The Golden Age of Horse Health

The American Association of Equine Practitioners is celebrating its golden anniversary in 2004, and will hold its 50th annual convention in Denver, Colo., Dec. 4-8. The AAEP was founded in December 1954, in Louisville, Ky., by 11 charter members and now boasts approximately 8,000 members in 57 countries. Based on past conference attendance averages, some 2,700 veterinarians, veterinary students, and technicians will be there, while guests and exhibitors in the trade show that accompanies the conference will bring the grand total to about 5,500.

The AAEP is dedicated to improving the health and welfare of the horse, to furthering the professional development of its members, and to providing resources and leadership for the benefit of the equine industry. See the accompanying sidebars for more information on this year's event.

Before reporting on an antispasmodic drug for treating colic which became available in the United States this year, here's a preview of new information on vaccines.

In fulfilling its goal of providing resources for the benefit of the equine industry, the AAEP publishes an invaluable resource to horse owners and veterinarians, simply titled, AAEP Guidelines for Vaccination of Horses. This concise yet comprehensive booklet provides recommendations for administering initial doses and boosters for different vaccines to different age groups and classifications of horses. The guidelines are periodically reviewed by an AAEP vaccination review committee. The guidelines have recently been updated, and expanded guidelines are expected for release to members at the 2004 convention.

Specifically, the new booklet will add information for West Nile virus (WNV) vaccine, which was not yet developed when Guidelines for Vaccination of Horses was last updated in 2001. Since then, the United States Department of Agriculture (USDA) has approved two equine WNV vaccines.

Recombitek, made by Merial, received approval from the USDA in December 2003, and was released to the market in January 2004. In medical terminology, the vaccine works by recombinant canarypox-vector technology. It is administered by intramuscular (IM) injection. The label recommends a two-dose vaccination protocol in previously unvaccinated horses. However, a study done by Merial found that a single dose of the vaccine appears to provide early protection against viremia after challenge with West Nile-infected mosquitoes in previously unvaccinated horses, even in the absence of measurable antibody titers in some horses. Horses vaccinated with Recombitek would need to be re-vaccinated annually.

The Merial study was published in the November 2004 issue of the American Journal of Veterinary Research (vol. 65, no. 11, page 1,462). In summary, one of nine treated horses developed viremia following challenge via West Nile-infected mosquitoes. By contrast, eight of nine control horses developed viremia following challenge.

West Nile-Innovator, an inactivated virus vaccine manufactured by Fort Dodge Animal Health, received its full license from the USDA in February 2003. In November 2003, Fort Dodge Animal Health received USDA approval for four combination vaccines that expand the protection of West Nile Innovator, and the company began shipping the combination vaccines in January 2004. The four-in-one West Nile-Innovator + EWT protects for West Nile, Eastern, and Western Encephalomyelitis, and tetanus. West Nile-Innovator + EW protects for the same but without the tetanus. The five-in-one West Nile-Innovator + VEWT protects for West Nile, Venezuelan, Eastern, and Western Encephalomyelitis, and tetanus. West Nile-Innovator + VEW protects for the same but without the tetanus.

Expect the updated AAEP guidelines to provide recommendations for administering initial doses and annual boosters of WNV vaccine to different age groups and classifications of horses.

The vaccination review committee found there was no need at this time to revise what was already in print. Existing guidelines for vaccines for other diseases are still accurate.

The 2001 update to Guidelines for Vaccination of Horses included a revision for vaccinating foals against equine influenza virus. Specifically, the revision was for the age at which to begin vaccinating foals from mares which had been vaccinated against flu four to six weeks prior to the foal's birth. A good prenatal care program prescribes vaccinating mares at this important juncture in their pregnancy. Doing so enables the first milk the mare produces after the foal's birth (colostrum) to be rich in antibodies. The newborn nurses and receives protection against infection through maternal antibodies in colostrum.

Veterinary research which preceded the 2001 guidelines update found vaccinating a foal younger than eight to nine months old from a mare which had received a timely flu vaccination resulted in foals showing decreased antibody responses to flu vaccine when compared to foals that had been vaccinated for flu after the maternal antibodies were gone, at about eight or nine months of age. The news regarding maternal antibody influence underscored the point that vaccinating pregnant mares against flu a month or so prior to the anticipated foaling date is extremely beneficial for young foals. Nursing foals are protected against flu by the passive transfer of maternal antibodies from the vaccines their dams receive.

When using an injectable flu vaccine, foals from vaccinated mares should receive their first dose of flu vaccine at nine months of age, followed by a second dose at 10 months, and a third dose at 11-12 months of age. Foals from non-vaccinated mares (mares not vaccinated four to six weeks prior to foaling) should receive a first dose of flu vaccine no later than six months of age, followed by a second dose at seven months, and a third dose at eight months. For both groups of foals, subsequent doses of injectable flu vaccine should be administered at three- to four-month intervals.

The AAEP Guidelines generally follows label recommendations for existing products, explained Dr. Robert Holland, who served on the AAEP vaccination review committee. Holland also is a senior technical service veterinarian at Pfizer Animal Health and is in private practice in Lexington.

Veterinarians must be alert for increased risk of exposure to particular diseases in different regions and seasons. Risk factors vary from farm to farm. The horse's upcoming schedule also must be kept in mind.

Young Thoroughbreds are often on the move--to prep facilities, sales grounds, training centers, and racetracks. Broodmares also ship to sales and new farms. In new surroundings, there is a constant risk of exposure to contagious respiratory tract infections. However, there is a short period after vaccination while the vaccine is immunizing the horse. This lag should be considered whenever horses are being put in high-risk situations. Be sure the horse has been vaccinated sufficiently in advance of a venue change.

In short, "Good preventive management in combination with a vaccination program can be very effective at reducing disease on your facility," Holland reminded readers.

Readers should note there are different strains of equine influenza. Different flu vaccines are available to fight different strains. However, flu virus is able to regroup--literally, to change itself--or new assaults on respiratory health. When mutation occurs, new vaccines are needed to fight the new strains of flu. A vaccine must contain an up-to-date flu strain to do its job. Nasal swabs of horses that have respiratory infections can help researchers catch new flu strains, but for that to happen, farms need to collect swabs and send them to a diagnostic laboratory.

"You have to have an up-to-date flu strain in the vaccine," Holland said. "We're very lucky the 1990s style vaccines appear to be effective right now. But flu has a tendency of wanting to change, to mutate. That's why it's important to do a nasal swab of the horse when you have a respiratory problem, and send that swab in to a diagnostic lab, to test for what virus or bacteria it might be."

Equine herpes virus (EHV), also called rhinopneumonitis, also presents different strains. EHV-1 is most dreaded by breeding farms, because it causes abortion in pregnant mares, or weak, nonviable foals.

Strangles, caused by Streptococcus equi, also can cause respiratory health problems in horses.

Intranasal vaccines for influenza and strangles were already in use at the time of the last publication of Guidelines. The recommended age of a first dose of intranasal flu vaccine is 11 months. Subsequent doses should be administered every six months. The recommended age of a first dose of intranasal strangles vaccine is six to nine months, with a second dose recommended three weeks later.

Pinnacle I.N., made by Fort Dodge, was the first intranasal equine strangles vaccine available to U.S. horse owners. It received its license in the spring of 1998.

Flu Avert, made by Intervet, was the first intranasal equine flu vaccine available to U.S. horse owners. It was launched in November 1999.

The Calvenza respiratory vaccines from Boehringer Ingelheim Vetmedica provide a choice of protection against either influenza or EHV separately, or in combination. Calvenza vaccines offer flexible administration either by intramuscular or intranasal administration, with a low incidence of vaccination site reactions, and they are approved for use in pregnant mares.

Managing a colic case in the U.S. took a big step forward when Boehringer Ingelheim received FDA approval for Buscopan in May 2004. The active ingredient is N-butylscopolammonium bromide, an antispasmodic and anticholinergic drug that relaxes smooth muscles and suppresses spasms of the digestive system. Though it does relieve abdominal pain by suppressing spasms, it is a different class of drug than analgesics. Although new to the U.S. horse community, the medication has been available for treating equine colic in other countries for decades. The drug was first registered in Germany, where the parent company is headquartered, in 1966.

Colic, which means abdominal pain, is an umbrella term applied to the clinical signs of a number of conditions that result in the disruption of normal intestinal motility. The term does not signify a single disease. Rather, it is a diagnostic term for the manifestation of any of several conditions which can occur due to exposure to different risk factors. Different types of colic (examples--impaction, gas, intestinal twist, and spasmodic) cause similar signs of distress, and require different treatment. The majority of cases pass quickly, and many resolve with no intervention. Yet acute colic is the leading medical cause of death in horses each year.

Success in treating colic is more likely when it is addressed early.

Sedatives and analgesics are often given when horses show distress from colic. Analgesics include non-steroidal anti-inflammatory drugs (NSAIDs), such as flunixin meglumine (Banamine). These drugs are widely used to relieve abdominal pain, but they can mask signs of a worsening colic, according to Dr. Robert M. Stenbom, manager of equine professional services for Boehringer Ingelheim.

"Buscopan will not mask the signs of a deteriorating colic situation," Stenbom said. "We're not trying to replace other colic medications. Buscopan is another tool that practitioners can use to address the colic problem, and to sort out at an early stage which ones are going to be serious. It's designed for the early stages of an undifferentiated colic."

Buscopan's antispasmodic properties facilitate diagnosis and prognosis. Buscopan is administered by intravenous injection. Response to spasmodic colic would be seen in 10-30 minutes. If the horse does not respond at all, the colic is other than spasmodic.

A single dose is recommended--this in itself has therapeutic value for spasmodic colic. "Spasm pain can be really severe. The analgesics and sedatives aren't enough to overcome that discomfort," Stenbom said.

Two doses at most would be given, but only to clarify a partial response to a first dose. Partial response indicates sources of colic pain other than spasm. "The other pain source typically points to more serious things," Stenbom said.

A horse that responds well to Buscopan can be put under observation, while one that clearly does not respond would require additional treatment. This might include abdominal surgery.

If it's one, two, three strikes you're out at the old ballgame, then for Equine Protozoal Myeloencephalitis (EPM), a complex and debilitating disease, time is running out. EPM, the number one cause of neurological problems in horses, is a progressive, degenerative disease of the central nervous system that causes lack of coordination in horses. Research into EPM has progressed by leaps and bounds in the last seven or so years, and we now have two FDA-approved EPM treatment drugs.

To review, Sarcocystis neurona, a protozoan parasite, is the organism that causes EPM. Horses are the aberrant host. Horses acquire S. neurona through exposure to feed, water, or fence or barn surfaces contaminated by infected fecal material from opossums, raccoons, skunks, armadillos, and cats--five animals which, to date, have been identified as intermediary hosts.

EPM is characterized by asymmetrical ataxia with or without muscle atrophy. It can cause minor coordination problems, severe gait deficits, or death. Some horses recover only to relapse and have symptoms recur when taken off treatment. Other horses never fully recover. Early, accurate diagnosis and treatment offer the best chance for success.

Marquis, manufactured by Bayer Animal Health, was the first antiprotozoal medication to receive FDA approval, in July 2001. Marquis is an oral paste containing the active ingredient ponazuril sulfone.

Navigator Paste, made by IDEXX, received FDA approval in November 2003. It is a nitazoxanide antiprotozoal oral paste, designed to kill S. neurona by shutting down cellular respiration of the target organism.

A possible third EPM treatment drug, diclazuril, is in development.

A vaccine would be the grand slam in the fight against EPM. Vaccines are the first line of defense in preventing disease, and prevention is always preferred to treatment. An EPM vaccine from Fort Dodge Animal Health was granted conditional license in December 2000. Until full licensure is acquired, the company is calling it Sarcosystis neurona vaccine.

Let's Discuss It
In the wide world of equine health and medicine, no stone has been left unturned by the AAEP. Vaccinations and treatments for the various viral and bacterial diseases that can affect horses are just a sample of the topics that are routinely covered at the organization's annual conventions. Besides sitting in on lectures, this year's conference attendees can participate in a table topic session on Dec. 5 entitled "Infectious Neurological Diseases - EPM, WNV, and EHV-1." The discussion will be led by Drs. Frank Andrews and Maureen Long. In addition, a member forum on Biologic and Therapeutic Agents on Dec. 4 will discuss vaccinations. By Bettina Cohen

Quick Product Reference
The trade show that accompanies the AAEP convention will feature the latest and most trusted products in horse health, and more than 300 exhibitors, including pharmaceutical companies, veterinary supply companies, publishers of equine health magazines such as The Horse, plus other equine industry organizations. AAEP Educational Partners Bayer Animal Health, Boehringer Ingelheim Vetmedica, Fort Dodge Animal Health, Intervet, and Pfizer Animal Health. IDEXX Pharmaceuticals and Merial also will exhibit.

Bayer Animal Health makes Marquis, an EPM treatment drug, and Legend and Legend I.V., a pair of joint pharmaceuticals that contain hyaluronic acid in intra-articular and intravenous preparations.

Boehringer Ingelheim manufactures an array of vaccines to protect horses against equine influenza virus, equine herpes virus (EHV), three strains of equine encephalitis (EEE, WEE, VEE), Potomac horse fever (PHF), rabies, strangles, and tetanus. The Calvenza respiratory vaccines offer intramuscular or intranasal delivery. For colic treatment, the company has launched the antispasmodic Buscopan.

Fort Dodge Animal Health makes the West Nile-Innovator vaccine plus four combination vaccines that protect horses from WNV and other encephalitis diseases that are available with or without tetanus protection; Pinnacle I.N.; and the dewormer medications, Quest and Quest Plus.

IDEXX makes Navigator Paste, the newer EPM treatment drug, and the first FDA-approved topical NSAID for equine joint pain management, Surpass Topical Cream, launched in spring 2004.

Intervet manufactures the intranasal Flu Avert vaccine, and vaccines to protect against EHV, the equine encephalitis diseases, PHF, rabies, strangles, and tetanus; also, the dewormers Safe-Guard and Panacur.

Merial makes Recombitek, a WNV vaccine that uses recombinant technology, and other equine vaccines, the FDA-approved ulcer treatment GastroGard, and the dewormers Eqvalan, Zimecterin, and Zimecterin Gold.

Pfizer Animal Health makes flu, EHV, and PHF vaccines, and dewormers, including Equimax. By Bettina Cohen

Thoroughbreds and Colic
The USDA's National Animal Health Monitoring System Equine 1998 study has estimated the incidence of colic in the North American horse population at 4.2 events per 100 horses per year. However, the incidence for Thoroughbreds was reported as much higher: 10.9 colic events per 100 horses per year. Any age horse is vulnerable, but the most likely group to experience colic is 18 months to five years of age--the training and racing ages for many Thoroughbreds. Close monitoring by observant attendants partially explains the higher incidence among Thoroughbreds compared to the overall horse population; but Thoroughbreds are exposed to multiple risk factors, one being a high grain feed program. For further reading, see Understanding Equine Colic, published by Eclipse Press in 2004.