A mob of 400 Dorper lambs (approximately 8 months of age) were being mustered for their upcoming sale. One lamb was found in the paddock and unable to ambulate. The affected lamb was presented to the Dubbo LHPA office in mid January 2011 with hindlimb paralysis of 72 hour duration. The owner reported similar findings in at least 6 others in the previous month. The lambs had been drenched and vaccinated with 5-in-1 clostridial at marking and weaning.
The recumbent male lamb was examined and was found to be quiet, alert, responsive and in body condition score 2.5. The wool was infested with numerous grass seeds. Mucous membranes and third eyelids were injected. The lamb was febrile. No abnormalities were detected on auscultation. The lamb was unable to stand. Palpebral response was normal. Cervical and thoracic spinal reflexes were intact. Thoracic limbs were normal.
Lumbar and sacral spinal reflexes were absent. Pelvic limbs were stiff, unresponsive to manual manipulation, tactile sensation, and reflexes were absent. However, a diminished deep pain response was able to be elicited. The lamb had a severely distended bladder and was dribbling urine. Due to deteriorating condition, the owner elected euthanasia and post-mortem examination.
Multiple abscesses were scattered throughout the lungs. The cranio-ventral portion of the lungs were severely affected with obliteration of normal architecture and filled with purulent material (Figure 1). The dependent chest cavity was also filled with yellow pus. The tracheobronchial lymph nodes were grossly enlarged (Figure 2). As identified on ante-mortem inspection, the bladder remained grossly distended with urine (Figure 3). Kidneys and ureters were normal.
The brain and dissection along the cervical and thoracic vertebrae appeared grossly normal. Beginning at approximately L3, yellow pus exuded from the vertebral musculature and when the vertebrae was cut longitudinally, purulent exudate completely filled the vertebral canal. Further caudal dissection of the vertebral canal revealed pus throughout the spinal canal extending caudally across 3-4 vertebrae (Figure 4). Osteomyelitis, severe osteolysis and spinal cord compression were evident.
Individual culture from the lungs, chest cavity and vertebral canal all revealed a pure growth of Arcanobacterium pyogenes.
Arcanobacterium pyogenes (formerly Actinomyces pyogenes) is commonly found as part of the resident microflora of skin and gastrointestinal, genital and upper respiratory mucous membranes of healthy animals.1 Arcanobacterium pyogenes is considered to be an opportunistic pathogen such that infection is generally initiated by some sort of direct physical trauma, immunological action, or infection by other microorganisms (e.g. bacterial or viral)1,2. Arcanobacterium pyogenes commonly causes osteomyelitis, nephritis, pneumonia, endometritis, abortion, and orchitis in sheep1,2.
The origin of the pulmonary and vertebral abscessation in this case is not clear. Vertebral body abscesses are commonly the result of 'ascending infection from post-tail docking or mulesing' in young lambs6. Mulesing however, was not considered a cause in this case as Dorper lambs are not routinely mulesed. Infective spinal cord lesions are commonly found in lambs 1 to 3 months of age, but have been reported in all age groups3,4,5,6.
In December and January 2011, the Central West LHPA identified numerous cases of young lambs with severe grass seed penetration and subsequent sepsis. It is possible that grass seed penetration may have been an initiating cause. Grass seed penetration and subsequent osteomyelitis in lumbar vertebrae has been reported in other species7. Another possibility is that haematogenous or pulmonary spread led to spinal abscessation or vice versa. This case is unusual in that vertebral body abscesses with metastatic spread is considered to be relatively uncommon4,8.