Epidemiology of tick-borne infections of livestock in the British uplands

Lauren Perrin - University of Salford

Project Summary

Changes to farm production subsidies have had a significant impact on livestock farming in the British uplands, provoking the maintenance of far less stock. The resulting decrease in grazing pressure potentially alters upland ecology in many ways, one of which is a shifting of the “infectious disease landscape” in which pathogens with transmission cycles favoured by a changing upland ecology will become of greater veterinary importance. Given that the consensus view of sustainable uplands is one in which wildlife is more abundant, pathogens able to exploit both wild-living and domesticated hosts are of particular concern. Tick-borne pathogens are not only a case in point, but also their threat is now augmented by increasing tick abundance, changing climate, and the extraordinary nationwide increase in the abundance of deer (that serve as a key host species). The three tick-borne diseases that pose the greatest threat to livestock in the UK uplands are (i) bovine babesiosis (redwater fever) caused by Babesia divergens, (ii) tick-borne fever caused by Anaplasma phagocytophilum, and (iii) louping ill caused by the louping ill virus. All three are transmitted by the catholic-feeding tick Ixodes ricinus, and have established wildlife reservoirs.

This project will simultaneously explore the epidemiologies of bovine babesiosis, tick-borne fever and louping ill, which, due to their insidious nature and the fastidiousness of their aetiological agents, remain poorly understood. The project’s aim is to identify factors that are important in shaping these epidemiologies. To obtain the requisite data, I will spend 36 months monitoring infections in livestock on three farms in the Cumbrian uplands (owned by the Forestry Commission, from whom my supervisors have an in principle agreement for collaboration). Concurrently I will quantify tick population dynamics on livestock pasture, and the prevalence of each infection in ticks. Finally, I will determine the composition of the wildlife community on, and in the vicinity of, the livestock pastures, and the relative role of the species within each community as blood-meal sources for ticks and as reservoirs for tick-borne pathogens.

Collation of these data will allow me to construct transmission pathway maps for each pathogen and identify which pathways are the most important in terms of transmission of infections to livestock. I will also analyse the data set using multi-variate statistical analyses to identify those factors that increase risk of infections in livestock. The longitudinal nature of my surveys will enable me to identify interactions between factors and the temporal nature of any relationships between these factors (e.g. high numbers of ticks in the spring predict high disease burden in livestock in autumn).

Taken together, these outputs should serve to enhance knowledge of the epidemiologies of tick-borne pathogens of livestock at a time when the threat they pose is only likely to increase. This knowledge has direct application for infection control as it will help identify potential breakpoints at which pathogen transmission can be most effectively interrupted.