Inefficient co-feeding transmission of Borrelia afzelii in two common European songbirds

Abstract

The spirochete bacterium Borrelia afzelii is the most common cause of Lyme borreliosis in Europe. This tick-borne pathogen can establish systemic infections in rodents but not in birds. However, several field studies have recovered larval Ixodes ricinus ticks infected with B. afzelii from songbirds suggesting successful transmission of B. afzelii. We reviewed the literature to determine which songbird species were the most frequent carriers of B. afzelii-infected I. ricinus larvae and nymphs. We tested experimentally whether B. afzelii is capable of co-feeding transmission on two common European bird species, the blackbird (Turdus merula) and the great tit (Parus major). For each bird species, four naïve individuals were infested with B. afzelii-infected I. ricinus nymphal ticks and pathogen-free larval ticks. None of the co-feeding larvae tested positive for B. afzelii in blackbirds, but a low percentage of infected larvae (3.33%) was observed in great tits. Transstadial transmission of B. afzelii DNA from the engorged nymphs to the adult ticks was observed in both bird species. However, BSK culture found that these spirochetes were not viable. Our study suggests that co-feeding transmission of B. afzelii is not efficient in these two songbird species.

Host dispersal shapes the population structure of a tick‐borne bacterial pathogen

“…Parus major has been shown experimentally to selectively amplify B. garinii and B. valaisiana , whereas B. afzelii prevalence in moulted adult ticks that fed as nymphs on this bird species tended to decrease in successive infestations of the birds with wild questing nymphs (Heylen, Matthysen, et al, ). The finding of this mammal‐associated genospecies in attached ticks derived from birds has been suggested to result from previously acquired infection from another (mammal) host because these spirochetes were found to be unviable by culturing (Heylen, Sprong, et al, ). In our study, all B. afzelii‐ positive ticks were nymphs and we cannot comment on birds' reservoir competence for B. afzelii with these findings because PCR does not allow distinguishing between viable and nonviable bacteria.…”

Getting under the birds’ skin: tissue tropism of Borrelia burgdorferi s.l. in naturally and experimentally infected avian hosts

“…It is possible that the concentration of Borrelia in internal organs and tissues may be very low, and its DNA concentration being under the sensitivity limit of our real-time PCR assay. Borrelia culture performed in parallel to PCR could potentially increase the detection chance (due to Borrelia multiplication in the growth media) and allows the distinction of viable spirochetes (with implications on infectiousness and potential for pathogenicity assessments [95]). Nonetheless, our study shows that skin biopsies are possibly the most useful and practical sampling method for assessing avian hosts' Borrelia infectiousness, on condition that the initial infection occurs in sufficient time prior to the sampling.…”

Fitness estimates from experimental infections predict the long-term strain structure of a vector-borne pathogen in the field

“…Larval ticks acquire spirochetes after feeding on an infected reservoir host and develop into infected nymphs that transmit the pathogen the following year to the next generation of reservoir hosts. B. afzelii and B. garinii are specialized on different classes of vertebrate hosts: rodents and birds, respectively 23 – 26 , and therefore rarely occur together in the same tick 27 – 30 . Local populations of both Borrelia species consist of multiple strains 21 , 31 – 34 , which are often defined by the highly polymorphic, single-copy ospC gene 35 – 38 .…”