The U.S. Department of Agriculture (USDA) announced that it has issued a license to Fort Dodge Laboratories, Inc., of Fort Dodge, Iowa, a division of Wyeth, for a vaccine to protect horses from viremia caused by the West Nile virus (WNV).

The horse vaccine, which was developed through a collaboration of the Centers for Disease Control and Fort Dodge, is the first fully licensed WNV DNA vaccine for animals in the United States. The vaccine contains genes for two WNV proteins, and therefore, does not contain any whole WNV, live or killed. Once the horse’s cells begin making proteins from the virus, they trigger a protective immune response.

In granting full licensure, USDA’s Center for Veterinary Biologics determined that the vaccine’s safety and efficacy have been satisfactorily demonstrated. Studies looking at how long the vaccine maintains its immunity are ongoing. However, the label contains a caution that vaccinated horses may not be eligible for export, as current commercially used tests may not be able to differentiate between this vaccine, conventional vaccines and horses that have been exposed to the actual virus.

WNV, a mosquito-borne disease, was first detected in the United States in 1999. The virus, which can cause encephalitis or inflammation of the brain in animals and, in some cases, humans, has been found in Africa, western Asia, the Middle East and the Mediterranean region of Europe. It has spread to all 48 of the continental United States.

WNV infection in horses may include both central nervous system and peripheral nervous system signs. From the first introduction of the virus in 1999 through December 2004, there have been 22,602 reported equine cases. Approximately one-third of horses that become ill with WNV die or must be euthanized.

This technology represents a new generation of vaccines. Traditional vaccine development involves either passing a disease-producing virus through a different species or cell type until it no longer causes disease but does create immunity, or by killing the virus in such a manner that allows it to produce immunity but no disease in the recipient. DNA vaccines, by contrast, use specific fragments of a pathogen’s unique genetic material to stimulate a targeted immune response from the host.

Once licensed by the USDA, a product of this nature can be marketed to the public. For information on the vaccine, contact Ft. Dodge Laboratories, Inc., at (800) 685-5656.


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