Final Report: Investigations on Arcanobacterium phocae in “Foot Pad Necrosis” of Mink

Patrick Boerlin: Department of Pathobiology Ontario Veterinary College, Guelph .

“Foot Pad Necrosis” (FPN) has been associated in the past with feeding seal meat to minks, and suspected to be caused by seal caliciviruses. However, the virus could be neither grown nor detected in foot pad lesions. Lesions have been induced by experimental injection of seal caliciviruses in minks, but not through feeding of infected seal meat. It is unclear if these lesions were really FPN. The disease occurs mainly during the breeding season in ‘hyperactive’ heavy males, but it has apparently behaved like a transmissible disease, even in the absence of seal meat feeding. Previous information suggested that Staphylococcus pseudintermedius and Streptococcus canis were regularly recovered from FPN lesions and could potentially be involved in its pathogenesis. These organisms are part of the normal flora of mink and the apparent transmissible nature of FPN suggested that specific strains of these two bacterial species, more able to cause the disease than others, could have emerged and spread across mink populations. To test this hypothesis, and with the support of the Canada Mink Breeder Association, we recently examined the diversity of coagulase-positive staphylococci and S. canis in minks with and without feet lesions. Our results first showed that Staphylococcus delphini rather than S. pseudintermedius was associated with FPN. Second, our molecular typing of S. delphini and S. canis strains from mink feet lesions and from healthy minks showed that no specific strain could be associated with the disease. This supports the hypothesis that any strain of these two organisms behaves in minks as opportunistic pathogens causing secondary infections on primary lesions of another etiology. However, during the course of this study, our collaborators at the Animal Health Laboratory isolated Arcanobacterium phocae from mink feet lesions at several occasions. Interestingly, A. phocae is known to occur regularly in sea mammals, including seals (hence the name “phocae”), which could suggest some links with the feeding of seal meat to minks. This organism is relatively fastidious and slow growing on bacterial culture media. Consequently, it gets overgrown and probably often overseen in the middle of all the bacteria from the normal flora of foot pads growing on such media. We strongly suspected that A. phocae is more frequent than it appears with classical bacteriological diagnostic methods. Therefore, we developed a sensitive real-time PCR for the specific detection of A. phocae. In laboratory experiments, this PCR was extremely sensitive. However, it needed to be validated on real world materials, including materials from mink feet. This PCR was subsequently used for comparison of samples from minks with feet lesions and healthy minks. The results of these studies (the previous ones on S. delphini and S canis and those from this study on A. phocae) are described in detail in a manuscript which has now been accepted for publication in the Canadian Journal of Veterinary Research.

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