Since being first detected in the region in the early 2000s anaemia due to Theileria orientalis has become a frequent diagnosis on the north coast. Early cases seen were in introduced adult cattle bought to the region from either areas west of the Great Dividing Range, or from southern parts of NSW or Victoria. Since then, cases in young home bred calves have been seen annually. In the 5 years between 2017 and 2021 there have been 117 cases of theileriosis recorded in the NSW DPI/LLS disease recording system, Livestock Health Management System (LHMS). Of these cases, 58 involve young homebred calves, with the remaining 59 involving cattle introduced to the region. The actual number of cases seen in the region is likely to be much higher than this given many private vets would diagnose based on signs and in-house testing, and many producers would be well aware of the signs, especially in young calves, and may not seek veterinary advice. The disease continues to be frustrating for owners and veterinarians given the lack of effective treatments available in Australia.
The clinical signs of bovine anaemia due to Theileria orientalis have been well described previously1,2.
Whilst diagnosis can often be made based on signalment and clinical signs, laboratory testing can be used to confirm a diagnosis. The presence of anaemia (often marked) as well as demonstration of the presence of the organism either in smears or via Theileria major piroplasm surface protein (MPSP) qPCR testing can be used to confirm a diagnosis. Both the level of parasitaemia in red blood cells and the number of gene copies in PCR testing often appear to be inversely proportional to the degree of anaemia, presumably because many of the parasitised red blood cells have already been removed from circulation. Many animals that are profoundly anaemic (PCV in the order of 8-10%) often have quite a low proportion of red blood cells parasitised (<5%), whereas those animals tested earlier in the course of the disease process may have 20-30% red blood cells with parasites.
The major piroplasm surface protein PCR test can distinguish between the presence of the 3 orientalis genotypes (Ikeda, Chitose and Buffeli) and also provide quantitative data on the parasite load3. When reporting qPCR results EMAI provide the following advice - Levels may be defined as low (< 15,000 gene copies), moderate (> 15,000 but < 300 000 gene copies), or high
(> 300 000 gene copies). Levels of Theileria infection of < 15 000 gene copies are commonly seen in herds where infection is subclinical. Levels of Theileria infection of > 15 000 gene copies are commonly seen in herds experiencing clinical cases of theileriosis. The majority (about 92%) of individuals with clinical theileriosis have a gene copy number above 15 000. However, both recovering and in contact animals often also have gene copy numbers above 15 000. When the gene copy number is above 300 000, 95% of individuals show clinical signs of theileriosis.
Necropsy findings include pale, often jaundiced carcase, with an enlarged ochre coloured liver and an enlarged spleen with jam-like contents. Spleen can be used for qPCR testing from dead animals.
Treatment of clinically affected animals remains a challenge, with no highly effective products available in Australia. Local private veterinarians on the mid north coast of NSW report some success with blood transfusions in affected adult cattle, using the technique described by Malmo et al.4. Blood transfusion of affected calves is more easily accomplished because of the relatively small amount of blood involved in making a significant difference to the calf's PCV. Minimising exertion and other stress factors remain important in managing affected animals. Often the stress of yarding worsens clinical signs and animals become recumbent when moved. Easy access to safe drinking water is important, as anaemic cattle bog in muddy dam edges and drown. Whilst affected animals are often treated with antibiotics such as oxytetracycline, the response to such treatments is usually poor. In young calves, pneumonia is often found in conjunction with Theileria so treatment with antibiotics and NSAIDs is appropriate. Some producers on the north coast have used toltrazuril (Baycox cattle coccidiocide, Bayer) in young calves as a prophylactic treatment given at about 4 weeks of age, though there is no evidence to suggest that this is effective in preventing or treating theileriosis5.
North coast LLS district veterinarians are frequently asked by producers for advice on managing the risk of theileriosis in introduced adult cattle. The degree of risk varies according to the region the cattle are coming from and the signalment of the cattle. Cattle from bush tick free areas of southern and western parts of NSW and southern states are at risk of developing clinical theileriosis from 6 -14 weeks after introduction. Disease is most severe in heavily pregnant cows and heifers, with losses over 30% in these mobs being seen. In addition to death of the cows, abortion and stillbirths is seen, further contributing to loss.
Producers considering introducing cattle from non-endemic areas should carefully consider the risk before doing so. Lower risk options, though still posing some degree of risk, include introducing weaners or unjoined heifers. When producers plan to go ahead with introductions the advice is to minimise all other stress factors as much as possible, ensuring nutritional needs, including trace minerals, are met and ensuring both internal and external parasite control is adequate. Stock should be kept in the least 'ticky' paddocks available and products used to minimise ticks. Products registered for bush tick control are limited to sprays and dips and these products offer very short periods of control only. Y-Tex Python ear tags are registered for paralysis tick control for up to 42 days and whilst not being registered for bush ticks have been used by some producers to manage tick burdens on introduced mobs. Cattle should be closely observed following introduction especially from 1 month to 3 months after arrival. Where stock are being moved from a marginal tick area, cattle could be tested for evidence of prior exposure, and therefore immunity, to Theileria. I have used the qPCR in these circumstances previously.