Detecting the silent carrier: can we eradicate strangles from endemic premises?

The University of Melbourne

  • Project code: PRJ-012165

  • Project stage: Current

  • Project start date: Thursday, July 2, 2020

  • Project completion date: Saturday, July 1, 2023

  • Journal Articles From Project: Globetrotting strangles: the unbridled national and international transmission of Streptococcus equi between horses Microbial Genomics (Issue: 2021;7:000528 on 8/3/2021)

  • National Priority: HOR-Thoroughbred diseases and parasites


Asymptomatic carrier horses are often implicated as the source of new outbreaks of strangles. Currently, there are no published studies on the proportion of horses that have been previously infected, or the proportion of those horses that remain an asymptomatic carrier under Australian management conditions.
This project will engage with a variety of horse facilities to determine the proportion of horses with antibodies to Streptococcus equi ss equi, using an ELISA test developed at the Animal Health Trust in Newmarket. Subsequent evaluation of antibody positive horses will determine the proportion of these previously infected horses that are asymptomatic carriers of S. equi. There are several methods of identifying carrier horses and these methods will be evaluated. Studies of these carrier horses will be undertaken to determine the most effective means of treating carrier animals to eliminate the bacteria and remove the risk of future outbreaks. Genomic studies of S. equi isolates from outbreaks will also be compared with isolates from carrier animals to evaluate the role of carrier animals in initiating new outbreaks of strangles.


Thoroughbred Horses

Research Organisation

The University of Melbourne

Objective Summary

1. Determine the proportion of horses that are seropositive to Streptococcus equi subspecies equi

2. Determine the proportion of previously infected horses that are asymptomatically infected with S. equi

3. Develop and evaluate protocols to identify carrier horses and evaluate methods to resolve their persistent infections

4. Compare the genome of S. equi strains from asymptomatically infected horses with strains from current outbreaks to examine the role of carrier horses in initiating new outbreaks of strangles