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Equine viral arteritis (EVA) is a highly contagious venereal disease affecting horses. This infection is relatively widespread in Europe but we have precautions in place in the UK to prevent it.

If UK breeders fail to comply with the Horserace Betting Levy Board (HBLB) guidelines, EVA could get in to this country and cause havoc to our breeding industry.

EVA is caused by a virus and is spread between horses in four ways:

• Through venereal contact between mare and stallion at mating
• Through droplets from the respiratory tract, spread by coughing and close contact between horses
• From stallion to mare through infected semen at AI
• Contact with aborted foetuses, fluids and placentas of mares which aborted due to EVA.

About 30% of infected stallions never eliminate the infection and remain as persistent shedders, spreading it for the rest of their lives. Alarmingly, many of these show no outward signs and their fertility is unaffected.

Mares mated or inseminated by a shedder will be infected and may become ill themselves. The virus may cause abortion in pregnant mares and severe respiratory disease in foals. There is no cure for EVA.

In an alarming outbreak in Leicestershire in 1993, a sport horse stallion was imported from Poland apparently with clear documentation that was later said to be incorrect. He arrived one autumn, covered his first mare next spring and infected her.

She in turn spread the infection to other mares, which were subsequently covered by other stallions on the stud, which also became infected. Artficial insemination caused further spread and soon more than 100 horses had EVA.

The consequences of EVA

The consequences were devastating for the individual stud and alarming for the whole equine industry. Careful control measures stopped that outbreak and other subsequent cases, but in the UK horses have little immunity and are at risk of developing the disease should the virus be imported again.

Although mares and geldings can be infected, only stallions are potential long-term shedders of the EVA virus. So the greatest risk to the British horse population is from importation of either an EVA-infected stallion or his semen. Those stallions could then go on to infect many more mares via breeding activities. There is also a risk that a mare or youngstock with EVA but few, if any, clinical signs might enter a stud and infect the stallions via the respiratory route.

Official import controls may be insufficient to prevent the disease coming in, particularly if documentation is inadequate and, as is usual, a stallion appears healthy. Breeders must be responsible and ensure their horses are safe, especially if they choose to import a breeding prospect. Anyone importing a stallion should ensure he is tested, even if they have no intention of breeding from him at that time.

Clear guidelines have been devised by the HBLB within its standard codes of practice to prevent further EVA outbreaks. These codes have been effective in stopping the disease in its tracks in this country so far.

The need for testing

The difficult concept to grasp is that the horse can look well but still be infected and be a spreader or shedder of disease. It is important that all stallions and mares are thoroughly screened each season before breeding starts. The precautions recommended are straightforward and logical.

Breeding stallions and teasers in the UK should be blood tested for EVA after 1 January but before mating, teasing or collecting semen. The results should be recorded in the horse’s passport. The risk with mares can vary, but the safest thing is to blood test prior to sending them to stud or for insemination to ensure they are clear. Ask your vet about the most appropriate action for your case.

Particular care should be taken if importing horses, semen or equine embryos. EVA virus survives in chilled and frozen semen and is not affected by the antibiotics added. Specialist veterinary advice should be taken before proceeding. In general:

• Before any importation, blood samples should be taken and sent to a recognised laboratory, not necessarily in the country of origin of the horse
• When a horse arrives from abroad, it should be isolated for 21 days
• A vet should take blood samples after arrival
• If semen is imported, blood test results for the stallion at the time of semen collection should be properly checked. A straw of the frozen semen should also be tested. This is called the “one straw” test
• Stallions that compete abroad can be infected at any time by the respiratory route, even if they do not cover mares while travelling.

What if EVA is confirmed?

If EVA is confirmed, you will have to stop breeding operations, seek immediate veterinary advice and inform DEFRA because EVA is a notifiable diseases in certain circumstances.

By following the HBLB guidelines rigorously and responsibly, we can avoid problems that the equine industry can well do without.

• This veterinary feature was first published in Horse & Hound (26 January, ’06)Looking for more articles on equine venereal diseases?View broodmares for sale near you

In 1977 — long enough ago to be nearly forgotten, but important enough to remember — a serious outbreak of an infectious form of equine venereal disease (VD) occurred in Newmarket and rapidly spread among nearby stud farms. The cause was a previously unidentified bacterial infection known as contagious equine metritis (CEM).

The key features of this condition are in the name — contagious means it is infectious, the equine bit is obvious and metritis means inflammation of the lining of the mare’s uterus or womb, which is the area attacked by the bug.

Contagious equine metritis is horse VD, so it is transmitted from broodmare to stallion or vice versa at mating. A teaser may also spread it, if they are allowed close contact with a mare. There is a risk of CEM being transmitted to mares through artificial insemination (AI), if the semen used comes from infected stallions. Infection can also be spread by people handling infected horses, so hygiene is important. Foals born to infected mares may also pick up the infection at birth and the disease is highly contagious.

The difficulty in controlling CEM is that infected stallions do not appear to have anything wrong with them. In mares, the severity of the infection varies: some appear normal; others will have an obvious dirty vaginal discharge, which usually shows two to seven days after mating. In the Newmarket outbreak, many mares showed obvious signs of infection, but this is not always so. Any mare coming into season early or breaking early in her cycle should be viewed with suspicion.

Affected mares have a reduced chance of conceiving during the acute phase of the disease. If an infected mare that is not in-foal is covered again, she may spread the infection to the stallion. He will infect other mares he covers and so it goes on — a depressing downward spiral of reduced fertility and serious disruption to breeding operations. The disease can have serious economic consequences.

Preventing CEM

To control the spread of CEM, the Horserace Betting Levy Board (HBLB) set up an advisory committee, which developed codes of practice for prevention of this and other infections. This code is revised and republished annually and has been effective in controlling outbreaks.

One outbreak of CEM was detected by swabbing a warmblood stallion in Somerset in spring last year. Prompt action and careful checking of other horses in contact with the stallion controlled it, so restrictions were lifted in May rather than the infection disrupting the whole stud season nationally, which could have happened.

More recently a mare in Oxfordshire tested positive to the notifiable disease contagious equine metritis (CEM). The mare had been imported from Germany. A movement order has been placed on her stables, and an investigation is under way to establish whether she has been used for breeding in the UK.

For CEM and other bacterial venereal infections, it is impossible to tell by looking at a horse whether they carry infection, so a scientific system of taking swabs has been devised. Your vet will be able to advise if your mare is a high or low risk. You should ask your vet to take the appropriate swabs from any horses used for breeding every year after 1 January but before any teasing or mating starts.

These swabs are sent to laboratories specially designated and checked by the HBLB. The swabs need to be tested within 48hr, hence you should avoid having it done on Fridays or weekends, when delays are more likely. It takes almost a week to produce the results, so do not leave it until the last moment. The results will be returned on an official laboratory certificate, which is this year coloured blue with a 2006 background.

Owners should not send any mare to a stallion unless he has an up-to-date negative CEM certificate. Stallion owners should not accept mares unless they have up-to-date negative certificates. If a case of CEM is confirmed, the stud must stop breeding operations, seek immediate veterinary advice and inform DEFRA because CEM is a notifiable disease.

Careful control, proper testing and good hygiene measures reduce the risk of an outbreak. If these guidelines are followed rigorously and responsibly by all involved with British horse breeding, then such problems can be avoided.

This information formed part of a breeding feature in Horse & Hound (26 January, ’06)

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Florencio, the reigning five-year-old World Champion dressage stallion, is to undergo a revolutionary treatment in Germany after testing positive for Equine Viral Arteritis (EVA).

The six-year-old Westfalian, currently standing at Kathmenn Stud in Vechta, Germany, has been used extensively across Europe. Last year, he covered approximately 500 mares, the majority by artificial insemination, and had been expected to cover even more in 2005.

EVA is a worldwide infectious disease. It can cause abortion in broodmares, as well as illness and sudden death in foals, and there is currently no known proven treatment. EVA is notifiable in the UK and Ireland (it has to be reported to DEFRA), so EU legislation should prevent importation of Florencio’s semen or an inseminated mare to the UK.

“Florencio tested positive in December when we were freezing semen for Holland and Germany,” explains Jeanette Nijhof, whose family stud owns two-thirds of the stallion. “So we tested him on an EVA negative mare of our own. Within 15 days of covering, she was positive, so he is definitely shedding [transmitting the disease].”

The family is attempting to treat the stallion — treatment is virtually unheard of before now.

“We’re trying a treatment from Prof Geise in Germany, who claims to have made five stallions negative again,” says Jeanette. “If all goes to plan, Florencio will be negative in May. If it works, it’ll be a revolution — the treatment is top secret, he won’t even tell us how it works.”

Although Florencio is off limits to British breeders — who are already inquiring about using the stallion — Jeanette estimates that 40-50% of the mare population in Holland is EVA positive. So if the treatment does not work, Florencio “may breed with them without risk,” according to Jeanette.

Vet Karen Coumbe says: “This just highlights the risks of getting EVA in the UK. Anyone importing semen or using a stallion from the continent must be very careful to ensure they do not bring the disease into Britain.”

Dr Richard Newton of the Animal Health Trust confirms that there are no known cures for the virus in Britain and no plans to research treatment in the UK, but adds: “In theory, you might be able to ‘chemically’ castrate horses — the carrier status of a stallion is dependent on testosterone — or take the virus out of the semen, as is possible with HIV in humans.”

This news article was first published in Horse & Hound (3 March, 2005)

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Concerns have been raised that cases of equine viral arteritis (EVA), a disease that can cause foals to be aborted or born weak, may be at risk of going undetected in Britain. A recent incident suggests that some of the tests less experienced laboratories are using to detect the disease are not stringent enough.

A horse owner in Devon, David Paddon, questioned the reliability of the new commercially available test, known as ELISA, after receiving contradictory lab results for a broodmare.

Paddon’s vet Marcus Langer explains: “The mare has shown a low level of antibodies [with the traditional test] for the past three years. This year the ELISA test came up negative, so I asked the lab to send it away to do the traditional test, which showed the significant level of antibodies. My concern is that the ELISA is not sensitive enough and like any test that is not totally accurate, may have serious implications.”

EVA is contagious and is spread via the respiratory system or, more usually, by artificial insemination or natural covering. Infected animals may show flu-like signs but some appear normal.

Infected stallions can “shed” the virus in their semen, and, because there is no effective treatment, a lifelong “shedder” becomes worthless.

A positive antibody test may indicate current or previous infection or earlier vaccination against the disease. The presence of antibodies does not necessarily mean that an animal is infectious to other horses.

Screening has traditionally been done using a Virus Neutralisation (VN) test, recommended by the World Organisation for Animal Health (OIE) and available at only three labs in the UK. A new ELISA test kit is now more widely available, but is not yet validated by the OIE.

Dr Richard Newton of the Animal Health Trust, which performs both VN and ELISA tests, says: “The VN test is not without its problems, and there has been pressure from the equine industry to introduce a quicker, more reliable test, which is why the ELISA has been developed. The European OIE EVA reference laboratory is presently evaluating all available EVA ELISA tests.

“Our concern relates to the use of commercial test kits that have not been properly validated because unpublished data suggests considerable variation in sensitivity between ELISAs.”

Horse & Hound asked Dr Peter Webb of Axiom in Devon, the lab which tested David Paddon’s mare, whether the failure to identify low levels of EVA antibodies could potentially lead to horses in the early stages of infection going undiagnosed.

“Theoretically, yes,” he replied. “But that’s the same with any serological test [involving blood serums].

“This horse was below the level detected by the ELISA, which means it is not worthy of further investigation. When we [sent off for] the more sensitive test, [antibody levels] showed up as being very low.”

Reproduction expert Jonathan Pycock, who wrote recently of the dangers of EVA in H&H, says: “EVA is a tremendous concern to the breeding industry. If it arrived in the UK it would spread very quickly.”

EVA occurs globally and although there have been few recent cases in the UK, where it is notifiable, there was an outbreak in Ireland last year. EVA testing is highly regulated in the thoroughbred industry, but unless a horse is being exported or imported (when it must, by law, be tested by DEFRA), there are no strict rules for the rest of Britain’s horses.

This news story was first published in Horse & Hound (30 September, ’04)

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The Horserace Betting Levy Board issued a warning this week to all horse breeders to maintain a high level of vigilance to avoid infectious diseases in the 2005 breeding season.

The recommendations for increased awareness in the equine breeding industry come as a result of recent cases of contagious equine metritis (CEM), a uterine infection of mares which results in temporary infertility in Britain, and cases of equine viral arteritis (EVA), a virus which may cause abortion or pregnancy failure in broodmares, in Ireland.

Isolated cases of equine herpes virus in Kent and the South West caused a degree of panic earlier this year – the most common strain of the virus, EEHV-1 can cause respiratory problems, abortion in pregnant mares and in rare cases paralysis. Libby Archer, HBLB Scientific Liaison Executive explains however, that the disease can be prevented “by appropriate management and strict attention to hygiene, as well as through the use of the EHV vaccination.”

All three are highly infectious conditions, which can cause widespread reduced fertility and serious disruption to breeding operations, in particular amongst the thoroughbred population in which the permitted covering season is short.

John Parker FRCVS, Chairman of the advisory committee responsible for the HBLB’s codes of Practice, said “recent cases of CEM in the UK and EVA in Ireland highlight the need for all breeders, regardless of the breed or type of horse they produce and whether they are using natural cover or artificial insemination, to implement the disease prevention measures in the codes.

“Outbreaks of CEM, EHV and EVA can have serious consequences, and it is the responsibility of all breeders to follow the Codes to safeguard their own and other horses, and stud activity generally,” he added.

Libby Archer agrees that all horse owners “have a great responsibility not only to their own horses, but also to other horses.

“One of the most important things in the instance of an outbreak of any of these diseases is communication with any horse owners whose animals may have been exposed to the disease,” she explains.

The code, the HBLB stresses, only provides minimum recommendations for breeders, although as CEM and EVA are notifiable diseases, Defra would step in and impose statutory measures in the event of an outbreak. EHV on the other hand, is not notifiable, but owners are advised to minimise the spread of the disease through self-imposed movement restrictions and by following the HBLB’s Code of Practice.

• For copies of the Codes (free of charge) contact the Horserace Betting Levy Board, 52 Grosvenor Gardens, London SW1W 0AU, tel: 020 7333 0043, stating your name, address and how many copies you want.

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The increasing traffic of sport horses around the world, particularly in the breeding season, means that the British horse industry needs to be extremely vigilant about equine viral arteritis (EVA), which is a highly contagious viral disease.

The virus causes a flu-like illness involving:

• fever
• depression
• swelling (especially of the limbs)
• inflammation around the eyes

It also causes weak foals or abortions, usually in the latter half of pregnancy.

Infection and diagnosis

Unusually, EVA can be spread by either a stallion with infected semen or in the air via the respiratory secretions of a recently infected horse, through close or direct contact.

After an average incubation period of seven days, EVA is shed in all bodily secretions for up to 21 days (possibly longer in urine). The virus may persist indefinitely in the stallion. Venereal transmission is believed to be the major cause of spreading the virus.

Particularly alarming is the fact that an infected stallion may shed the virus in his semen for the rest of his life. Also, the virus can be preserved in fresh, chilled or frozen semen and spread by artificial insemination. The fertility of shedder stallions is not affected and they show no clinical signs, but they can infect mares during mating or through artificial insemination.

A definite diagnosis cannot be made without lab tests because the clinical signs are vague. Tests can isolate the virus from nose and throat swabs, blood, urine or semen samples. Evidence of EVA exposure can be found by taking an initial serum sample as soon as possible after signs appear, followed by a second sample 10–14 days later to detect a rise in the EVA antibody levels.

Testing and treatment

In the UK, the two main risks are EVA-infected stallions which are shedding the virus in their semen, and semen imported from shedding stallions.

Stallions which have been used for breeding or have been competing overseas and are returning to the UK for breeding activities should be tested on their return and not be used until the results are known.

Two blood samples are taken at least 14 days apart and sent to a DEFRA-approved laboratory for testing and the stallion isolated during this time. If the results indicate no exposure to the virus (seronegative), breeding may proceed.

If the stallion shows evidence of exposure to the disease (termed seropositive), DEFRA should be informed and further tests done to confirm that the stallion is not shedding. Many stallions can be seropositive for EVA, but if they are not shedding it in the semen, there is no problem.

Vaccination will cause a stallion to be seropositive and this is why it is vital to have the blood tested negative before vaccinating him. The negative result should be certified and recorded by a vet in the passport before administering the vaccine.

UK-based stallions should also be blood tested every year to monitor their EVA status, and should be vaccinated whenever a suitable, proven vaccine is available. A killed vaccine (Artervac, Fort Dodge Animal Health) is available in the UK and is now widely used here. Certain countries will not accept the importation of seropositive animals.

Mares imported from overseas should be blood tested within 28 days of import. The mare should be isolated for three weeks on arrival, with blood tests carried out immediately and repeated at least two weeks later. Many studs in the UK are requiring confirmation that mares are negative for EVA prior to arrival at stud. This would be the preferable option for control.

At present, there is no effective treatment for a chronically infected stallion. Such animals can remain persistently infected with the virus in the reproductive tract for variable amounts of time, from several months to a period of years and, in some cases, the lifetime of a particular stallion. There is no evidence that mares, geldings or foals which acquire the infection congenitally become carriers.

EVA risks in Britain

The virus is found throughout the world, but its prevalence varies between countries. In mainland Europe, it is widespread, resulting in high horse population immunity and low-grade signs of disease.

Except for a controlled outbreak in 1993, the UK has been relatively free from EVA. This means that, in contrast to mainland Europe, the UK horse population has little immunity to the disease and the consequences if the virus were imported again could be catastrophic.

In countries with a high prevalence of the virus, the horse population eventually gains immunity to the disease, which may explain why breeders in some countries adopt a different, more relaxed attitude to EVA, but this wouldn’t work in the UK.

In Britain, EVA is a notifiable disease, which means that, by law, anyone who owns, manages or examines a horse must notify DEFRA if they suspect it may be infected.

Health papers

• There are health regulations relating to semen import, and it is best that these papers, certifying that the stallion or semen has tested negative for EVA, accompany any shipment of semen.
• There is a possibility that the stallion could have been exposed to EVA between the negative test and semen collection. This means that breeders and importers of semen should do their very best to check that any imported semen complies with health regulations and is free from EVA.
• Familiarise yourself with health papers — information can be downloaded from the DEFRA website (www.defra.gov.uk) or from local animal health divisional offices. Don’t be the one who brings EVA into the UK!
• Breeders must take responsibility for reducing the risks of importing contaminated semen. With imported chilled semen, the only safeguard possible is to ask the agent supplying the semen for evidence of the stallion’s EVA status at the time of collection.Further information about EVA and its prevention is available in:
• The Horserace Betting Levy Board (HBLB) Code of Practice, updated annually
• Equine Viral Arteritis: an information leaflet on protecting the UK horse population from this disease. This leaflet was issued jointly by the HBLB and the British Equine Veterinary Association (BEVA)
• The BEVA Code of Practice for The Use of Artificial Insemination in Horse BreedingThis article first appeared in Horse & Hound (24 June, ’04)Looking for more articles on equine venereal disease?View broodmares for sale near you

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Horse breeders and vets have been alerted to a case of contagious equine metritis (CEM) which can make stallions and broodmares infertile.

DEFRA say its vets are now tracing any mares covered by the infected stallion from a yard in Wiltshire and any semen collected from it.

The UK has been free of the disease since 1998.

Mark Collins from the British Equine Veterinary Association said: “It’s disappointing that there’s been this case as we have very strict controls in this country, with all mares being routinely swabbed.

“But it’s good that it has been picked up outside the breeding season. Hopefully, if all the contacts are found, it won’t go any further.”

According to DEFRA, the owner of the stallion will be expected to take measures to prevent and control the spread of the disease, including isolating the infected stallion and stopping and mating or collection of semen until it’s been established that the infection has cleared up.

In a statement, the organisation said: “We would expect the current outbreak to be controlled using the Code of Practice but are prepared to be more directly involved, using the statutory measures, if appropriate.”

STOP PRESS

DEFRA has now confirmed a second case of CEM. It’s been found in a mare that had been covered by the infected stallion.

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