ARCHIVE: Equine Viral Arteritis
If you suspect signs of any notifiable disease, you must immediately notify your local Animal Health Office.
- Latest situation
- Code of practice
- What is EVA?
- How does the infection spread?
- How is the disease diagnosed?
- How is EVA treated?
- EVA Vaccine
- Pre-vaccination blood test
Equine viral arteritis (EVA) was confirmed in (i) a stallion in Staffordshire on 2 August 2010 and (ii) a stallion in West Sussex on 8 December 2010.
Breeding restrictions were put in place on the infected stallions in each case and investigations were begun, to establish the likely origin of the infection, as well as any mares that may have been affected. The disease is being controlled in line with the industry agreed Horse Betting Levy Board (HBLB) Codes of Practice.
There are no human health implications associated with this disease.
In the UK, Equine Viral Arteritis (EVA) is a disease which is notifiable by law under The Equine Viral Arteritis Order 1995 made under section 88 of the Animal Health Act 1981.
Under the Order, anyone who owns, manages, inspects or examines a horse must notify their local Animal Health office when:
- they suspect the disease in a stallion, either on the basis of clinical signs or following blood or semen testing;
- they suspect disease, either on the basis of clinical signs or following blood testing, in a stallion or mare that has been mated or artificially inseminated within the past 14 days.
Full details of the exact notification requirements are in the EVA Order 1995.
Under the Order, Defra may:
- serve notices prohibiting the use for breeding of the suspect stallion and any semen obtained from it unless permitted under licence by a veterinary inspector, or an inspector acting under the direction of a veterinary inspector;
- take samples or obtain information in order to establish whether disease is present and, if so, the extent to which it has spread.
The Code of Practice produced by the Horserace Betting Levy Board sets out recommendations for horse breeders for the prevention and control of diseases during the breeding season. It also sets out measures to control infected horses. Any occurrence of this disease in the UK will be controlled in line with the industry-agreed HBLB Code of Practice.
Equine Viral Arteritis (EVA) is a contagious disease caused by the equine arteritis virus (EAV). The virus occurs worldwide including mainland Europe.
There are no human health implications associated with this disease.
There is also no risk from this disease to species other than equidae.
A. Routes of infection - All horses
Infection spreads through transmission of the virus between horses in 4 main ways:
- venereal infection of mares by stallions during mating
- artificially inseminating mares with semen from infectious stallions
- contact with aborted foetuses and other products of parturition
- direct contact in droplets from the respiratory tract (e.g. through coughing and snorting)
B. The Shedder Stallion
Stallions can pose a significant risk of disease transmission if undetected. On infection, the virus localises in his accessory sex glands and the virus may be “shed” i.e. excreted it in his semen, for several weeks afterwards, or for many months or years, and possibly for life. After recovery from acute illness, his fertility is not affected and he will show no further clinical signs of infection even though he may still be infectious. Shedder stallions will infect susceptible mares during mating, or after insemination with the stallion's semen, and these mares may, in turn, infect in-contact animals through either mating or via the respiratory route.
It is important to note that the shedder stallion is always seropositive (ie past or existing infection indicated in a blood test) but that a seropositive stallion is not necessarily a shedder.
Breeders using artificial insemination (AI) must note that the virus can survive in chilled and frozen semen.
Teasers are also a potential source of the virus and should be subjected to the same precautions as stallions.
Available evidence indicates that the 'carrier' state does not occur in mares, i.e. mares can become infected, and be infectious, but they are not believed to remain infectious for a long time, either continuously or intermittently.
The variety and severity of clinical signs of EVA vary widely. Infection may be obvious or there may be no signs at all. Even when there are no signs, infection can still be transmitted and stallions might still become shedders.
EVA can cause abortions. Other signs include fever, depression, lethargy, stiff movement, runny nose, conjunctivitis, (‘pink eye’), swelling of the lower parts of the legs, around the eye and of the reproductive organs.
Because of the variability or the possible absence of symptoms, clinical diagnosis is not always possible. Laboratory diagnosis is therefore essential. This requires appropriate samples, which are nasopharyngeal swabs, heparinised or EDTA blood, semen, serum and possibly urine, to be taken by a veterinary surgeon and sent to a specialist laboratory. In blood samples, laboratories look for antibodies to the virus (serological test); in both blood and semen samples, they look for the virus itself (virus isolation (VI) tests).
Where abortion may be EVA-related, detailed clinical information must be sent to the laboratory with the foetus and its membranes.
In addition to the VI test, PCR testing may be used to provide an initial indication of EAV (equine arteritis virus) in semen.
There is no treatment available for EVA itself, although there may be treatments to alleviate some of its symptoms. These should be determined by the attending veterinary surgeon.
A licensed vaccine (Artervac, Fort Dodge) is available in the UK and Europe, but with different national restrictions on use. Consult your veterinary surgeon on uses allowed in your country. In the UK, the vaccine can be used in all horses and ponies over nine months of age. It should be used as per the datasheet, which recommends booster vaccination every six months.
It is important to note that vaccinated horses will become seropositive and this cannot be distinguished from true infection. You discuss such vaccination with your veterinary surgeon and obtain advice that is relevant to the use of your horse. Horses should be blood tested before vaccination to show that they are likely to be free of infection at the time of vaccination, and vaccination must be maintained unbroken every six months thereafter; otherwise additional laboratory testing will be needed to distinguish positive test results that are due to vaccination from those that may be due to infection.
Details about the prior blood test and the vaccination, both primary and booster, should be recorded in the horse's passport.
If the passport includes a section titled Laboratory Health Test, details about the test should be recorded in that section by a veterinary surgeon.
If the passport does not include a section titled Laboratory Health Test, or the horse does not have a passport, the following records, certified by a veterinary surgeon, should be kept:
- Date when the pre-vaccination blood sample was taken.
- Type of test.
- Certificate from the laboratory showing the blood test result, and the identity of the laboratory that carried out the test.
Details should be recorded by a veterinary surgeon in the section of the passport titled Vaccinations Other Than For Equine Influenza. The details are the date and place when the vaccination was given, and the name and batch number of the vaccine.
If these details cannot be entered in a passport, a record of the same details, certified by a veterinary surgeon, should be kept.
A post-vaccination blood sample may be taken to confirm seroconversion as a result of either primary or booster vaccination. The same records as set out above for pre-vaccination tests should be kept.
The above records are important as evidence of previous seronegativity for breeding and export purposes. Some importing countries require this information for vaccinated horses, either in passports or official export certificates.
For official export certification purposes, samples for EVA blood testing must be sent to a Government laboratory, i.e. the Veterinary Laboratories Agency, Addlestone.
As the vaccine's efficacy is not yet fully known, owners should monitor the horse's antibody response after vaccination, in consultation with the veterinary surgeon.
Vaccination is only one part of disease prevention; owners should read the HBLB codes of practice for advice. Biosecurity an important part of good management and owners should not breed from horses or use semen of unknown EVA and CEM status.
Following the advice as set out in the HBLB Code of Practice remains essential to prevent EVA infection in horses.
Page last modified: August 2, 2010