Osteomyelitis

Signs are often non-specific at first. Acute cases show lameness, heat, swelling and pain over the bone, with fever, poor appetite and difficulty standing; nearby joints may become septic. Chronic cases persist for months with draining tracts, bone destruction and sequestra, and ruminants with jaw involvement lose condition because chewing is hard. Broilers with vertebral lesions sit on their hocks or become paralysed. Radiographic changes lag behind the clinical onset, so early films may look normal; CT, MRI and deep tissue or bone culture help confirm it.

Osteomyelitis is inflammation of bone and bone marrow, usually from bacterial infection, that destroys and kills bone while provoking reactive new bone. Bacteria reach bone through the blood (haematogenous spread, mainly in young animals, where slow blood flow in metaphyseal vessels offers a foothold), or directly via open fractures, surgical implants, bite wounds or neighbouring infection. They adhere to bone matrix and build biofilms that shield them from immune defences and antimicrobials. Upregulated RANKL drives osteoclast bone resorption, and vascular damage causes ischaemia and necrosis. Dead bone becomes a non-vascular sequestrum that drugs cannot reach, and new bone (involucrum) forms around it, turning the infection chronic.

Osteomyelitis occurs across domestic species. Staphylococci, especially S. aureus, are the most common agents overall; others include streptococci, E. coli, Pseudomonas, Salmonella, Trueperella and anaerobes, and in dogs and cats fungi such as Aspergillus, Blastomyces and Cryptococcus. Foals develop polymicrobial haematogenous infections, largely Gram-negative, predisposed by failure of passive transfer; calves are infected with Trueperella pyogenes or Salmonella. In pigs mandibular and vertebral forms are linked to tail-biting. Broilers suffer bacterial chondronecrosis with osteomyelitis (S. aureus, Enterococcus cecorum, E. coli), driven by rapid growth. Dogs, horses and camelids often develop it after fracture repair, and ruminants in the mandible. Open fractures, contaminated implants, crowding and poor hygiene raise risk.

Degenerative joint disease, osteochondrosis and physitis also cause lameness with bone or joint changes, as do non-infected trauma and exertional rhabdomyolysis; in poultry, non-bacterial spondylolisthesis mimics vertebral osteomyelitis. Because radiographic signs lag and symptoms are vague, deep tissue or bone culture rather than surface swabs, supported by CT or MRI, is used to confirm infection.

Bone (metaphysis, cortex, marrow), vertebrae and intervertebral discs, mandible, long bones at fracture or implant sites, adjacent joints, soft tissue draining tracts

Reduce known risk factors: failure of passive transfer in foals, contaminated open fractures and surgical implants, high stocking density and poor hygiene, tail-biting in pigs, and very rapid growth in broilers.

Acute cases often respond to culture-guided antimicrobials alone. Chronic or implant-associated infection needs debridement, often implant removal and prolonged therapy, and may persist or recur. Untreated foal osteomyelitis carries high mortality.