Parasites of the raccoon dog – an invading species

Invasive species have a marked negative influence on the biodiversity of ecosystems and may contribute to the transmission of diseases. During the 1920s until 1950s, thousands of Raccoon dogs were deliberately introduces to the eastern European countries from the Far East, in order to enrich the wild with this new valuable fur animal.

The Raccoon dog is considered the most successful invading mammal in Europe, and in the last 20 years, it has invaded the western part of Denmark, namely Jutland. The Danish ministry of Environment reacted to the new threat by deciding to eradicate this species. In 2011, all animals shot and/or accidentally killed by traffic (N=70) were sent for post mortem analysis at the National Veterinary Institute.

Concurrently, foxes originating from the same areas (N=60) were examined by post mortem analyses to compare helminth infections in the two species. Eight helminth species were isolated from both hosts; however, foxes harboured more helminth species per infected animal (average 3,1 helminth species/fox) than raccoon dogs (average 1,7 helminth species/raccoon dog).

Prevalences of nematodes (Uncinaria stenocephala, Toxocara canis and Toxascaris leonine) and cestodes (Mesocestoides sp. and Taenia spp.) were significantly higher in foxes compared to that for raccoon dogs, while the latter had significantly higher prevalences of the two trematode species Alaria spp. and Echinostomatidae.

Trematodes of the species Cryptocotyle spp. were equally prevalent in both of the hosts. No infections with Echinococcus multilocularis or Trichinella spp. were detected in any of the hosts. Morphologically, helminths of both hosts were identically with the exception of Alaria isolated from raccoon dogs which were highly abundant but significantly stunted in size.

By comparing these results with those obtained from other countries, we can clearly see that raccoon dogs are not well established in Denmark. Helminths currently recovered from Danish raccoon dogs are mainly those that have direct life cycles or can be transmitted through amphibian or insect intermediate hosts, while those transmitted by rodents are less prevalent.