Reappearance of Taenia ovis krabbei muscle cysts in a roe deer (Capreolus capreolus) in Denmark after 60+ years, with a possible role of a grey wolf (Canis lupus) as definitive host

Taenia ovis krabbei is a parasite with a sylvatic life cycle in which carnivores are definitive hosts and Cervid are intermediate hosts. Foraging on pasture contaminated with eggs of T. o. krabbei is the primary cause of infection to Cervids, and the larval stages usually develop in heart and skeletal muscles causing pathological changes and severe illness. There is no zoonotic risk in consumption of game meat infected with T. o. krabbei, but for aesthetic reasons, the infected meat is not regarded of high quality and usually discarded. The present report describes the reappearance of T. o. krabbei in a roe deer Denmark after more than 60 years. The cysticerci were isolated from the thigh muscle of a male roe deer shot in northern Jutland, and the diagnosis was based on histostological analysis, morphology of the rostellar-hooks as well as molecular typing of the mitochondrial cytochrome c oxidase I (cox1) gene. Shortly after this discovery, a wolf died in a nearby locality and worms T. o. krabbei was recovered from its intestine, and the diagnosis was based on morphology of the rostellar-hooks and molecular typing of the cox1 gene. By phylogenetic analysis, the Danish roe deer and wolf isolates were clearly grouped together with other isolates of T. o. krabbei from wolves in Finnoscandinavia. In mainland Europe, T. o. krabbei is primarily a parasite of wolves and this individual wolf has probably travelled around 800 km before it died. This unexpected reappearance of a wolf in Denmark after almost two decades could be a mere coincidence, but can also explain the introduction of this parasite during wolf introduction. Domestic dogs, in the other hand, could play a role in transmission of T. o. krabbei in that area, but this has yet to be tested. Deer infections with T. o. krabbei were reported in all German counties that border Denmark. It is also possible that similar deer infections were already present in other areas in Denmark, but unnoticed.