Efficacy, duration, and onset of immunogenicity of a West Nile virus vaccine, live Flavivirus chimera, in horses with a clinical disease challenge model.
BACKGROUND
West Nile virus (WNF) is a Flavivirus responsible for a life-threatening neurological disease in man and horses. Development of improved vaccines against Flavivirus infections is therefore important.


OBJECTIVE
To establish that a single immunogenicity dose of live Flavivirus chimera (WN-FV) vaccine protects horses from the disease and it induces a protective immune response, and to determine the duration of the protective immunity.


METHODS
Clinical signs were compared between vaccinated (VACC) and control (CTRL) horses after an intrathecal WNV challenge given at 10 or 28 days, or 12 months post vaccination.


RESULTS
Challenge of horses in the immunogenicity study at Day 28 post vaccination resulted in severe clinical signs of WNV infection in 10/10 control (CTRL) compared to 1/20 vaccinated (VACC) horses (P<0.01). None of the VACC horses developed viraemia and minimal histopathology was noted. Duration of immunity (DPI) was established at 12 months post vaccination. Eight of 10 CTRL exhibited severe clinical signs of infection compared to 1 of 9 VACC horses (P<0.05). There was a significant reduction in the occurrence of viraemia and histopathology lesion in VACC horses relative to CTRL horses. Horses challenged at Day 10 post vaccination experienced moderate or severe clinical signs of WNV infection in 3/3 CTRL compared to 5/6 VACC horses (P<0.05).


CONCLUSIONS
This novel WN-FV chimera vaccine generates a protective immune response to WNV infection in horses that is demonstrated 10 days after a single vaccination and lasts for up to one year.


CONCLUSIONS
This is the first USDA licensed equine WNV vaccine to utilise a severe challenge model that produces the same WNV disease observed under field conditions to obtain a label claim for prevention of viraemia and aid in the prevention of WNV disease and encephalitis with a duration of immunity of 12 months.
College of Veterinary Medicine, University of Florida, 2015 SW 16th Ave., Gainesville, Florida, USA.
M T
MT
Long
E P J
EP
Gibbs
M W
MW
Mellencamp
R A
RA
Bowen
K K
KK
Seino
S
S
Zhang
S E
SE
Beachboard
P P
PP
Humphrey
D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D002678:Chimera; D004306:Dose-Response Relationship, Immunologic; D005260:Female; D006734:Horse Diseases / Q000453:epidemiology / Q000517:prevention & control*; D006736:Horses; D008297:Male; D011897:Random Allocation; D012449:Safety; D012720:Severity of Illness Index; D013997:Time Factors; D016896:Treatment Outcome; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000009:adverse effects / Q000276:immunology*; D014766:Viremia / Q000662:veterinary; D014774:Virulence; D014901:West Nile Fever / Q000453:epidemiology / Q000517:prevention & control / Q000662:veterinary*; D053060:West Nile Virus Vaccines / Q000008:administration & dosage / Q000009:adverse effects / Q000276:immunology*; D014902:West Nile virus / Q000276:immunology* / Q000472:pathogenicity
D000914:Antibodies, Viral; D014613:Vaccines, Attenuated; D053060:West Nile Virus Vaccines