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

Abstract

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 Theileria 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 Theileria orientalis infection.

LABORATORY FINDINGS: Using a T. orientalis type-specific PCR assay that targeted the single subunit rRNA gene, all of six animals tested were positive for T. orientalis type Ikeda. Blood samples collected from clinically affected cattle in 11 subsequent outbreaks from throughout the North Island showed that T. orientalis 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, T. orientalis type 5 was detected in one cow from the Waikato region.

DIAGNOSIS: The presence of T. orientalis 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.

CLINICAL RELEVANCE: Two new types of T. orientalis 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.

KEY WORDS:

• Theileria orientalis
• Ikeda
• anaemia
• cattle
• bovine
• index case herd

Acknowledgements

The authors would like to thank the large number of farmers, veterinarians, and pathologists who contributed by providing data, and members of the virology staff at the Animal Health Laboratory for their technical inputs. A few that deserve special mention are: Edna Gias, Della Orr, Mary van Andel, Naya Brandenburg and Jamie Fraser from the Investigation and Diagnostic Centre (MPI); Mark Stephenson from the Epicentre, Massey University; Laura Brandt, Janice Thompson, Gen D'Amours, Michael Hardcastle, Isobel Gibson, from Gribbles; Sandy McLachlan, dawn Seddon, from New Zealand Veterinary Pathology; Grant MacPherson, Kamo Veterinary Clinic; Gerald Pinckney, Vetplus; Meredith Love, The Vet Centre Ruawai; Anah Vorgers, The Rural Service Centre Veterinary Clinic; Ben Hitchcock, Anexa Animal Health, Te Kauwhata; Don Moore, Bayvets; David Hawkins, Franklin Veterinary Services; Graeme Ewenson, Dargaville Veterinary Centre; Garth Riddle, Bay of Islands Vet Clinic; Angus Campbell, Northland Veterinary Group; Ben Allott, Tararua Vets; Allen Heath, AgResearch. A special thanks also to the haematology staff at Gribbles and NZVP for their detailed work assessing Theileria numbers.

Notes

¹ http://dx.doi.org/10.1080/00480169.2015.1090355

*Non-peer-reviewed