Scientists at the Animal Health Trust in England have discovered that Streptococcus equi, the bacterial cause of the equine respiratory disease known as "Strangles," has genetic characteristics typically found in Yersinia pestis, the causative agent of human plague. Although S. equi does not present a risk to people, it could be said to represent the equine equivalent of human plague.
Scientists at the AHT are currently developing blood tests capable of identifying horses that recover from the disease but who remain long-term carriers of strangles. This will reduce disease spread.
Once recovered, most animals will eliminate S. equi fairly rapidly. However, approximately 10% become carriers. The bacterium usually resides in the guttural pouches and can do so for several years after the outbreak. If they are not identified, carriers can be released into a susceptible population, causing new outbreaks.
Carriers can be difficult to detect and negative results from a single nasopharyngeal swab do not prove that an animal is not infected. Three consecutive negative swabs over a two-week period tested for culture and PCR testing will provide strong evidence that shedding has ceased and the infection has been eliminated. However, guttural pouch endoscopy followed by bacteriological analysis of guttural pouch washes is the preferred method for identifying carriers.
It is hoped that the new diagnostic blood test being developed at the Animal Health Trust will provide an improved means of diagnosis.
Safe and effective strangles vaccines are also being designed at the AHT that can be widely used throughout the equine community.
One vaccine product from AHT research was recently found to be safe on intramuscular administration to horses; researchers are seeking funds to continue the development of this exciting new strangles vaccine.