New study shows one dose of PreveNile produces a rapid immune response and can be used to boost colostral immunity in previously vaccinated broodmares

One dose of PreveNile West Nile virus vaccine is efficacious and creates a strong immune response in previously vaccinated pregnant mares, according to a new study from Intervet/Schering-Plough Animal Health presented at the American Association of Equine Practitioners (AAEP) Convention in December. The research represents the first of its kind in evaluating how new, technologically advanced West Nile vaccines such as chimeras stimulate the pregnant mare’s immune system post-vaccination.

“The mortality rate of horses infected by West Nile virus can be as high as 50 percent,” says Cynthia Gutierrez, D.V.M., Senior Equine Technical Services Veterinarian for Intervet/Schering-Plough Animal Health and lead researcher of the study. “This is why it is so important that horse owners remain diligent in their West Nile vaccination practices, particularly for broodmares that are in an immunosuppressive state due to their pregnancies.”

Gutierrez says the primary goal of the study was to confirm that PreveNile is efficacious as a booster in previously vaccinated pregnant mares to induce a strong immune response, as well as to confirm the vaccine can be used in pregnant mares to induce colostral immunity.

The research Eighty-one broodmares – within four to eight weeks of foaling and previously vaccinated for West Nile virus with a commercially available killed-virus vaccine – were studied. All of the mares were from the same farm and were managed according to the same protocol.

After an initial blood sample was pulled to evaluate existing titer (antibody) levels, the mares were boostered with an intramuscular single dose of PreveNile. Titer levels were measured again at three weeks post-vaccination, and all 81 mares, regardless of initial titer level, had at least a four-fold increase in titer – indicating an anamestic response, or a rapid increase in antibodies.

“The four- to eight-fold increase in titer levels we saw with this study provides evidence that one administration of a West Nile virus chimeric vaccine likely would provide yearly immunization in broodmares, as well as provide high levels of antibody required for colostral immunity,” Gutierrez says.

No adverse injection-site reactions occurred, and all of the mares delivered live, healthy foals.

One-dose. One time. Introduced in 2006, PreveNile is the only West Nile virus vaccine that requires just one dose for primary immunization and features the most comprehensive label claim of all WNV products.

Previous intrathecal challenge studies have demonstrated 12-month duration of immunity against clinical West Nile virus in yearlings and older horses (1). PreveNile also has been shown to be safe in horses, foals and pregnant broodmares (2).

“Results indicate one dose of PreveNile in pregnant mares with low antibody levels appears highly efficacious for stimulating colostral antibodies, further substantiating the vaccine’s relevance in helping to prevent West Nile disease,” Gutierrez concludes. “For equine veterinarians this research helps them make decisions with confidence in terms of designing and implementing vaccination protocols using technologically advanced vaccine preparations.”

Board-certified equine reproduction specialist Kelly Stich, D.V.M., Dip. A.C.T., from Hillcrest Animal Clinic in Lincoln, Neb., agrees. “It means a great deal to me as a reproductive specialist to see a published study showing efficacy in broodmares in regard to the PreveNile vaccine.” She adds, “My clients rely on me for advice on vaccination programs that are safe and provide good protection to their broodmares and nursing foals.”

For more information about PreveNile, or to learn more about Intervet/Schering-Plough Animal Health’s full line of innovative, high-quality equine health products, visit www.prevenile.com or www.intervetusa.com.

About Intervet/Schering-Plough Animal Health Intervet/Schering-Plough Animal Health, based in Boxmeer, the Netherlands, is focused on the research, development, manufacturing and marketing of animal health products. The company offers customers one of the broadest, most innovative animal health portfolios, spanning products to support performance and to prevent, treat and control disease in all major farm and companion animal species. Intervet/Schering-Plough Animal Health is a fully owned business unit of Merck & Co., Inc., based in Whitehouse Station NJ, USA. For more information about Intervet/Schering-Plough Animal Health visit: www.intervet.com and www.merck.com.

About Merck Today’s Merck is working to help the world be well. Through our medicines, vaccines, biologic therapies, and consumer and animal products, we work with customers and operate in more than 140 countries to deliver innovative health solutions. We also demonstrate our commitment to increasing access to health care through far-reaching programs that donate and deliver our products to the people who need them. Merck. Be Well. For more information, visit www.merck.com.

PreveNileR is the property of Intervet International B.V. or affiliated companies or licensors and is protected by copyright, trademark and other intellectual property laws. Copyright C 2010 Intervet International B.V. All rights reserved.

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(1) Long MT, Gibbs EP, Mellencamp MW, Bowen RA, Seino KK, Zhang S, Beachboard SE, Humphrey PP. Efficacy, duration, and onset of immunogenicity of a West Nile virus vaccine, live Flavivirus chimera, in horses with a clinical disease challenge model. Equine Vet J. 2007 Nov;39(6):491-7.

(2) Long MT, et al. Safety of an attenuated West Nile virus vaccine, live Flavivirus chimera in horses. Equine vet J. 2007;39:486-490.