First report and histological features of Chlamydia pecorum encephalitis in calves in New Zealand.

Case History: Between September and October 2013, 40 of 150 crossbred Friesian dairy calves on a farm in the Manawatu region of New Zealand developed neurological signs when between 1 and 3 months of age. Calves were grazed in multiple mobs and calves from each mob were affected. A variable response was observed to initial treatment with thiamine, fluoroquinolone antibiotics and non-steroidal anti-inflammatory drugs.

Clinical And Pathological Findings: Affected calves exhibited a range of neurological signs that included generalised depression, hind limb ataxia with a stiff gait, and knuckling of the fetlocks. In advanced cases, calves became recumbent with opisthotonous. Over a 4-week period, 13 calves died or were subject to euthanasia and a thorough necropsy was performed on three of these calves. Necropsy findings included fibrinous peritonitis, pleuritis and pericarditis, with no gross abnormalities visible in the brain or joints. Histology of the brain was possible in seven of the affected calves, with lesions ranging from lymphocytic and histiocytic vasculitis and meningoencephalitis, to extensive thrombosis and neutrophilic inflammation. Immunohistochemistry using an anti-chlamydial lipopolysaccharide antibody revealed positive immuno-staining in all seven cases, with no brain samples exhibiting immunostaining for Histophilus somni. DNA was extracted from a sample of fresh brain from one case and chlamydial DNA sequences were amplified by PCR and found to be identical to Chlamydia pecorum. PCR was also performed on formalin-fixed brain tissue from three of the other cases, but no chlamydial DNA was amplified.

Diagnosis: Chlamydia pecorum meningoencephalomyelitis (sporadic bovine encephalomyelitis).

Clinical Relevance: This is the first time that C. pecorum has been confirmed as a cause of clinical disease in New Zealand. Practitioners should be aware of this disease as a differential in calves with neurological signs, and submit samples of formalin-fixed brain as well as fresh brain to enable confirmation of suspected cases using PCR analysis. Furthermore, these cases illustrate that the histological lesions in the brains of calves with C. pecorum are more variable than previously reported, and pathologists should be aware that histological features may overlap with those traditionally ascribed to other organisms, such as H. somni.