Research effort on birds' reservoir host potential for Lyme borreliosis: A systematic review and perspectives

Wide spectrum of tick-borne pathogens in juvenile Ixodes ricinus collected from autumn-migrating birds in the Vistula River Valley, Poland

BACKGROUND

Migratory birds serve as potential hosts for ticks and can be reservoirs of tick-borne pathogens (TBPs). The aim of our study was to investigate the prevalence of TBPs in juvenile Ixodes ricinus collected from Erithacus rubecula, Turdus merula, and Turdus philomelos passing through the Vistula River Valley, Poland - one of the most important European north-south routes for migratory birds.

METHODS

To detect TBPs in collected ticks we used a high-throughput microfluidic real-time PCR method. In addition, we performed a phylogenetic analysis of Borreliella garinii flaB and Rickettsia helvetica ompB sequences, considering haplotype diversity through a Median Joining Network.

RESULTS

Our results showed a high prevalence and wide spectrum of TBPs in both larvae and nymphs of I. ricinus. Overall, including co-infections, 47.41% of the tested tick specimens were infected with at least one TBP. Borreliaceae spirochetes were detected in ticks collected from all examined bird species. Ticks (larvae and nymphs) collected from T. merula showed the highest prevalence of Bo. garinii (33.33%), Bo. burgdorferi s.s. (7.69%) and Borrelia miyamotoi (2.56%), while the highest number of ticks infected with Bo. valaisiana were collected from T. philomelos (8.11%). In turn, the highest prevalence of R. helvetica (20.00%) was observed in ticks collected from E. rubecula. Additionally, infections with A. phagocytophilum (5.00%), Ehrlichia spp. (2.50%), Ba. divergens (2.50%) and Ba. venatorum (2.50%) were only confirmed in ticks collected from this bird species. The phylogenetic analysis of Bo. garinii revealed that the detected haplotype circulates widely across various hosts and is geographically widespread, while the haplotype of R. helvetica is mainly detected in ticks in Central Europe.

CONCLUSIONS

Ticks carried by T. merula, T. philomelos, and E. rubecula migrating along the Vistula River Valley, Poland are characterized by a high prevalence and a wide spectrum of detected TBPs. Tested ticks carry widespread strains of Bo. garinii, in contrast to R. helvetica, which is mainly found in Central Europe. Therefore, further research on the possible role of birds as reservoirs of TBPs is needed.

An integrative framework for tick management: the need to connect wildlife science, One Health, and interdisciplinary perspectives

Vector-borne diseases pose a significant threat to human and animal health worldwide. Their emergence is influenced by various factors such as environmental changes, host characteristics, and human behavior. The One Health approach is necessary to thoroughly investigate tick-borne diseases and understand the complex interactions between environmental, animal, and human health. Anthropogenic changes have impacted predators, leading to cascading effects on wildlife prey species and the emergence of vector-borne diseases. The increase in global trade and travel has led to the introduction of several invasive vector species, increasing the risk of zoonotic pathogen spillover. Tick and tick-borne disease research requires an interdisciplinary approach to address challenges in a One Health paradigm.

Survey of Tick-Borne Zoonotic Agents in Ixodes Ticks Carried by Wild Passerines during Postbreeding Migration through Italy

Recently, increasing attention has been posed on the role of migrating birds in the spread of ticks and indirectly of tick-borne pathogens (TBPs). Despite, Italy is considered a bridge between continental Europe and North Africa and a necessary path to connect Mediterranean countries, few studies have been conducted on ticks collected from birds migrating through this country and associated TBPs. The aims of this research were to estimate the infestation burden and identify tick species feeding on migratory birds, and perform a molecular screening for TBPs. During autumn migration (2019-2020), birds were inspected for ticks in a ringing station located in north-east Italy. Ticks were identified and screened for tick-borne encephalitis virus (TBEV), Borrelia burgdorferi sensu latu, Rickettsia spp., Ehrlichia spp., Neoehrlichia spp., Anaplasma phagocytophilum, and Bartonella spp. Ixodes ticks (n = 209) were feeding on 2.6% of passerines (88/3411). Most of these (208/209) were Ixodes ricinus, except one Ixodes frontalis. Eight bird species were infested: common blackbird, redwing, brambling, song thrush, common chaffinch, European robin, water pipit, and coal tit. Rickettsiales showed a low prevalence, from 1.4% of Ehrlichia spp., 4.3% of A. phagocytophilum, up to 7.2% of Rickettsia spp.. Borrelia burgdorferi s.l. had the highest prevalence, 54.6%, and several zoonotic genotypes were identified: B. garinii, B. valaisiana, B. afzeli, B. burgdorferi sensu stricto, and B. miyamotoi. All specimens were negative for TBEV and Bartonella spp.. Although the tick burden was generally low, most of the vectors (>60%) were positive for at least one pathogen, highlighting the relevance of a continuous monitoring of migrating birds as potential sources of pathogen dispersal.

Host adaptation drives genetic diversity in a vector-borne disease system

The range of hosts a pathogen can infect is a key trait, influencing human disease risk and reservoir host infection dynamics. Borrelia burgdorferi sensu stricto (Bb), an emerging zoonotic pathogen, causes Lyme disease and is widely considered a host generalist, commonly infecting mammals and birds. Yet the extent of intraspecific variation in Bb host breadth, its role in determining host competence, and potential implications for human infection remain unclear. We conducted a long-term study of Bb diversity, defined by the polymorphic ospC locus, across white-footed mice, passerine birds, and tick vectors, leveraging long-read amplicon sequencing. Our results reveal strong variation in host breadth across Bb genotypes, exposing a spectrum of genotype-specific host-adapted phenotypes. We found support for multiple niche polymorphism, maintaining Bb diversity in nature and little evidence of temporal shifts in genotype dominance, as would be expected under negative frequency-dependent selection. Passerine birds support the circulation of several human-invasive strains (HISs) in the local tick population and harbor greater Bb genotypic diversity compared with white-footed mice. Mouse-adapted Bb genotypes exhibited longer persistence in individual mice compared with nonadapted genotypes. Genotype communities infecting individual mice preferentially became dominated by mouse-adapted genotypes over time. We posit that intraspecific variation in Bb host breadth and adaptation helps maintain overall species fitness in response to transmission by a generalist vector.

Detection of Pathogens and Ticks on Sedentary and Migratory Birds in Two Corsican Wetlands (France, Mediterranean Area)

Birds are one of the most species-diverse vertebrate groups and are susceptible to numerous hematophagous ectoparasites. Migratory birds likely contribute to the circulation of these ectoparasites and their associated pathogens. One of the many migration paths crosses the Mediterranean islands including Corsica and its wetlands, which are migration stopovers. In our study, we collected blood samples and hematophagous ectoparasites in migratory and sedentary bird populations in two coastal lagoons: Biguglia and Gradugine. A total of 1377 birds were captured from which 762 blood samples, 37 louse flies, and 44 ticks were collected. All the louse flies were identified as Ornithomya biloba and all the ticks were from the Ixodes genus: Ixodes sp. (8.5%), I. accuminatus/ventalloi (2.9%), I. arboricola/lividus (14.3%), I. frontalis (5.7%) and I. ricinus (68.6%). Five pathogens were detected: Anaplasma phagocytophilum, Erhlichia chaffeensis, and Rickettsia helvetica in ticks, and Trypanosoma sp. in louse flies. Ehrlichia chaffeensis and the West Nile virus were both detected in bird blood samples in Corsica. This is the first report of these tick, louse fly and pathogen species isolated on the bird population in Corsica. Our finding highlights the importance of bird populations in the presence of arthropod-borne pathogens in Corsican wetlands.

Diversity of Tick-Borne Pathogens in Tick Larvae Feeding on Breeding Birds in France

Birds play a role in maintaining tick-borne diseases by contributing to the multiplication of ticks and pathogens on a local scale during the breeding season. In the present study, we describe the diversity of tick and pathogen species of medical and veterinary importance in Europe hosted by 1040 captured birds (56 species) during their breeding season in France. Of the 3114 ticks collected, Ixodes ricinus was the most prevalent species (89.5%), followed by I. frontalis (0.8%), I. arboricola (0.7%), Haemaphysalis concinna (0.5%), H. punctata (0.5%), Hyalomma spp. (0.2%), and Rhipicephalus spp. (0.06%). Because they may be representative of the bird infection status for some pathogen species, 1106 engorged tick larvae were screened for pathogens. Borrelia burgdorferi sensu lato was the most prevalent pathogen genus in bird-feeding larvae (11.7%), followed by Rickettsia spp. (7.4%), Anaplasma spp. (5.7%), Babesia spp. (2.3%), Ehrlichia spp. (1.4%), and B. miyamotoi (1%). Turdidae birds (Turdus merula and T. philomelos), Troglodytes troglodytes, and Anthus trivialis had a significantly higher prevalence of B. burgdorferi s.l.-infected larvae than other pathogen genera. This suggests that these bird species could act as reservoir hosts for B. burgdorferi s.l. during their breeding season, and thus play an important role in acarological risk.