Abstract
Lyme disease cases caused by Borrelia burgdorferi s.l. bacteria is increasing steadily in Europe, in part due to the expansion of the vector, Ixodes ricinus. Wild reservoir hosts are typically recurrently infested. Understanding the impact of these cumulative parasite exposures on the host’s health is, therefore, central to predict the distribution of tick populations and their pathogens. Here, we have experimentally investigated the symptoms of disease caused by recurrent infestations in a common songbird (Parus major). Birds were exposed three times in succession to ticks collected in a Borrelia endemic area. Health and immune measures were analyzed in order to investigate changes in response to tick infestation and Borrelia infection rate. Nitric oxide levels increased with the Borrelia infection rate, but this effect was increasingly counteracted by mounting tick infestation rates. Tick infestations equally reduced haematocrit during each cycle. But birds overcompensated in their response to tick feeding, having higher haematocrit values during tick-free periods depending on the number of ticks they had been previously exposed to. Body condition showed a similar overshooting response in function of the severity of the Borrelia infection. The observed overcompensation increases the bird’s energetic needs, which may result in an increase in transmission events.
Highlights
Lyme disease cases caused by Borrelia burgdorferi s.l. bacteria is increasing steadily in Europe, in part due to the expansion of the vector, Ixodes ricinus
Correspondence and requests for materials should be addressed to D.J.A.H. www.nature.com/scientificreports/. Their pathogens jointly affect the physiological health status of their natural wildlife hosts, both in a chronic and an acute way. One such vector-pathogen system that enables us to address these questions consists of the blood-sucking tick, Ixodes ricinus, and the tick-borne Borrelia burgdorferi s.l. bacteria
Ixodes ricinus is the main vector of the Borrelia bacteria in Europe, that infests a wide range of terrestrial vertebrate host species, including birds, reptiles and mammals
Summary
Lyme disease cases caused by Borrelia burgdorferi s.l. bacteria is increasing steadily in Europe, in part due to the expansion of the vector, Ixodes ricinus. Ixodes ricinus is the main vector of the Borrelia bacteria in Europe, that infests a wide range of terrestrial vertebrate host species, including birds, reptiles and mammals This tick has a three-stage life cycle (larva, nymph, and adult), and it feeds once during each developmental stage[13]. The highest abundances of questing ticks (April–July) coincides with the season when birds rear their nestlings and, with the moment when nestlings fledge[13,17,18,19] At this time of the year, songbirds that forage inside the habitat of I. ricinus (i.e. the lower vegetation strata) are repeatedly exposed to and infested with Borrelia infected ticks. We experimentally study (1) the effects of repeated exposure to the Ixodes ricinus -Borrelia system on a number of health parameters in a common bird species, the great tit (Parus major L.), (2) whether these effects relate to the tick loads, the degree of infection with the tick-borne pathogen, or both and (3) whether the acute infestation effects depend on the degree of previous infestations with ticks and/or Borrelia
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