Differential Role of Passerine Birds in Distribution of Borrelia Spirochetes, Based on Data from Ticks Collected from Birds during the Postbreeding Migration Period in Central Europe

Abstract

Borrelia spirochetes in bird-feeding ticks were studied in the Czech Republic. During the postbreeding period (July to September 2005), 1,080 passerine birds infested by 2,240 Ixodes ricinus subadult ticks were examined. Borrelia garinii was detected in 22.2% of the ticks, Borrelia valaisiana was detected in 12.8% of the ticks, Borrelia afzelii was detected in 1.6% of the ticks, and Borrelia burgdorferi sensu stricto was detected in 0.3% of the ticks. After analysis of infections in which the blood meal volume and the stage of the ticks were considered, we concluded that Eurasian blackbirds (Turdus merula), song thrushes (Turdus philomelos), and great tits (Parus major) are capable of transmitting B. garinii; that juvenile blackbirds and song thrushes are prominent reservoirs for B. garinii spirochetes; that some other passerine birds investigated play minor roles in transmitting B. garinii; and that the presence B. afzelii in ticks results from infection in a former stage. Thus, while B. garinii transmission is associated with only a few passerine bird species, these birds have the potential to distribute millions of Lyme disease spirochetes between urban areas.Lyme borreliosis, the most frequent tick-borne human disease in the northern hemisphere, is a multisystemic disorder caused by spirochetes belonging to the genus Borrelia (12). At least seven Borrelia species have been obtained from the tick Ixodes ricinus (Acari: Ixodidae) in Europe: B. afzelii, B. bissettii, B. burgdorferi, B. garinii, B. lusitaniae, B. spielmanii, and B. valaisiana (30,33). Various reservoir hosts seem to harbor different Borrelia species, which is explained by differential properties of the hosts' complement systems (17). Generally, B. afzelii is a rodent specialist, B. garinii and B. valaisiana are associated with birds, and B. lusitaniae is associated with lizards (7,16,22,32). The clinical manifestations of Lyme borreliosis in humans differ depending on the Borrelia species; B. garinii is associated with neurological diseases, while B. burgdorferi and B. afzelii are more likely to cause arthritis and cutaneous symptoms, respectively (2, 4, 5, 36).Ixodid ticks may attach to a host for 24 to 48 h, which is sufficient time for some birds to travel hundreds of kilometers along migration routes before ticks complete their feeding and drop off (31). The role of migratory birds in distributing Lyme disease spirochetes to new areas has been established in North America (25,28,37).Recently, it has become clear that the bird host competency for maintaining and transmitting Borrelia spirochetes is different in different bird species. Pheasants in the United Kingdom (15, 16) and blackbirds and song thrushes in Central Europe (13, 35) have been shown to be important reservoirs of B. garinii and B. valaisiana. However, little is known about the other migrating passerine bird species with respect to their competence as Lyme disease reservoirs and transmission abilities.Here we characterized tick infestation in migratory passerine bird species ...

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