Disease Characteristics & Distribution
Theileriosis is caused by a small protozoan parasite that infects both red and white blood cells of cattle. The theileria parasite is spread by blood sucking arthropod insects, particularly various species of ticks which parasitise cattle. Theileriosis can affect cattle of all ages, however heavily pregnant, lactating, and stressed cows tend to be at greatest risk, due to resultant reduction in immunity.
On a global scale there are variations in diseases caused by the different species of the parasite, with the most severe being east coast fever, which is endemic in African countries however exotic to Australia. It has long been considered that tropical and sub-tropical climates tend to favour the survival and transmission of the theileria.
A species of the parasite, Theileria buffeli, has been known to be present in Queensland since around 1910, being introduced with the cattle tick from Japan. This parasite has been relatively non-pathologic. Recently however, there have been reported cases of theileriosis in several states of Australia, which resulted in severe production losses and deaths in dairy and beef herds. Controversy has surrounded these outbreaks, as to whether they have been caused by the same species of theileria that has been in Queensland since the early 1900’s, or in fact whether it is a different species of the parasite. Research is currently underway in NSW regarding this.
Recently we have seen the prevalence of theileriosis increase in the Tamworth district and the eastern fall country around Walcha, which is unusual given the climatic zones that have been traditionally associated with the parasite.
Clinical Signs of Disease
The main signs that affected cattle have shown in recent outbreaks include:
- Fever (rectal temperature > 39ºC)
- Drop in milk production
- Depression, weakness and inappetence
- Difficulty breathing, with rapid and shallow breaths
- Increased heart rate.
- Less commonly seen clinical signs that can be seen include: excessive salivation, diarrhoea, constipation, swelling of lymph nodes, and brown urine.
The disease can result in death of the affected cow; however a rapid recovery is also possible. The variation in clinical syndromes is due to individual cow immunity and tolerance, and also variations due to different strains of the parasite.
A blood sample needs to be taken from the affected cow for diagnosis. A blood smear is then made to examine for the parasite associated with red blood cells. It is important to get a blood sample early in the stage of infection, as the spleen removes the parasitised blood cells, which can result in an apparently normal blood smear.
To date there is no one effective treatment for theileriosis in Australia. We have attempted treatment with halofuginone administered orally, which is the typical treatment for cryptosporidium in calves. To have any beneficial effect, this treatment needs to be administered in the early stage of infection, thus early detection of clinical signs is of paramount importance. It is also potentially possible to combine this treatment with a blood transfusion and/or fluid therapy. Other described therapies include: oxytetracycline, primaquine and buparvaquone; however the described success of these drugs are limited.
Control & Prevention
Many of the recent reported serious cases of theileriosis have been associated with the movement of stock. It is unclear at this stage whether the stress of transport causing immune compromisation, or the exposure to new parasites on relocation is associated with disease outbreak. However both are important considerations when buying in new stock.
In tropical climates, tick control is an important point in managing tick-borne blood parasites. Whilst we do not see many ticks in the Tamworth district, they could still be implicated in disease transmission, as could other biting insects. Thus topical insecticides are worth consideration.
Hygiene is also an important point in preventing the disease. Always ensure a new needle is used for each cow when administering injections.