An Outbreak of Haemolytic Anaemia Associated with Infection of Theileria Orientalis in Naive Cattle

Case History: An outbreak of haemolytic anaemia occurred when 87 cattle were introduced from a presumed non-infected herd from south Otago to a herd in Northland (n=580 cows), New Zealand, where theileriosis is endemic.

Clinical Findings: Clinical signs associated with Theileria spp. infection included lethargy, anorexia, inappetance, pale mucous membranes, and varying severity of anaemia. In the naive imported cattle, 11/29 (38%) of those tested showed haematological signs of anaemia (haematocrit (HCT) <0.25 L/L). A negative association was present between the HCT and the number of Theileria spp. organisms counted using light microscopy (correlation coefficient=-0.4; p<0.05). Haemoparasites consistent with Theileria spp. were observed on examination of a blood smear. Theileria orientalis group (Theileria buffeli/orientalis) species was confirmed using PCR and DNA sequencing, and other causes for anaemia were excluded in the most clinically severely affected cow. The 18S sequence data and phylogenetic analysis of the CoxIII sequences showed samples had the greatest similarity to T. orientalis Chitose from Japan.

Diagnosis: Haemolytic anaemia associated with infection of T. orientalis.

Clinical Relevance: Previous reports have suggested that T. orientalis group species may be non-pathogenic in healthy cattle, and an incidental finding in blood samples. However, this investigation provided evidence that in New Zealand, this pathogen is capable of causing clinical disease in cattle not necessarily debilitated by another disease. The potential for disease should be considered when naive cattle are brought in from non-endemic to endemic regions, for instance cattle from the South Island moved to regions where the vector for T. orientalis group species, Haemaphysalis longicornis, is active, and T. orientalis is present.