ROB FAIRLEY
It has been about eight years since the first case of sporadic bovine encephalomyelitis (SBE) was diagnosed in New Zealand. The causative organism, Chlamydophila pecorum, was however isolated much earlier (2000) in a healthy goat on a Waikato farm as part of an investigation*.
Since the first diagnosis of SBE in cattle, many outbreaks of the disease in calves have been seen in several parts of New Zealand and particularly in Canterbury. Some cases present as solitary or a few animals with severe neurological disease, but the most common presentation has been a few calves with severe clinical disease (that is indistinguishable clinically from other calf neurological problems), and large numbers of calves with mild clinical signs. These calves are listless, weak, may have mild hind limb ataxia and may knuckle on their hind fetlocks. Some calves have trouble getting up but once up, can walk around. Most affected calves will be febrile, and some that seem clinically normal may also have a temperature.
The numbers of calves affected in these outbreaks has been as many as 80 or more (the problem can be very significant). Fortunately, most of the mildly-affected calves respond rapidly to tetracycline treatment. The calves with severe clinical signs do not respond.
Laboratory diagnosis is mainly based on histological examination of the brain of severely affected calves. This can be supported by PCR for Chlamydophila pecorum on fresh brain (not all cases are positive) and we have occasionally detected the organism by PCR in EDTA blood. At post mortem there may be no lesions but some may have evidence of pleuritis or peritonitis (often as clumps of exudate).
Several practitioners who have seen the presentation of large numbers of calves with mild ataxia have indicated they would immediately suspect the disease if it presented in the same way on another farm. If you encounter a case with many calves like this but without a severely affected calf to do histological examination of the brain, it would seem appropriate to presume that it might be SBE and treat with tetracycline. Taking EDTA blood samples from some of these calves pre-treatment for Chlamydophila PCR might be worthwhile to try and confirm the diagnosis (we have done too few to know how reliable this might be, but it is worth trying).
*Surveillance 29(3) 2002