Abstract
BackgroundBirds 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.MethodsTicks 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.ResultsA 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.ConclusionsThe 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.Graphical
Highlights
Birds can act as reservoirs of tick-borne pathogens and can disperse pathogen-containing ticks to both nearby and remote localities
Tick-associated microorganisms, with proven, suspected, or unknown human pathogenicity which have been detected in bird-infesting ticks in Europe include Borrelia afzelii [2,3,4,5], Borrelia burgdorferi (s.s) [2, 4, 6, 7], Borrelia garinii [2,3,4,5, 7, 8], Borrelia lusitaniae [9], Borrelia turdi [3, 5, 10,11,12], Borrelia valaisiana [2,3,4, 10, 11, 13], Borrelia spielmanii [4, 5], Borrelia miyamotoi [2, 4, 14], Neoehrlichia mikurensis [4, 14,15,16], Rickettsia aeschlimannii [16, 17], Rickettsia africae [17], Rickettsia helvetica [14, 16, 18, 19], Rickettsia japonica [16], Rickettsia monacensis [16], Anaplasma phagocytophilum [14, 19], Babesia venatorum [16], Babesia microti [16], tick-borne encephalitis virus (TBEV) [16, 20], Alkhurma haemorrhagic fever virus (AHFV) [21], and Crimean-Congo haemorrhagic fever virus (CCHFV) [22]
Ticks collected from birds and seasonal dynamics of infestation pattern A total of 4601 bird individuals (4788 bird captures) of 65 species was examined for ticks at least once during the study period, i.e. 15 March–15 June and 15 July–15 November 2009, at the Ottenby Bird Observatory
Summary
Birds can act as reservoirs of tick-borne pathogens and can disperse pathogen-containing ticks to both nearby and remote localities. Certain potentially human-pathogenic microorganisms are vectored by ticks Some of these microorganisms may be harboured in both ticks and birds. Microorganism-containing vector-competent ticks, while feeding on a susceptible avian host, can transmit the microorganism to its host. Transmission of a blood-borne microorganism can take place in the opposite direction, whereby infectious, transmission-competent birds (transmission hosts or reservoir-competent hosts) can infect feeding, susceptible ticks. During their flights birds can act as “vehicles” for the geographic spread of different types of human-pathogenic microorganisms, i.e. for microorganisms which are maintained in both birds and ticks, for microorganisms mainly or only present in ticks, and for microorganisms mainly or only present in birds. Tick-associated microorganisms, with proven, suspected, or unknown human pathogenicity which have been detected in bird-infesting ticks in Europe include Borrelia afzelii [2,3,4,5], Borrelia burgdorferi (s.s) [2, 4, 6, 7], Borrelia garinii [2,3,4,5, 7, 8], Borrelia lusitaniae [9], Borrelia turdi [3, 5, 10,11,12], Borrelia valaisiana [2,3,4, 10, 11, 13], Borrelia spielmanii [4, 5], Borrelia miyamotoi [2, 4, 14], Neoehrlichia mikurensis [4, 14,15,16], Rickettsia aeschlimannii [16, 17], Rickettsia africae [17], Rickettsia helvetica [14, 16, 18, 19], Rickettsia japonica [16], Rickettsia monacensis [16], Anaplasma phagocytophilum [14, 19], Babesia venatorum [16], Babesia microti [16], tick-borne encephalitis virus (TBEV) [16, 20], Alkhurma haemorrhagic fever virus (AHFV) [21], and Crimean-Congo haemorrhagic fever virus (CCHFV) [22]
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