Resurrection and redescription of Varestrongylus alces (Nematoda: Protostrongylidae), a lungworm of the Eurasian moose (Alces alces), with report on associated pathology

BACKGROUND: Varestrongylus alces, a lungworm in Eurasian moose from Europe has been considered a junior synonym of Varestrongylus capreoli, in European roe deer, due to a poorly detailed morphological description and the absence of a type-series. METHODS: Specimens used in the redescription were collected from lesions in the lungs of Eurasian moose, from Vestby, Norway. Specimens were described based on comparative morphology and integrated approaches. Molecular identification was based on PCR, cloning and sequencing of the ITS-2 region of the nuclear ribosomal DNA. Phylogenetic analysis compared V. alces ITS-2 sequences to these of other Varestrongylus species and other protostrongylids. RESULTS: Varestrongylus alces is resurrected for protostrongylid nematodes of Eurasian moose from Europe. Varestrongylus alces causes firm nodular lesions that are clearly differentiated from the adjacent lung tissue. Histologically, lesions are restricted to the parenchyma with adult, egg and larval parasites surrounded by multinucleated giant cells, macrophages, eosinophilic granulocytes, lymphocytes. The species is valid and distinct from others referred to Varestrongylus, and should be separated from V. capreoli. Morphologically, V. alces can be distinguished from other species by characters in the males that include a distally bifurcated gubernaculum, arched denticulate crura, spicules that are equal in length and relatively short, and a dorsal ray that is elongate and bifurcated. Females have a well-developed provagina, and are very similar to those of V. capreoli. Morphometrics of first-stage larvae largely overlap with those of other Varestrongylus. Sequences of the ITS-2 region strongly support mutual independence of V. alces, V. cf. capreoli, and the yet undescribed species of Varestrongylus from North American ungulates. These three taxa form a well-supported crown-clade as the putative sister of V. alpenae. The association of V. alces and Alces or its ancestors is discussed in light of host and parasite phylogeny and host historical biogeography. CONCLUSIONS: Varestrongylus alces is a valid species, and should be considered distinct from V. capreoli. Phylogenetic relationships among Varestrongylus spp. from Eurasia and North America are complex and consistent with faunal assembly involving recurrent events of geographic expansion, host switching and subsequent speciation.