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.
Issue link: https://thehorse.epubxp.com/i/636486
20 TheHorse.com THE HORSE February 2016 "Equine protozoal myeloencephalitis (EPM) is caused by microscopic para- sites that are excreted by opossums and later ingested by horses when grazing or from contaminated feed," says Weese. The parasite attacks the brain and spinal cord, which can lead to serious central nervous system damage and even death if not detected and treated. The only recommended way to avoid EPM at this time is to prevent opossum access to your feed and hay and, thus, prevent your horse from ingesting opos- sum poop, both of which are easier said than done. Stabled horses fed from sealed feed bins are less likely to ingest opos- sum feces; however, horses turned out on pasture, which is widely recommended to avoid stable vices, allow natural forag- ing behavior, and social interaction, are particularly susceptible. The Bloodsucker Unlike the more rapid disease onset frequently seen with the viral encephalitides and EPM, the horse trapped in this story suffers more subtly. At first you can't put your finger on what is wrong: A slight lameness that shifts from one limb to an- other, a lack of energy, some subtle behavior changes, and perhaps muscle wasting. Ixodes tick species, such as the blacklegged or deer tick, transmit the bacterium responsible for Lyme disease to horses. Lyme disease is difficult to diag- nose, partly because the signs of disease are hard to pinpoint and partly because the blood test can only determine if the horse has been exposed to the bacterium Borrelia burgdorferi and not whether he is actively infected. Horses residing in areas known to harbor Ixodes ticks, such as the Mid-Atlantic and northeastern states, the Midwest, and California, might benefit from vaccination. (Note: There is no licensed Lyme vaccine for horses, but some veterinarians use a canine vaccine off-label, and researchers are testing it in horses: TheHorse.com/36637.) Check horses daily for ticks, especially around the ears, in the mane and tail, and in the hairs at the back of the fetlock, and remove ticks carefully. "Several canine-approved tick repel- lents are used in horses, but dose, applica- tion sites, and efficacy are unknown," says Tom Divers, DVM, Dipl. ACVIM, ACVECC, Steffen Professor of Veteri- nary Medicine and section chief of large animal medicine at Cornell University's College of Veterinary Medicine, in Ithaca, New York. "An equine-approved perme- thrin and piperonyl butoxide product for tick prevention is available, but published clinical studies (on its application and usefulness) in horses could not be found." Another way to reduce your property's tick crop is by keeping pastures mowed and brush-free. Unlike other pathogens that politely follow the immune system's common rule of, "once you've had it, you can't get it again," B. burgdorferi natural infection does not induce strong immunity, making reinfection a reality. Moreover, ticks can cause more diseases than just Lyme (such as piroplasmosis and anaplasmosis). The Microscopic Menace While mucking stalls out at the end of the barn, you hear a splattering sound that concerns you. A search for its source leads you to your mare's stall. She is groaning in discomfort and suffering from a terrible bout of diarrhea. Worse, she seems close to adopting the sawhorse stance synonymous with every horse owner's worst nightmare: laminitis. "There are multiple causes of diarrhea in horses that can be spread from other animals, one of the most notable being the bacterium Salmonella," says Weese. Salmonellosis affects many mammals, including horses, cattle, pigs, dogs, cats, wildlife, and even humans. Salmonella enterica serovars most commonly cause diarrhea, septicemia (bacterial invasion of the bloodstream), or both. Horses become infected when they ingest the bacterium in the environment from either other sick animals or apparently healthy animals that are "carriers." Once ingested, the bacterium invades the gastrointestinal tract lining and causes profuse diarrhea. Horses that are carriers can shed bacteria after stressful scenarios, such as transport or parturition (foaling), posing a serious risk for other horses and foals. "Strict biosecurity protocols should be utilized immediately on any farm with a diarrheic horse," advises Weese. Another cause of diarrhea in horses that shouldn't be overlooked is Potomac horse fever (PHF). The animals respon- sible for sharing this disease with horses are snails and aquatic insects, such as mayflies and dragonflies, parasitized by Neorickettsia risticii-infected flukes. Horses get infected when they inadver- tently ingest infected aquatic insects. In addition to diarrhea, classic signs of PHF often include a very high fever (104-105°F), colic, anorexia, depression/ lethargy, and possibly laminitis. Due to PHF's potentially devastating consequences, many field veterinarians in high-risk areas, such as the northeastern United States, will almost automatically treat horses with a fever that live close to water during the summer months, says Peter R. Morresey, BVSc, MACVSc, Dipl. Wildlife and livestock species such as pigs might serve as reservoirs for proliferative enteropathy. There are multiple causes of diarrhea in horses that can be spread from other ani- mals, one the most notable being the bacte- rium Salmonella." DR. SCOTT WEESE Opossums can excrete parasites in their feces that cause neurologic disease in horses. INTERSPECIES THREATS