Recently we are becoming more aware of the emerging threat of tick borne fever. This disease of cattle and sheep is caused by Anaplasma phagocytophilum, a bacterial infection that is mainly spread by Ixodes ricinus, the same tick that transmits Redwater. Biting flies may also be involved in the spread of the disease. The organism infects and destroys white blood cells.

Also called pasture fever in Europe, it usually occurs every spring and in early summer, when dairy cows are turned out. After infestation with infected ticks, it usually takes 5-14 days for animals to show clinical signs. These include fever (105-108°F), depression, inappetence, milk drop and sometimes respiratory signs and coughing. Early embryonic death and abortion can occur, usually as a result of fever. Temporary infertility can occur in bulls and rams. The disease also causes a marked immunosuppression, which can lead to secondary infections and may also limit the efficacy of vaccines.

Animals usually improve quickly if they are treated with specific antibiotics, but relapses can occur. While recovered animals may have some resistance to reinfection, this residual immunity may only last a few months. Younger cattle are less prone to severe clinical signs and may develop a better residual immunity when exposed to infection.

Control of tick borne fever should include the regular use of acaricides, which are effective against ticks. Efforts should be made, where feasible, to keep animals out of areas with higher tick densities. Ticks are very susceptible to drying out, so they need moist, humid environments, such as rough under-grazed pastures as well as hedges, headlands and roadways. Fallow deer in particular are probably an important reservoir of ticks and the tick borne fever in Ireland, so areas where these deer proliferate may be at extra risk. There may also be merit in reserving higher-risk pastures for younger cattle, which are less susceptible and while allowing them to develop better immunity.

For the last 20 years there has been a decreasing incidence of Redwater in Ireland. This was explained by the declining numbers of ticks on agricultural land due to land improvements and the use of ivermectin pour-ons. This is contrary to the growing evidence in Europe, where tick numbers and range are increasing due to climate change. The decrease in Redwater may even be due to the increasing prevalence of tick borne fever, which may be able to suppress the Redwater agent through host immunosuppression.

What we do know is that we cannot be complacent about ticks. Talk to your vet about this complex disease which is probably being underdiagnosed all over the country.

*John Berkery works at Mulcair Veterinary Clinic, Newport, Co Tipperary, part of XLVets, a group of practices working to achieve a better future for agriculture and veterinary in Ireland. Visit www.xlvets.ie.