Outbreaks of canine distemper in Dutch and Belgian mink farms

Background: Vaccination of farmed minks against canine distemper virus (CDV) has proved to be very effective. In the Netherlands, vaccination of farmed minks against CDV was mandatory until the closure of the local agricultural product boards at the end of 2014. Objectives: To describe the first documented outbreaks of CD in Dutch mink farms since the closure of the agricultural product boards, as well as an outbreak in Belgium, with special attention to genotyping of the isolates. Methods: A full post-mortem was performed on three carcasses per submission from farms A–C and on two carcasses from farm D. Molecular detection with subsequent typing was performed on eleven samples originating from four different farms. To assess genetic diversity partial sequences of the H gene of CDV were compared based on phylogenetic analysis. Results: In 2017, there was a sudden series of CD outbreaks affecting four mink farms in the Netherlands (A–C) and Belgium (D). Gross, histologic and immunohistochemical findings were similar. There was a degree of genetic similarity between the viruses on farms A and D (98.5%) and between the viruses on farms B and C (97.3%), but the viruses from farms A and D belonged to a different clade than the viruses from farms B and C. Higher mortalities were reported in white and pastel minks. Conclusions: Findings indicated that the difference in severity of the outbreaks was partially related to the genetic composition of the farm populations. Vaccination against CDV on Dutch and Belgian mink farms seems warranted.