Immunologic responses to West Nile virus in vaccinated and clinically affected horses.
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.
Davidson
Ann H
AH
Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA.
Traub-Dargatz
Josie L
JL
Rodeheaver
Racquel M
RM
Ostlund
Eileen N
EN
Pedersen
Douglas D
DD
Moorhead
Ron G
RG
Stricklin
Joe B
JB
Dewell
Renee D
RD
Roach
Susan D
SD
Long
Rachel E
RE
Albers
Sara J
SJ
Callan
Robert J
RJ
Salman
M D
MD
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*
D000914:Antibodies, Viral; D014765:Viral Vaccines