Getting to Grips with Strangles and Other Streptococcal Diseases

Getting to Grips with Strangles and other Streptococcal Diseases

20-22 May, 2015 Elsinore, Denmark

With financial support from the NZERF (New Zealand Equine Research Foundation) and the University of Waikato, I was able to attend the workshop “Getting to Grips with Strangles and other Streptococcal Diseases – A Havemeyer Foundation Workshop” in Elsinore, Denmark. These workshops are an opportunity for the experts in the field to give papers, have in-depth discussions and collaborate with each other. Being a highly specific workshop there were approximately 40 people in attendance with 28 papers presented. Iceland, France, the United Kingdom, Denmark, the United States, Sweden, Germany, the Netherlands, Italy and New Zealand were represented. It was a fantastic opportunity as a PhD student to interact with and learn from those working on the same horse infections which make up the basis of my thesis. I was able to get ideas on how to progress my workfor typing the Streptococcus zooepidemicusisolates I have accumulated, new target genes to use in diagnostics and potential collaborators. There was no shortage on offers of help; the contacts made were invaluable. Ray was also able to present our findings on 2 cases of New Zealand strangles caused by the Pinnacle I.N. vaccine which has recently been accepted for publication by the journal Vaccine. By attending we also gained valuable insights into Streptococcal infections which will be of interest to the equine community.

Image 1: Strangles Workshop Participants, Elsinore 2015

Streptococcus equi

Several studies have shown differences between left and right guttural pouches with regards to the presence/absence of mucus, abscess protrusions and S. equi. Guttural pouch lavages were more likely to find S. equi then nasopharyngeal swabs or washes. This implies that when testing for carriers, a combined left and right guttural pouch lavage should be used.

There is still a need for a safe and effective vaccine for strangles with DIVA (Differentiating Infected from Vaccinated Animals) capabilities. Work is being done by the Animal Health Trust(AHT) group in the UK on a live vaccine strain of S. equicontaining six gene deletions and administered IM (intermuscular). The Strangvac vaccine which is based on three recombinant proteins derived from S. equi and produced in E. coli from the Intervacc group, Sweden is closer to being commercially available. It has shown good efficacy in challenge studies administered via a combination of intranasal and subcutaneous routes. IM administration is being investigated, showing encouraging results for safety and tolerability but is awaiting clinical trials.

Streptococcus zooepidemicus

S. zooepidemicus is a pathogen of many animals including the horse. Genomic evidence has provided some possible answers to its ability to survive and successfully exploit many different host environments. A recombinase (PinR) was found that can act as a reversible transcription switch, changing the bacterial phenotype increasing the population’s diversity. The AHT researchers suggested that this gives S. zooepidemicus a bet-hedging solution; to be pre-adapted to whatever environment it finds itself in.

With respect to reproduction, evidence suggests that S. zooepidemicus resides deep within the endometrial tissue with persister cells (dormant/slow-growing cells tolerant to antibiotics and other stressors) playing a role in chronic/recurrent endometritis. Work in Denmark is being put into characterising S. zooepidemicus persister cells. Another study has shown that a colonal infection of S. zooepidemicus(isolates with indistinguishable genotypes) isassociated with mare risks such as increased age, high parity and poor vulvar conformation and associated with reduced pregnancy rates.

A respiratory outbreak of S. zoopeidemicus in the Icelandic horse population was reported at the 2012 “Getting to Grips with Strangles and other Streptococcal Diseases” workshop. This year they reported a follow up on that outbreak which highlighted the ability of pathogenic strains of S. zooepidemicus to persist in healthy horses. The strain causing the original outbreak was isolated from healthy horses with genome sequencing showing some genetic change relative to the original strain.

Olivia Patty

Dr Ray Cursons, University of Waikato