title: Evaluation of a commercially available modified-live Streptococcus equi subsp equi vaccine in ponies.
abstract: OBJECTIVE
  To evaluate a commercially available modified-live Streptococcus equi subsp equi vaccine for safety and persistence in vaccinated ponies and to detect recombination or reversion events in the vaccine strain.
  
  
  METHODS
  5 ponies that were 1.5 to 8 years old (group 1) and 4 ponies that were 6 months old (group 2).
  
  
  METHODS
  Ponies were vaccinated, with a subsequent booster vaccination 2 to 3 weeks later, and monitored for 50 days. At booster vaccination, an equal amount of a tetracycline-resistant wild-type strain of S equiwas administered. Recovery of all strains was performed by use of bacteriologic culture and PCR assays.
  
  
  RESULTS
  Ponies in group 1 had background antibody titers against S equi antigen before vaccination despite the lack of known exposure to S equi. Ponies in group 2 were immunologically naïve. Increases in anti-S equi antibody titers were detected in both groups. Ponies in group 1 did not have clinical signs of disease caused by S equi. In group 2, all ponies developed abscesses in retropharyngeal lymph nodes; 1 pony developed severe clinical disease and was euthanized. The vaccine strain was recovered from ponies in group 2 for up to 24 days after vaccination.
  
  
  CONCLUSIONS
  Although the vaccine was successful in inducing IgG antibodies against S equi in all ponies, findings suggested that the vaccine may have caused substantial morbidity and some deaths in the young ponies. In young ponies, the vaccine strain persisted in tissues for weeks; however, no evidence of recombination was detected.
authors.affiliation: Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA. Luke_Borst@ncsu.edu
authors.forename: Luke B
authors.initials: LB
authors.lastname: Borst
authors.forename: Sheila K
authors.initials: SK
authors.lastname: Patterson
authors.forename: Saraswathi
authors.initials: S
authors.lastname: Lanka
authors.forename: Anne M
authors.initials: AM
authors.lastname: Barger
authors.forename: Richard L
authors.initials: RL
authors.lastname: Fredrickson
authors.forename: Carol W
authors.initials: CW
authors.lastname: Maddox
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005260:Female; D006734:Horse Diseases / Q000276:immunology / Q000517:prevention & control*; D006736:Horses; D007087:Illinois; D008198:Lymph Nodes / Q000382:microbiology / Q000473:pathology; D008297:Male; D013290:Streptococcal Infections / Q000276:immunology / Q000517:prevention & control / Q000662:veterinary*; D022541:Streptococcal Vaccines / Q000008:administration & dosage* / Q000276:immunology; D018502:Streptococcus equi / Q000276:immunology*; D014611:Vaccination / Q000662:veterinary*; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000276:immunology
chemical_list: D001426:Bacterial Proteins; D022541:Streptococcal Vaccines; D014613:Vaccines, Attenuated