Theileriosis is a tick-borne disease caused by an intracellular blood parasite that in NZ is carried by the cattle tick Haemaphysalis longicornis. Although it may cause tick irritation and local reactions in all species, it is currently believed that H.longicornis only transmits theileriosis to cattle.
Signs of Theileriosis are those associated with anaemia and include: pale membranes, 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.
Unfortunately our treatment options are currently limited in NZ and are mainly restricted to symptomatic and supportive care.
Minimise stress, handling and transport of affected animals.
Engemycin, at 20-25ml/cow/day has shown to show improvement in some cases, whether it affects the parasite itself, or helps with concurrent issues. If no improvement is seen in 2-3 days it is recommended that treatment is stopped as the stress of injections and movement may worsen the anaemia/clinical signs.
Blood transfusions – are an option for valuable, anaemic animals.
Buparavaquone – this is the preferred international treatment of choice, however is very limited in availability.
Always consult with your veterinarian and remember to observe the prescribed withholding periods before marketing products of treated animals.
Control and Prevention Options.
In areas where Theileria is commonly found (endemic areas) most adult cattle are found to be immune. In Northland Theileriosis has been noted frequently in the last year, and stock in areas like this should be closely inspected.
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 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. When using insecticides always consult with your veterinarian and remember to observe the prescribed withholding periods before marketing products of treated animals.
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. 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 – i.e. 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.