Migratory birds as disseminators of ticks and the tick-borne pathogens Borrelia bacteria and tick-borne encephalitis (TBE) virus: a seasonal study at Ottenby Bird Observatory in South-eastern Sweden

Background

Birds can act as reservoirs of tick-borne pathogens and can also disperse pathogen-containing ticks to both nearby and remote localities. The aims of this study were to estimate tick infestation patterns on migratory birds and the prevalence of different Borrelia species and tick-borne encephalitis virus (TBEV) in ticks removed from birds in south-eastern Sweden.

Methods

Ticks were collected from resident and migratory birds captured at the Ottenby Bird Observatory, Öland, Sweden, from March to November 2009. Ticks were molecularly identified to species, and morphologically to developmental stage, and the presence of Borrelia bacteria and TBEV was determined by quantitative real-time PCR.

Results

A total of 1339 ticks in the genera Haemaphysalis, Hyalomma, and Ixodes was recorded of which I. ricinus was the most abundant species. Important tick hosts were the European robin (Erithacus rubecula), Blackbird (Turdus merula), Tree pipit (Anthus trivialis), Eurasian wren (Troglodytes troglodytes), Common redstart (Phoenicurus phoenicurus), Willow warbler (Phylloscopus trochilus), and Common whitethroat (Sylvia communis). Borrelia bacteria were detected in 25% (285/1,124) of the detached ticks available for analysis. Seven Borrelia species (B. afzelii, B. burgdorferi (s.s.), B. garinii, B. lusitaniae, B. turdi, B. valaisiana, and B. miyamotoi) were identified. B. turdi was recorded for the first time in ticks in Sweden. The number of Borrelia cells per tick ranged from 2.0 × 10⁰ to 7.0 × 10⁵. B. miyamotoi-containing ticks contained a significantly higher median number of Borrelia cells than B. burgdorferi (s.l.)-containing ticks. B. garinii and B. miyamotoi were the most prevalent Borrelia species in tick larvae. Larvae of I. ricinus with B. garinii were removed from seven bird species, particularly S. communis and A. trivialis, which may suggest that the larvae had contracted the Borrelia bacteria from or via these birds. Also, a high percentage of tick larvae containing B. miyamotoi was removed from E. rubecula. All ticks were negative for TBEV.

Conclusions

The results corroborate the view that the contributions of birds to human disease are substantial, particularly as blood hosts for ticks and for their short-, medium-, and long-distance dispersal. Moreover, several ground-foraging bird species appear to be important for the maintenance and dispersal of Borrelia species. The absence of TBEV in the ticks conforms to other similar studies.

Hedgehogs, Squirrels, and Blackbirds as Sentinel Hosts for Active Surveillance of Borrelia miyamotoi and Borrelia burgdorferi Complex in Urban and Rural Environments

Lyme borreliosis (LB), caused by spirochetes of the Borrelia burgdorferi sensu lato (s.l.) complex, is one of the most common vector-borne zoonotic diseases in Europe. Knowledge about the enzootic circulation of Borrelia pathogens between ticks and their vertebrate hosts is epidemiologically important and enables assessment of the health risk for the human population. In our project, we focused on the following vertebrate species: European hedgehog (Erinaceus europaeus), Northern white-breasted hedgehog (E. roumanicus), Eurasian red squirrel (Sciurus vulgaris), and Common blackbird (Turdus merula). The cadavers of accidentally killed animals used in this study constitute an available source of biological material, and we have confirmed its potential for wide monitoring of B. burgdorferi s.l. presence and genospecies diversity in the urban environment. High infection rates (90% for E. erinaceus, 73% for E. roumanicus, 91% for S. vulgaris, and 68% for T. merula) were observed in all four target host species; mixed infections by several genospecies were detected on the level of individuals, as well as in particular tissue samples. These findings show the usefulness of multiple tissue sampling as tool for revealing the occurrence of several genospecies within one animal and the risk of missing particular B. burgdorferi s.l. genospecies when looking in one organ alone.

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

Birds are hosts for several zoonotic pathogens. Because of their high mobility, especially of longdistance migrants, birds can disperse these pathogens, affecting their distribution and phylogeography. We focused on Borrelia burgdorferi sensu lato, which includes the causative agents of Lyme borreliosis, as an example for tick-borne pathogens, to address the role of birds as propagation hosts of zoonotic agents at a large geographical scale. We collected ticks from passerine birds in 11 European countries. B. burgdorferi s.l. prevalence in Ixodes spp. was 37% and increased with latitude. The fieldfare Turdus pilaris and the blackbird T. merula carried ticks with the highest Borrelia prevalence (92 and 58%, respectively), whereas robin Erithacus rubecula ticks were the least infected (3.8%). Borrelia garinii was the most prevalent genospecies (61%), followed by B. valaisiana (24%), B. afzelii (9%), B. turdi (5%) and B. lusitaniae (0.5%). A novel Borrelia genospecies "Candidatus Borrelia aligera" was also detected. Multilocus sequence typing (MLST) analysis of B. garinii isolates together with the global collection of B. garinii genotypes obtained from the Borrelia MLST public database revealed that: (a) there was little overlap among genotypes from different continents, (b) there was no geographical structuring within Europe, and (c) there was no evident association pattern detectable among B. garinii genotypes from ticks feeding on birds, questing ticks or human isolates. These findings strengthen the hypothesis that the population structure and evolutionary biology of tick-borne pathogens are shaped by their host associations and the movement patterns of these hosts.

Borrelia burgdorferi (sensu lato) in ectoparasites and reptiles in southern Italy

BACKGROUND

Borrelia burgdorferi (sensu lato) is a complex containing pathogenic bacteria of which some species, such as Borrelia lusitaniae, use birds, small mammals and reptiles as reservoirs. In Italy, the bacteria have been detected in reptilian and avian reservoirs in the northern and central regions.

RESULTS

Here, 211 reptiles from three orders [Squamata (Sauria with seven species in five families and Ophidia with 11 species in three families), Crocodylia (one family and two species), and Testudines (two families and two species)] were examined for ectoparasites and molecular detection of B. burgdorferi (s.l.) in three different sites of southern Italy, an area for which no information was previously available on the occurrence of borreliosis in animals and humans. Borrelia lusitaniae was molecularly detected in larvae and nymphs (11.6%) of Ixodes ricinus infesting lizards (i.e. Podarcis muralis, Podarcis siculus and Lacerta bilineata) and in 12.3% blood samples of P. siculus. Finally, B. lusitaniae and Borrelia garinii were detected in 5.1% (32/630) of questing I. ricinus.

CONCLUSIONS

These results show the circulation of B. lusitaniae in southern Italy and suggest that P. siculus could play a role as a reservoir, representing a potential medical threat to humans living in or visiting these localities.

Role of mustelids in the life-cycle of ixodid ticks and transmission cycles of four tick-borne pathogens

BACKGROUND

Elucidating which wildlife species significantly contribute to the maintenance of Ixodes ricinus populations and the enzootic cycles of the pathogens they transmit is imperative in understanding the driving forces behind the emergence of tick-borne diseases. Here, we aimed to quantify the relative contribution of four mustelid species in the life-cycles of I. ricinus and Borrelia burgdorferi (sensu lato) in forested areas and to investigate their role in the transmission of other tick-borne pathogens. Road-killed badgers, pine martens, stone martens and polecats were collected in Belgium and the Netherlands. Their organs and feeding ticks were tested for the presence of tick-borne pathogens.

RESULTS

Ixodes hexagonus and I. ricinus were found on half of the screened animals (n = 637). Pine martens had the highest I. ricinus burden, whereas polecats had the highest I. hexagonus burden. We detected DNA from B. burgdorferi (s.l.) and Anaplasma phagocytophilum in organs of all four mustelid species (n = 789), and Neoehrlichia mikurensis DNA was detected in all species, except badgers. DNA from B. miyamotoi was not detected in any of the investigated mustelids. From the 15 larvae of I. ricinus feeding on pine martens (n = 44), only one was positive for B. miyamotoi DNA, and all tested negative for B. burgdorferi (s.l.), N. mikurensis and A. phagocytophilum. The two feeding larvae from the investigated polecats (n = 364) and stone martens (n = 39) were negative for all four pathogens. The infection rate of N. mikurensis was higher in feeding nymphs collected from mustelids compared to questing nymphs, but not for B. burgdorferi (s.l.), B. miyamotoi or A. phagocytophilum.

CONCLUSIONS

Although all stages of I. ricinus can be found on badgers, polecats, pine and stone martens, their relative contribution to the life-cycle of I. ricinus in forested areas is less than 1%. Consequently, the relative contribution of mustelids to the enzootic cycles of I. ricinus-borne pathogens is negligible, despite the presence of these pathogens in organs and feeding ticks. Interestingly, all four mustelid species carried all stages of I. hexagonus, potentially maintaining enzootic cycles of this tick species apart from the cycle involving hedgehogs as main host species.

Road-killed mammals provide insight into tick-borne bacterial pathogen communities within urban habitats

Small- and medium-sized mammals play an important role in the life cycle of tick-borne pathogens in urban habitats. Our aim was to apply the general protocol, DAMA (documentation-assessment-monitoring-action), which is an integrated proposal to build a proactive capacity to understand, anticipate, and respond to the outcomes of accelerating environmental change. Here we tested whether road-killed carcasses in urban areas are useful sources of tissue and parasite samples to investigate these species' contribution to the epidemiology of vector-borne diseases. We collected 29 road-killed and 6 carcasses with different causes of mortality (23 northern white-breasted hedgehogs and 12 from seven other mammal species) mainly from Budapest, Hungary. We used quantitative and conventional PCRs to determine pathogens in 90 collected tissues (52 from hedgehogs; 38 from other species) and 417 ticks that were only found on hedgehogs. Tissue samples revealed a wide range of bacteria including human zoonotic pathogens identified as Anaplasma phagocytophilum ecotype I, Borrelia afzelii, B. spielmanii, Borrelia miyamotoi, Rickettsia helvetica, and Bartonella species. Among the 23 collected hedgehog carcasses, 17 (74%) were infected with A. phagocytophilum, 6 (26%) with Borrelia burgdorferi s.l., 12 (52%) with R. helvetica, and 15 (65%) with Rickettsia sp. Furthermore, we report the first detection of Rickettsia sp. infection in European moles and lesser weasel and R. helvetica in stone marten. Through sequencing B. afzelii, R. helvetica, R. monacensis and A. phagocytophilum ecotype I were identified in the ticks removed from the carcasses. We showed that road-killed urban mammal species are exposed to multiple tick-borne pathogens but further studies have to clarify whether they, in fact, also have a role in their maintenance and spread. Our study also demonstrates that roadkill can be used in the risk assessment of potential human infection and in the implementation of the DAMA protocol.