Could we eradicate strangles in equids?

Abstract

Views: Commentary 377 S (Streptococcus equi subsp equi infection) is a globally distributed and highly contagious equine scourge first described by veterinarians of ancient Rome. Outbreaks are associated with loss of condition, disruption of training and riding activities, cost of veterinary care, and lethal sequelae including disseminated (bastard) strangles and purpura hemorrhagica. The overall complication rate can be as high as 20% of affected animals, with a case fatality rate of up to 8%. Control of strangles is based on various approaches, including screening, quarantine, and immunization. Fully effective and safe vaccines providing long duration of immunity are not available, and the task of developing such vaccines, even with complete genome sequence data for S equi and Streptococcus zooepidemicus, is recognized to be considerable. A recent American College of Veterinary Internal Medicine consensus statement from the United States and United Kingdom on guidelines for treatment, control, and prevention was 12 pages, a length that emphasizes the complexity of control measures. In the United Kingdom, the Codes of Practice Guidelines on Strangles published by the Horserace Betting Levy Board is shorter and, like the consensus statement, focused on dealing with outbreaks. It notes the advisability of informing the relevant breeders’ associations of infection, but acknowledges that there is no legal requirement for this, even for purposes of export. There are no guidelines in Canada agreed to by the horse industry. Strangles has all the hallmarks of an infection that should and could be eradicated (Appendix 1). The causative agent replicates only in equids and survives only briefly in the environment. It causes serious loss through morbidity and death, as well as through cost and implementation of control measures in outbreaks. Because it is not reportable, its presence may fail to be disclosed for economic or other reasons, and therefore, the disease may be introduced unknowingly causing demoralization and conflict. Recent work has shown that the organism is a unique biovar or genovar of an ancestral S zooepidemicus. It appears to be genetically frozen, and unlike most pyogenic streptococcal species, antigenic variation of surface virulence-associated proteins including SeM is slight or absent. In many ways, S equi is an archaeologic relic that could be consigned to history. Could we eradicate strangles in equids?