Is your horse suffering from failing coordination, perhaps combined with weakness or muscle loss? A horse owner's first thought would be lameness. However, for a horse exhibiting these symptoms with no obvious cause for lameness they may have something much more serious and much harder to spot. Equine Protozoal Myeloencephalitis is a diseases caused by a parasite infection in the brain and spinal cord. As it progresses, it affects the central nervous system of the horse and can cause a variety of symptoms. This disease is difficult for veterinarians to diagnose as the symptoms often mimic a number of different neurological disorders. If left untreated, horses can experience irreparable damage to their nervous system which will cause the horse to soon lose the ability to stand and death will eventually occur.

Symptoms of Equine Protozoal Myeloencephalitis

The most common symptoms of Equine Protozoal Myeloencephalitis are ataxia or asymmetric incoordination, weakness and spasticity or tight muscles. However, they can also manifest symptoms common with any neurological disorder such as seizures, abnormal behaviour, a strange gait, and facial paralysis. Equine Protozoal Myeloencephalitis affects the central nervous system, but it can also affect other areas of the brain to mimic the symptoms of other problems. Although uncommon, the protozoa can infect the nerves in the throat which can cause paralyzed flaps in the throat, snoring, or a variety of odd airway noise.

In a study of the disease, they found that some of the early symptoms included dropping food, decreased tongue tone and facial paresis as well as the aforementioned weakness and lameness.

Though veterinarians recommend Equine Protozoal Myeloencephalitis be caught early, it can take weeks or months for the symptoms to even manifest. Horses will often try to compensate when they lose feeling in the muscle from neurological damage, this is why symptoms will only manifest when the horse can no longer do that. By that time, it may be too late to help. However, if a horse has been showing signs of tiredness or even a slight stumble, this is an early warning sign.

Causes of EMP

There is only one cause of Equine Protozoal Myeloencephalitis and that is the parasite Sarcocystis Neurona, or S.nuerona for short. S.nuerona is an interesting parasite as in order to complete its life cycle it needs to live in two hosts--the intermediate and the definitive. Animals like cats, racoons, and skunks have been shown to be prime intermediate hosts while the opossum is the definitive host. The intermediate hosts ingest the parasite in which it breeds within their muscle tissue.

When the intermediate host animals die and are ingested by the opossum, the opossum can transfer it to their feces. It is only after it has been released by the opossum that it can infect horses. Horses are usually infected when they drink water or graze in areas that have been exposed to opossum feces. The horse is considered an aberrant host as it serves as a dead end for the parasite's life cycle. It cannot be excreted into feces nor can the parasite reproduce into the muscle tissue. The parasite is contained in the brain or spinal cord, killing the cells of the host as it moves throughout them.

EMP Diagnosis

Because Equine Protozoal Myeloencephalitis can mimic other neurological disorders, quite a few ancillary diagnostic procedures may need to be ran in order to rule out other disorders. If horse owners suspect their horse may be infected with this parasite, suggest it to the veterinarian. The current diagnostic test for Equine Protozoal Myeloencephalitis is an immunoblot analysis of serum and CSF. With this quick test, they can rule out or confirm a parasite as the cause and move onto other possible neurological disorders or treatment.

Treatment for Equine Protozoal Myeloencephalitis

With Equine Protozoal Myeloencephalitis, ongoing exposure can lead to permanent damage to the brain and nervous system. Once Equine Protozoal Myeloencephalitis is diagnosed it should be treated as quickly as possible to prevent any further damage. The most common treatment for Equine Protozoal Myeloencephalitis is dihydrofolate reductase inhibitors. As the name suggests, dihydrofolate reductase inhibitors stop the function of the molecule dihydrofolate reductase which both bacteria and parasites need to grow, multiply and live. While the S.nuerona cannot multiply within the horse, dihydrofolate reductase inhibitors will kill it off within a few weeks.

Dihydrofolate reductase inhibitors are given orally to a horse twice a day for 120 days. The long dosage is to assure that the parasite is completely killed and to prevent exposure to the parasite again from the environment. This effectively gives the owner time to rid the horses environment of parasite exposure points.

Prevention of EMP

Once a horse has contracted Equine Protozoal Myeloencephalitis, it is clear that the parasite is within their usual environment. For those who own multiple horses, once the infection has been discovered, they should have their other horses tested. Along with testing, all the horses should given new sources of food and water. This means clean water buckets with fresh water as well as temporary relocation to a new pasture. However, many veterinarians will recommend switching horses to feed or hay just to make sure that they are not exposed.

There is no vaccine to prevent this parasite, though there is one that has been developed using merozoites. However there has been no clinical evidence or research done to support that it actually does work. So in order to control this parasite, horse owners must control the carriers. As opossums are scavengers, be sure to keep all road kill or animal carcass away from grazing land for horses. The current recommended prevention standard is to keep opossums away from hay, grain, pasture or water that the horses may be using. This can be done by merely keeping the areas above their reach or sealed. Some horse owners have used live traps to transport the opossum off of their property while others use the kill on sight strategy.


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