Joint Lubrication and Injury Response (AAEP 2011)

by: Christy Corp-Minamiji, DVM
January 19 2012, Article # 19463


A horse's athletic success depends on the health of his joints, and veterinarians are continually studying up on how best to maintain athletic joints and manage injury. During a presentation at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas, Larry Bramlage DVM, MS, Dipl. ACVS, an equine surgeon at Rood & Riddle Equine Hospital, in Lexington, Ky., gave veterinarians an "introduction to joint therapy." He described the lubrication mechanisms within the joint and the natural responses of the joint to injury.

Bramlage pointed out that when a joint is damaged, veterinarians see typical and consistent signs: a lame horse and a distended joint with increased amount of watery joint fluid. While the human impulse is to "fix" these types of signs, Bramlage pointed out that these very clinical signs are "a superficial part of the joint's response to insult."

The interior of the joint consists of the articular cartilage, which covers the bone ends, and the synovium that lines the inside of the joint capsule. Both cartilage and synovium are bathed in joint fluid, but they are lubricated by different means and have different responses to insult.

Bramlage referenced a study evaluating pain within the joint in which examiners found that while pulling on the synovium itself was excruciating, cartilage has no nerve endings and cartilage stimulation is not painful.

Hyaluronic acid (HA) lubricates the synovium, while water lubricates the cartilage through a sort of "sponge" mechanism. Weight-bearing compresses cartilage and fluid is forced out, preventing friction. Proteoglycan in the cartilage matrix reinflates it, and more proteoglycan means better inflation. Insults to the joint can exhaust proteoglycan supplies over time. When proteoglycan can no longer restore the water in the cartilage matrix, the lack of lubrication produces wear and tear. "Cartilage degrades silently and with very little pain," says Bramlage.

If damage can occur within the joint in the absence of pain, can joint pain ever be good? The answer is yes because it protects the joint. Since synovial lining lubrication plays such a large role in pain sensation, Bramlage went on to point out that under-lubricated synovium and its accompanying "drag" causes pain with joint motion and is the reason flexion tests work.

Loss of lubricating HA allows an influx of protein and fibrin into the joint, he noted. Fibrin collects debris and sticks it to the synovial villi (carpetlike projections) to prevent it from circulating in the joint. Then the synovium must eliminate it.

However, the debris removal process and its associated inflammation causes the villi to stick together and lose their capability to collect additional debris. If this situation goes on too long, the joint will eventually exhaust the villi, and lose its ability to produce HA. The result will be chronic effusion, or joint fluid buildup.

Bramlage points out the problem with a damaged joint: It is "difficult to improve upon the joint's normal response (to insult), but that normal response might not allow performance. Treatment then must aid in performance without trying to eliminate the joint's natural response to injury."

Equine Rhinitis in Respiratory Infection Cases (AAEP 2011)

by: Nancy S. Loving, DVM
January 23 2012, Article # 19482


When considering viral respiratory infections in horses, a common assumption among veterinarians is animals are infected with either influenza or rhinopneumonitis (a respiratory condition--mostly of young horses--caused by equine herpesvirus). However, another viral infection--equine rhinitis--is commonly responsible for respiratory disease outbreaks. Andres Diaz-Mendez, Med Vet, MSc, of the University of Guelph presented information about equine rhinitis virus A (ERAV) at the 2011 American Association of Equine Practitioners Convention, held Nov. 18-22 in San Antonio, Texas.

Diaz-Mendez described clinical signs of ERAV, which mimic those seen with equine influenza or rhinopneumonitis: nasal discharge ranging from serous (clear, runny) to mucopurulent (thick, greenish-white), fever, and cough. In one study of nasal swabs from horses with acute respiratory disease, researchers found the prevalence of influenza was 56%, ERAV was 42%, and 24% of the horses were infected with both viruses. He explained that ERAV affects both the upper and lower airways with moderate inflammation that exacerbates inflammatory airway disease (IAD) and recurrent airway obstruction (heaves).

Genome sequencing of ERAV has shown that any changes since it was first isolated in 1962 have been very minor, as the currently circulating virus is 96% similar to when it was first identified. This is in contrast to equine influenza virus, which mutates frequently.

In Diaz-Mendez's study he induced experimental infection in a dozen 8- to 12-month-old healthy ponies by suppressing their immune systems with the corticosteroid dexamethasone three days prior to viral exposure. Within 24 hours of exposure, clinical signs began to appear as fever and increased wheezing lung sounds.


By Day 3, the ponies' submandibular (under the jaw) lymph nodes were enlarged and they had nasal discharge and tracheal mucus that was confirmed with endoscopy; the tracheal mucus persisted until Day 21. Lower airway samples revealed viral shedding Days 5 to 7. In the infected ponies an antibody response appeared by Day 7 that persisted to Day 21, along with airway inflammation lasting for three weeks. By Day 21, the lymph nodes were still enlarged but nasal discharge had abated.

Equine rhinitis virus can have a marked impact on health and performance by its effects on both the upper and lower respiratory tracts persisting for three weeks. Diaz-Mendez noted that infection with ERAV might be considerably underestimated in the equine population and, thus, practitioners should consider it when presented with a horse with acute respiratory viral infection. In addition, he pointed out that equine rhinitis virus might be associated with episodes of other respiratory conditions, such as IAD and heaves. At this time there is no vaccine available to protect against equine rhinitis virus.

Diaz-Mendez continues to research ERAV and received one of three inaugural $25,000 Boehringer Ingelheim Vetmedica Equine Research Awards at the convention for a study proposal. In a study to be completed in 2012 he'll examine the response of equine airway epithelium to ERAV infection and he'll perform viral surveillance.

Three Additional EHV-1 Cases Confirmed in California

by: Erica Larson, News Editor
January 18 2012, Article # 19462


Three additional cases of equine herpesvirus-1 (EHV-1) were confirmed in California over the weekend, bringing the total number of cases in the current outbreak to eight, according to a statement from the California Department of Food and Agriculture (CDFA).

On Jan. 11 a gelding residing on a "large multidiscipline facility with no movement of horses on or off the property" tested positive for the debilitating virus. He was quarantined on the farm and is receiving veterinary care.

On Jan. 12 testing confirmed that two additional horses on the property were EHV-1-positive. Those horses were also isolated and quarantined on the same farm and are receiving veterinary attention. On Jan. 13, two additional horses on the premises tested positive for the virus.

Over the weekend, three additional cases were confirmed. New information from the CDFA indicates that only one horse has displayed neurologic signs; however, all eight have been quarantined on the property and are receiving veterinary attention.

"All exposed horses on the property are being monitored, and enhanced biosecurity measures have been implemented," the statement read. "The source of the outbreak has not been identified."

Further, an epidemiologic investigation into the outbreak showed that the current situation is in no way linked to any of the three EHV-1 outbreaks California saw in 2011, the statement noted.


Although it's not transmissible to humans, EHV-1 is highly contagious among horses and camelids, and it is generally passed from horse to horse via aerosol transmission (when affected animals sneeze/cough) and contact with nasal secretions. The disease can cause a variety of ailments in equines, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and myeloencephalopathy (EHM, the neurologic form).

Myeloencephalopathy is characterized by fever, ataxia (incoordination), weakness or paralysis of the hind limbs, and incontinence. Should a horse with potential EHV-1 exposure display any of the aforementioned clinical signs, a veterinarian should be called to obtain samples and test for the