The Horse

DEC 2018

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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TheHorse.com | The Horse December 2018 25 protozoal sporocysts into the environ- ment via feces. Secondary, or intermedi- ate, hosts include raccoons, cats, skunks, and armadillos. Horses are dead-end hosts, unable to transmit the disease to other horses. Horses ingest opossum feces in feed, in water, or while grazing, and while researchers aren't exactly sure how sporocysts migrate from the GI tract to the central nervous system (CNS), they suspect they cross the blood-brain barrier through cell transport into the brain and spinal cord. Prevention No immunization exists for EPM. However, management practices can help minimize exposure, including: ■ Preventing opossums from accessing your horse's feed, water, hay, and envi- ronment in general; and ■ Reducing brush near horse housing and maintaining distance between wooded areas and horses to reduce the likelihood of opossums frequenting your pastures and barns. Also, avoid leaving things out overnight that will attract opossums, such as pet food. Unfortunately, it's difficult to prevent EPM because the hosts, protozoa, and horses share environments. Clinical signs Horses with EPM can exhibit signs similar to those caused by many other CNS diseases. Signs can be moderately acute (coming on quickly) or more gradual, which is one reason EPM can be so difficult to diagnose. Both infective organisms cause the same clinical signs, but while N. hughesi can be found throughout the country, EPM cases caused by it seem more com- mon on the West Coast. Case horse A 15-year-old Warmblood gelding in Southwest Ohio suddenly lost body control and developed an abnormal gait. The signs were pretty dramatic, says Gilsenan—a Grade 3 of 5 neurologic. He could walk without risk of falling, but the veterinarians were worried he might fall on a circle or going down- or uphill. To the owner's knowledge, the horse had no history of trauma to the skull or spine. When the gelding came in, EPM was at top of the list of suspected diagnoses, Gilsenan said, but he and his colleagues needed to perform testing to confirm it. His evaluation and diagnosis When we do a neurologic exam, we try to localize the lesion and figure out what part of the nervous system is likely to be affected. This horse's attitude and cranial nerve reflexes were normal, but he had a really long-strided, almost stiff appearance to all four limbs. He also dragged his toes and, when you circled him, he'd swing his hind limbs out. At a stop he had a hard time standing squarely; all four feet pointed in different directions. Those findings led us to localize the lesions to the spinal cord—most likely in the neck, since that's where neural pathways origi- nate that affect the front and back limbs. With signs of spinal cord disease, get neck radiographs to rule out: 1. Narrowing of the spinal canal due to arthritis or developmental reasons, and 2. Trauma to the neck. This horse's radiographs were normal. Next, we did a spinal tap to help dif- ferentiate causes of disease. We tested the cerebrospinal fluid (CSF), which showed he had a really high proportion of CSF antibodies (against S. neurona) compared to those in his blood, and that allowed us to make the EPM diagnosis. Treatment Gilsenan describes his ap- proach: Because the horse's prognosis depends on how soon treatment begins, your veterinarian will most likely start treating a suspect EPM case with any of several antiprotozoals before test results even arrive. In most cases treatment lasts 28 days, with four weeks to see improvement. In some instances treatment might extend to two or three months. It can be difficult to decide when to finish treatment, as we don't have a means of determining when the infection is completely cleared. Adjunctive therapies that might help, at the veterinarian's discretion, include: ■ Corticosteroids; ■ Vitamin E as a central nervous system healing aid; and ■ Levamisole as an immunomodulator. Outcome This horse responded well to treatment. He returned to normal over four to six weeks. About 25% of horses fully recover, and about 80% improve at least one grade; these horses might return to being ridden safely. Visual effects (muscle wasting) resolve as the horse resumes exercise and regains strength. Potomac Horse Fever (PHF) Treating veterinarian: Bryan Waldridge, DVM, MS, Dipl. ABVP, ACVIM, internal /DERUDWRU\7HVWLQJ6HUYLFH6SHFLDOL]LQJLQ (TXLQH,QIHFWLRXV'LVHDVHV 5HVSLUDWRU\6HTXL(+9(+9,QIOXHQ]D5HTXL 1HXURORJLF(30(+9:19 *DVWURLQWHVWLQDO&ORVWULGLXPGLIILFLOHDQGSHUIULQJHQV&U\SWRVSRULGLXP &RURQDYLUXV5RWDYLUXV/DZVRQLD3+)6DOPRQHOOD5HTXL 3DQHOVDQGLQGLYLGXDOWHVWVDYDLODEOH (TXLQH'LDJQRVWLF6ROXWLRQV//& %XOO/HD5G6XLWH/H[LQJWRQ.< ZZZHTXLQHGLDJQRVWLFVROXWLRQVFRP About 25% of horses with EPM recover fully, and about 80% improve at least one neurologic grade.

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