b'AAEP FORUM TRACY E. NORMAN, VMD, MA, DIPL. ACVIM, CVATheHorse.com/AAEP-ForumPotomac Horse Fever: A Happy OutcomeI ts good to be a horse vet in the sum- Horses can get mer. The spring rush of routine well-ness work and breeding and foaling isPotomac horse fever over, the show horses have gone to work,from ingesting the \x07ukes that carry the and it is time to take a breath. Except causative bacteria summer is the season for diarrhea. (released by aquatic So it was as I was sitting down to din- snails) or the water-ner one blazing hot evening last sum- borne insects they mer when my phone alerted me to aninfect.emergency. When I arrived at the farm, the mare, Molly, was in her shed with her head down, evening meal untouched. ISTOCK.COMShe had a fever of 103.6F, an increased heart rate, fluidy gut sounds, and a small amount of diarrhea behind her. I ex-plained to her owner, Joe, that in our areaassured him it was good she was vacci- lazy river of her bloodstream as they do the most likely diagnosis that would fitnated. The vaccine doesnt always preventin healthy horses. Low concentrations of her signs was Potomac horse fever (PHF). disease completelyin part because therecertain electrolytes and proteins revealed He was puzzled at my statement, as hisare multiple strainsbut it helps reducethat her intestinal lining was leaky and horse was current on her vaccines, whichdisease severity and complications suchthe site of all that inflammation. Fortu-included PHF. And, besides, his horsesas laminitis. Horses with PHF, just asnately, these changes werent severe, and never left the farm or had contact withthose with other conditions that causeher kidney and liver function markers other horses. He was also worried aboutcolitis (lower intestine inflammation), canwere fine. her herdmate and asked what he could dobecome gravely ill and require hospi- When I called Joe to let him know the to protect the gelding.talization for intensive care to managebloodwork results, he said Molly was feel-I explained that the biggest risk factorspotentially fatal complications.ing better and was grazing and drinking for his horses were that they lived inI suggested we collect blood to evaluatewater. We weighed the pros and cons of an endemic region (where PHF com- Mollys blood cell counts, proteins, andtaking Molly to a hospital for treatment, monly occurs) within 5 miles of a bodyorgan function, to help determine if weand Joe elected to try treatment on the of natural water and that we were havingcould treat her on the farm. While I wasfarm. For the next five days, a veterinar-a hot, rainy summer. Potomac horseat it, I grabbed a tube for PHF blood test- ian would need to visit Molly and admin-fever is not contagious; rather, snails anding (the bacteria can be detected by PCRister intravenous oxytetracycline (vets aquatic insects carry the causative agentin blood and manure) and some ma- can also administer oral tetracyclines). I (Neorickettsia risticii). The bacteria livenure to test for PHF and other potentialreturned to the farm to give her the first within parasites that infect the snailsdiseases. Unfortunately, I wouldnt havedose, and we devised a plan to support and insects. This Russian-doll qualitythe results until the following week. MollyMolly and monitor her progress. has made this organism challenging forwould need to be treated promptly, soAs it was, Molly responded well, researchers to describe. Horses get sickI would have to treat her based on herfeeling much better after her first dose when they ingest parasites (in naturalhistory, physical exam, and bloodwork.of antibiotic, normal after the second, bodies of water) or infected insects. Mea- Before leaving the farm, I gave Molly aand on the last day of medication she sures to protect the horses feed, hay, anddose of flunixin meglumine (Banamine)was hard to catch. The tests we sent water include turning off barn lights thatto help lower her fever. out confirmed PHF. I was grateful that attract insects at night, keeping storedMollys bloodwork showed that herJoes prompt attention to Molly and her hay covered with a tarp, and limitingbody was mounting a major inflamma- vaccine protection helped us give her a grazing next to streams and creeks. tory response, with decreased white bloodgood outcome. For more information on Joe asked me how his horse could becells; her white cells were on high alertPHF, visit TheHorse.com/topics/potomac-sick if she was current on her vaccines. Iand not floating peacefully through thehorse-fever. hAmerican Association of Equine Practitioners, 4033 Iron Works Parkway, Lexington, KY40511859/233-0147www.aaep.org12August 2019The Horse | TheHorse.com'