REVIEW ARTICLE
Global ecology and epidemiology of Borrelia garinii spirochetes
Pär Comstedt, Phd†, Tobias Jakobsson, MD and Sven Bergström, Professor*
Department of Molecular Biology, Umeå University, Umeå, Sweden
Published: 28 October 2011
http://www.infectionecologyandepidemiol ... /view/9545
The marine infection cycle
Olsen et al. (5) were the first to isolate Borrelia spirochetes from Ixodes uriae. The ticks were collected from razorbills (Alca torda) on an isolated island in the Baltic Sea where no mammals were present. As seabirds were the only blood host available for the ticks, a marine enzootic infection cycle was suggested, where B. garinii circulating among colonial seabirds depend on I. uriae as the only vector (5). The distribution of this marine infection cycle was then studied since large seabird colonies are present globally. I. uriae were collected from seabirds at nine different locations worldwide. B. garinii spirochetes with identical flagellin B (flaB) genes were found in ticks from both the southern hemisphere (Campbell Island, New Zealand, and Crozet Islands) and the northern hemisphere (Egg and St. Lazaria Islands, USA) suggesting that seabirds can act as long-distance carriers of the infection (Fig. 1; 10). As the ticks only feed for a few days and the birds’ migration causes them to spend longer periods of time above or in open water, the spirochetes are probably transported as a latent infection in the birds, rather than by infected ticks. A phylogenetic analysis of I. uriae from both the southern and the northern hemisphere also suggests separate reproduction cycles of the ticks (50). It has been shown that a latent B. burgdorferi (s.s.) infection can be reactivated when the birds are subjected to stress as in the case of seasonal migration (51). This could further aid in the global dispersal of B. burgdorferi (s. l.) infected ticks. B. garinii is by far the most prevalent species isolated from seabirds and I. uriae, even though occasionally also B. lusitaniae and B. burgdorferi (s.s.) have been found (52). As discussed earlier, B. garinii is one of the most prevalent species found among I. ricinus and I. persulcatus in Europe and Asia. However, the marine infection cycle increases the habitat to include also the North Pacific Ocean (Egg and St. Lazaria Islands outside Alaska, USA) and the North Atlantic Ocean (Gull Island, Canada). This suggests B. garinii is present on both the West and the East coasts of North America (10, 53).
Fig 1
Fig. 1. Global distribution of Borrelia garinii in the marine infection cycle. Seabird colonies where B. garinii spirochetes are known to be present are indicated with a circle. The seabird colonies are: 1. Hornöya Island, Norway (9); 2. Faroe Island, Denmark (61); 3. Flatey Island, Iceland (10); 4. Commander Island, Russia (8); 5. Malgrundet Island, Sweden (62); 6. Bonden Island, Sweden (5); 7. Campbell Island, New Zealand (10); 8. Crozet Islands (10); 9. Egg and St. Lazari Islands, USA (10); 10. Gull Island, Canada (53).
Surprisingly, B. garinii have also been isolated from I. uriae found in seabird colonies located in extreme climate zones such as the Arctic and the subAntarctic regions as well as the Bering Sea littoral (8–10). Seabird colonies where B. garinii infected I. uriae or birds have been found are indicated in Fig. 1. When comparing seabird-associated B. garinii strains from Arctic Norway (Hornöya Island) with other isolates collected from seabird colonies on Faroe Islands, identical IGS were found (9). Also, close to identical IGS were found when comparing the Arctic B. garinii isolates to those isolated from migrating passerine birds and LB patients in southern Sweden. This supports the theory of birds as global carriers and disseminators of B. garinii, also with potential impact on human health. This will be discussed more in detail later in this review article.
Aside from the marine infection cycle, other enzootic cycles involving avian hosts and specialized tick species have been studied. The tick Ixodes dentatus has been described as vector for Borrelia spp. It is to a large extent ornitophagous and has been proposed a potential factor in maintenance and dispersal of Borrelia spp. (54). Also, B. garinii and B. burgdorferi (s.s.) have been found in Ixodes lividus, which is almost exclusively associated with Sand Martins (Riparia riparia) (55).
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Hier een stukje over garinii van de I. uriae teek van de zeevogels hoe die bij de I. ricinus teek terecht kan komen:
Interaction between the terrestrial and the marine infection cycle
Borrelia garinii spirochetes are found among rodents and passerine birds as well as among seabirds, suggesting that there has to be some overlap between the marine and the terrestrial infection cycles. The marine infection cycle is restricted to different seabirds and the open sea. I. uriae ticks are very wide ranging in their choice of seabird host, but the ticks are seldom found outside seabird colonies. Therefore, an interaction with the terrestrial infection cycle has to take place within the seabird colony. Rodents searching for food and resting migratory passerine birds are possible candidates mediating contact with I. uriae or I. ricinus. The frequency by which I. uriae feed on rodents and other birds is however not known. On some islands in the Baltic Sea, where the I. uriae and I. ricinus habitats overlap and seabirds as well as migrating passerine birds nest side by side, host cross-over may be possible. Furthermore, B. garinii isolates with identical IGS have been found in both I. ricinus and I. uriae collected from the Swedish islands Norrbyskär and Bonden, separated only by 25 km (62).
En hier een stukje over de verschillende strains van garinii:
To further study the global ecology of this species, the IGS of 77 B. garinii isolates of diverse biological and geographical origins were compared by Comstedt et al. (8), where 20 different genetic variants were found. The seabird-associated strains as a group, isolates from seabirds or I. uriae, represented 32% of the sample collection, but comprised 50% of the IGS types. This suggests that B. garinii associated with seabirds constitute a more diverse group of spirochetes than the terrestrial group. Indeed, the 20 IGS types grouped into six phylogenetic clusters, all including B. garinii circulating among seabirds. Five of the clusters also involved isolates from migrating passerine birds. Furthermore, B. garinii isolated from clinical samples were found in three of the clusters. Strains originating from one seabird colony on Commander Islands in far eastern Russia also did not group together. Instead, some of them were more closely related to B. garinii isolated from European LB patients or passerine birds. One of the most complex genetic variant contained B. garinii isolates from I. ricinus-infesting migrating birds in Sweden, questing I. ricinus from Lithuania, as well as both skin and cerebrospinal fluid isolates from LB patients. Other genetic variants identified represented B. garinii from I. uriae and I. ricinus as well as isolates from migrating passerine birds. Because the B. garinii isolates did not necessarily cluster according to geography, biological hosts, or tick vectors, this again supports the theory of a frequent exchange of strains between the marine and the terrestrial infection cycles (8). The range of IGS identity between as well as within different B. garinii strain collections is summarized in Table 2. Even though some collections are limited in size, the overall pattern suggests extensive sequence variation among the strains, but also occasionally high sequence identity (IGS identities above 99% between two or more strains representing different collections are indicated in bold numbers in Table 2).
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