NJDA Division of Animal Health: Recent Cases of Potomac Horse Fever

 

HORSE OWNERS IN NJ & PA should be aware of some isolated episodes of Potomac Horse Fever.  Please read below statement.

 

 

 

 

 

 

New Jersey Department of Agriculture
Memo
To:     Veterinarians
       
From:   Nancy E. Halpern, DVM, State Veterinarian      
       
Date:   September 27, 2007

Re:     Recent Cases of Potomac Horse Fever

In the past month, several horses on a New Jersey horse farm were treated for moderate to high fevers, with possible neurological signs in 2 horses, and diarrhea and laminitis in one horse. One affected horse died and the necropsy was inconclusive. Paired serum taken from two of the other horses, including the horse with diarrhea, came back with significantly elevated titers for Potomac Horse Fever. Tests were negative for Equine Herpes Virus, Eastern and Western Equine Encephalomyelitis and West Nile Virus for all affected horses.

Potomac Horse Fever is caused by the bacteria Neorickettsia risticii. Clinical signs include fever, depression, poor appetite and, in most cases, diarrhea. Some horses may develop laminitis, swelling of their lower limbs and pregnant mares may abort. Most horses respond well to antibiotic treatment but the disease can be fatal. Very severe cases require intensive care.

Blood work taken during early onset may show an increase in white blood cells, this is often transient.  Paired samples taken 10 days apart can also be used to measure antibody levels produced in response to the infection. The level of antibodies produced by vaccination is much lower than that produced by the disease and this can be distinguished in the paired samples. For serology testing, a 1ml serum sample shall be shipped packed in ice and the cost of the test is $14.50 with results in 1 or 2 days. Serology can be masked by treatment with antibiotics and tends to have many false positives hence diagnosis is more specific by using PCR testing of the blood and or feces. To enhance the chances of detection, the assay should be performed on both blood and fecal samples, as the presence of the organism in blood and feces may not necessarily coincide.  Specimens to be submitted should include 1 ml of anticoagulated blood; cecal or colonic mucosal scraping.  Scraping should be submitted in sterile, leak-proof container and should be kept cold during shipment.  The cost of the molecular test is $45.50 and turn around time is 3 to 5 working days.

Clusters of cases are not usually seen but may occur in facilities located near waterways. The disease is considered endemic in New Jersey. While vaccination does not always prevent the disease, it is thought that vaccination may decrease the severity of the symptoms.

Potomac Horse Fever is not a reportable disease but the New Jersey Department of Agriculture encourages veterinarians and producers to contact the Division of Animal Health at 609-292-3965 if unusual symptoms are seen in animals or multiple cases of disease are seen on a farm or in a geographical area.