indicate that horses that have recovered from infection caused by epidemic or paralytic strains of EHV-1 pose any greater risk for infection of susceptible horse populations than a random assortment of animals.”

All previous postings from the Maine Department of Agriculture can be seen on the Department’s website at: http://www.maine.gov/agriculture/ or on the Division of Animal Health and Industry website at: http://www.maine.gov/agriculture/ahi/diseases/index.html#EHV1