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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

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  • 1 Merial Ltd, 115 Transtech Dr, Athens, GA 30601.
  • | 2 College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80552.
  • | 3 Merial Ltd, 115 Transtech Dr, Athens, GA 30601.
  • | 4 Merial Ltd, 3239 Satellite Blvd, Duluth, GA 30096.
  • | 5 College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80552.
  • | 6 Aventis Pasteur, Connaught Campus, 1755 Steeles Ave, Toronto M2R 3T4, ON, Canada.
  • | 7 Merial SAS Ltd, 254 rue Marcel Mérieux, Lyon 69007, France.
  • | 8 Merial Ltd, 3239 Satellite Blvd, Duluth, GA 30096.
  • | 9 Merial SAS Ltd, 254 rue Marcel Mérieux, Lyon 69007, France.

Abstract

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.

Animals—20 mixed-breed horses.

Procedure—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 and Clinical Relevance—In horses, a single dose of the recombinant canarypox virus-WNV vaccine appears to provide early protection against development of viremia after challenge with WNVinfected 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. (Am J Vet Res 2004;65:1459–1462)

Abstract

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.

Animals—20 mixed-breed horses.

Procedure—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 and Clinical Relevance—In horses, a single dose of the recombinant canarypox virus-WNV vaccine appears to provide early protection against development of viremia after challenge with WNVinfected 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. (Am J Vet Res 2004;65:1459–1462)