title: Immunologic responses to West Nile virus in vaccinated and clinically affected horses.
abstract: OBJECTIVE
  To compare neutralizing antibody response between horses vaccinated against West Nile virus (WNV) and horses that survived naturally occurring infection.
  
  
  METHODS
  Cross-sectional observational study.
  
  
  METHODS
  187 horses vaccinated with a killed WNV vaccine and 37 horses with confirmed clinical WNV infection.
  
  
  METHODS
  Serum was collected from vaccinated horses prior to and 4 to 6 weeks after completion of an initial vaccination series (2 doses) and 5 to 7 months later. Serum was collected from affected horses 4 to 6 weeks after laboratory diagnosis of infection and 5 to 7 months after the first sample was obtained. The IgM capture ELISA, plaque reduction neutralization test (PRNT), and microtiter virus neutralization test were used.
  
  
  RESULTS
  All affected horses had PRNT titers > or = 1:100 at 4 to 6 weeks after onset of disease, and 90% (18/20) maintained this titer for 5 to 7 months. After the second vaccination, 67% of vaccinated horses had PRNT titers > or = 1:100 and 14% had titers < 1:10. Five to 7 months later, 33% (28/84) of vaccinated horses had PRNT titers > or = 1:100, whereas 29% (24/84) had titers < 1:10. Vaccinated and clinically affected horses' end point titers had decreased by 5 to 7 months after vaccination.
  
  
  CONCLUSIONS
  A portion of horses vaccinated against WNV may respond poorly. Vaccination every 6 months may be indicated in certain horses and in areas of high vector activity. Other preventative methods such as mosquito control are warranted to prevent WNV infection in horses.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Ann H
authors.initials: AH
authors.lastname: Davidson
authors.forename: Josie L
authors.initials: JL
authors.lastname: Traub-Dargatz
authors.forename: Racquel M
authors.initials: RM
authors.lastname: Rodeheaver
authors.forename: Eileen N
authors.initials: EN
authors.lastname: Ostlund
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Pedersen
authors.forename: Ron G
authors.initials: RG
authors.lastname: Moorhead
authors.forename: Joe B
authors.initials: JB
authors.lastname: Stricklin
authors.forename: Renee D
authors.initials: RD
authors.lastname: Dewell
authors.forename: Susan D
authors.initials: SD
authors.lastname: Roach
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Long
authors.forename: Sara J
authors.initials: SJ
authors.lastname: Albers
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Callan
authors.forename: M D
authors.initials: MD
authors.lastname: Salman
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000096:biosynthesis* / Q000097:blood; D003430:Cross-Sectional Studies; D009033:Culicidae / Q000821:virology; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005260:Female; D006734:Horse Diseases / Q000097:blood / Q000276:immunology* / Q000517:prevention & control; D006736:Horses / Q000276:immunology*; D008297:Male; D009032:Mosquito Control; D009500:Neutralization Tests / Q000662:veterinary; D010948:Viral Plaque Assay / Q000662:veterinary; D014765:Viral Vaccines / Q000008:administration & dosage / Q000276:immunology*; D014901:West Nile Fever / Q000097:blood / Q000276:immunology / Q000517:prevention & control / Q000662:veterinary*; D014902:West Nile virus / Q000276:immunology*
chemical_list: D000914:Antibodies, Viral; D014765:Viral Vaccines