Dispersal of ticks and tick-borne pathogens by birds Dynamics of birds’ transport of ticks to Norway

...........................................................................................................................................6 This thesis.........................................................................................................................................7 List of papers. ...................................................................................................................................8 Abbreviations and definitions ..........................................................................................................9 Introduction ....................................................................................................................................11 Background ....................................................................................................................................12 The importance of ticks as disease vectors.................................................................................13 Tick biology ...............................................................................................................................15 Vector and host competence.......................................................................................................17 The ticks’ vertebrate hosts..........................................................................................................18 Bird Migration............................................................................................................................19 Aims of the study ...........................................................................................................................21 Literature about ticks on migratory birds .......................................................................................22 Designing a study of ticks imported by birds.................................................................................23 Biometric data ............................................................................................................................23 Wind trajectories ........................................................................................................................23 Genetic markers..........................................................................................................................24 Are the ticks imported or not?....................................................................................................25 Ethical issues ..................................................................................................................................26 Materials and Methods ...................................................................................................................27 Tick genetics: Making new microsatellites (Paper I) .................................................................27 Tick genetics: Study of tick family groups (Paper II) ................................................................27 Collection of ticks from birds (Paper III) ...................................................................................27 Collection of blood samples from cows and detection of Babesia divergens antibodies (Paper IV) ..............................................................................................................................................28 Detection of Borrelia spp. in ticks (Paper V).............................................................................29 Synopsis .........................................................................................................................................30 Paper I: Primer note. Identification and characterisation of 17 microsatellite primers for the tick, Ixodes ricinus, using enriched genomic libraries. ..............................................................30 Paper II: Multiple paternity in Ixodes ricinus (Acari: Ixodidae), assessed by microsatellite markers. ......................................................................................................................................30 Paper III: Transport of ticks by migratory passerine birds to Norway. ......................................30 Paper IV: Detection of Babesia divergens in southern Norway using an immunofluorescence antibody test in cow sera. ...........................................................................................................31 Paper V: Transport of Ixodes ricinus infected with Borrelia species to Norway by northwardmigrating passerine birds............................................................................................................31 5 General discussion..........................................................................................................................32 Transport of ticks to new areas by birds.....................................................................................32 Spreading of tick-borne pathogens by birds...............................................................................36 Conclusions ....................................................................................................................................41 Acknowledgements ........................................................................................................................42 References ......................................................................................................................................43 Figures and tables...........................................................................................................................53 Appendices .....................................................................................................................................65 Appendices .....................................................................................................................................65 Index...............................................................................................................................................68 Papers I-V.......................................................................................................................................70 6 ABSTRACT Hard ticks (Ixodidae) are important disease vectors for humans and animals. In rich and temperate countries, human medicinal aspects are of the most concern to the public, while tick-borne diseases in livestock have immense economic consequences in tropical and subtropical countries. Tick-borne encephalitis is an emerging disease in Norway, and the prevalence of Lyme borreliosis and tick-borne encephalitis has increased in several northern European countries. Ticks feed on the blood from vertebrate hosts. They have a very limited mobility and are dependent on their hosts for dispersal. This study examines birds’ capacity for spreading ticks and tick-borne diseases across long distances and geographical barriers. Four bird observatories were used in the study, including Lista, on the southwestern coast of Norway, and three more eastern coastal islands: Jomfruland, Store Færder and Akeröya. During the spring migrations of 2003 to 2005, 9,768 passerine birds from the four bird observatories were examined for ticks. From these birds, 713 carried a total of 517 larvae and 1,440 nymphs. The highest prevalence of tick infestation was observed in the Turdus species and other ground-feeding birds, e.g., the robin (Erithacus rubecula) and dunnock (Prunella modularis). With the exception of 10 nymphs and 1 larva, the predominant tick species was Ixodes ricinus. Seven nymphs of Hyalomma rufipes and 1 larva of Dermacentor sp. were also found, which must be a new species for Norway. The prevalence of tick infestation and the number of ticks per bird varied with location, year and month. Blackbirds (Turdus merula) caught at Lista and Jomfruland, which are localities with many ticks, had more ticks than those from locations with few or no ticks, suggesting local tick recruitment. A similar study in 1965–1970 at Akeröya and Store Færder found ticks on 4.2% of the birds, while this study found infestation of 6.9% at the same localities (P<0.001), suggesting an increase in infestations. Borrelia spp. was found in 70/513 nymphs (19 B. afzelii, 38 B. garinii, 2 B. turdi and 11 B. valaisiana) and in 14/172 larvae (10 B. garinii, 1 B. turdi and 3 B. valaisiana). B. turdi is new to Europe, but was previously found in I. turdi, a tick species that is a parasite to birds in Japan. Ticks collected from birds of the Turdus spp. had a higher prevalence of Borrelia spp. than ticks from the other passerine genera. Therefore, the Turdus spp. is particularly important. The high prevalence of Borrelia may be related to Borrelia infection of the birds and transmission of Borrelia through co-feeding. Ticks that were co-fed with a Borreliainfected tick had an increased probability of being infected with the same Borrelia species. Ticks collected on birds from Lista were less likely to have Borrelia than ticks found on birds from the more eastern localities. The prevalence of the different Borrelia species in ticks collected from migratory birds may be related to migration routes. Sera from 306 healthy pastured cows from 24 farms along the southern Norwegian coast were tested for Babesia divergens by an immunofluorescence antibody test. This test showed a frequency of around 50% positive in the western part of the coast of West Agder and in the eastern part of East Agder and Telemark, while approximately 5% positive was found in the coastal area between these locations. Bovine babesiosis is a declining disease in Norway, which could be continuously reintroduced by birds. By using 17 microsatellites of I. ricinus, Mendelian laws were used to show that broods of tick larvae had more than one father, which would give the offspring a higher genetic diversity than if there were only one father. This could facilitate the colonisation of a new locality if engorged female ticks were brought to new locations by birds. Even though it is difficult to prove that birds are responsible for new tick species and tick-borne pathogens in new areas, the findings of this study suggest that birds are capable of introducing these ticks, and it is difficult to find an alternative explanation for the emergence of tick-borne encephalitis in Norway.