Equine atypical myopathy, also known as atypical myoglobinuria, or EAM is a fatal disease of horses (

equidae Equidae (sometimes known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, asses, and zebras, and many other species known only from fossils. All extant species are in the genus '' Equus'', ...

) characterized by acute

rhabdomyolysis Rhabdomyolysis (also called rhabdo) is a condition in which damaged skeletal muscle breaks down rapidly. Symptoms may include muscle pains, weakness, vomiting, and confusion. There may be tea-colored urine or an irregular heartbeat. Some of th ...

. It is caused by the ingestion of the seeds or young shoots of sycamore tree. EAM has a high fatality rate.

Cause

Atypical myopathy is a commonly fatal form of equine

caused by the toxin

Hypoglycin A Hypoglycin A is a naturally occurring amino acid derivative found in the unripened fruit of the Ackee tree ('' Blighia sapida'') and in the seeds of the box elder tree ('' Acer negundo''). It is toxic if ingested, and is the causative agent of Ja ...

(HGA). HGA is a naturally-occurring amino acid contained by trees and shrubs of

Sapindaceae The Sapindaceae are a family of flowering plants in the order Sapindales known as the soapberry family. It contains 138 genera and 1858 accepted species. Examples include horse chestnut, maples, ackee and lychee. The Sapindaceae occur in tempera ...

family. Horses can become poisoned by eating the seeds or seedlings of

Acer pseudoplatanus ''Acer pseudoplatanus'', known as the sycamore in the British Isles and as the sycamore maple in the United States, is a species of flowering plant in the Sapindus, soapberry and lychee family Sapindaceae. It is a large deciduous, broad-leaved ...

(called Sycamore in the UK or more widely Sycamore Maple) or

Acer negundo ''Acer negundo'', the box elder, boxelder maple, Manitoba maple or ash-leaved maple, is a species of maple native to North America. It is a fast-growing, short-lived tree with opposite, compound leaves. It is sometimes considered a weedy or inv ...

(Box Elder). The amount of HGA in sycamore seeds may vary. The toxin affects to the functioning of horse’s muscle cells by slowing down or stopping the energy production. Even if atypical myopathy is not contagious it can affect either to individual horse or several horses in the same stock. Some horses may be more resistant to the toxin than others due to genetic differences and different grazing habitats. Changes in weather conditions and temperature may contribute to the propensity of being affected, which is the reason why many cases are reported during autumn and spring.

Diagnosis

Diagnosis can be confirmed by clinical examination and laboratory tests. In most cases treatment needs to be started before getting the laboratory test results as the confirmation of diagnosis may take several days. First symptoms are usually muscular weakness, soreness and stiffness causing problems with walking and breathing. Within hours of first symptoms horse may be unable to stand and in 72 hours of the onset of signs mortalities may occur. The mortality rate of atypical myopathy is high; only 30-40% of affected horses survive. EAM affected horse’s urine is dark red or brown. Sweating and muscle trembling can be observed while moving. Horses may hang their heads down and be apathetic. Symptoms resemble

colic Colic or cholic () is a form of pain that starts and stops abruptly. It occurs due to muscular contractions of a hollow tube ( small and large intestine, gall bladder, ureter, etc.) in an attempt to relieve an obstruction by forcing content out ...

symptoms except that EAM affected horse doesn’t lose appetite. The body temperature, heart rate and respiratory rate may be normal in some cases.

Prevention

As treatment is still unsuccessful in the majority of cases the main emphasis is on prevention. Risk of atypical myopathy can be reduced by checking pasture for sycamore plants regularly and avoid letting horses graze in pastures where are sycamore trees. In case there are fallen sycamore leaves and seeds in pasture they should be cleaned from the ground. Fresh and clean water should be easily accessible all the time. Keeping the stock size appropriate reduces the risk as there is enough proper grazing for every horse. Taking care of regular

vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulating ...

s and

anthelmintic Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. They may a ...

treatments decreases the risk. The presence of HGA in pasture can be tested by submitting a sample to laboratory.

Treatment

EAM affected horses are in need of intensive care. There is no

antitoxin An antitoxin is an antibody with the ability to neutralize a specific toxin. Antitoxins are produced by certain animals, plants, and bacterium, bacteria in response to toxin exposure. Although they are most effective in neutralizing toxins, the ...

for HGA but some medications can be used to stop absorption of the toxin. Symptomatic treatment includes intravenous fluid therapy, supplementation of

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

and

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism o ...

as well as administration of

carnitine Carnitine is a quaternary ammonium compound involved in metabolism in most mammals, plants, and some bacteria. In support of energy metabolism, carnitine transports long-chain fatty acids into mitochondria to be oxidized for energy production, an ...

vitamin E Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitami ...

selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...

and

riboflavin Riboflavin, also known as vitamin B2, is a vitamin found in food and sold as a dietary supplement. It is essential to the formation of two major coenzymes, flavin mononucleotide and flavin adenine dinucleotide. These coenzymes are involved in ...

Anti-inflammatory Anti-inflammatory is the property of a substance or treatment that reduces inflammation or swelling. Anti-inflammatory drugs, also called anti-inflammatories, make up about half of analgesics. These drugs remedy pain by reducing inflammation as o ...

medication is used to decrease the pain and possibly increase the chance to survive. Supportive therapy includes the regular emptying of the

bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

. Affected horse should be kept warm. Horses usually recover completely if they survive the first days after being affected. Recovery may still take several months.

References

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External links

Equine Atypical Myopathy: The disease
Horse diseases