Different Competence as a Lyme Borreliosis Causative Agent Reservoir Found in Two Thrush Species: The Blackbird (Turdus merula) and the Song Thrush (Turdus philomelos)

Passerine birds are significantly involved in the dissemination of Borreliella spp. bacteria (formerly Borrelia burgdorferi sensu lato complex), the causative agent of most common and important tick-spread disease Lyme borreliosis. Among several dozen investigated passerine bird species, thrushes (Turdidae) have been reported as a relatively good pathogen reservoirs and disseminators. The principal aim of the study was to identify the differences in Borreliella spp. reservoir competence between two widespread and showing similar behavior thrush species. A total of 157 Ixodes ricinus ticks (19 larvae, 138 nymphs) were collected from 26 blackbirds ( Turdus merula ) and 20 song thrushes ( Turdus philomelos ) living in the same forest habitat (northeastern Poland). All, at least partially engorged ectoparasites, were tested for the presence of Borreliella spp. DNA using the nested-PCR technique. No significant difference of tick prevalence was found, with 88.5% blackbirds and 70% of song thrushes infested. Screening for Borreliella spp. in ticks revealed that both tick infection prevalence (49.2% vs. 18.9%) and mean number of infected individuals engorging on birds (2.27 vs. 0.35) were higher in blackbirds. Both the investigated thrush species presumably could participate in the pathogen circulation, although with different efficiencies. The greater reservoir competence of blackbirds suggests the differentiated dynamics of host–pathogen interactions among selected species, and consequently their potentially disparate role in the ecology of Lyme borreliosis.