World Vets Meet
The World Equine Veterinary Association (WEVA) meets every other year with two goals in mind: 1) to offer up-to-date veterinary and research topics in a professional setting outside North America and the United Kingdom; and 2) to raise money in order to hold intermediate meetings in intervening years in parts of the world where there is a dearth of veterinary education.
The 2009 WEVA Congress was held in Guarujá, São Paulo, Brazil, which ranks among the top 10 countries with the highest population of equids. It boasted one of the largest gatherings in WEVA's 24-year history with attendance of 1,175; 951 veterinarians and 224 exhibitors and accompanying persons. There were 44 speakers from around the world who gave 115 lectures, plus 326 abstracts presented (85 oral and 241 posters).
Incoming WEVA President Tim Greet, BVMS, FRCVS, MVM, Cert EO, DESTS, Dipl. ECVS, of Rossdales Equine Hospital in Newmarket, England, said in his post-Congress address: "The Brazilians organized a fantastic conference. We all enjoyed fabulous hospitality and had an action-packed scientific program. We also elected a junior vice president, Dr. Ravi Reddy (BVSc, MRCVS) from India, who will hopefully follow me in the president's job. Equally importantly, we have decided that our next biennial conference will be held in Hyderabad, India, between the second and sixth of November, 2011.
"Added to that, we have organized an intermediate meeting in Hungary at Debrecen on May 28th and 29th, 2010, and there is the possibility of another intermediate meeting in Thailand," he continued.
"WEVA has taken every opportunity to enroll as many national equine veterinary associations from around the world in order that we can truly be said to represent the profession globally; at the last count there were 29 national equine veterinary member associations spanning all the continents. Our aim is to continue to help underwrite regional meetings, and with the support of the more established and wealthier national associations, to encourage the less-developed ones to create better continuing education programs." He said by improving the education of veterinarians in countries that have important equine industries, but not the equine veterinary expertise, "WEVA can genuinely contribute to improving equine welfare in a very practical way."
Following are synopses of some of the WEVA presentations. More articles, and longer versions of these articles, can be found on TheHorse.com.
Applied Equine Research Award
At each WEVA Congress an Applied Equine Research Award is given to an outstanding researcher. The 2009 award, sponsored by Intervet/Schering-Plough Animal Health (ISPAH), went to Steeve Giguère, DVM, PhD, Dipl. ACVIM, professor of large animal medicine at the University of Georgia.
Giguère's clinical interests are in large animal cardiology, neonatology, and equine respiratory disorders. His research interests include infections caused by Rhodococcus equi in foals, equine neonatal immunology, and pharmacokinetics/ pharmacodynamics of antimicrobial agents in horses.
Upon accepting his award, Giguère said, "I am honored to have been selected for this award. Research is almost invariably a result of teamwork, and I would like to thank all the graduate students, residents, and collaborators I have had the opportunity of working with over the years."
R. equi research Giguère said one of his specific interests is studying R. equi, a bacterium that causes a serious--and sometimes fatal--pneumonia in foals. In fact, a U.S. survey indicated that respiratory disease is the third-leading cause of illness in foals, and it ranks second as a cause of death, following injury or wounds.
R. equi can also cause gastrointestinal (GI) lesions in foals, including abscessation of colonic lymph nodes and ulcers throughout the colon. Foals with these types of lesions have a poor prognosis.
R. equi is common in environments of many horse farms in North America. However, clinical disease in foals can be "absent, sporadic, or endemic," noted Giguère.
He asked the audience: "Why are foals affected? Are they immunosuppressed? Do they have a naïve immune system? We need to know this to develop a vaccine."
Giguère gave a very intricate overview of the equine immune system, discussing the components of the immune system es-sential for protection against R. equi. One of the cytokines (inflammatory mediators) essential for protection is interferon (IFN)-gamma. The problem is that foals are believed to be deficient in their ability to produce IFN-gamma.
Giguère presented data showing that when foals are infected with a relatively low number of bacteria, inducing mild lesions but not causing clinical signs of disease, their IFN-gamma induction is as good as or even better than that of adult horses. In contrast, if their immune systems are overwhelmed with a large number of bacteria, there is a switch in the type of immune response they mount, and they develop severe pneumonia.
Treatment of R. equi Giguère said for the past 20 years, a combination of erythromycin and rifampin has been the treatment of choice for foals with R. equi pneumonia. However, problems included poor and variable oral absorption, requirement for frequent administration, and side effects of diarrhea and hyperthermia.
In last 10 years other combinations of drugs have been used in humans and animals. Giguère and his colleagues looked at the pharmacokinetics and pharmacodynamics of drugs in the same family as erythromycin. Giguère said he was looking to see which antibiotics provided concentrations in the respiratory tract that are above what is needed to inhibit growth of R. equi.
In a retrospective study Giguère and his colleagues compared the efficacy of different drugs and drug combinations. They found giving foals clarithromycin-rifampin versus erythromycin-rifampin resulted in higher short- and long-term treatment success and fewer days with fever.
The researchers then asked: Are there alternative drugs that might work better or have fewer side effects?
"Doxycycline is active against R. equi in vitro (in the laboratory) and the concentrations achieved in the lungs are above the minimum inhibitory concentration of the pathogen," said Giguère. "However, there is not data indication whether doxycycline is as good as the combination of a macrolide and rifampin."
Tilmicosin is approved for shipping fever in cattle, noted Giguère. He said a single dose gives 12 days of antibiotic coverage. The researchers found plasma concentrations were low, but concentrations in the lung and cellular linings were higher than in plasma. "The problem is tilmicosin is not very active against R. equi," he said.
Sleep Disorders and Seizures
I.G. Joe Mayhew, BVSc, FRCVS, PhD, Dipl ACVIM, ECVN, head of Massey Equine and professor of equine studies at Massey University in New Zealand, relayed the current body of knowledge regarding sleep disorders, seizures, and epilepsy in both foals and adult horses.
"Fainting" has been described in Suffolk, Shetland, Fell, Warmblood, and Miniature Horse foals beginning at a few weeks of age. Affected foals show daytime sleepiness and episodes of partial or total cataplexy (i.e., flaccid paralysis and lack of normal limb reflexes). Adult-onset inherited narcolepsy has not been reported in horses; however, sporadic idiopathic hypersomnia, or sleep attacks, occur in a variety of breeds. Narcolepsy is characterized by drowsiness, hanging of the head, buckling of knees, and, in some animals, sudden and total collapse to the ground, usually with full recovery in seconds.
In both adults and foals, the sleep attacks appear to be lifelong conditions, but they can sometimes be treated with the antidepressant drug imipramine administered via injection two to three times daily. Mayhew said such treatment usually is not recommended if the patients aren't injuring themselves during their episodes.
In neonatal foals, seizures generally indicate sepsis and/or hypoxic or ischemic encephalopathy (i.e., dummy or barker foals). Adolescent foals, particularly Arabians, can suffer from an inherited form of adolescent epilepsy that is treatable and resolves over time.
Like narcolepsy, epilepsy manifested by repeated generalized seizures with no apparent underlying disease process has not been reported in adult horses. Instead, generalized seizures in adults appear to be most commonly caused by:
- Viral encephalitis;
- Hepatoencephalopathy (brain and nervous system damage as a complication of liver disorders);
- Leukoencephalomalacia (a softening of the white matter of the brain) due to Fusarium spp mycotoxicosis;
- Other toxicities;
- Brain abscesses, and
- Equine protozoal myeloencephalitis (EPM).
Anticonvulsant therapy is indicated in affected horses with cluster seizures or more than one seizure per month, or if the patient injuries itself and the animal's owner will not consider euthanasia. Phenobarbital alone or in combination with potassium bromide is the treatment of choice. Guidelines for administration are included in Mayhew's new book Large Animal Neurology (Wiley-Blackwell, UK, December 2009).
Mayhew said these animals are unsafe to ride until they have remained seizure-free while off of medication for six months.
Mayhew also advised, "24-hour video recording can be a powerful tool to capture episodes of sleep and seizures and help the veterinarian in making an accurate diagnosis and prognosis."
Guttural Pouch Anatomy, Problems
Guttural pouches are more than just ill-defined air-filled vats located somewhere in the horse's head, said Julie Fjeldborg, DVM, PhD, an associate professor in the department of large animal sciences at the University of Copenhagen, Denmark.
Guttural pouches are of interest to both veterinarians and horse owners, as they contain a number of important structures. Arteries such as the internal carotid artery, and several cranial nerves, including the facial, glossopharyngeal, vagus, accessory, and hypoglossal nerves, also course through the guttural pouches.
The guttural pouches, unique to a limited number of mammals, such as the horse, rhinoceros, and the South American forest mouse, are paired diverticulae of the Eustachian tubes that connect the middle ear to the pharynx (which extends from the rear of the mouth and nasal passages to the larynx and esophagus). Each guttural pouch has a volume of approximately 300 mL to 500 mL. The exact function of the guttural pouches remains elusive, even though scientists discovered them more than 200 years ago. One theory is that the guttural pouches serve as "brain cooling devices."
"It is important to note that the guttural pouches are not sterile. They contain the same bacterial composition as the pharynx," explained Fjeldborg.
Since there is only a very thin membrane (approximately 45 to 200 microns) that wraps around these delicate structures to separate potential pathogens or necrotic pus from major arteries and cranial nerves, it is clear that guttural pouch disease requires immediate treatment, said Fjeldborg.
Some of the more common diseases of the equine guttural pouch include:
- Empyema (the collection of pus);
- Mycosis (fungal infection); and
- Otitis media or interna (inflammation of the middle or inner ear).
When it comes to diagnosis of guttural pouch problems, the endoscope is the veterinarian's best friend. He or she can pass the scope via the nasal passages to access the guttural pouches where they communicate with the pharynx.
The veterinarian can use endoscope-guided flushes of the pouch(es) with a nonirritating solution when treating some gut-tural pouch diseases.
Failure to conceive and early embryonic death negatively impact the breeding industry; however, late-term abortions also occur and should not be ignored, said Michelle M. LeBlanc, DVM, Dipl. ACT, a reproduction specialist at Rood & Riddle Equine Hospital in Lexington, Ky.
Late-term abortion is a loss of pregnancy after seven months of gestation. "Mares at risk for late-term abortion include those with a surgical or medical crisis, placentitis (inflammation of the placenta), (those that) are off feed for many days, have devel-oped laminitis, or equine Cushing's disease," explained LeBlanc.
Clinical signs of impending abortion late in gestation include: early udder development; placental abnormalities noted on ul-trasound examination; and vulvar discharge.
"Most often, there are no warning signs," advised LeBlanc.
A veterinarian can use a variety of tests to diagnose late-gestation abnormalities, including ultrasound examination of the placenta and fetus and measurement of maternal hormonal levels and electrolyte levels in the mare's milk. LeBlanc said it can be useful to measure the combined thickness of the uterus and placenta when assessing a mare for placentitis. Researchers have found that a combined thickness of greater than 1.5 cm could indicate placentitis (normal thickness at 10 months of gestation is 1.2 cm or less).
Mares diagnosed with placentitis require aggressive management. LeBlanc recommends combining therapy, including anti-biotics, anti-inflammatory drugs, and immunomodulators.
However, LeBlanc said combining such drugs can block abortion of a dead fetus, resulting in the development of severe me-tritis (inflammation of the lining of the uterus). Alternatively, the deceased fetus can become mummified or crushed.
Mares undergoing treatment for placentitis that are at risk for late-term abortion require veterinary examinations at least once weekly, as deadly complications can develop rapidly. "If complications such as metritis or retention of a dead fetus develop, the mare is not likely to conceive again that season if not treated aggressively after the abortion," advised LeBlanc.
Tendon Sheaths and Lameness
Tendon sheaths--the thin connective tissue wrapped around the tendons and containing synovial fluid--can be a potential cause of lameness.
"Diagnosing lameness originating from tendon sheaths is increasing with awareness and increased availability and use of magnetic resonance imaging (MRI)," reported Lisa A. Fortier, DVM, PhD, Dipl. ACVS, associate professor of large animal surgery at Cornell University.
The three most commonly affected tendon sheaths are the digital tendon sheath, which wraps around the superficial and the deep digital flexor tendons; carpal tendon sheath, which also wraps around the superficial and deep digital flexor tendons in the back of the knee (carpus); and the tarsal tendon sheath, which wraps around the superficial and deep digital flexor tendons near the back of the hock (tarsus).
Diagnostic techniques frequently used to identify tendon sheath injury or damage include ultrasonography and tenoscopy, which involves inserting an endoscope into the tendon sheath, she explained.
"Tenoscopy provides a minimally invasive approach for maximal exposure to tendon sheaths and their structures," said For-tier.
While the prognosis will vary from case to case based on the exact underlying source of the lameness, "Many horses return to full athletic performance post-tenoscopy once the adhesions or scar tissue masses have been removed, or the con-stricting annular ligament (the structure that holds the superficial and deep digital flexor tendons in place as they pass the fetlock joint) has been transected (cut)," advised Fortier.
Early return to exercise following tenoscopy is desirable, as return to exercise is crucial to prevent re-formation of adhesions, she said.
By Kimberly S. Brown and Stacey Oke, DVM, Msc
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