WNV Vaccine Study Abstract Released

Fort Dodge Animal Health recently received USDA approval to release the following abstract regarding the West Nile virus vaccine and its efficacy. More information on the topic was presented in today's sessions at the World Organisation for Animal Health (Office International des Epizooties--OIE) meeting "Vaccines for OIE list A and Emerging Diseases" in Ames, Iowa. This study was done on normal healthy horses, isolated from natural exposure. Watch the web site tomorrow for more information on this story from the study's authors.

For more information on West Nile virus, visit http://www.TheHorse.com/wnv.

Equine Vaccine for West Nile Virus
by T. Ng, D. Hathaway, N. Jennings, Y.W. Chiang, H.J. Chu. Biological Research and Development, Fort Dodge Animal Health

The West Nile virus (WNV) was first isolated and identified from birds, mosquitoes, and mammals including horses in three states of the northeastern United States in 1999. Since then, WNV infection has been spread to southeastern and Midwestern states. In order to meet the urgent need of controlling the WNV infection in equine population, we have developed a killed WNV vaccine. A dose titration study in horses was first conducted to evaluate serum neutralization antibody responses against WNV in horses.

Horses were randomized into three vaccinated and one control groups. Horses were vaccinated with the test vaccine at low, median, and high doses, respectively. All vaccinated horse were administered the test vaccine intramuscularly twice, three weeks apart. Serum samples were collected periodically and were measured for serum neutralization titers using plaque reduction neutralization test.

Twelve months after the second vaccination, horses vaccinated with the median dose of WNV vaccine and non-vaccinated control horses were experimentally challenged with WNV. After challenge, horses were monitored for rectal temperature and any clinical signs twice daily for two weeks and once daily thereafter until 21 days post challenge (DPC). Serum samples were collected twice daily for two weeks and once weekly thereafter for detection of viremia. Horses were euthanized and necropsied on 21 and 22 DPC. Cerebrospinal fluid (CSF), spinal cord (cervical, thoracic, and lumbar) and brain (frontal, occipital, medulla oblongata, and brain stem) tissue samples were examined for gross pathology and collected for virus isolation.

Nine out of 11 (81.8%) controls developed viremia after challenge, while only one out of 19 (5.3%) vaccinates had transient viremia. No WNV associated clinical signs were observed in any of the challenged animals throughout the observation period. No febrile responses were observed in any of the challenged horses. No WNV was isolated from any of the tissue or CSF samples collected from any of the challenged horses. Results from this study demonstrate a significant protection (94% of preventable fraction) against viremia in horses vaccinated with the killed WNV vaccine and the long duration of the protective immunity.


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