Abstract

Strangles, caused by Streptococcus equi, is one of the most frequently diagnosed infectious disease of horses worldwide. We defined the global population structure of this important host-restricted pathogen revealing a population replacement in the late 19th or early 20th century and providing new insights into the epidemiology of outbreaks at local, national and international levels.

Genome information was exploited to develop a new multicomponent subunit vaccine, Strangvac, that protected 95% of ponies two weeks after third vaccination. However, protection fell after 2 months and further improvements to strangles vaccines are required.

Recently, we developed a barcoded transposon directed insertion-site sequencing (TraDIS) functional genomics platform for S. equi. The barcoded TraDIS method minimised the effects of stochastic loss and facilitated the identification of 368 genes that were required for fitness in Welsh mountain ponies. These genes included four of the eight components of Strangvac, suggesting that TraDIS can inform vaccine design.