Abstract
BackgroundThe geographical expansion of the tick Ixodes ricinus in northern Europe is a serious concern for animal and human health. The pathogen Anaplasma phagocytophilum is transmitted by ticks and causes emergences of tick-borne fever (anaplasmosis) in livestock. The transmission dynamics of the different ecotypes of A. phagocytophilum in the ecosystems is only partly determined. Red deer and roe deer contribute to circulation of different ecotypes of A. phagocytophilum in continental Europe, while the role of moose for circulation of different ecotypes is not fully established but an important issue in northern Europe.MethodsWe determined infection prevalence and ecotypes of A. phagocytophilum in moose (n = 111), red deer (n = 141), roe deer (n = 28) and questing ticks (n = 9241) in Norway.ResultsAs previously described, red deer was exclusively linked to circulation of ecotype I, while roe deer was exclusively linked to circulation of ecotype II. Surprisingly, we found 58% ecotype I (n = 19) and 42% of ecotype II (n = 14) in moose. Both ecotypes were found in questing ticks in areas with multiple cervid species present, while only ecotype I was found in ticks in a region with only red deer present. Hence, the geographical distribution of ecotypes in ticks followed the distribution of cervid species present in a given region and their link to ecotype I and II.ConclusionsMoose probably function as reservoirs for both ecotype I and II, indicating that the ecotypes of A. phagocytophilum are not entirely host-specific and have overlapping niches. The disease hazard depends also on both host abundance and the number of immature ticks fed by each host. Our study provides novel insights in the northern distribution and expansion of tick-borne fever.
Highlights
The geographical expansion of the tick Ixodes ricinus in northern Europe is a serious concern for animal and human health
Roe deer came from around Vestby municipality, Akershus county; moose came from Siljan municipality in Telemark county, Vennesla, Songdalen, Audnedal and Marnardal municipality in Vest-Agder county, and Andebu, Lardal and Re municipality in Vestfold county; red deer came from Florø municipality, Sogn & Fjordane county, Drangedal and Skien municipality in Telemark county and Lardal in Vestfold county; questing ticks came from counties Møre & Romsdal and Sogn og Fjordane in the west and Akershus and Østfold in the east
Anaplasma phagocytophilum DNA was found in 70% of the moose, in 82% of the roe deer and in 94% of the red deer (Table 1)
Summary
The geographical expansion of the tick Ixodes ricinus in northern Europe is a serious concern for animal and human health. The pathogen Anaplasma phagocytophilum is transmitted by ticks and causes emergences of tickborne fever (anaplasmosis) in livestock. Pathogens transmitted by Ixodes ricinus cause disease emergence in northern areas of Europe with serious implications for animal and human health [1,2,3]. Anaplasma phagocytophilum is the causative agent of human granulocytic anaplasmosis [8], and it causes disease and economic losses in livestock [9]. Due to the high genetic diversity, A. phagocytophilum was formerly even split in three different species [12]. This genetic diversity has probably arisen as a response to evasion of immune defenses of phylogenetically different vertebrate host groups [13]
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