Strangles is a contagious disease of the respiratory tract of horses produced by Streptococcus equi subsp. equi, a Lancefield's group C β haemolytic bacterium. It produces a mucopurulent secretion of the anterior airways, as well as lymphadenitis and abscesses. The bacteria synthesizes several pathogenicity factors such a hyaluronic acid capsule, hyaluronidase, streptolisin O, streptokinase, IgG Fc receptors, peptidoglican and protein M. Among these factors, protein M deserves special importance due to its antifagocitic and adherence properties. The disease has high morbidity and low lethality, and produces economic losses due to low performance and treatment. Clinical diagnosis and treatment are done easily, but prophylaxis is hampered by the low potency of vaccines, that protect around 50 % of vaccinated animals. Strangles may occur during all the year, but cold and humid weather favors the survival of streptococci, making animals that live in regions with those characteristics more prone to infection. New vaccines using purified or subunit antigens have been developed aiming to increase their potency and to avoid undesirable side effects. The demonstration that bacteria strains show differences in their antigenicity, called attention on the selection of appropriate strains to use as antigens.
strangles; vaccine; Streptococcus equi subsp. equi
