EVA Protocol

Protocol for Testing Stallions for Persistent Equine Arteritis Virus Infection
Screening of Horses for Research Purposes and for Breed Registry Requirements by P. J. Timoney and Dr. Balasuriya.

Facts about Equine Viral Arteritis (EVA) / Equine Viral Arteritis Testing

• EVA testing is mandatory for all activated stallions.
• Batches of frozen semen should also be tested.
• Equine Viral Arteritis (EVA) is an acute upper-respiratory tract infection caused by a specific herpes virus that may also cause abortion. The disease affects members of the horse family and is characterized by high fever, nasal discharge and edema in limbs.
• Persistence of the virus or the carrier state can occur in a significant percentage of infected stallions but not in mares, geldings or sexually immature colts. Equine arteritis virus localizes in certain of the accessory sex glands in the reproductive tract and is discharged in the semen of carrier stallions at the time of breeding.
• Carrier stallions shed the virus constantly in the semen, but not in the respiratory secretions or urine, nor has it been detected in the white cells of these animals. The virus can be transmitted by the venereal route to susceptible (antibody negative) mares. Infectivity of EVA is preserved in refrigerated or frozen semen and the disease can be spread through the use of fresh-cooled or frozen semen.

Screening a Stallion for the Carrier State

• Serological Testing: The stallion should first of all have his blood tested for the presence of neutralizing antibodies. If the sample is negative (titer <1:4), then there is no need to test the stallion for presence of the virus in his semen.
• Virus Isolation from Semen: If a stallion tests positive for EVA (titer 1:4 or greater) in the blood, the semen should be tested for the presence of the virus.
• The serological test for equine viral arteritis is usually put up on Tuesday of every week and the final result read on Friday of the same week. Because of the demand for the test, please contact Ms. Kathy Shuck (859-257-4757, ext 81170) to confirm when the lab is able to test the sample(s) you may wish to submit.

Blood or semen should be sent to:
Ms. Kathy Shuck
Maxwell H. Gluck Equine Research Center
Department of Veterinary Science, University of Kentucky
Lexington, KY 40546-0099

Ph: 859-257-4757, Fax: 859-257-8542

EVA Testing and Prevention Protocol
Guidelines for breeding a mare to an EVA shedding stallion

• The mare should be tested for serum neutralizing antibodies to EVA at least 30 days prior to breeding. A blood sample should be submitted to a veterinary medical diagnostic laboratory approved by the USDA to conduct the serological test. Based on the results, the following procedures are recommended.

Antibody Negative - Non-pregnant Mare

• If the mare is serologically negative, she should be vaccinated as soon as possible with the modified live virus vaccine against EVA*. After vaccination, she should be isolated for 21 days to allow her time to develop adequate protective immunity against subsequent exposure and to prevent the minimal risk of spreading the vaccine virus to any susceptible horses with which she might come into contact. Twenty-one days following vaccination – but not earlier - the mare may be bred to a shedding stallion.
• Twenty-one days following vaccination, the mare may be bred to a shedding stallion. She should not be bred to a shedding stallion during those 21 days.
• After being bred for the first time to a shedding stallion, the mare should be isolated for 21 days from any horses that are serologically negative for antibodies to the virus. Subsequent breedings do not require an additional period of isolation.
• Occasionally a mare may be vaccinated against EVA, but is not bred to a shedding stallion that year. In that case, the mare should be revaccinated before being bred to a shedding stallion. No isolation is necessary following re-vaccination.

Antibody Negative - Pregnant Mares

• The modified live virus vaccine against EVA* is not approved for use in pregnant mares.
• A mare that is in good health may be vaccinated after foaling. However, a mare that has had a complicated foaling, or is otherwise not in good health, should not be vaccinated until she has regained her health. The foal should also be in good health and at least two weeks old before its dam is vaccinated. There is minimal risk that foals out of serologically negative mares may be exposed to the vaccine virus when the mare is vaccinated against EVA.

Re-vaccination

• Mares that will be bred to shedding stallions should receive an annual booster vaccination against EVA 21days prior to breeding. No isolation is necessary following re-vaccination.

Antibody Positive - All Mares

• Mares that test serologically positive can be bred to a shedding stallion without the need for prior vaccination against EVA.

Guidelines for Breeding Stallions

• Prior to the breeding season (at least 60 days is recommended), the stallion should have his blood tested for EVA neutralizing antibodies.

Antibody Negative (titer less than 1:4)

• If serologically negative, the stallion should be vaccinated with a licensed modified live vaccine against EVA* and isolated for 30 days after vaccination. An annual booster vaccination against EVA should be given on a regular basis every 12 months but no sooner than 30 days prior to being used for breeding.

Antibody Positive (titer 1:4 or greater)

• If the stallion is found serologically positive for EVA serum neutralizing antibodies, without written evidence certifying his negative serological status prior to vaccination, he needs to be tested for presence of the carrier (shedding) state. This can be determined by either one of the following methods:
• Attempted isolation of equine arteritis virus from two separate ejaculates collected and submitted to a laboratory approved by the USDA to conduct this test;

• Test breeding the stallion to 2 serologically negative mares at least twice on each of two consecutive days (four covers) and the mares checked for the development of serum antibodies to the virus 28 days after breeding.

Antibody Positive Non-shedding Stallions

• Serologically positive stallions with written certification of negative antibody status against EVA prior to vaccination need not be tested for virus shedding.
• Serologically positive stallions for antibodies from natural exposure that have previously been tested and found to be non-shedders should have written confirmation of their non-shedder status and receive an annual booster vaccination.

EVA Antibody Shedding Positive Stallions

• Shedding stallions can be used for commercial breeding provided they are managed in accordance with the above guidelines.
• Stallion owners and stallion managers should disclose the shedding status of their stallions to mare owners, breed associations and, where required, to state authorities.
• Shedding stallions can be safely bred to adequately immunized mares or to mares that have tested serologically positive for neutralizing antibodies to equine arteritis virus.
• Occasionally, shedding stallions will spontaneously stop shedding the virus. Owners may wish to retest the semen of shedding stallions from time to time to determine if the stallion is still shedding the virus.

Other Recommendations
Teaser Stallions

• Teaser stallions should be vaccinated annually against EVA in accordance with this protocol.
• Identification of Carrier (shedding) Stallions
• It is recommended that breed associations publicly disclose the names of those stallions registered with their breed association that are confirmed shedders of EVA.

Prevention of the Carrier State

• Breeding stallions that are found serologically negative for antibodies to equine arteritis virus should be vaccinated against EVA to prevent the development of the carrier state.
• In order to prevent the carrier state as well as to prevent equine arteritis virus infection, colts under 270 days of age that are serologically negative for antibodies to the equine arteritis virus should be vaccinated against EVA. Written certification of their negative serological status to equine arteritis virus should be obtained before vaccination.

Use of Modified Live Vaccine against EVA*

• It is essential to have written official certification of a horse’s negative serological status to EVA prior to initial vaccination against this disease.
• Mares that will be bred to shedding stallions should receive an annual booster vaccination against equine arteritis virus prior to being used for breeding purposes.
• *ARVAC®, Ft. Dodge Laboratories, Ft. Dodge, Iowa

American Horse Council
The testing and prevention protocol was developed by the EVA Working Group of the AHC and was published in May of 1997. The AHC recommends adoption of this protocol as part of good breeding practice. The protocol provides a practical and realistic approach that permits the use of shedding stallions or infected semen.