Identification of a human strain of Streptococcus dysgalactiae subsp. equisimilis in a dog: a new zoonosis?

Objectives: Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an important and sometimes lethal pathogen in humans, while it has been considered mainly as opportunistic in animals. Very limited cases of SDSE diseases have been described in dogs so far. Several zoonoses are caused by a close contact between humans and animals. Recently, a PCR protocol for distinction between SDSE of human (hSDSE) and equine origin has been optimised. The objective of this work was to evaluate if dogs may harbour human SDSE, with consequent potential impact on human health. Methods: Forty-seven beta-haemolytic streptococci isolated from different clinical specimens from dogs have been identified by PCR. The four strains identified as S. dysgalactiae have been tested by PCR for identifying the subspecies and for detecting a sequence of the streptokinase (skc) precursor gene of hSDSE. Results: Forty-one out of 47 streptococci strains have been identified as Streptococcus canis and four strains were S. dysgalactiae. One S. dysgalactiae strain resulted positive for the skc precursor gene specific of hSDSE, while the other three strains were negative. The dog had fever, was lacking appetite, had enlarged and painful retro-pharyngeal lymph nodes and significant increase of the tonsillar volume Conclusion: This is the first detection of a SDSE strain of human origin in dogs. Dogs infected by hSDSE might represent a potential risk for human health. This risk should be better investigated because of the close contact between pets and humans, including children. Species identification of beta-haemolytic streptococci isolated from dogs is usually not requested in veterinary clinical microbiology for economic reasons. If SDSE transmission between dogs and humans will be confirmed, a rapid identification of hSDSE in infected dogs could be useful for preventing the bacterial transmission to humans, with particular attention to children and immunocompromised people.