Cattle parasite makes presence felt in NZ

The following is an edited version of a veterinary paper describing the disease in NZ.

The first published report of T. orientalis in New Zealand was in 1984. This explained that the occurrence of this parasite in NZ was unsurprising because at that time cattle were imported from Britain and Australia where the parasite was known to occur.

Despite the parasite not being identified in NZ before then, it was already likely to have been present for several years. The reason it remained undetected until then is open to conjecture.

Following the first description of T. orientalis in NZ, the number of reported cases increased until 1985 when the Whangarei Animal Health Laboratory diagnosed 60 cases or outbreaks, with the most common presenting signs being ill-thrift, drop in milk and meat production, anorexia, malaise, depression and diarrhoea. This disease then disappeared before re-emerging four years later in Wairoa and Northland.

It was suggested that T. orientalis was widespread in NZ and when environmental conditions were appropriate for the multiplication of ticks – and when susceptible animals were present – the disease appeared.

Rawdon described the investigation of jaundice, pyrexia, collapse and death in a 20-month-old steer from north Waikato. Examination of blood smears from this animal revealed over 50% of erythrocytes to be parasitised with T. orientalis. The authors of this study ruled out other causes of haemolytic anaemia and concluded that T. orientalis was the responsible agent and the primary cause of death.

In 2009 one outbreak of anaemia associated with infection by Type 1 (Chitose) strain of T. orientalis in a group of cattle moved from South Otago to Northland was described as affecting 38% of investigated animals with 1% mortality. This investigation concluded that members of the T. orientalis group present in NZ were capable of causing disease in cattle not necessarily debilitated by another disease.

In December 2012, the Ministry for Primary Industries' Animal Health Laboratory first identified T. orientalis Ikeda, which had not previously been identified in NZ. Since late 2012 outbreaks of anaemia associated with T. orientalis Ikeda have been reported in dairy and beef cattle herds located in Northland, Auckland, Waikato, Taranaki, Manawatu/Wanganui, Bay of Plenty and Wellington.

Outside the known endemic tick areas the impact of the disease appears to be much less severe. The number of outbreaks in cattle herds has steadily increased since T. orientalis Ikeda was first identified in NZ.

In the early stages of the epidemic, genotyping of T. orientalis from these outbreaks was carried out and one was identified asT. orientalis Ikeda strain. Other strains present were T. orientalis Chitose and T. orientalis Buffeli. The Ikeda strain reportedly has greater pathogenicity than other endemic strains present in NZ.

It is not possible to say how long the Ikeda strain has been present in NZ. Testing of stored serum samples for T. orientalis organisms, prior to December 2012, from investigations from Northland collected since 2008 failed to detect the Ikeda strain.

Conclusion

Theileria orientalis is an economically important parasite of cattle in NZ, Australia and Japan, especially where naïve animals are introduced into an endemic area or in animals under stress.

Awareness of the risks posed by the parasite is required to enable management practices to be implemented to minimise its impact.

Reprinted courtesy of the New Zealand Veterinary Journal.