Co-infection of wounds with Arcanobacterium phocae and Streptococcus halichoeri in farm mink - Disease mechanisms and diagnostic

PhD student: Oliver Legarth Honoré

Background

In 1996 a new disease was observed within fur animals in Canada. The disease was characterized as rapid forming necrotizing wounds.

Later in 2007, the first cases emerged in Finland. In 2015, the first confirmed cases of FNP were recorded on five Danish mink farms. It remains unknown how many farms are affected by the disease.
 
The disease was originally referred to as necrotizing pododermatitis in Canada and Fur animal Epidemic Necrotizing Pyoderma (FENP) in Finland from 2014. In this thesis, the disease will be referred to as Fur animal Necrotizing Pyoderma (FNP).

FNP was of great concern for the Danish fur industry in the 2010’s and was estimated to be one of the greatest threats towards animal welfare and a cause of extensive economic loss within the fur industry.

FNP is associated with two bacterial pathogens: Arcanobacterium phocea and Streptococcus halichoeri. Both bacteria were first characterized in marine mammals and it is believed that this the entry point into mink farms in USA and Canada. However, seal meat has not been used for mink feed in Denmark and it is instead believed that the disease spreads via transfer of animals.  

The disease is especially observed during two distinct periods of the year. These rapid forming necrotizing wounds are seen in early spring (breeding season) and early autumn (August-September).

Treatment of the disease has shown poor results and it is hypothesized that FNP can be associated with reduced breeding results as well as animal welfare and skin quality.

Purpose of the project

The purpose of this project was:

  • To increase the general understanding of FNP. To evaluate if this disease affects the reproduction of mink and thus create more awareness within the industry.
  • To evaluate if FNP wounds can be associated with multispecies biofilm formation by designing two novel species-specific Fluorescent in Situ Hybridization (FISH) probes.
  • To evaluate the potential production of toxins, explaining the rapid development of the wounds.
  • Increase the diagnostics of FNP by designing high throughput diagnostic methods.
  • And finally, to evaluate a potential treatment for the disease, as there at the time of the project start, was poor success with treatment of FNP wounds.

Results

The main results of this project are:

  • Evidence that FNP directly affects the breeding results on mink farms. Females whom have encountered a FNP-positive male produce 14% fewer kits in average and have a relative higher risk of becoming barren.
  • The rapid forming necrotizing wounds are associated with a multispecies biofilm formation, where proximity of the bacteria in the biofilm appears to reflect the severity of the disease.
  • Furthermore, it appears that toxin production from Arcanobacterium phocea is a major part of the pathogenesis, as an animal model with sterile filtrated supernatant was able to replicate some of the known pathological changes associated with FNP.
  • This project has furthermore developed enhanced diagnostics of FNP. Prior to this project FNP was diagnosed using traditional growth of bacteria. During this project, new qPCR primers have been produced and optimized so that both bacteria can be found in the same setup and plate.

A new non-antibiotic treatment was evaluated in this project. Mink were washed with a mild acid solution to see if this could improve wound healing as it had been shown in other animals. However, this resulted in adverse effects and reduced fur quality; therefore, this treatment cannot be recommended. The advice for the breeders remains to euthanize all animal with FNP wounds.

Future perspectives

Since all mink production has been terminated in Denmark due to COVID-19, the future perspectives within this area are limited. However, there are many mink producing countries oversees where this knowledge can be of great value.

Treating wounds with biofilm formation is known to be problematic and further research into understanding the mechanisms within a biofilm is an exciting research area.