Intervet Inc. has announced the availability of PreveNile. The new modified-live vaccine (MLV) for horses is the first one-dose West Nile virus (WNV) vaccine available for primary immunization. "PreveNile offers the most advanced WNV technology available for horses," says Marv Jahde, Intervet's Marketing Manager of Equine Products. "PreveNile is the first and only one-dose USDA-approved equine WNV vaccine labeled for prevention of viremia and as an aid in the prevention of disease and encephalitis caused by WNV infection. Other WNV vaccines on the market are only labeled as an aid in the prevention of viremia and require two doses for primary immunization."
In research studies conducted by Maureen Long, DVM, Dipl. ACVIM, assistant professor of large animal veterinary medicine at the University of Florida, PreveNile was tested using a severe intrathecal challenge model that causes viremia and clinical signs of disease consistent with those observed in horses naturally infected with WNV under field conditions. Long says this type of testing enables researchers to work with live WNV and induce clinical signs of disease under controlled conditions.
"PreveNile is proven 95% effective and shown to significantly reduce clinical signs of WNV in horses vaccinated with a single dose as compared to unvaccinated horses," says Long. "Vaccination resulted in 100% survivorship and resulted in a statistically significant reduction in clinical signs of WNV disease. In addition, the vaccine was shown to provide full 12 month protective immunity against WNV disease in unvaccinated yearlings.
"This type of protection is particularly important for na‘ve and previously unvaccinated horses, providing added assurance in the face of an outbreak," Long adds.
PreveNile is based on ChimeriVax technology from Acambis, a leading biotechnology company specializing in the discovery, development and manufacturing of human vaccines to prevent and treat infectious diseases such as WNV, dengue, Japanese encephalitis, and smallpox.
"This is the same technology being tested for the first-ever human WNV vaccine, which is currently in Phase II research trials," says Jahde. "The ChimeriVax technology combines two similar flaviviruses (yellow fever--YF, and WNV) into one, creating a chimera vaccine."
PreveNile is a WN-YF chimera vaccine created by replacing the structural genes of the attenuated human yellow fever (YF-17D) vaccine with the structural genes of WNV.
The YF-17D human vaccine is a safe, highly effective, well-tolerated, attenuated vaccine that has been used for more than 60 years in more than 400 million people.1
The chimera vaccine technology is more convenient because it stimulates immunity, both cell-mediated and humoral, without requiring a "booster" dose. In addition, only a single-dose of PreveNile is required for horses previously vaccinated with other WNV vaccines. PreveNile does not disseminate into the tissues of vaccinated animals and does not shed or spread from the host animal.
"One-dose administration translates into greater convenience for the veterinarian, less cost for the horse owner and less stress on the horse," says Craig Barnett, DVM, Intervet Senior Equine Technical Services Specialist. "A MLV provides a broader and quite often longer-lasting immunological response, incorporating both humoral and cell-mediated immunity."
Do We Need Another WNV Vaccine?
"WNV never can be eradicated," says Long. "The virus continues to pose a significant threat to both humans and horses." Long, considered one of the leading equine immunologists, says vaccine technologies continue to improve and evolve.
There is no cure for WNV. According to USDA's Animal and Plant Health Inspection Service, more than 30% of the 23,750 cases of WNV diagnosed in horses since 1999 have resulted in death.2 A sound vaccination program along with good environmental management practices, such as the elimination of standing water and use of mosquito repellent, provide the best means for controlling spread of the virus.
"PreveNile represents the next generation of equine WNV vaccine technologies, which provide long duration of immunity, and more efficacious protection with a single dose," says Long. "In addition, the vaccine is non-adjuvanted, with 99.9% of vaccinated horses in field safety studies showing no post-injection site reactivity."
Use in Pregnant Mares and Foals
In field trials, 302 pregnant mares were vaccinated, including 17 mares in the first trimester of gestation, 11 mares in the second trimester of gestation and 274 mares in the third trimester of gestation. No post-vaccine adverse events were observed in any of the mares. Studies to evaluate safety in these mares through foaling are ongoing.
PreveNile can be used safely in foals, beginning at four months of age, as well as horses previously vaccinated with another WNV vaccine.
PreveNile vaccination consists of a single, 1-mL dose administered intramuscularly. Refer to the package insert for complete vaccination directions. Revaccinate annually with a single dose.
"Intervet is continually working to advance the field of equine medicine," says Jahde. "PreveNile represents our commitment to providing the most efficacious, convenient and technologically advanced products for veterinarians and horse owners."
For more information about PreveNile and the full line of Intervet equine products, contact Intervet Customer Service at 800/441-8272 or visit www.intervetusa.com.
1 Monath TP. Yellow fever: an update. Lancet 2001:1:11-20.