Enzootic bovine leukosis in New Zealand--a case report and update

Enzootic bovine leukosis was diagnosed in an 8-year-old Friesian cow which had lost condition and was milking poorly. The cow had a severe nonregenerative anaemia, panhypoproteinaemia and lymphoid leukaemia. At necropsy there was widespread lymphoid infiltration of many organs, including the abomasal mucosa, myocardium, uterus, kidney, lymph nodes and bone marrow. Antibodies against bovine leukaemia virus were detected in the serum. Although clinical enzootic bovine leukosis is rare in New Zealand, having been confirmed on only five properties, infection with the causative agent, bovine leukaemia virus, is more widespread. The results of a recently completed survey of bulk milk samples using an enzyme-linked immunosorbent assay for bovine leukaemia virus antibodies suggest that there are about 300 dairy herds in the country with a bovine leukaemia virus infection level of at least 5-10%. The economic impact of enzootic bovine leukosis on the productivity of New Zealand's dairy cattle population is probably still negligible but the introduction of control or eradication schemes in Europe and North America could sooner or later lead to restrictions on the export of live cattle and genetic material from New Zealand.