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Vaccine. 2015 Feb 25;33(9):1160-7. doi: 10.1016/j.vaccine.2015.01.019. Epub 2015 Jan 15.

Vaccination with a live multi-gene deletion strain protects horses against virulent challenge with Streptococcus equi.

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Animal Health Trust, Lanwades Park, Kentford, Newmarket CB8 7UU, United Kingdom.
Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Herts AL9 7TA, United Kingdom.
Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 OES, United Kingdom.
Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, United Kingdom.
Animal Health Trust, Lanwades Park, Kentford, Newmarket CB8 7UU, United Kingdom. Electronic address:


Strangles, caused by Streptococcus equi subspecies equi (S. equi) is one of the most frequently diagnosed infectious diseases of horses and there remains a significant need to develop new preventative vaccines. We generated a live vaccine strain of S. equi containing deletions in six genes: sagA, hasA, aroB, pyrC, seM and recA, which was administered to nine Welsh mountain ponies via the intramuscular route. Four vaccinated ponies developed adverse reactions following the first vaccination from which the live vaccine strain was isolated. Two of these ponies were withdrawn from the study and seven ponies received a second vaccination, one of which then developed an adverse reaction. Nine control ponies injected with culture media alone developed no adverse reactions. Following challenge with a virulent strain of S. equi, none of the seven vaccinated ponies had developed clinical signs of strangles eleven days post-challenge, compared to six of nine control ponies over the same period (P=0.0114). A lymph node abscess was identified in one of the seven vaccinated ponies at post-mortem examination, whilst all nine control ponies had at least one lymph node abscess (P=0.0009). Three of the six vaccinated ponies that were protected from strangles had not developed an adverse reaction following vaccination, suggesting that a better understanding of the pro-inflammatory responses to S. equi could lead to the development of a live attenuated vaccine against strangles that is safe for administration via intramuscular injection.


Horses; Immunomodulatory proteins; Strangles; Streptococcus equi; Vaccination

[Indexed for MEDLINE]

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