Veterinary internal medicine is a growing specialty that boasts nearly 400 large animal internal medicine specialists, many of them focusing on horses. In a time when humans seek out experts in varying medical fields, it's only logical that we seek the same for our animals.

Diplomates of the American College of Veterinary Internal Medicine (ACVIM) have been trained, tested, and approved to be veterinary internists. These specialist veterinarians, along with Diplomate candidates, gather annually for the ACVIM Forum, which consists of three days of presentations and discussions devoted to new developments in the veterinary internal medicine field. The 2006 Forum was held in Louisville, Ky., May 31-June 3. Presentations ranged from cutting edge treatments for common ailments and conditions to valuable reviews on rare diseases. Following are highlights from the Forum.

Biosecurity and Equine Diseases

Probably one of the most well-attended equine sessions of the forum was a lunchtime discussion sponsored by Pfizer Animal Health, in which a panel of internists presented information on recent outbreaks of salmonella and fielded questions from attendees. Salmonella bacteria can cause debilitating intestinal problems and life-threatening diarrhea. Salmonella can affect foals and adults, and it is spread easily by horse-to-horse contact and by fomites (shared tools, water buckets, hands, etc., on which bacteria can "hitch a ride" to the next victim). Seemingly well horses can harbor the bacteria, and when stressed, they can shed it or become ill.

So an ill horse that's stressed by traveling and adapting to a hospital environment is a prime candidate to shed Salmonella bacteria, even if that wasn't the orginal illness.

Practitioners from several university hospitals and private facilities say their practices are spending $10,000-$30,000 per year on surveillance of incoming horses for Salmonella, and that it has paid off for them. An outbreak of the disease among hospital patients is deleterious for animals with already compromised health.

"We need to be logical about the transmission risk and segregating different horses," explained Paul Morley, DVM, PhD, Dipl. ACVIM, associate professor, Epidemiology and Biosecurity, director of Biosecurity, James L. Voss Veterinary Teaching Hospital director, Animal Population Health Institute, Colorado State University. "This is part of the basic structure of a sound biosecurity program," he said. "But we don't really know how much is enough."

Some practices are testing every animal that comes in the door and isolating those that culture positive, and many are also testing facilities with the use of Swiffer samples from surfaces in the hospital.

Preventing and managing hospital- acquired cases of salmonella require educating the client.

"We need to be open and up front" about the possibility of these infections, said Fairfield T. Bain, DVM, Dipl. ACVIM, ACVP, ACVECC, of Hagyard Equine Medical Center in Lexington, Ky. "Ethically, our primary responsibility is the patient, and we need to explain (to the client) if there's a higher risk."

He mentioned a study that revealed 85% of horses on one farm were shedding Salmonella, and he said many farm managers are realizing these infections aren't just a hospital problem anymore.

Rhodococcus equi

An entire morning was devoted to this economically significant disease that infects young foals, often within hours of birth. Stephen Hines, DVM, PhD, Dipl. ACVP, of Washington State University, reported on the pathophysiology of the disease and prospects for preventing it.

R. equi is a bacterium in the soil that can travel to, and multiply within, the foal's lungs, causing a deadly pneumonia if it is not caught and treated early. Hines described the possibility of developing vaccines with genetic targets that could help prevent the disease. It is notoriously difficult to test such vaccines, however, because of the expense of foal studies and the fact that veterinarians still aren't quite sure how foals acquire the disease-- exposure could happen in a number of ways.

Hines reported on recent research revealing foals are interferon-gamma- deficient at birth (see page 20), suggesting a potential target for preventing disease with immunomodulators that seek to boost interferon-gamma levels.

He also said that since research has shown ingestion could be the foals' primary exposure to R. equi, the oral route could be the "key to inducing protective immunity."

Lyme Disease Update

As many as 20% of adult horses in certain areas of the United States are infected with Borrelia burgdorferi, the spirochete (a type of spiral-shaped bacterium) that causes Lyme disease, according to Cornell University researcher and clinician Tom Divers, DVM, Dipl. ACVIM. Horses are infected through Ixodes tick bites. Divers said that many horses in endemic areas are, or have been, infected, which is evidenced by the fact that 75% of horses in the Northeast and Mid-Atlantic states already have antibodies against the organism.

What is less clear is the association between finding those antibodies and concluding that the horse has Lyme disease. A spectrum of clinical signs are linked with Borrelia infection, but many--or even most--horses with active infections don't have clinical signs of disease. Therefore, the finding of an antibody titer is not necessarily an indication that the horse should be treated for Lyme disease.

The clinical signs that are typically attributed to Lyme disease (so named because early investigations centered around clusters of the disease in humans around Lyme, Conn.) include fever, stiffness and lameness in multiple limbs, painful muscles, hypersensitivity of the body surface and resentment of touch or pressure, joint swelling, and dullness or other changes in behavior. Signs of Lyme disease have been confused with osteochondritis dissecans (OCD), degenerative joint disease (DJD), tying-up, and equine protozoal myeloencephalitis (EPM), among others.

In a study led by Divers, none of the 27 ponies experimentally infected with B. burgdorferi developed overt clinical signs of disease even though when the ponies' tissues were examined, the organism was found in several sites. The tissues most likely to harbor B. burgdorferi were lymph nodes (especially in the region of the infecting tick bite), muscle, fascia (the whitish tissue that connects muscles to subcutaneous tissue or binds muscles together in bundles), and synovial (joint) membranes in all limbs. Less frequently, the spirochete ended up in the heart, kidney, or meninges (membranes covering the brain and spinal cord).

Vaccinated horses generate serum antibodies as they do in response to natural infection, but tests are available that enable veterinarians to distinguish between vaccine-induced antibodies and those induced by natural exposure to the organism. Divers said vaccination is likely to be of limited value once a horse is infected. Natural infection doesn't do much better at stimulating a protective immune response; persistent infection and re- infection, even after a bout of naturally acquired disease, are common.

The mainstay of treatment is administration of antimicrobials such as oxytetracycline (which must be given intravenously), doxycycline, and ceftiofur. Non-steroidal anti-inflammatory drugs can be administered to control muscle and joint pain, and chondroprotective agents and acupuncture can be helpful adjunctive treatments.

Evidence suggests that infected ticks must remain attached to a horse for at least 24 hours for transmission of the B. burgdorferi organism. For this reason, aggressive tick control measures such as insecticidal sprays or wipes might be the most effective measure of all for preventing the disease.


Recurrent painful inflammation and pathologic changes in the eyes of horses with equine recurrent uveitis (ERU, also known as moon blindness) could be caused by the persistence of invasive bacteria called Leptospira in affected horses' eyes and the resultant immune response directed to the area. Divers described recent research on leptospirosis, the disease caused by these bacteria.

Leptospira are spirochetes that cause devastating infections in humans, horses, and other animals. In horses, leptospiral organisms can cause abortion--sometimes sporadic cases and sometimes in storms--and they can cause urinary tract disease, including kidney infection and failure. The bacteria are shed in the urine of infected animals, and horses are exposed to it when they drink water in which infected animals have urinated. The risk of transmission is greatest for horses in pastures with standing water that are shared with other species of animals, such as cattle.

Although abortion and kidney infection are severe, the organism is getting increased research attention at present because of its association with ERU, which used to be called periodic ophthalmia or moon blindness because the condition waxes and wanes in severity and was thought to be influenced by lunar cycles.

Evidence suggests ERU might be the most common cause of horse blindness.

The Leptospira organisms reach the eye after dispersal in the blood. Targeting of the leptospires by cells and molecules of the immune system results in a condition known as anterior uveitis, the clinical signs of which are squinting, severe engorgement of the blood vessels of the sclera (the white part of the horse's eye), corneal edema (which makes the surface of the eye appear whitish or bluish-gray), tearing, pinpoint pupils, and a hazy appearance to the aqueous humor in the anterior chamber. Observation of such signs should prompt veterinary evaluation.

If the horse has recurrent flare-ups of uveitis, then cataracts, adhesions between the horse's lens and iris, degeneration of the vitreous body, and blindness can develop. Appaloosas are more likely to get ERU than other breeds.

Uveitis can have many causes, such as eye injuries, equine influenza virus, and Onchocerca and Strongylus parasites, but leptospirosis is increasingly being recognized as an important causative agent. Veterinarians have traditionally managed uveitis by focusing on control of the inflammation, but Divers suggested that an antimicrobial should be added to treatment protocols to help control the infection if leptospirosis is suspected or identified.

Even though antibodies can be found in the aqueous humor, the organism is able to persist, suggesting that other elements of an effective immune response might not be operant in the eye. Researchers are focusing on vaccine development and better treatments for intraocular infection.

New Nutrition Software

Researchers are finishing the new National Research Council report that describes nutritional requirements of the horse. It is expected to be released this fall. This information will be used to predict the daily nutrient requirements of horses in various physiologic states, i.e., pregnancy, exercise, or growth.

The software also will be used to facilitate teaching of equine nutrition and will assist in developing research models that will help scientists better understand nutrition requirements of the horse.

"We envision these as the culmination, but really it's a starting point," said Robert J. Van Saun, DVM, MS, PhD, Dipl. ACT, Dipl. ACVN, of University Park, Pa. "These software models set the stage for continued development. More research is required to move to the next level of understanding."

Equine Herpesvirus-1 (EHV-1)

This disease has been a widespread problem in the past few years. There are vaccines available against respiratory forms of the disease, but there are no clear vaccine recommendations to prevent the deadly neurological form of the illness.

Researchers are attempting to develop better vaccination recommendations. Paul Lunn, BVSc, PhD, MRCVS, Dipl. ACVIM, of Colorado State University, reviewed prospects for EHV-1 prevention, including the possibility of new modified live vaccines that could manipulate the EHV-1 genome if it were to enter the horse, rendering it incapable of causing immunosuppression and thus illness.

An Athlete's Heart

When it comes to the equine heart, size matters, says Lesley Young, BVSc, PhD, DVA, Dipl. ECEIM, DVC, MRCVS, who completed research on the topic at the Animal Health Trust in Newmarket, Suffolk, United Kingdom. Young explained the significance of equine heart size, its ability to oxygenate the body, and its use as an athletic predictor in untrained racehorses.

To determine if heart size actually plays a role in athletic performance, Young examined data from 483 race-fit Thoroughbreds. Using VO2max (the best indicator of cardiorespiratory performance) and echocardiography, she categorized horses by anaerobic capacity and heart size. VO2max incorporates both the consumption and the delivery of oxygen to the muscles.

Young said her results indicated, "the first direct evidence that cardiac size influenced athletic performance in a group of Thoroughbreds."

However, she said, "The data doesn't show that echocardiography can predict performance in untrained animals. It does give us evidence that we might be able to."

Not-So-Easy Breathing

The terms recurrent airway obstruction (RAO or heaves) and inflammatory airway disease (IAD) are often wrongfully used interchangeably to describe horses with non-infectious respiratory disease. Bonnie Rush, DVM, MS, Dipl. ACVIM, professor of equine medicine at Kansas State University, explained basic differences between the two.

RAO is a common respiratory disease in horses that is characterized by chronic coughing, nasal discharge, and difficulty breathing. The average age of horses developing RAO is around nine years old. Thoroughbred mares older than seven are at the greatest risk for developing RAO. However, all breeds and genders are affected by the disease.

Rush said, "Most of these horses I diagnose by physical exam alone, and look for response to treatment. If I treat them and they're unresponsive, I'm going to take chest films."

Because of more frequent inhalations/exhalations caused by respiratory diseases, using X rays to diagnose RAO is very difficult. But chest X rays can help rule out other types of diseases, such as pneumonia.

IAD horses usually have low-grade pulmonary inflammation. IAD is predominantly seen in horses age two and younger.

Diagnostics for IAD can include endoscopic examination, bronchial lavage, and bronchial challenge tests (which measure the degree of airway hyperresponsiveness to stimuli). In addition, Rush said she often cultures the lower respiratory tract.

Both diseases can severely affect the horse's performance and need to be addressed by a veterinarian.

Skin Disease

Stephen White, DVM, Dipl. ACVD, a professor in the Department of Medicine and Epidemiology at the University of California, Davis (UC Davis), said there are three categories for hypersensitivity (non-insect-bite related) skin diseases. These include food allergies, atopic dermatitis (a predisposition to allergic disease in response to environmental allergens), and contact allergies caused by chemicals, bedding, inhaled dust, or other allergenic agents.

True food allergies are rare according to White. Those that are seen (real or presumed) are often diagnosed using changes in the horse's history such as itching or hair loss after switching feeds.

Diagnosing atopic dermatitis requires closer examination of clinical signs that can include pruritus (a sensation within the skin that causes itching), alopecia (partial or complete loss of hair in areas), and sometimes pyoderma (pus-filled lesions caused by infection or inflammation). White also suggests using intradermal tests (IDT, a surface skin test against known allergens) or serological allergen test for further diagnosis.

Contact allergies can also be defined by changes to the horse's environment, such as new bedding or new products being used. Contact reactions are generally localized to the point of contact.

White explained the horse's complete history, including any home remedies the horse owners might have applied to the skin, should always be taken into consideration when evaluating the horse.

"The take-home message here is that horses with these diseases generally have a higher incidence of positive reactions than healthy horses, but that the diagnosis cannot solely be made on the basis of the IDT or serologic testing alone," White said.


Short abstracts on new developments in internal medicine were also presented.

Fluid Shifts in Dehydrated Patients UC Davis researchers say vets might soon be able to use a non-invasive procedure to detect fluid shifts in dehydrated horses and respond with treatment more readily than with usual methods, such as blood work.

The new technology multi-frequency bioelectrical impedance analysis (MF-BIA), uses alternating low-frequency electrical current to make predictions about body composition, including body fluids.

Aging and the Aortic Valve There is a decrease in contractile function of the aortic valve with age, resulting in aortic valve disease, says U.K. researchers. The investigators aren't sure if an increase in collagen in the valve is a response to reduction in contractile function, or if the increased stiffness of the valve is brought about by the increase in collagen.

Test for Insect Hypersensitivity According to a Swedish study, IgE serum level tests were not sensitive enough and produced too many false positives to be used as a diagnostic screening test for insect hypersensitivity in horses.

However, researchers said the test methods can be used to measure elevated IgE serum levels as they respond to specific reactions, allowing practitioners to identify specific allergens and treat accordingly.

IV Ulcer Treatment Intravenous omeprazole, because of its potency and long-acting effect, can be useful for treating horses with conditions such as gastric reflux, which restrict oral omeprazole paste administration, according to researchers at the University of Tennessee.

Tahitian Noni Juice Although more research is needed, Tahitian Noni Equine Essentials, an herbal product made from the Morinda citrifolia tree, could have uses as an anti-inflammatory agent, according to a cooperative study by the University of Wisconsin School of Veterinary Medicine and the University of Nevada.

Predicting Pulmonary Hypertension As a part of a larger study, researchers at Cornell and Pennsylvania confirmed that horses with RAO are at increased risk of developing pulmonary hypertension. They are currently perfecting a model using pulmonary artery measurements to predict moderate to severe pulmonary hypertension in horses with RAO.

Take-Home Message

Specialists and researchers are working to make horses healthier, developing new resources to prevent and treat diseases, and striving to share that information with colleagues and horse owners. For more on the ACVIM conference see

By Stephanie Church, Chad Mendell, and Kim Sprayberry, DVM, Dipl. ACVIM

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