Equid Blog : Horse Health & Diseases : University of Guelph : Ontario Veterinary College : Equine Infectious Diseases

Hard to believe that the whole conundrum about contagious equine metritis (CEM) that is still affecting the Canadian equine industry started a little bit more than a year ago, when a Quarter Horse stud in Kentucky tested positive for the causative agent, Taylorella equigenitalis. Tracing the contacts of that stud lead to the quarantine and testing of 990 horses in 40 states, as well as 19 mares in Canada, including 9 in Ontario. Out of 274 exposed stallions, 22 were ultimately found to be positive, none of which had any detectable clinical signs that they were infected, meaning if they hadn’t been tested, they may have kept on going about their business breeding – and possibly infecting – mares for years to come. The rest of the exposed horses were mares, five of which turned out to be infected. One particularly interesting fact was that four of these mares had been bred by artificial insemination - previous to this it was thought that CEM was only readily transmissible by live cover from an infected stud, not via semen shipped in a straw.

Thankfully all of the Canadian mares were negative, but unfortunately the Canadian equine industry is still suffering the consequences of what has happened to our close southern neighbour. Fourteen countries have increased import requirements for Canadian (and obviously US) horses in terms of CEM testing, and another major blow was the loss of Canada’s low-risk status with the UK's Horserace Betting Levy Board (HBLB).

Canada must maintain strict import requirements for horses to prevent CEM from getting into the country. Most of the horses imported into Canada come from CEM-positive countries, and it’s getting more difficult to argue not including the US on that list as well. The risk is constantly present, and remaining diligent about quarantine and testing – and rules like ensuring horses are not on antibiotics for some other reason when they’re cultured – is key. Semen import restrictions for semen coming from the US to Canada will stand for 2010. While this certainly causes a headache for breeders, requiring an import permit and a health certificate for the stud stating that it has not stood on a CEM-quarantined farm, is it enough to protect Canadian horses? The next step would be to require all studs to be tested for CEM before their semen can be imported to Canada. That is no small request. Testing a stud involves culturing the stud himself, and then having him test-breed two mares which then also need to be culture-negative. Anecdotally the entire process can cost in the neighbourhood of $5-7K per horse, which at the moment all needs to be borne by the horse owner. That gives you some idea of what an enormous undertaking it was to quarantine and test 274 exposed stallions during last year’s outbreak.

In the US, 87% of exposed horses have now been cleared, and there have been no new positives in the last 8 months. However, there are still 17 states where there are quarantined farms. There is talk of voluntary testing of over 2000 studs in the US in 2010, as well as targeted surveillance of stallions imported in the last 10 years and those standing at large AI centers. Only time will tell if these extra efforts will serve to calm the fears of countries that are now hesitant to import horses and semen from the US, or whether they will reveal more cases of CEM and confirm the fears that CEM may have unknowingly become endemic in the US in the past decade.

More information on CEM is available in our archives.

This blog is based on a presentation by Dr. Tracey Chenier, a theriogenologist and faculty member at the Ontario Veterinary Collge, given at the recent 2010 Ontario Veterinary Medical Association Conference.

Photo credit: David Campbell (click for source)

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The UK's Horserace Betting Levy Board (HBLB) has published their 2010 Codes of Practice for prevention and control of equine infectious diseases.  As part of these codes, Canada and the US have lost their low-risk status for contagious equine metritis (CEM) because of the large 2008-2009 US outbreak of the disease (the HBLB calls it a US and Canadian outbreak, which isn't actually true). Canada is included presumably because of the number of exposed horses that entered the country (and the number of other unknown exposed horses that could have entered given the scope of the US outbreak) and perhaps the somewhat passive response by federal authorities in Canada.

The loss of low-risk status greatly affects how Canadian mares are handled upon arrival to breeding facilities in the UK, and will create major hassles for people moving horses to the UK for breeding. There's no indication whether this is a permanent change or whether it may be revisited with more information on the status of CEM in North America.

Image source: http://animalphotos.info/a/

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The Horse.com reports that the ongoing contagious equine metritis (CEM) investigation in the US has now identified more than 820 exposed or positive horses. (Note the important difference between potentially exposed and positive - the vast majority of exposed horses will end up being negative). The expanse of this investigation is impressive, involving horses in 48 states.  The investigation is taking a long time because of the prolonged testing required to determine that exposed horses are indeed negative for the causative pathogen, Taylorella equigenitalis. This testing is also quite expensive, which make this disease a significant burden on the system even when only a few horses are infected.

Not a lot of new information has come to light recently. Hopefully that's a sign that the outbreak has finally been contained. Unfortunately, it's now known that some of the infected horses were positive for quite some time (years), and tracking all potentially exposed and infected animals over such a long period of time can be very difficult. The most recently diagnosed case was a stallion that was infected in 2006, if not earlier. The potential for spread of the disease, therefore, is still concerning, although two months have passed since the last new case was reported. The efforts to test exposed horses, costly and time-consuming as they are, are crucial due to the potentially even more costly consequences if CEM becomes established throughout the US (and therefore, almost inevitably, in Canada).

More information about CEM and the US outbreak can be found on the USDA website.

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Canadian horse breeders are calling for efforts to streamline semen importation requirements that have been implemented by the Canadian Food Inspection Agency in response to the "outbreak" of contagious equine metritis (CEM) in the US. The new regulations and increased paperwork are causing tremendous problems for breeders trying to import semen in a timely manner. Any delays in clearing semen shipments at customs can result in decreased viability of the semen as well as problems scheduling personnel to perform insemination of the recipient mares. Sometimes, samples can't get through at all. Breeders shipping semen from the US must get health papers (sometimes from someone a few hours away) to send with shipments. Many of the challenges are simply logistical and bureaucratic problems that should be able to be addressed with some common sense and willingness to help. Regulatory and industry personnel need to figure out ways to address these problems without compromising the health of Canadian horses. 

While important regulations should be reviewed to see if they can be more practical and efficient, it is critical that biosafety not be sacrificed for convenience. The impact of a single case of CEM in Canada would be tremendous. It's increasingly clear the the CEM situation in the US is not completely understood.  It is not a readily definable outbreak with a clear source that can be tracked. Rather, this disease appears to be have been present in the US for a few years (at least), and that efforts to get the situation back under control will be very complicated. A "loose" effort in Canada could have disasterous effects.

Many equine veterinarians are concerned that the regulations currently in place are not adequate to prevent CEM from entering Canada. One major concern is the failure to evaluate horses moving across the border. The current regulations only deal with horses from farms where CEM has been diagnosed - it's far from certain that US authorities know where all the CEM-infected animals are. Since transmission of CEM is more likely during live breeding than artificial insemination, horses from these farms are a big concern. This is also potentially a situation where well-intentioned rules could have the wrong effect. Some people are shipping their horses to the US for breeding, because sending them down and bringing them back up doesn't require any extra precautions for CEM if the farm is not a "known" CEM farm. If there are some breeding farms that are infected but not identified, which is definitely possible, then the unregulated movement of these breeding animals could create a very hazardous scenario.

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The investigation of the outbreak of contagious equine metritis (CEM) in Kentucky last month continues throughout many states in the USA, and has also spilled over into Canada.  At this time, four farms in Alberta and six farms in Ontario remain under quarantine.  These farms either received frozen semen from one of the three infected Kentucky stallions in the spring of 2008, or have mares that were shipped to Kentucky for artificial insemination with semen from one of these stallions.  So far, no confirmed cases of infection have been reported on any of these farms.

The Canadian Food Inspection Agency (CFIA) is responsible for the investigation of reportable animal diseases in Canada, including the current CEM investigation.  Representatives of the CFIA will present an update on the situation at the Breeds & Industry Delegate Assembly at the Equine Canada Convention in Ottawa on February 7.

Any horse in Canada suspected of being affected by CEM must be reported to the CFIA.  The most apparent, classic sign of CEM in mares is a thick, purulent (pus) vaginal discharge after breeding, without systemic illness (i.e. no fever or depression).  However, some mares and almost all stallions can carry the causative organism, Taylorella equigenitalis, without any obvious clinical signs of infection, which is why the disease can be difficult to control if people aren't careful.  Taylorella equigenitalis does not affect people.

The CFIA has made several recommendations to Canadian horse owners to try to prevent the spread of this disease into Canada, and to prevent its spread should it be found here at any time:

• Until the outbreak investigation in the USA is complete and the disease is contained, use extreme caution or simply refrain from importing breeding animals, semen, embryos etc. from the USA.
• Emphasize strict hygiene measures when handling breeding animals.  Wear disposable gloves when washing or otherwise coming into contact with a horse's tail or genitalia.  Change gloves (and wash your hands!) before handling another horse.
• Use separate equipment (e.g. buckets, sponges, tail wraps) for each horse.  Any equipment that must be shared should be thoroughly cleaned and then disinfected between horses.  Taylorella equigenitalis is susceptible to most common disinfectants, including bleach.

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In December 2008, an outbreak of contagious equine metritis (CEM) was reported in Kentucky. The index case was a healthy stallion that underwent routine testing for exportation of semen and the causative agent, Taylorella equigenitalis, was isolated by cutlure on December 15. By the end of the month, three more stallions on the same farm were also identified as infected. At the moment, it is estimated that there are 28 horses in Kentucky and another 156 horses outside Kentucky that have been exposed. Another 250 horses are being traced across 27 states. The last outbreak of CEM in the USA was in 1979 in Missouri, although a few sporadic cases have been identified in the country in the last three decades. It is a reportable disease in both the USA and Canada, and there are strict import (and export) regulations for horses entering the USA and Canada from CEM-positive countries.

CEM is a venereal disease of horses. It is spread by stallions who can carry the bacteria on their external genitalia without any noticeable clinical signs, as well as by infected mares, during breeding. The bacterium can also be transmitted through artificial insemination, particularly on contaminated equipment. The diseases causes temporary infertility in mares. Typically mares do not conceive when they are first infected, but if a mare does become pregnant she may abort, or the foal may be born a carrier. Some mares develop a heavy purulent vaginal discharge (pus) for up to two weeks after breeding, but others may only have a shortened heat cycle. Some mares will clear the infection on their own, but in some cases a mare may become a chronic carrier of T. equigenitalis and transmit the bacteria to stallions during breeding. The organism does not cause any clinical signs in stallions, so the only way to detect the bacteria in males is to culture it. However, T. equigenitalis is notoriously difficult to grow in a laboratory, so false-negative results can occur. Therefore adjunctive tests are also used, and additional testing methodologies (including molecular techniques such as PCR) are being developed for the detection and study of this organism.

The good news is that infected horses can be treated, and T. equigenitalis is typically susceptible to most common antibiotics. Local treatment and repeated flushing of the external genitalia of infected horses is also part of the treatment regimen. Compared to other diseases, the spread of CEM is also relatively easy to control, because it is only transmitted by breeding (either live cover or artificial insemination). The major problem is that this disease is also one that can easily “fly under the radar” for some time before it is discovered, because carrier animals show no clinical signs of infection, and stallions in particular, as in this case, may expose many mares before the bacterium is discovered. Hopefully this outbreak will be brought rapidly under control so that the equine industry in the USA can avoid devastating economic loses due to the presence of this disease.

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