# Subcutaneous Dirofilaria repens infection in an imported dog in Denmark

## TL;DR

A fully mature Dirofilaria repens worm was found in a dog imported to Denmark, indicating the parasite's expanding range into Northern Europe.

## Contribution

This is the first report of a fully mature female D. repens in a dog in Denmark.

## Key findings

- A mature female D. repens was isolated from a subcutaneous nodule in a dog imported from Italy.
- Molecular and morphometric analyses confirmed the species as D. repens.
- The presence of the parasite in Denmark suggests a risk of future local transmission due to suitable mosquito vectors and climate.

## Abstract

The filarioid nematode Dirofilaria repens infects mainly dogs and is transmitted by vector mosquitoes when biting the definitive host. The parasite has mainly been reported from Eastern and Southern Europe, but during recent decades it has expanded its geographic range to some countries in Central and Northern Europe. Here, we report the finding of a fully mature female D. repens in a dog in Denmark.

A female specimen of the filarioid nematode Dirofilaria repens (superfamily Filarioidea, family Onchocercidae) was isolated from a ruptured subcutaneous nodule in an 18 months old Border Collie on the Danish island of Bornholm. The dog was born in Italy, where it lived for the first 3 months of its life, whereafter it was imported to Denmark via Switzerland. Species diagnosis was based on molecular methods (Polymerase chain reaction PCR and sequencing of ribosomal DNA (rDNA, ITS) and mitochondrial DNA (mtDNA, COX1, NADH) in combination with morphometric characterization. The viviparous nematode was relatively small (total length 102 mm, broadest width 0.6 mm). It had a prominent uterus containing numerous eggs at different embryonation stages, some of which showed fully developed microfilariae.

Dirofilaria repens was originally reported from Southern Europe and Asia, but during recent decades, it expanded its distribution area northwards, allowing autochthonous transmission to occur in Germany, Poland, Estonia, Latvia, Lithuania and Finland. The present report provides the first description from Denmark of a fully mature female worm in a dog imported from Italy. Known vectors include species of mosquitoes within the genera Aedes, Anopheles Coquillettidia and Culex, which are endemic in Denmark, reflecting the risk of future autochthonous transmission also in Denmark, where climatic conditions now allow larval development in the vectors. Although suspected to be an imported case, it cannot be excluded that the infection was contracted in Denmark.