BackgroundBirds play a major role in the maintenance of enzootic cycles of pathogens transmitted by ticks. Due to their mobility, they affect the spatial distribution and abundance of both ticks and pathogens. In the present study, we aim to identify members of a pathogen community [Borrelia burgdorferi (s.l.), B. miyamotoi, ‘Ca. Neoehrlichia mikurensis’, Anaplasma phagocytophilum and Rickettsia helvetica] in songbird-derived ticks from 11 locations in the Netherlands and Belgium (2012–2014).ResultsOverall, 375 infested songbird individuals were captured, belonging to 35 species. Thrushes (Turdus iliacus, T. merula and T. philomelos) were trapped most often and had the highest mean infestation intensity for both Ixodes ricinus and I. frontalis. Of the 671 bird-derived ticks, 51% contained DNA of at least one pathogenic agent and 13% showed co-infections with two or more pathogens. Borrelia burgdorferi (s.l.) DNA was found in 34% of the ticks of which majority belong to so-called avian Borrelia species (distribution in Borrelia-infected ticks: 47% B. garinii, 34% B. valaisiana, 3% B. turdi), but also the mammal-associated B. afzelii (16%) was detected. The occurrence of B. miyamotoi was low (1%). Prevalence of R. helvetica in ticks was high (22%), while A. phagocytophilum and ‘Ca. N. mikurensis’ prevalences were 5% and 4%, respectively. The occurrence of B. burgdorferi (s.l.) was positively correlated with the occurrence of ‘Ca. N. mikurensis’, reflecting variation in susceptibility among birds and/or suggesting transmission facilitation due to interactions between pathogens.ConclusionsOur findings highlight the contribution of European songbirds to co-infections in tick individuals and consequently to the exposure of humans to multiple pathogens during a tick bite. Although poorly studied, exposure to and possibly also infection with multiple tick-borne pathogens in humans seems to be the rule rather than the exception.

Brown hares (Lepus europaeus) are shown to facilitate grazing by Brent Geese (Branta bernicla) in a temperate salt marsh in the Netherlands by retarding vegetation succession for >25 yr. Winter grazing by hares prevented the shrub Atriplex portulacoides from spreading in younger parts of the salt marsh. Clipping experiments showed that Atriplex had poor recovery after removal of aboveground tissue, which makes Atriplex vulnerable for hare attack. Once Atriplex swards were cut to the ground to mimic hare grazing, Brent Geese visited those sites more than twice as frequently than untouched control plots. Goose visitation was reduced when bushes of Atriplex were planted. Large parts of the core feeding area of Brent Geese would be unsuitable for goose grazing if hares were not present. A reduction of at least 44% in the carrying capacity of the marsh for Brent Geese was calculated in the absence of hares. Vulnerability of Atriplex to hare grazing and the high food intake of geese are key elements to this facilitative pattern. Additionally, hares reduced the number of dead Artemisia maritima stems in grassy swards, which otherwise might have hampered grazing by geese. Facilitation by herbivores such as hare, rabbit, cattle, and sheep is likely to be a prominent factor enhancing feeding conditions for Brent Geese all along the northwest European coast.

2001. Home ranges of brown hares in a natural salt marsh: comparisons with agricultural systems. Acta Theriologica 46: 287-294.This is the first study on spatial behaviour of brown hares Lepus europaeus Pallas, 1778 based on radio-telemetry in a natural system, which we contrast with data from agricultural systems. Radio tracking took place in a Dutch salt marsh over a 10-month period, with intensive tracking sessions during April/May and December/January. Six hares could be followed in both periods and in total 1224 fixes were collected. Average home range size was calculated as 28.7 ± 8.5 ha when using Adaptive Kernell method (Mimimum Convex Polygon: 27.3 ± 9.0 ha) on 90% of all fixes. Such values are in the lower end of the range of those obtained for agricultural systems. Home range size did not differ between sexes, day and night, or across seasons. However, the size of the core range (50% of fixes) was twice as large in May compared to the winter period, and thus inversely related to food availability. Unlike in agricultural systems, use of space by hares did not change over the course of the season. This probably reflects the patchy nature of the natural habitat which provides food and shelter throughout the year in a confined area.

Tularaemia, a disease caused by the bacterium Francisella tularensis, is a re-emerging zoonosis in the Netherlands. After sporadic human and hare cases occurred in the period 2011 to 2014, a cluster of F. tularensis-infected hares was recognised in a region in the north of the Netherlands from February to May 2015. No human cases were identified, including after active case finding. Presence of F. tularensis was investigated in potential reservoirs and transmission routes, including common voles, arthropod vectors and surface waters. F. tularensis was not detected in common voles, mosquito larvae or adults, tabanids or ticks. However, the bacterium was detected in water and sediment samples collected in a limited geographical area where infected hares had also been found. These results demonstrate that water monitoring could provide valuable information regarding F. tularensis spread and persistence, and should be used in addition to disease surveillance in wildlife.

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