Page 25 - New Mexico Horse Breeder, Fall

Diagnosis
“The best way to diagnose PHF is to identify these bacteria in a sample of blood or feces. This is done with a PCR (polymerese chain reaction) test. This detects bacterial DNA in either the blood or feces,” says Wilson.
The sample can be sent to a lab that does PCR tests, and results are usually obtained in less than
a week. “We usually get test results back within
a couple of days. But if we suspect that the horse might have PHF, we start treating the animal immediately before we get the test results,” she says.
“Despite the fact that multiple horses on a farm might be exposed to PHF, usually only one horse gets sick. By contrast, if there are multiple horses developing diarrhea, we would suspect something infectious (and contagious horse to horse) like salmonella, although I have had farms with multiple horses get PHF,” Wilson says.
“It can be confusing, because the horse may just look like a mild colic or an impaction because they are dull and not passing manure. The fever would be a clue, however, because we don’t see fever in impaction cases. If we run blood work, their white cell count is low, and that’s not typical of impaction colic, either.” In these instances, most veterinarians would start treatment in case it is PHF.
Since this disease is widespread (and not just in the region of the Potomac River),
there is a move to change the name and call
it equine neorickettsiosis. “People should not think their horse is not at risk just because they don’t live in the Potomac region. The disease has been recognized in almost every state, but identification of clinical cases has only been done in 14 states. There doesn’t seem to be any regional trend to those 14 states,” she says.
Cases that have just mild colic, fever and decreased appetite may be something else. “There are some tick-borne disease, like anaplasma, that can look very similar and are also responsive to tetracycline,” says Wilson.
TreaTmenT
The horses that do get diarrhea usually need very intensive treatment, and are usually best treated in
a hospital situation rather than on the farm. “It is best to get them treated as quickly as possible, before they get secondary complications from dehydration and become endotoxic. This can certainly make the prognosis worse and the treatment more prolonged. The quicker we can get a horse on antibiotics, the quicker the horse will respond,” says Wilson.
The antibiotic most commonly used is oxytetracycline, given intravenously. “In a mild case, this can be done on the farm, but if the horse has diarrhea and is dehydrated, it needs IV fluid support and other supportive care— and laminitis prevention. This is not something a person should cut corners with,” she says.
Some horses need very intensive care, but most of them recover and don’t develop laminitis. “It does require extensive treatment if they have a severe case, but I’ve also seen many mild cases.”
The antibiotic most commonly used to treat PHF is oxytetracycline and it is given intravenously. If the horse has diarrhea and is dehydrated, it needs IV fluid support and other supportive care including laminitis prevention.
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