Assessment of the efficacy of a single dose of a recombinant vaccine against West Nile virus in response to natural challenge with West Nile virus-infected mosquitoes in horses.
OBJECTIVE
To determine the onset of immunity after IM administration of a single dose of a recombinant canarypox virus vaccine against West Nile virus (WNV) in horses in a blind challenge trial.


METHODS
20 mixed-breed horses.


METHODS
Horses with no prior exposure to WNV were randomly assigned to 1 of 2 groups (10 horses/group). In 1 group, a recombinant canarypox virus vaccine against WNV was administered to each horse once (day 0). The other 10 control horses were untreated. On day 26, 9 treated and 10 control horses were challenged via the bites of mosquitoes (Aedes albopictus) infected with WNV. Clinical responses and WNV isolation were monitored for 14 days after challenge exposure; antibody responses against WNV after administration of the vaccine and challenge were also assessed in both groups.


RESULTS
Following challenge via WNV-infected mosquitoes, 1 of 9 treated horses developed viremia. In contrast, 8 of 10 control horses developed viremia after challenge exposure to WNV-infected mosquitoes. All horses seroconverted after WNV challenge; compared with control horses, antibody responses in the horses that received the vaccine were detected earlier.


CONCLUSIONS
In horses, a single dose of the recombinant canarypox virus-WNV vaccine appears to provide early protection against development of viremia after challenge with WNV-infected mosquitoes, even in the absence of measurable antibody titers in some horses. This vaccine may provide veterinarians with an important tool in controlling WNV infection during a natural outbreak or under conditions in which a rapid onset of protection is required.
Siger
Leonardo
L
Merial Ltd, 115 Transtech Dr, Athens, GA 30601, USA.
Bowen
Richard A
RA
Karaca
Kemal
K
Murray
Michael J
MJ
Gordy
Paul W
PW
Loosmore
Sheena M
SM
Audonnet
Jean-Christophe F
JC
Nordgren
Robert M
RM
Minke
Jules M
JM
D000330:Aedes / Q000821:virology; D000704:Analysis of Variance; D000818:Animals; D000914:Antibodies, Viral / Q000276:immunology; D028121:Canarypox virus / Q000276:immunology; D006734:Horse Diseases / Q000276:immunology* / Q000517:prevention & control* / Q000821:virology*; D006736:Horses; D014765:Viral Vaccines / Q000276:immunology*; D014901:West Nile Fever / Q000662:veterinary*; D014902:West Nile virus / Q000276:immunology*
D000914:Antibodies, Viral; D014765:Viral Vaccines