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Theileria .. Emerging Disease in Cattle
Theileria has recently been diagnosed on a dairy farm in Takaka. The Tasman has been classed as a moderate risk area for the disease but with warmer weather and an increase in the tick population we will start to see cases on this side of the hill. Since the first reports of anaemia in beef and dairy cattle appeared from Northland in spring 2012 there’s been an increase in reported cases from Northland down to the central North Island and now the top of the south. It can affect both beef and dairy herds.
What is Theileria?
Theileria is a blood parasite that damages red blood cells and causes anaemia in cattle.
What to look out for:
Signs of Theileriosis are those associated with anaemia and include: pale or yellow mucous membranes ie. gums, vulva and whites of the eyes., depression, lethargy, lack of appetite, exercise intolerance, (lagging behind the mob) downer cows that do not respond to treatment and in some instances cattle may collapse and die if stressed or forced to move or run. Pregnant cows may abort and still births are common. In dairy cows a drop in milk production will occur and somatic cell counts may rise.
How do herds/animals get Theileria?
It is passed between animals by ticks. These ticks can be brought in by infected cows moving onto the property or vectors such as dogs or rabbits.
The tick lifecycle consists of four stages – egg, larva, nymph and adult. Theileria are not transferred from the adult to the egg. However, once hatched if a larva becomes infected with Theileria the tick remains infected through the later nymphal and adult life stages.
Adult ticks are active mainly during early summer, larvae from late summer to early winter, and nymphs mainly in spring. Nymphs will be dormant during winter becoming active as the weather becomes more favourable in the spring.
All stages live at the base of pasture plants. Each stage, apart from eggs, needs to feed on a warm-blooded host to progress to its next life stage. During questing (searching for a host) ticks will climb up plant stems and attach to a passing animal.
Feeding lasts anywhere from 5 to 14 days, longer with older stages and after feeding the larva, nymph or adult tick drops off the host and returns to the bottom of the pasture to mature to the next stage, or to lay eggs if it is an adult tick.
When is it most likely to occur?
Spring and autumn have been the predominant disease periods. This is due to the high levels of stress around calving and drying off, peak milk lactation is also a time of concern.
Stock movements, environmental conditions, stress in the herd, concurrent disease, tick populations and prior exposure to the disease are likely contributing factors.
A presumptive diagnosis can be made on presentation with pale/yellow membranes and a drop in production are the normal clinical signs. This can be confirmed by a blood test.
The treatment used depends on the severity of clinical signs. Stress is a big factor in the severity of clinical cases. Supportive care and good husbandry around these times will help lessen the impact of the disease.
Establishing once a day milking for affected cows and increased nutrition can speed up recovery and prevent drying off.
The best drug used to treat Theileria is Buparvaquone. This has been used in Australia for some time but has only recently become available in New Zealand. Unfortunately as it has not undergone clinical trials here and because of our stringing export requirements the meat and milk withholding times are long: currently for meat this is 18 months, and for milk 43 days also milk from treated cows must not be fed to bobby calves (OK for replacement calves). Bobby calves born to treated cows must not enter the food or feed chain.
Efficacy of Buparvaquone is good providing use is timely, appropriate and used with other disease management methods.
Previous to the introduction of Buparvaquone high doses of Engemycin had been used to treat clinical cases with some success.
Cows that are very anaemic with a PCV (packed cell volume is a measure of red blood cell loss) around 10% will require a blood transfusion. For this healthy donor cows must be chosen and checked that they are not also affected by Theileria. This can be done on farm in an emergency situation if we have the equipment. Cows given blood transfusions recover quickly and can often return to milking.
Control and prevention options
In areas where Theileria is commonly found (endemic areas) most adult cattle are found to be immune. This disease is mainly a problem in naive herds that have not had any exposure to the disease. With time and controlled levels of exposure most herds will develop a good level of immunity. We cannot completely control the tick population and therefore the spread of the disease but it is possible to greatly lessen the impact.
Calves should be examined closely when they are 6-12 weeks old as this is the time when temperatures are increasing and ticks will be starting to attach to stock.
Introduced cattle should be examined closely when they arrive on farm, and are starting to settle in over the next few weeks – as this is commonly when stressors are maximal and clinical disease may present.
In districts where Theileria is normally not present, but cattle from Theileria infected areas have been introduced (such as cattle been grazed away or cattle bought in from endemic areas), check home cattle regularly between two and six months after the introductions. If signs of disease are noted, seek veterinary advice as treatment when animals are mildly affected has been most successful.
Avoid importing animals from known affected properties, however where the health status of bought-in stock is unknown, treatment with a registered tick treatment such as Bayticol may be advisable prior to introduction. Bayticol has a nil milk and meat withhold.
Cattle may require treatment every two to three weeks for a few months during summer and autumn, but it must be noted that over-use of tick products can cause resistance within the tick population. Therefore it is important to remember that tick treatments should not be the only method of tick control – each stage of the life cycle of the tick is only on the body for a short period of time. For beef farmers rotational grazing practices may also help control ticks; the use of sheep or deer may act as ‘vacuum cleaners’ to remove ticks from pasture before the introduction of cattle.
Theileria can also spread by way of blood transmission – ie use of a needle or ear taggers on an infected animal being then used on an uninfected animal, or even biting flies. It is therefore very important to disinfect equipment between cattle to help prevent the spread and control flies in sheds and facilities.
Please contact us if you have any questions or wish to set up a Theileria control plan for your individual farm.