Investigation of the index case herd and identification of the genotypes of <i>Theileria orientalis</i> associated with outbreaks of bovine anaemia in New Zealand in 2012

<div><p></p><p>CASE HISTORY AND CLINICAL FINDINGS: On 7 September 2012 the Ministry for Primary Industries was notified of a dairy cow with regenerative anaemia (haematocrit (HCT) 0.08 L/L) in a herd of 465 Jersey-Friesian cross cows (index case herd) in the Northland region of New Zealand. Organisms consistent with <i>Theileria</i> spp. were present in red blood cells on a blood smear. No other causes of anaemia were detected following examination of affected cows. Blood samples collected from 29 randomly selected cows on 26 September 2012 showed that 24 (83%) were anaemic (HCT≤0.24 L/L) and therefore fitted the case definition for bovine anaemia associated with <i>Theileria orientalis</i> infection.</p><p>LABORATORY FINDINGS: Using a <i>T. orientalis</i> type-specific PCR assay that targeted the single subunit rRNA gene, all of six animals tested were positive for <i>T. orientalis</i> type Ikeda. Blood samples collected from clinically affected cattle in 11 subsequent outbreaks from throughout the North Island showed that <i>T. orientalis</i> Ikeda type was a common finding, but mixed infections with Chitose type were also identified. In addition, using a PCR assay that targeted the major piroplasm surface gene, <i>T. orientalis</i> type 5 was detected in one cow from the Waikato region.</p><p>DIAGNOSIS: The presence of <i>T. orientalis</i> type Ikeda, as well as type 5, was confirmed in cattle from outbreaks of bovine anaemia in herds throughout the North Island of New Zealand.</p><p>CLINICAL RELEVANCE: Two new types of <i>T. orientalis</i> were identified in this investigation, that were associated with a sudden rise in cases of bovine anaemia. The body of evidence showed that the Ikeda type was implicated as the cause of disease observed in this epidemic.</p></div>