Oil based vaccines, as used in Australia to control ovine paratuberculosis, provoke a local tissue reaction that can include granulomatous cellulitis and lymphadenitis. If the vaccine is incorrectly administered into the midline of the dorsal cervical area, the subsequent local reaction can press on the cervical cord producing progressive paralysis. This has occurred in outbreak form. Producers have named it 'OJD staggers' (Windsor PA and Eppleston J, 2006). We report three cases in which 'OJD staggers' occurred at low prevalence in young sheep.
CASE 1. Bathurst
The owner of a property running 1500 Merino ewes and 1500 Merino wethers north of Bathurst reported that he had seen 3-5 lambs affected by a progressive weakness in the hindquarters each year for several years. In July 2003 then RLPB district Veterinarian Greg Simpson confirmed ovine segmental axonopathy on this property. Previously all affected lambs were Merinos (the progeny of joining Merino rams to 75% of his flock) which is consistent with the presumed inherited nature of this condition (Harper et al., 1986), but this year crossbred lambs were also affected. The owner reported that affected lambs initially showed weakness and a swaying gait in the hindquarters. They readily collapsed. However, the disease progressed to the point where the lambs either died or were euthanased.
Two affected 10 month old crossbred lambs were examined. Both were bright, alert and responsive. They stood weakly with a wide based stance and dropped hind quarters and moved with swaying hindquarters. When forced they readily collapsed and rolled over or settled in sternal recumbency. Corneal, palpebral, menace and pupil light reflexes were normal but patellar reflexes were exaggerated.
Both lambs had cervical abscesses above to atlanto-occipital space. These abscesses exuded thin yellow pus when opened. However, they were culture negative.
The owner of a property north of Young reported two of 1200 July-August 2008 drop Merino ewe lambs that were unable to rise. The remainder of the ewe lambs and the wether portion of the drop appeared normal. The lambs had been vaccinated with Gudair and 6:1 at marking, re-vaccinated with 6:1, and drenched with moxidectin prior to weaning onto lucerne in late November.
One ewe, recumbent for 10 days, ate and drank if hand fed but was unable to rise. The second was initially able to stand if assisted but had forelimb paresis with knuckling. However, the paresis progressed until she was also non-ambulatory by about day 5. Both lambs were bright and alert, eating well when handfed and showed no other signs of disease. There was no response to calcium supplementation, drenching or selenium (included in the drench). Blood parameters were unremarkable. The mob FEC averaged 420 epg.
The lambs were post-mortemed. Lamb 1, which had been down >10days, showed a visible depression of the spinal cord at C2-C3. On further examination of the vertebral column, a small greenish swelling could be seen impinging on the spinal canal space from between C2-C3. On further dissection, there was free-flowing purulent material in this swelling. Lamb 2 had a much more obvious (and typical) granulomatous reaction which could be felt within the vertebral column muscles surrounding C2-C4. This lesion was approximately 700 x 500 x 500mm in size and extended down between the joints of the cervical vertebrae. There was no free flowing material associated with this lesion. By following the granulomatous reaction from muscle level to skin, it would appear that the Gudair vaccine was given almost midline and approximately 5-10 cm below the recommended site.
CASE 3. Wagga Wagga
The owner of a merino flock located north of Wagga Wagga reported a sudden onset of ataxia in l6 unweaned merino lambs out of approximately 800 and in 1 merino hogget out of approximately 800 in September 2004. The owner first noticed ataxia one week prior to weaning. The ataxia became worse with stress. The neurological disorder slowly progressed until affected animals went down, unable to rise. The same merino bloodlines had been used in this flock for 20 years. No crossbred lambs were affected. No plants that are known to cause neurological disease were identified in the paddocks where the sheep had grazed. The lambs had been vaccinated with Gudair vaccine at marking and with 6 in 1 vaccine at marking and at weaning. They were drenched with an anthelmintic at weaning in late August 2004.
Wagga DV Tony Morton examined affected lambs one week after weaning and observed that they walked with flexed carpii and a mild extension of the hind limbs. A post-mortem was performed on two recumbent lambs. No significant lesions were observed grossly. The brain and a 10cm section of spinal cord from the two lambs were submitted for histopathology. Segmental suppurative poliomyelitis with subsequent Wallerian degeneration was found in one section of spinal cord, suggestive of a spinal cord abscess.
No significant lesions were in the spinal cord section from the second lamb. Affected lambs showed a partial response to oxytetracycline. Four weeks later, in October 2004 another three hoggets and one crossbred lamb displayed the same signs along with seven of 800 merino weaners. Wagga VO Sarah Robinson examined the affected animals. They were alert with a normal head carriage but were weak with limb paresis. The lambs also had wounds on the plantar and palmar surface of the pasterns and sometimes on the dorsal surface of the carpus. They were able to stand without fatigue but with a wide hind limb stance with apparent decreased muscle tone and sagging in all four limbs.
No knuckling was observed. When moved about in a larger yard the following symptoms were observed: bunny hopping with the hind legs; exaggerated hip wobble/sway; left and right fore limb and hind limb crossing; flexed appearance to all joints; hind limbs over-stepping fore limbs and tracking outside fore limbs (but not consistently); hind limbs collapsing to one side; fore limb stumble, hind limbs keep going, animal nose dives and somersaults. Once down the affected animal struggled to get up. Symptoms were worse when stressed and the condition did not improve after rest.
The following year recurrence of the neurological disease was reported. Six hoggets and seven lambs were affected. It is likely that the hoggets were the same animals affected the previous year. The lambs had been marked recently, with Gudair vaccination carried out at the time of marking. The affected sheep were depressed and had a low head carriage. A limb paresis syndrome was observed with symptoms as seen the previous year. One lamb was moribund. It initially showed paresis of forelimbs when first noticed 5 days previously then deteriorated rapidly until it was unable to stand.
A post-mortem was performed on one lamb in October 2004. No abnormalities were noticed grossly. The brain and spinal cord were submitted for histopathology. A section of cervical spinal cord at C1-C2 was found to have acute axonal degeneration suggestive of trauma. Inadvertent injection into the vertebral canal was considered.
A post-mortem was performed the moribund lamb seen in August 2005. An abscess adjacent to the vertebral body of axis (C2), extending into spinal canal was found. One of the affected hoggets was also post-mortemed. A large abscess adjacent vertebral body of axis (C2) with copious purulent exudate into spinal canal was found.
The affected section of the spinal column was submitted for bacterial culture. A profuse mixed growth including Arcanobacter pyogenes was cultured from one sheep and a profuse predominant growth of Arcanobacter pyogenes was cultured from the other sheep.
The marked local tissue reaction sometimes provoked by oil-based vaccines can produce complications (Windsor and Eppleston 2006, Morton 2008). These complications are minimised if the vaccine is injected as recommended, caudal to the ear and lateral to the midline. The cases presented again demonstrate that the vaccination of lambs on the cervical midline risks either local tissue reaction or infection that impinges on the cervical cord.
The differential diagnosis of paresis in otherwise bright and alert young sheep in southeastern Australia includes myopathy associated with selenium and or vitamin E deficiency, injury to the cervical cord, vertebral osteomyelitis and from pathological fractures and bone pain associated with osteomalacia. Cervical abscesses secondary to vaccination should also be included on this list.
It is our experience that cervical abscess subsequent to oil-based vaccines can track along tissue planes and may not be immediately obvious on post-mortem. A thorough examination of the cervical neck and cord is recommended.