Detection and molecular characterization of the mosquito-borne filarial nematode Setaria tundra in Danish roe deer (Capreolus capreolus)

Abstract

Setaria tundra is a mosquito-borne filarial nematode of cervids in Europe. It has recently been associated with an emerging epidemic disease causing severe morbidity and mortality in reindeer and moose in Finland. Here, we present the first report of S. tundra in six roe deer (Capreolus capreolus) collected between October 2010 and March 2014 in Denmark. The deer originated from various localities across the country: the eastern part of the Jutland peninsular and four locations on the island Zealand. With the exception of one deer, with parasites residing in a transparent cyst just under the liver capsule, worms (ranging from 2 to >20/deer) were found free in the peritoneal cavity. The worms were identified as S. tundra by morphological examination and/or molecular typing of the mitochondrial 12S rRNA and cox1 genes, which showed 99.1-99.8% identity to previously published S. tundra isolates from Europe. Roe deer are generally considered as asymptomatic carriers and their numbers in Denmark have increased significantly in recent decades. In light of climatic changes which result in warmer, more humid weather in Scandinavia greater numbers of mosquitoes and, especially, improved conditions for development of parasite larvae in the mosquito vectors are expected, which may lead to increasing prevalence of S. tundra. Monitoring of this vector-borne parasite may thus be needed in order to enhance the knowledge of factors promoting its expansion and prevalence as well as predicting disease outbreaks.

Keywords: Filarial nematode; Meat hygiene; Peritoneal cavity; Roe deer; Setaria tundra; Vector borne.

Graphical abstract

Fig. 1

Geographical origin (black dots) of Setaria tundra recovered from six infected roe deer. A: October 2010, B: May 2011, C: December 2012, D: May 2013 (two cases), and E: March 2014.

Fig. 2

Morphology of adult worms of Setaria tundra (A–C) and microfilaria (D and E) recovered from roe deer in Denmark. A: Cephalic region showing the bifid projections (bp) carried on top of a peribuccal crown (pc) and one of the four cephalic papillae (cp). B: Posterior end of male worm with papillae weakly visible (arrowheads). C: Posterior end of female worm showing a knob at the tip of the tail (arrow head), that possesses longitudinal grooves and pores, a papilla (pa), and a collar composed of a row of bosses (co). D: Microfilaria collected from a female worm. The length of the microfilaria including the sheath (white arrow heads) was approximately 316 μm, whereas the microfilaria was approximately 287 μm, with a blunt anterior end and a tapering posterior end. E: Setaria tundra coiled under the liver capsule (case 3). Scale bars indicated for all but figure E.

Fig. 3

Neighbor-Joining phylogenetic relationship of four isolates of Setaria tundra from distant localities in Denmark. The analysis was based on cox1 gene sequences (578 bp). Percentage bootstrap support from 1000 replicate samples is indicated at the right of the supported node. Accession numbers for sequences obtained from GenBank are given in parentheses, followed by origin of isolate, only applicable to S. tundra. The scale bar indicates distance.