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ATYPICAL MYOPATHY, EQUINE - UK: (ENGLAND)
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International Society for Infectious Dieases
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Date: 20 Nov 2009
Source: The Cumberland News [edited]
<http://www.cumberland-news.co.uk/news/fatal_horse_disease_breaks_out_in_cumbria_1_639486?referrerPath=home>
Fatal horse disease breaks out in Cumbria
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A disease has broken out in Cumbria which can be fatal for horses.
The disease -- known as Atypical Equine Myositis/Myoglobinuria -- has
claimed the life of at least one horse and 4 others have had to
undergo aggressive treatment.
Veterinarian Neil Frame, from Frame, Swift and Partners in Penrith,
said: "It is very worrying but we are quite lucky that the ones we
have treated have recovered quickly after aggressive treatment. The
signs are usually a stiffness in the limbs followed rapidly by
generalised muscle weakness and then recumbency for prolonged
periods. The other main sign is cherry black or dark brown
discolouration of the urine. A percentage of horses will never rise
again and need euthanasia due to terminal heart failure and
respiratory disease -- horses are not designed to lie on their side
for prolonged periods."
The disease causes huge damage to the skeletal muscles causing the
horses to weaken and go down. The damaged muscle cells release
myoglobin (the oxygen carrying pigment of muscle) which causes the
discolouration of urine but also can cause renal failure as the
myoglobin destroys the kidney tubes.
Mr Frame said the disease, which is spreading across the Penrith,
Appleby and Kirkby Stephen areas, tends to affect younger horses at
grass. He said: "It has an 80 percent mortality rate but we have only
lost one one of 5 horses so far. There were 2 cases in southern
England in 2007 and a big outbreak in Belgium in 2005. We have found
that the horses we have treated have been at the younger end of the
scale -- about 5 to 6 years old. One of them was 8 years old."
Treatment must be rapid and involves administering huge volumes of
intravenous fluids to prevent kidney failure, pain relief and
intensive nursing. The cause of the disease is thought to be a
mycotoxin which can grow on pastures after a dry spell, followed by
wet, squally weather.
Mr Frame added: "The disease will disappear after a prolonged frosty
spell which is thought to kill the mycotoxin growing on the pasture."
Horse owners should make sure that all their horses are adequately
vaccinated, wormed and other diseases treated properly to remove all
stress. They should be given as much shelter as possible.
For more information go to <http://www.frameswiftandpartners.co.uk>.
[Byline: Pam McClounie]
--
Communicated by:
ProMED-mail Rapporteur George A. Robertson
[This disease has been around, in various parts of the world since,
by some accounts, 1934, and by others only since the 1980's.
Regardless of when it was recognized, a defined etiology has not yet
been found.
The most probable hypothesis concerning the etiology of atypical
myopathy is the one incriminating a toxin (phytotoxin, mycotoxin or
bacterial toxin), eaten and absorbed directly or produced in situ.
The disease most often appears acutely with little or no clinical
signs for observation. The rare premonitory signs described by owners
consist of lethargy, decrease of appetite, signs of colic, stiffness
or lameness. These are not specific signs and could indicate a number
of equine diseases.
All horses presenting atypical myopathy suffer from severe,
generalised weakness and are frequently found in lateral recumbency.
Sometimes, they are found dead on pasture without showing any warning
signs. Signs of colic can be present, most probably due to the
difficulty to urinate. The distension of the bladder could indeed
explain the signs of colic that usually disappear once the
veterinarian empties the bladder. However, colic sign unresponsive to
bladder emptying may indicate coexistence of abdominal colic and
atypical myopathy.
Horses still able to walk present with stiffness, particularly
visible at the hindquarter. It is important also to check other
horses present on the same pasture for stiffness, because it may be
that there are early warning signs in the other animals.
In general, horses suffering from atypical myopathy are depressed.
Often, they show difficulty or even inability to get on their feet
and/or to stay standing. Muscular tremor and localized or generalized
sudation can be observed. In spite of the severity of the clinical
signs, often affected horses still want to eat (try to grasp any hay
or grass that is near their mouth). No clinical signs have been
reported related to the central nervous system, but occasionally,
some some paddling has been observed. This might be interpreted as a
sign of suffering or/and anxiousness and/or desire to get up. It is
important to mention that compared to the intense suffering of
exertional myopathy, atypical myopathy seems less painful.
The dark coloured urine is probably the most specific clinical sign
of atypical myopathy. If possible, collect a urine sample to show
your vet to help him make a correct diagnosis.
The mucosae are congested (abnormally red) or less often, cyanotic
(purple). Taking the rectal temperature reveals generally an
important hypothermia (less than 36 DEGC [96.8 DEG F], whereas it is
between 37 and 38 DEGC [98.6-100.4 DEG F] in a healthy horse). This
hypothermia is probably a consequence of the fact that the horse is
laying on the pasture, not able to move or get up, often in the cold
(most of the cases arrive in autumn or spring, during cold nights).
The horses often show difficulties in breathing progressing over
time. Their heart rate is often increased (> 60 beats/minute compared
to 40 beats/minute for a normal resting horse), and their respiratory
rate sometimes also. Most of the time, the gut sounds are normal.
In addition to the classical treatment for any kind of myopathy, it
is necessary to empty the bladder frequently because horse affected
by atypical myopathy may have difficulty urinating. The bladder
distension can become important and painful and may induce colic signs.
A wide epidemiological investigation on Belgian cases confirmed for
atypical myopathy has been undertaken. This study enabled the
identification of factors that tends to favour atypical myopathy.
From these identified factors, some preventive measures can be
proposed. However, this study focused on Belgian cases. Differences
between countries in atypical myopathy-associated risk factors should
exist since the flora, pasture characteristics and management of
horses and pastures may differ markedly.
Comparison of outbreaks within countries will be of value to narrow
the common factors between affected areas. This will be of great help
in our quest for the aetiological agents and strengthen our knowledge
of epidemiology. This is the reason why we encourage horses owners
and veterinarians confronted to a case to communicate us the
information concerning a suspected cases by the use of the clinical
questionnaire (to be filled in by the veterinarian) and the
epidemiological questionnaire (to be filled in by the owner of the horse).
While there are some clinical signs similar to that of "white muscle
disease" involving selenium and vitamin E, it does not seem closely
related. However, I can find no reference to any nutritional studies
regarding these factors and this disease.
Another differential is Equine Exertional Rhabdomyolysis (ER) or
Tying Up or Azoturia or Monday Morning Disease. This is a disease
that sounds similar to this atypical myocitis with a few exceptions.
Rhabdomyolysis typically occurs in horses that are worked hard during
the week (what ever days that may be) then given a rest, but remain
on the working ration which is often high in carbohydrates. There
appears to be a genetic link in this trait as well.
This disease may also have a factor of low vitamin E and selenium.
Clinical signs of reluctance to move, sweating, elevated heart and
respiratory rates as a result of the pain, anxious expression,
shifting of weight from side to side, standing hunched and tense,
passing reddish-brown urine, dehydration, shock, and inability to
rise usually occur shortly after the animal is returned to the normal
working routine.
The primary difference that I think distinguishes these 2 syndromes
is that Rhabdomyolyisis occurs in working horses when returned to
work after a rest but still consuming the high carbohydrate ration.
Atypical myopathy appears to be occurring in all horses, even those
on pasture without a working schedule.
Portions of this comment have been extracted from:
<http://www.myopathieatypique.be/fr/produit_detail.php?ID_produit=77&&sscategorieID=50>.
The Cumbria region of the UK may be seen at
<http://www.picturesofengland.com/mapofengland/counties-map.html>.
- Mod.TG]
....................tg/ejp/dk
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