Ticks

Last update: 15 March 2011

Tick-borne diseases (TBD) are an increasingly important public health issue in Europe, with ecological, climatic and socio-economic differences at national and regional levels determining which diseases are more likely to emerge and spread in certain areas rather than others. Among the possible drivers of TBD emergence, climate is an important geographic determinant of vector distribution (though not necessarily of disease distribution, see the EDEN project for more details). Other potential causal pathways of changes in TBD distribution may include changing land use patterns, increased density of large vertebrate hosts for adult ticks (such as deer), habitat expansion of rodent hosts, changes in recreational and occupational human activity, public awareness, vaccination coverage and tourism. Many of these factors have yet to be tested epidemiologically and applied to public health actions.

EDENext’s TBD group will be focusing in particular on Crimean-Congo haemorrhagic fever (CCHF) and newly emerging diseases, mainly borne by Ixodes ricinus, caused by different bacteria and parasites. CCHF is a tick-borne RNA virus responsible for outbreaks of severe haemorrhagic fever in humans. Over the past decade it has emerged or re-emerged in several Balkan countries, Turkey, south-western regions of the Russian Federation and the Ukraine with relatively high fatality rates. Possible reasons for the re-emergence of CCHF may include climate and/or anthropogenic factors such as changes in land use, agricultural practices or hunting activities and movement of livestock, all of which may influence host-tick-virus dynamics.

The emergence and spread of pathogens transmitted by the tick Ixodes ricinus are of greater public health relevance in the European Union (EU) than other endemic and exotic tick species which gain more medical and veterinary attention. For example, I. ricinus is considered the most important vector of Human Granulocytic Anaplasmosis, caused by Anaplasma phagocytophilum, currently considered the most medically important emerging TBD in the EU. In Europe, this disease is known to cause fever in goats, sheep and cattle, and it emerged as a human disease in 1996. Anaplasma phagocytophilum has also been detected in a wide spectrum of free-living vertebrates, birds and lizards, including rodents and free-living ungulates.

Other tick-transmitted infections of growing concern in the EU include those caused by Babesia microti and Babesia EU 1. There have also been recent records of spotted fever group rickettsioses transmitted by I. ricinus caused by newly recognised pathogens such as Rickettsia slovaca, R. helvetica, R. aeschlimannii and flea-borne rickettsioses (R. typhi, R. felis). However this increase in incidence may be due to improved diagnostic techniques, and an assessment of their current distribution and potential spread is essential.          

Last update: 15 March 2011

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