AAEP Veterinarians Discuss Pigeon Fever

Veterinarians are reporting increasing numbers of horses being diagnosed with pigeon fever.

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Veterinarians across the United States and Canada are reporting increasing numbers of horses being diagnosed with Corynebacterium pseudotuberculosis infections, also known as pigeon fever. Practitioners discussed the disease and related developments during a table topic sessions at the 2013 American Association of Equine Practitioners convention, held Dec. 7-11 in Nashville, Tenn.

Once limited to arid regions of North America, this Gram-positive intracellular, facultative anaerobic bacteria (meaning they can survive and grow with or without oxygen) has been reported as far east as Virginia and north into Alberta, Canada. But pigeon fever might be under-reported in some regions due to the frequency of occurrence and horse owners and farm managers’ familiarity with the course of treatment. The nitrate-positive biotype of this organism causes three variants of disease in horses: external abscessation, internal abscessation, and ulcerative lymphangitis (an infection of the limbs). External abscesses commonly arise on the pectorals, sheath, ventrum (underside), mammary gland, inguinum (groin), or axillary (armpit) region. Less commonly internal abscesses might develop in the abdominal or thoracic (chest) cavities with or without previous external abscess formation. Internal infection is believed to represent 10% of cases, while lymphangitis represents approximately 1% of cases. No vaccine is currently marketed for prevention of the disease.

The soil-dwelling bacteria is believed to be spread by biting flies or through skin abrasions, so veterinarians recommend owners and farm managers work to reduce fly populations around horses. Additionally, many practitioners utilize barrier protection and employ varying degrees of quarantine for affected horses. Veterinarians drain purulent (pus-containing) material into a disposable receptacle (i.e., a plastic bag-lined bucket) to avoid ground contamination.

Veterinarians confirm C. pseudotuberculosis infection by culturing purulent material. A polymerase chain reaction test is now commercially available as well. Additionally, they might employ the synergistic hemolysis inhibition test to help diagnose the disease in cases of internal abscessation. However, in a recent publication researchers determined that marked elevations in this titer were more indicative of active external or internal infections rather than internal abscessations specifically. Internal medicine specialists commonly use ultrasound and body cavity centesis (using a hollow needle to puncture and draw out fluid) to confirm internal abscesses caused by C. pseudotuberculosis, in addition to routine lab work and physical examination

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