Research
Current and recent projects
Explaining the upsurge of tick-borne encephalitis (TBE):
In collaboration with 15 partners across Europe within the EU-funded EDEN project , we have shown that climate change [pdf] cannot explain the dramatic upsurge of TBE incidence that occurred in 1993 in most central and eastern European countries. The epidemiological patterns are too heterogeneous in time and space to be explained by the more or less uniform pattern of climate change. Rather, differential degrees of socio-economic transition following the end of Soviet rule led to increased contact between people and infected ticks in forests [pdf]. Decreases in TBE incidence in Latvia since 1999 appear to be due more to changing behaviour in response to perceived risk than to increased vaccination rates. The more gradual, but marked increase in TBE incidence in several western European countries is being explored.
Modelling tick population dynamics and disease transmission:
Modelling the seasonal dynamics of the major European tick vector, Ixodes ricinus, will provide a powerful tool for predicting differential disease transmission potential in time and space. Recent advances, by including complex overwinter diapause events, are close to giving us an almost fully functional model.
OTRG supplied the accurate biological basis for Hans Heesterbeek’s (Utrecht University, The Netherlands) novel next-generation matrix method of modelling the basic reproduction number (the R0 value) of Lyme borreliosis and TBE.
Tick distribution in the UK:
Predictive risk maps for the presence of Ixodes ricinus in the UK reveal that this tick is widespread throughout the British Isles, but patchily distributed according to climate and areas of woodlands and other habitats large enough to house populations of deer, that are the principal hosts for adult ticks. Ticks are thought to have become more abundant over the past decade, possibly due to increases in deer distribution and numbers, and also perhaps to changes in sheep husbandry.
Public awareness and response to perceived risk of Lyme disease: Woodlands offer valuable recreational resources. As part of the UK Research Councils' Rural Economy and Land Use (RELU) Programme, we are exploring the balance between the real risks of Lyme disease, depending on the abundance of ticks and visitor use of different habitats within woodlands, and adequate awareness of those risks [link to http://www.forestresearch.gov.uk/fr/INFD-77CEKT].
Past achievements
The Oxford Tick Research Group has pursued a variety of research projects covering a broad range of activities, all directed at understanding the complex system of tick-borne diseases at many different scales.
Laboratory experiments on the interactions of ticks, hosts and transmitted parasites: Testosterone has proved to play a role in determining the degree of innate and acquired resistance shown by natural host species to ticks and the infectivity of Babesia microti from rodents to ticks.
Field observations and experiments on tick ecology and natural enzootic cycles of tick-borne pathogens: Transmission cycles of the various species of Borrelia burgdorferi s.l., that cause Lyme borreliosis, depend on the quantitative relationship of ticks with their different host species. As well as mice and voles, squirrels and pheasants play significant transmission roles. Ticks have an impact on male pheasant territoriality that may predispose heavily infested birds to contact even more ticks questing in woodlands. Sheep support enzootic cycles purely via the non-systemic infections transmitted between co-feeding ticks.
The coincident aggregated distributions of larval and nymphal ticks on rodents ensures that each nymph transmits tick-borne encephalitis virus to many co-feeding larvae, thereby ensuring a sufficiently high transmission potential to maintain enzootic cycles.
Modelling tick population dynamics and disease transmission: Analyses of field data on the African tick Rhipicephalus appendiculatus and the European tick Ixodes ricinus have yielded estimates of rates of the primary demographic processes, birth (or development) and death. The resultant population model of R. appendiculatus captures the variety of seasonal patterns across its full geographical range.
Analysis of regional, continental and global patterns of the distribution of vector-borne pathogens in relation to environmental conditions as revealed by satellite imagery:
Our predictive risk maps of tick-borne encephalitis and malaria give insight into the biological processes underlying the epidemiological pattern of the present. TBE foci appear to depend on the synchronous seasonal feeding of nymphal and larval Ixodes ricinus, which in turn is statistically associated with more rapid spring warmimg of the land surface temperature. Our methods have permitted us to predict how these patterns might change in the future under the influence of climate change. These predictions, however, depend on the reliability of climatologists’ scenarios of future climate. Moreover, they are untestable (until the future arrives) and therefore, by definition, not scientific.
This has also been applied to Bovine TB, indicating that the distribution of this infection does have strong environmental correlates.