Vector-borne nematodes, emerging parasites in Finnish cervids

There is a growing body of literature documenting the expansion of emerging parasites to sub-arctic areas. The potential impact of global warming on shifts in the spatiotemporal distribution and transmission dynamics of vector-borne diseases in domesticated and wild ungulates may be remarkable [1]. Recent Finnish studies have revealed an array of Filarioid nematodes and associated diseases that appear to be emerging in northern ungulates [2-4]. Members of the genus Setaria (Filarioidea: Onchocercidae) are found in the abdominal cavities of artiodactyls (especially Bovidae), equids and hyracoids. All produce microfilariae which are present in host blood [5], and known vectors are haematophagous mosquitoes (Culicidae spp) and horn flies (Haematobia spp.) [6]. The Filarioid nematode Setaria tundra was first described in semi-domesticated reindeer (Rangifer tarandus tarandus) in Arkhangelsk area, Russia [7]. Setaria infections appear to have emerged in Scandinavian reindeer not later than in the 1960’s. In 1973, S. tundra was observed for the first time in northern Norway where there was an outbreak of peritonitis in reindeer, as there was in Sweden, too. Also in 1973, tens of thousands of reindeer died in the northern part of the Finnish reindeer husbandry area. Severe peritonitis and large numbers of Setaria worms were commonly found. Following this, the incidence of Setaria in reindeer in Scandinavia diminished. According to meat inspection data and clinical reports from practising veterinarians, the latest outbreak of peritonitis in reindeer started in 2003 in the southern and middle part of the Finnish reindeer herding area. In the province of Oulu, the proportion of reindeer viscerae condemned in meat inspection due to parasitic lesions increased from 4.9 % in 2001 to 47 % in 2004 and in Lapland from 1.4 % in 2001 to 43 % in 2006. The focus of the outbreak moved approximately 100 km northwards yearly so that in 2005 only the reindeer in the northernmost small part of Finland (Upper Lapland) were free of changes. In the same time the outbreak seems to have settled in the southern area. [2]. The causative agent was recognized both morphologically and molecular biologically as S. tundra. DNA sequence of S. tundra parasitising reindeer in North Finland was deposited in GenBank under accession number DQ097309. [2,3]. The habitus of reindeer calves heavily infected with S. tundra expressed decreased welfare; low body condition and undeveloped winter fur coat. The meat inspection findings of peritonitic reindeer carcasses included ascites fluid, green fibrin deposits, adhesions and live and dead S. tundra nematodes. Histopathologically, changes indicated granulomatous peritonitis with lymphoplasmacytic and eosinophilic infiltration. No specific bacterial growth was found. No significant impact on meat pH values nor on organoleptic evaluation of meat was found. There was a significant positive correlation between worm count and the degree of peritonitis and a negative correlation between the degree of peritonitis and back fat layer [2]. Earlier, Setaria yehi has been associated with low grade chronic peritonitis in Alaskan reindeer [8] and S. tundra with mild to severe peritonitis together with Corynebacterium sp. in Swedish reindeer [9]. Our studies revealed that S. tundra can act as a significant pathogen for reindeer, which was evident at both ante and postmortem inspection and in histological examination. In order to monitor the S. tundra parasite dynamics in nature, parasite samples from wild cervids has also been collected [2]. In moose (Alces alces), the most abundant wild cervid in the reindeer herding area, only few cases Finnish Food Safety Authority Evira, Fish and Wildlife Health Research Unit, P.O. Box 517, FI-90101 Oulu, Finland Laaksonen and Oksanen Acta Veterinaria Scandinavica 2010, 52(Suppl 1):S3 http://www.actavetscand.com/content/52/S1/S3