Box elder seeds implicated in Seasonal Pasture Myopathy

A toxin present in the seeds of the box elder tree has been found to cause Seasonal Pasture Myopathy.

Seasonal Pasture Myopathy (SPM), a highly fatal muscle disease, occurs particularly in the Midwestern United States and eastern Canada.

Horses with SPM suffer from severe, generalised muscle weakness. They are often unable to get to their feet, or only do so with difficulty. If they are still able to walk, they have a stiff gait - especially of the hindquarters. Affected animals have elevated heart rates, and show profuse sweating and muscle twitching.

The underlying disease process has been shown to be an acquired enzyme deficiency (MADD: multiple acyl-CoA dehydrogenases deficiency) in skeletal muscle.

A similar condition, Atypical Myopathy (AM), occurs in Europe.

Recent research, led by Dr Stephanie Valberg, of the University of Minnesota, showed that the seeds of the box elder tree (Acer negundo) contain hypoglycin A, which can cause SPM.

The study involved 12 horses with seasonal pasture myopathy The researchers examined farms on which SPM had occurred, looking for common factors, and compared them with unaffected farms. Seeds from box elder trees were present on all of 11 SPM-affected pastures and 61% of 23 control pastures.

Examination of box elder seeds from the SPM pastures showed they contained hypoglycin A, a branched-chain amino acid. Once ingested, hypoglycin A is metabolised into MCPA (methylenecyclopropylacetic acid) a toxic compound, which is known to cause multiple acyl-CoA dehydrogenase deficiency (MADD).

The researchers explain that the MCPA “would have a major impact on energy generation, particularly when horses are mobilising fat because of a negative energy balance.” They add ”a negative energy balance was probably promoted in SPM horses by offering little supplemental feed while horses were housed on overgrazed pastures, in some cases during inclement weather conditions.”

Writing in the Equine Veterinary Journal, they conclude: “For the first time, SPM has been linked to a toxin in seeds abundant on autumn pastures whose identified metabolite, MCPA, is known to cause acquired MADD, the pathological mechanism behind SPM and AM.”

“Further research is required to determine the lethal dose of hypoglycin A in horses, as well as factors that affect annual seed burden and hypoglycin A content in Acer species in North America and Europe.”

Read more at www.equinescienceupdate.com

Insect compound may help laminitis

Veterinarians at the University of California, Davis, School of Veterinary Medicine have announced plans for a clinical trial of an experimental drug that has shown promise in treating horses with laminitis.

They report that four horses suffering from laminitis have been treated with the investigational anti-inflammatory drug so far. One experienced a complete remission that has lasted for more than a year, and three others have shown some improvement.

A paper on the first case has been accepted for publication by the Journal of Veterinary Anaesthesia and Analgesia. The journal editors authorised the authors to disclose their findings ahead of publication.

“This is an unusual step for us to announce this so far in advance, but because euthanasia is often the only way to alleviate pain in severe laminitis, we felt that it was important to let the veterinarians and horse owners know that this compound has shown potential as a treatment,” said Alonso Guedes, an assistant professor in the School of Veterinary Medicine.

A clinical trial to assess the drug’s safety and establish a tolerable dose for the compound is expected to begin early 2013. Further clinical trials would be needed to establish the drug’s effectiveness as a laminitis treatment.

The experimental compound, known as t-TUCB, belongs to a group of anti-inflammatory compounds called sEH (soluble epoxide hydrolases) inhibitors. It stems from a discovery made more than 40 years ago by UC Davis entomology professor Bruce Hammock while doing basic insect biology research.

In the paper, Guedes reports the case of a 4-year old Thoroughbred mare that was participating in a study into treating tendon injuries using stem cells, having been retired from racing following such an injury.

The mare developed acute laminitis, which deteriorated despite treatment including cold immersion, antibiotics, leg wraps, and nonsteroidal anti-inflammatory drugs. Before resorting to euthanasia, Guedes and the veterinary team decided to try one last treatment, t-TUCB.

The veterinarians administered the experimental compound intravenously early on the eighth day of the mare's laminitis. They report that, after receiving the first dose, the horse remained standing in the stall most of the day, became interested in her surroundings and walked voluntarily. The mare’s demeanor, posture and mobility continued to improve over four days of treatment.

No adverse affects from t-TUCB were observed, and the mare has remained laminitis-free for twelve months.

Hammock said that work aimed at moving t-TUCB and related compounds toward clinical use is advancing in several areas. He and Guedes are working on compounds with potential for targeting pain and arthritis in companion animals.

See the UC Davis video..

Do local anaesthetics affect MRI findings?

 

Don't rush to carry out MRI evaluations after performing intrasynovial anaesthesia of the digital flexor tendon sheath, warn researchers at the University of Guelph, in Canada. Their work shows that local anaesthetic injected into the digital sheath results in changes that are visible on the magnetic resonance image for at least 72 hours.

The very act of injecting local anaesthetic into tissues can produce physical changes that need to be taken in to account when interpreting bone scans and ultrasound images. Until recently, knowledge of how local anaesthetic techniques influenced the appearance of magnetic resonance images was limited.

Researchers, led by Dr Belinda Black, at the University of Guelph 's Ontario Veterinary College conducted a study into whether anaesthesia of structures in the equine foot caused changes that were detectable on subsequent MRI evaluation.

The study involved fifteen healthy adult horses. None of them was lame, neither had they received non-steroidal anti-inflammatory drugs or undergone perineural or intrasynovial anaesthesia in the previous two weeks.

A baseline MRI examination of both front feet of each horse was carried out before performing the local anaesthetic techniques on one forelimb, selected at random. Mepivicaine was injected around the lateral and medial palmar digital nerves; into the podotrochlear (navicular) bursa; the digital flexor tendon sheath and the distal interphalangeal joint.

The MRI examination was repeated 24 and 72 hours after injection and the images compared.

The research team found that in the case of palmar digital nerve blocks, and injections in the podotrochlear bursa and distal interphalangeal joint, the MRI findings were not significantly different from baseline 24 and 72 hours after injection.. So, they suggest that, when these structures appear distended in MR images after diagnostic anaesthesia, it probably is a true reflection of disease and not simply due to the anaesthetic injection.

This information is particularly important, they point out, since distal interphalangeal joint effusion had been reported as the most common finding on MR images of the equine foot.

In contrast, injection of mepivicaine into the digital flexor synovial sheath resulted in distension of the sheath which was still present 24 and 72 hours later.

Dr Black comments that, although a definite time frame for resolution of digital flexor tendon sheath distension was not determined, she recommends waiting more than 3 days between intrasynovial anaesthesia of the digital flexor sheath and MRI assessment.

She concludes: “our study showed that perineural anaesthesia of the palmar digital nerves and intrasynovial anaesthesia of the podotrochlear bursa or distal interphalangeal joint in sound horses did not have any significant effect on the interpretation of subsequent MR images. However, intrasynovial anaesthesia of the digital flexor tendon sheath caused a significant iatrogenic increase in synovial fluid, which was detectable on subsequent MR images for at least 72 hours.”

Read more at www.equinescienceupdate.com

Hendra vaccine released

Australian horse owners will welcome the news of the introduction of a vaccine* to help protect horses against the deadly Hendra virus. The vaccine, which is available only under permit from accredited veterinarians, will also assist in breaking the cycle of transmission that puts humans at risk of contracting this potentially lethal virus.

Hendra virus is a serious zoonotic infectious disease transmitted by flying foxes shedding the virus in their saliva, urine, aborted foetuses and/or reproductive fluids. Horses are thought to contract the virus by ingesting feed or water contaminated with one of these sources of infection.

With a high mortality rate, Hendra virus has claimed the lives of 81 horses, including nine deaths in 2012 alone. There is no known cure, so the vaccine is positioned to become the most effective defence against this virus.

“This vaccine significantly decreases the risk of exposure to Hendra virus for horse owners, handlers and veterinarians. For that reason, the Australian Veterinary Association recommends that all horses be vaccinated against the Hendra virus,” said Dr Ben Gardiner, President, Australian Veterinary Association (AVA).

“The vaccine will also help to protect the health of horses and is a major win for anyone working in the equine industry, including veterinarians.”

Read more at www.equinescienceupdate.com

Equine Grass Sickness Vaccine Study

Researchers at the Animal Health Trust, Newmarket and the Royal (Dick) School of Veterinary Studies, University of Edinburgh are collaborating in a pilot trial of a vaccine to protect against equine grass sickness.

Equine grass sickness (EGS) is a frequently fatal disease of horses; more than 85% of affected animals die.  It has been reported in several northern European countries, but occurs most frequently in Great Britain, having been first recognised in Scotland over 100 years ago.

The cause is still not known for certain, but it seems likely that toxins from Clostridium botulinum type C are involved.

The pilot study, based in eastern Scotland, has enrolled a total of 100 horses and ponies. This small scale trial is in preparation for a full vaccine trial, which will involve at least 1000 horses and ponies, and is likely to commence in 2013-2014 subject to securing sufficient funding.

Although there is still a lot of work to do before launching the full nationwide vaccine trial, this initial pilot study will help to ensure that the trial design will be practical to perform on a larger scale.

Dr Jo Ireland of the Animal Health Trust, who is piloting the vaccine trial, explains: ‘This is very exciting news and we are working flat out to get the study up and running. There is still a lot of work to do before launching the full nationwide vaccine trial, and this initial study will help us to ensure that the trial design will be practical to perform on a larger scale.’

The Equine Grass Sickness Fund is spearheading the campaign to raise funds for the full vaccine trial, which is being run in collaboration with the Animal Health Trust, The (Dick) Vet and Liverpool University’s School of Veterinary Studies.

Kate Thomson, spokesperson for the Fund, said ‘We are over the moon that the vaccine trial is finally here, but fundraising now starts in earnest to ensure that the full trial can go ahead. Grass sickness takes a terrible annual death toll, and we are appealing to every horse owner in the UK to help bring an end to the disease by donating to this cause’.

If you would like to support the equine grass sickness vaccine trial by making a donation to the Equine Grass Sickness Fund, please visit www.grasssickness.org.uk

New study to investigate headshaking in horses

Headshaking syndrome is an intermittent, apparently involuntary, movement of the horse’s head. It may occur at rest or at exercise. The signs may be so severe as to prevent the horse being ridden.
It is not an uncommon problem, and proves very frustrating to treat. It is thought to be due to pain in the sensory nerves supplying the face (trigeminal nerve).

Although some progress has been made towards both diagnosing and treating the condition in horses, the pathology of the disease remains unknown and further research is needed.

Caudal compression of the infraorbital nerve currently offers the best prognosis for a successful outcome compared with other treatments.

The procedure was developed by Veronica Roberts and colleagues at the University of Liverpool's Veterinary School. Now Clinical Fellow in Equine Medicine in the University of Bristol’s School of Veterinary Sciences, Roberts has received a grant from the British Neuropathological Society to investigate possible focal demyelination of the nerve as a cause of headshaking in horses.

Demyelination is the most common cause of trigeminal neuralgia in people, so the research team will look to see if it is involved in the equine condition. They will collaborate with Seth Love, Professor of Neuropathology at the University of Bristol's School of Clinical Sciences, as he has carried out work in this area in people.

To find a more effective treatment and to understand the disease, Dr Roberts is requesting that anyone who is considering euthanizing a horse due to headshaking to contact her for possible inclusion in her study.