A Clear and Present Danger: Tick-borne Diseases in Europe

Paul Heyman; Christel Cochez; Agnetha Hofhuis; Joke van der Giessen; Hein Sprong; Sarah Rebecca Porter; Bertrand Losson; Claude Saegerman; Oliver Donoso-Mantke; Matthias Niedrig; Anna Papa

Disclosures

Expert Rev Anti Infect Ther. 2010;8(1):33-50. 

In This Article

Who's the Predator, Who's the Prey?

Biodiversity and disease risk are, in most cases, closely linked. The problem is scientifically challenging as it assumes understanding of complex multispecies systems.[26] The irony is clear: while man is largely responsible for the present loss in biodiversity, his best protection from vector-transmitted diseases lies in high biodiversity. One striking example is tick-borne encephalitis virus (TBEV) and Apodemus mice. Apodemus mice – one of the main hosts for TBEV – do not become viremic but facilitate virus transmission through a nonviremic process, that is, co-feeding of ticks; in this case, an infectious nymph and susceptible larvae.[27–29] The probability of co-feeding on the same mouse is small when rodent population density is high thus decreasing the virus transmission rate. When rodent population density is low, not enough ticks become infected to allow persistence of the virus. At the same time, transmission success is influenced by noncompetent hosts such as deer; large mammals are the targets of adult ticks but these hosts generally do not act as competent hosts. High deer populations will thus attract many questing ticks and cause virus loss from the system. High biodiversity and high host population densities thus act in favor of human health although the effect might be dual in that, in this case, deer reduce infection prevalence in ticks but boost tick population density at the same time.[28] Except for Borrelia spp., Ixodes ricinus is also a competent vector for anaplasma, bartonella, Babesia and Rickettsia spp., in addition to TBEV. The virus circulates in large parts of Europe and is slowly expanding its distribution area northwards.[30,31] In recent years, ticks have been transported over large distances by companion and other domestic animals, especially dogs that travel with their owner.[32] Probably due to this accidental import, Dermacentor reticulatus – whose distribution range was limited to southern and eastern Europe – has reached mid- and northern Europe and has, due to prolonged periods with mild winters, established viable colonies. This is, amongst others, the case in The Netherlands where canine babesiosis has already made several victims amongst domestic dogs.[33,34] Another southern European tick, Rhipicephalus sangineus, has been reported in northern regions.[33] This tick is the vector for potentially life-threatening pathogens such as Rickettsia rickettsii, Rickettsia conorii and Rickettsia massiliae.[35,36]

This review will focus on the most important tick-transmitted pathogens circulating in Europe (Borrelia, anaplasma, Babesia, TBEV, Rickettsia spp. and Crimean-Congo hemorrhagic fever [CCHF] virus [CCHFV]).

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