CASE NOTES
ANAEMIA CAUSED BY THEILERIOSIS*
Ted Irwin, North West Livestock Health and Pest Authority
Posted Flock & Herd July 2012
Introduction
Benign theileriosis has been causing increasing occurrences of disease on the coast and inland in NSW. It is a protozoal organism spread by ticks that parasitises the blood cells leading to anaemia in cattle. It has also been known to cause abortion in pregnant cattle, calf deaths, and generalised ill-health and drop in milk production. In dry stock the condition is still generally mild, mostly affecting pregnant or stressed animals. The Ikeda strain of theileria, which originates from Japan, has been identified as the strain most likely to have led to an increase in the occurrences of clinical disease due to Theileria infections in Australia. In areas where the organism is endemic, cattle tend to have immunity and are unaffected. It is only when naive animals or calves are exposed to the Ikeda strain of theileria that there is clinical disease.
History
A mob of 122 PTIC Angus cows of mixed ages were purchased from a property near Launceston in Tasmania and moved to a property near Terry Hie Hie, south east of Moree in July 2011. Their journey has not been detailed. The North West LHPA was contacted after the owner had 10 adult cow mortalities in the space of 6 weeks up to mid-October. A number of cows had also calved and the calves appeared unaffected. The property traded cattle regularly and had a backyard feedlot operation running in conjunction with a traditional pasture based system.
Clinical findings
The mob of cattle was examined in the yards and a total of seven cows were examined in the crush. The cattle were in varied condition ranging from body condition score 3 to score 2 and numerous animals had 'rusty' coloured coats. Of the seven cows examined in the crush, all had pale mucous membranes and cow number one, the worst affected, showed signs of weakness. Clotted blood, EDTA blood, and Lithium Heparin blood were taken from each animal and sent to EMAI. The rectal temperature of cow number 1 was 39.7. This was the only temperature recorded. The cattle were not examined for the presence of ticks
DIFFERENTIAL DIAGNOSES
Differential diagnoses for this case included theileria, tick fever, chronic fascioliasis, rock fern poisoning, and copper toxicity or deficiency.
Results
Conclusion
The results are overwhelmingly consistent with disease caused by the Ikeda strain of Benign Theileriosis. Sub-optimal levels of copper may also have played a part in ill-thrift of some animals.
Discussion
This case is of interest for a number of reasons. Most notably it is one of the first examples where theileria has been transmitted between introduced cattle and home bred cattle, both of which are from a non-endemic area for theileria.
The second interesting fact about this case is the possibility that alternative vectors have been involved. These cattle were introduced in July to an area that is not heavily infested with ticks at a time when tick activity would be low. Lice activity at this time however would have been at or nearing its peak. Experimentally lice have been shown to transmit the disease. These cattle were not thoroughly examined for ticks but none had been noted by the owners.
All animals examined were considered to have pale mucous membranes. Of all the seven bloods taken however, only one was substantially below the reference range for cattle, having a PCV of 0.15. In fact two of the cows had PCV's of 0.24, within the reference range, and another three had PCV's of 0.22, just 0.01 outside of the reference range. Only six bloods were examined for PCV. These results would indicate that either dehydration was a factor, falsely elevating the PCV of these cows, or that the reference range for cattle is too low. Visually they appeared anaemic and so it would seem reasonable to assume they would have PCV's below the reference range for normality.
Finally, it is worth noting that disease due to Benign Theileriosis may become more prevalent in inland NSW as increasing numbers of inland properties become endemic for the disease through trading and movement of cattle back from the coast. As the disease is most evident in pregnant or stressed animals, young weaners moved west for growing pose the greatest threat to breeding mobs in the area. More work also needs to be conducted to ascertain whether lice are indeed a possible vector for the disease in non-endemic areas.
* Postscript: At the time of writing this article, the author used the term 'benign theileriosis'. This term has been in use to distinguish this disease from the far more serious diseases caused by other species of Theileria not present in Australia, such as east coast fever (caused by Theileria parva) that occurs in Africa, and Tropical Theileriosis (caused by T. annulata). As the disease typified by this case report can result in significant mortalities, the disease occurring in Australia is now referred to as "Bovine Anaemia caused by Theileria orientalis group."