Diagnosis & Treatment
Obviously, diagnosis and treatment need to be rapid, but unfortunately diagnosis of PHF is not easy. The fever, depression, and loss of appetite may appear many hours before the diarrhea. There may be mild colic symptoms, but this doesn't happen consistently. In this early stage, a "sick horse" may be all that's obvious to you as the owner. (Note: This is a good time to emphasize that any sick horse should always have his temperature taken, and all horses with a fever who are off their feed should be examined by your veterinarian.) These "sick horses" will often be assumed to "have a virus," but don't stop there. If you get your veterinarian out at this early stage, he/she will be able to detect abnormal intestinal activity and often changes in the color of the gums that will tip him/her off to the fact that there is an intestinal problem.
When the diarrhea appears, PHF will definitely be high on the list of possible problems afflicting your horse, but other infectious causes of diarrhea-such as Salmonella and/or Clostridia-can cause the same symptoms. Your veterinarian will want to run blood tests to check for dehydration, electrolyte problems, and white blood cell changes that will sometimes help establish and confirm the diagnosis. A definite diagnosis can be made by PCR testing of your horse's blood or manure. This type of test detects the genetic material of the organism. Antibody testing is also available, but there can be false positives if your horse has been exposed to PHF before. Both PCR testing and antibody determination also take time, and time is something the PHF horse does not have!
After considering all the factors, including where you live and how common PHF is in your area, your veterinarian may decide to treat before any test results are back. Horses treated with intravenous oxytetracycline usually respond very well, especially if the problem is caught in its early stages. Flunixin meglumine (Banamine®) is given to help control pain and counteract the effects of the toxins. Your horse's feet may be iced to help block damaging toxin effects on the laminae. Many horses also require intravenous fluids and electrolytes to replace losses from severe diarrhea.
Vaccination
There is a vaccination for PHF, but it is used sporadically, depending on risk. The vaccine works against only one strain of the organism, while there are multiple different strains that can infect your horse. Disease development in vaccinated horses has been reported several times. A study in New York showed that it's more cost effective to recognize clinical cases of PHF and treat them promptly than it is to keep all the horses on your farm vaccinated against the disease. You should consult with your own veterinarian, however, prior to making any vaccination decisions for your horse. If you do decide to vaccinate, your horse must receive an initial vaccine and then a booster vaccine in two to four weeks for first-time use.
Your best defenses against Potomac Horse Fever are:
• Be observant. If your horse seems "off," check it out.
• Always alert your veterinarian if your horse has a fever and is off his feed.
• Keep horses away from natural water sources.
• Keep your water troughs free of dead flies.
• Avoid leaving on lights around your barn at night.
