Chief Scientific Officer Intervacc AB Stockholm, Stockholms Lan, Sweden
Abstract: Background – Strangles, caused by Streptococcus equi subspecies equi, is one of the most prevalent infectious diseases of horses leading to significant levels of morbidity, mortality and economic cost. In 2022 a recombinant fusion protein vaccine, Strangvac, was launched for sale in Europe. Strangvac does not contain the proteins SEQ2190 or SeM, which are used in a dual antigen iELISA that identifies horses exposed to S. equi with a reported sensitivity of 93.3% and specificity of 99.3%.Hypothesis/Objectives – We hypothesised that the exposure of vaccinated horses to S. equi leads to a positive serological test result, enabling the identification of protected horses.Animals – Blood serum samples from 41 horses were collected by veterinarians attending three outbreaks of strangles to determine if they had been exposed to S. equi as part of outbreak investigations.Methods – Serum samples from the case series were analysed using the dual antigen iELISA for strangles.Results – Four of 10 vaccinated horses tested seropositive in outbreak 1. All three non-vaccinated clinical cases of strangles and eight of 17 vaccinated horses tested seropositive in outbreak 2 (see Figure). Six of 11 vaccinated horses tested seropositive in outbreak 3.Conclusions and clinical importance – All three clinical cases and 18 of 38 (47%) vaccinated horses tested positive for exposure to S. equi, but none of the 38 vaccinated horses developed clinical signs of strangles. Our data provide evidence supporting a protective effect of vaccination with Strangvac against natural exposure to S. equi.
