Streptococcus equi causes strangles, which is the most severe and costly bacterial infection in the horse. It is highly contagious and a single case can lead to inhibition of activities in riding schools, cessation of racing events etc. Conventional vaccines on the market, based on attenuated strains or killed bacteria, are inefficient or have serious side effects.

A new vaccine, Strangvac, has been developed which is based on three recombinant fusion proteins derived from S. equi. Sixteen Welsh Mountain Ponies have been vaccinated with Strangvac, followed by experimental infection with S. equi. Only one of them became pyrexic, whereas 16 non-vaccinated control ponies all became ill by infection. Significant differences between the groups were found also in clinical signs of infection, levels of inflammatory markers and post mortem analysis.  No adverse reactions were noted. The proteins in Strangvac are surface localised on S. equi, required for bacterial adherence and targets for opsonic antibodies, and one is an IgG-protease of key importance for immune evasion. Other combinations of fusion proteins, than those used in Strangvac, have also been tested as vaccines, with protection levels ranging from poor to excellent (Strangvac).

Immunogenicity of Strangvac is good; high titre antibodies are formed in sera and in nasal washes against all proteins encompassed in the fusion constructs.

Shelf life stability of Strangvacis satisfactory and process development for large-scale production under GMP has begun. An on going clinical study will address the duration of protection and vaccination schedule.