Causative organisms of equine nuchal bursitis

Summary

Equine nuchal bursitis occurs as nonseptic inflammation, which may be secondary to trauma, or can be caused by bacterial infection. Many of the earliest described nuchal bursitis cases were associated with the bacteria Brucella abortus in horses in contact with cattle. B. abortus has since been eradicated from the United States, making this organism an unlikely cause of equine nuchal bursitis now. The spirochete Borrelia burgdorferi, the causative agent of Lyme disease, has recently been associated with equine nuchal bursitis in the Northeastern United States, often accompanied by elevated serum B. burgdorferi outer surface protein A antibodies. Other bacteria reported in nuchal bursitis cases include Trueperella pyogenes, Streptococcus equi subsp. zooepidemicus, Burkholderia cepacia complex, Enterococcus faecalis, Staphylococcus spp., Bacillus spp., Escherichia coli and Actinobacteria spp. The causative bacterial agent in equine septic nuchal bursitis cases cannot be distinguished based on clinical signs, imaging findings or bursal fluid cytology alone, warranting the submission of nuchal bursa fluid or synovium for aerobic and anaerobic culture and B. burgdorferi polymerase chain reaction. Next-generation sequencing of these specimens could be considered in cases where other diagnostics have not identified a causative organism. Septic equine nuchal bursitis cases are typically managed with a combination of antimicrobial therapy and surgical intervention, resulting in variable outcomes.