Oral Presentation 64th International Conference of the Wildlife Disease Association 2015

Ticks, birds and tick-borne diseases: the terrestrial cycle (#65)

Dieter Heylen , Hein Sprong , Erik Matthysen

The importance of birds as reservoir hosts for tick-borne diseases has been recognised for many decades. Due to the difficulties inherent in studying birds in natural conditions, the appreciation of their role as reservoirs has lagged behind. We are currently studying the ecological processes involved in the interactions between ixodid ticks and European songbirds. Epidemiological parameters were obtained from experiments and long-term observational data (15 years) of the sheep tick (Ixodes ricinus), the tree-hole tick (Ixodes arboricola) and Ixodes frontalis, parasitizing some of Europe’s commonest songbirds, the great tit (Parus major) and blackbird (Turdus merula).  Both songbirds are recognised as a reservoir host for Borrelia burgdorferi s.l. Immature developmental stages of Ixodes ricinus, the most important vector of tick-borne zoonotic diseases in Europe, are frequently found on songbirds. Ixodes arboricola is a wide-spread nidicolous tick, adapted to a lifestyle inside tree-holes where it infests roosting and breeding birds (e.g. great tits), while Ixodes frontalis is an ornithophilic tick that also infests open-nesting birds (e.g. blackbirds).  In addition, these ticks are considered as competent carriers of Borrelia burgdorferi s.l. and Tick-borne encephalitis virus, though their ability to transmit those pathogens and therefore maintain it in birds has not been determined yet.  We will report on the main factors that explain spatio-temporal infestation risks, defined by ecological risk models making use of detailed vegetation maps in conjunction with micro-climatological variables and the birds’ life-history parameters.  Furthermore, we will present experimentally obtained data on the virulence of ticks, the birds' resistance mechanisms, as well as the host-mediated transmission mechanisms. Additionally, the possibility of closed enzootic cycles between birds and ornithophilic ticks, with Ixodes ricinus as a bridge vector, will be discussed based on experimental data.