In recent years, theileriosis has caused serious illness and death in naive cattle introduced to the Mid North Coast from areas west of the Great Dividing Range. This article describes field research to record the progress and outcome of theileria infection in a group of ten dairy heifers introduced into a Taree dairy herd from South Australia in October 2011.
The Taree dairy herd featured in this study suffered significant losses in a group of pregnant cows purchased from Forbes early in 2011. Wanting to import some very good quality Ayrshire blood from a South Australian herd, they decided to avoid heavily pregnant cows, and purchased 10 two year old just-joined heifers.
The introduced heifers were monitored weekly, with the first bleed being on the day they arrived. At the second bleed, they all had very heavy tick burdens common bush tick (Haemophysalis longicornis). They were treated with deltamethrin at that time, and tick burdens decreased dramatically after that.
Laboratory testing of the blood samples taken each week included:
After bleed 5, EMAI also began testing the bloods using a Theileria antibody Elisa they were developing.
PCR was negative for the first two bleeds, but detected Theileria in 9/10 animals at Bleed 3.
Smears only detected - 1% parasitaemia in 4/10 animals at week 3, but all animals had significant parasitaemias on smears at week 5.
PCR's positive for Ikeda showed up first at the week 3 bleed (9/10 positive).
By week 5 all were positive for Ikeda, 8/10 were positive for Chitose, and 7/10 were positive for Buffeli.
Some cows were treated with oxytetracycline (Bivatop 200 mg/ml at 20 ml I/M) and/or erythromycin (Erymicin 200 mg/ml at 25 ml I/M), depending on clinical observations and blood results. At the earlier Theileria outbreak, the owners felt that Bivatop had been of some benefit.
No animals in this group died, although a number of them suffered anaemia and weight loss. Cow 7 was very severely affected, with marked weight loss and photosensitisation.
Packed Cell Volume (%)
This trial demonstrated that Theileria challenge of cattle introduced to the Mid North Coast can be almost immediate, especially if the cattle are introduced at times of the year when ticks are active. Although these heifers had heavy tick burdens by the second week after arrival, tick numbers have been low or undetectable in other serious cases of theileriosis.
Three weeks after these heifers arrived, 9 of the 10 returned positive PCR results for theileria. Although the Buffeli strain of Theileria is considered to have been endemic throughout the Mid North Coast for many years, the 'newer' Ikeda and Chitose strains appeared earlier in the blood of these heifers (based on PCR results).
Recent research in Australia (Eamens et al, 2013; Kamau et al, 2011) has demonstrated an association between the Ikeda strain of Theileria and clinical signs of disease. Serious illness attributed to theileriosis had occurred on this property earlier in 2011, so it was not surprising that PCR testing confirmed the presence of Ikeda during this study.
In eight of the 10 heifers, the Theileria parasitaemia peaked 6 weeks after arrival and then declined, regardless of whether antibiotics were used at week 6 or not. In many of the heifers a decline in PCV preceded the peak in parasitaemia.
We would like to thank Michael and Janine Eagles, the owners of these heifers, for participating in this study.
Graeme Eamens and the staff of the Elizabeth Macarthur Agricultural Institute (EMAI) are thanked for performing the laboratory testing featured in this report.