Tick-borne diseases - a threat against grazing cattle in a warmer climate

The aims of the project were to i) perform a pilot study to investigate the occurrence of infectious agents in ticks and blood samples from outdoor cattle which have been affected by serious disease problems most likely caused by tick-borne infections, and ii) to investigate if tick prophylactics can reduce the risk for disease problems among grazing young-stock. The long-term aim is to reduce the risk for tick-borne infections among grazing cattle. 

The study showed presence of new infectious agents, a Mycoplasma wenyonii-like species and bovine parvovirus-2, in blood samples from cattle that were clinically sick most likely due to tick-borne infection. It can not be excluded that these infectious agents may have had importance for clinical disease. We also found that infection with Anaplasma phagocytophilum was very common in the herd. It is possible that such infection can cause immune suppression making the animals extra sensitive to other infections and, in turn, more clinical diseases. Mixed infections are probably of importance for the course of disease as such can lead to more severe disease than single infections. We also found that wild deer in the area are not an important source of A. phagocytophilum in cattle. 

That ticks are a vector for infection with A. phagocytophilum was confirmed by findings of DNA from this bacteria in ticks collected from cattle. Tick prophylactics is often a part of the recommendation to control such infections. In the animal group studied in this project tick profylactics in May did, however, not have any effect on the investigated variables for growth and diseases. The fact that all young stock had antibodies to A. phagocytophilum already before the treatment can also have affected the results.

To further investigate the importance of the M. wenyonii-like species detected the intention is to produce a PCR-test for this species that can be used to investigate a larger number of samples for the presence of this species. We also hope to investigate presence of this species in collected ticks.

Introduction of new infectious agents via ticks can lead to new diseases and/or that already known infectious diseases can get worse. Increased morbidity and mortality is costly for the industry. By increasing the knowledge of this area the need for preventive measures and measures for early detection and possible treatmen of affected animals can be identified.