Strangvac: A recombinant fusion protein vaccine that protects against strangles, caused by Streptococcus equi

The host-restricted pathogen Streptococcus equi causes strangles in the horse, which is characterised by abscessation of the lymph nodes of the head and neck. The disease is endemic throughout the world causing considerable welfare and economic cost to the horse industry. Here we report the results of three studies where ponies were vaccinated with combinations of recombinant fusion proteins to optimise vaccine production and the level of protection conferred. Optimal protection was conferred by a prototype multicomponent subunit vaccine, Strangvac 4, which contained eight proteins CNE, SclC, SclF, SclI, EAG (fused as CCE), SEQ_402, SEQ_0256 (fused as Eq85) and IdeE. Across the three experiments only three of 16 ponies vaccinated with Strangvac 4 became pyretic compared to all 16 placebo-vaccinated control ponies (P < .001). S. equi was recovered from the lymph nodes of eight Strangvac 4-vaccinated and 15 control ponies (P = .016). None of the ponies vaccinated with Strangvac 4, or the other prototype vaccines developed adverse reactions following vaccination. Our data provide evidence in support of the further clinical development of the Strangvac 4 vaccine.