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Title: A Lymphatic dwelling filarioid nematode, Rumenfilaria andersoni (Filarioidea; Splendidofilariinae), is an emerging parasite in Finnish cervids

Author
item LAAKSONEN, SAULI - Finnish Food Safety Authority
item OKSANEN, ANTTI - Finnish Food Safety Authority
item Hoberg, Eric

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2015
Publication Date: 4/16/2015
Citation: Laaksonen, S., Oksanen, A., Hoberg, E.P. 2015. A Lymphatic dwelling filarioid nematode, Rumenfilaria andersoni (Filarioidea; Splendidofilariinae), is an emerging parasite in Finnish cervids. Parasites & Vectors. 8:228.

Interpretive Summary: Climate warming in conjunction with translocation and introductions of invasive species are dramatically altering the distributions of parasites and parasitic disease in free-ranging, semi-domestic and domestic ungulates with considerable consequences for food security. Environmental impacts of climate warming, especially changing patterns of distribution for parasites and diseases requires baselines against which perturbation and emerging host-parasite associations may be assessed. Survey and inventory to establish baselines provides authoritatively identified specimens and the foundations for recognizing invasions and geographic colonization in space and time. Recent studies revealed rapid geographic expansion of filarioid nematodes into northern Finland. In addition to Setaria tundra, unidentified and very abundant filarioids, representing Rumenfilaria andersoni, were found inhabiting the lymphatic vessels of reindeer. Filarioid nematodes require blood feeding insects as vectors for their transmission. During strategic survey from 2004 through 2009, Rumenfilaria andersoni was found to be a common and abundant parasite in semi-domestic reindeer (64%) and wild forest reindeer (41-100%); moose (7.5-12%), white-tailed deer (15-22%) and roe deer (3%) were also revealed as definitive hosts; all constituted previously unrecognized host species in Fennoscandia. Density and prevalence of in moose and white tailed deer suggests the nematode may be adapted to these Alceini and Odocoileini, and that these cervids may be among the primary hosts of R. andersoni and reservoirs for transmission in Finland. Rumenfilaria andersoni was originally introduced and established in Finland coincidental with translocation of white-tailed deer from North America in 1935; subsequent invasion and emergence appears driven by climate-related factors, especially elevated summer temperatures, in Fennoscandia. The critical influences of climate change and what have been regarded as extremes in weather and summer temperature in geographic expansion of filarioids have been clearly demonstrated. It is probable that almost any filarioid nematodes parasitizing animals can, under proper circumstances, infect humans and undergo some degree of development. Consequently, the dynamics of transmission, the roles of various definitive and intermediate hosts, impacts on free-ranging cervid populations, immunological factors associated with infection, and possible pathways for anticipation and prevention of outbreaks should constitute the focus for future studies of these parasites. Results of this study are of significance for ungulate husbandry involving semi-domestic and domesticated stock, and for wildlife managers and disease specialists in understanding the factors that control invasion by pathogens.

Technical Abstract: Background-Recent studies revealed expansion of filarioid nematodes into the northern Finland. In addition to Setaria tundra, unidentified and very abundant filarioids, representing Rumenfilaria andersoni, were found inhabiting the lymphatic vessels of reindeer. Our study explores the biology and dynamics of rapid geographic expansion of R. andersoni, defining prevalence and density of microfilariae among 4 new cervid hosts in Finland while developing a context for host-parasite ecology in Fennoscandia and more broadly in the Arctic. Methods- Blood samples were evaluated for presence of microfilariae (modified Knott,s technique; identification by comparative morphology) from 1576 semi-domestic reindeer, 8 captive reindeer, and free-ranging cervids including 862 moose, 105 wild forest reindeer, 114 white tailed deer and 73 roe deer. Statistical analyses were performed with Stata 9 (StataCorp LP, USA) software. Additionally, estimation of the prepatent period and the efficacy of ivermectin treatment were investigated. Results- Rumenfilaria andersoni was found to be a common and abundant parasite in reindeer (64%) and wild forest reindeer (41-100%). Also moose (7.5-12%), white-tailed deer (15-22%) and roe deer (3%) were revealed as definitive hosts. Ivermectin was not efficient against adult parasites. The prepatent period was estimated to be about five months. Conclusions- Rumenfilaria andersoni was identified in 3 endemic cervids and the introduced white-tailed deer, all constituting previously unrecognized host species in Fennoscandia. Among moose, the risk of infection and the overall prevalence and intensity was substantially lower than levels observed among subspecies of Rangifer. White-tailed deer had a relatively high prevalence and density of rmf, whereas our limited data for roe deer indicated that the nematode may not be abundant or is emerging. Density and prevalence of rmf in moose and white tailed deer suggests the nematode may be adapted to these Alceini and Odocoileini, and that these cervids may be among the primary hosts of R. andersoni and reservoirs for transmission in Finland. Rumenfilaria andersoni was originally introduced and established in Finland coincidental with translocation of white-tailed deer from North America in 1935; subsequent invasion and emergence in the past 70-80 years may have been driven by climate-related factors in Fennoscandia.