The Department of Agriculture in August issued a conditional license to Fort Dodge Laboratories Inc. of Fort Dodge, Iowa, for a vaccine intended to aid in the prevention of disease in horses caused by West Nile virus. Citing special circumstances, the USDA Animal and Plant Health Inspection Service announced it would issue the license for one year.
APHIS issues conditional licenses for veterinary biologics products to meet an emergency situation, limited market, local situation, or special circumstance. Under these regulations, a product shown to be pure and safe and to demonstrate a reasonable expectation of efficacy may be licensed while data to establish efficacy and potency are still being obtained.
West Nile virus is a mosquito-borne virus that was first detected in the United States in 1999. The virus, which can cause encephalitis in animals and humans, has been found in Africa, western Asia, the Middle East, the Mediterranean region of Europe, and, most recently, in various parts of the United States.
In 1999 and 2000, 85 horses in the United States were infected with the virus, and 32 of these died. Viral infection in horses may affect the peripheral and central nervous systems. The most common signs of West Nile virus infection in horses have been stumbling or incoordination, weakness of limbs, partial paralysis, muscle twitching, and death. Fever has been detected in less than a quarter of all confirmed cases.
Conditional licenses are generally issued with restrictions and for a limited time. At the end of the conditional license period, data obtained in support of the product's efficacy, potency, and product performance are evaluated to determine whether the conditional license should be renewed or a regular product license may be issued.
In keeping with these regulations, the vaccine has been issued a conditional license for one year. The product is restricted to use by a veterinarian in states where use of the product has been approved by the appropriate state regulatory authorities. Authorities in several states, including those where the virus has not reached, such as Utah, Nebraska, and Nevada, have already done so. See page 775 for additional information.
Horse owners planning to ship their animals to other countries should be aware that vaccinated animals might not meet the import requirements of those countries because of the presence of certain antibodies in their blood. Although the presence of this antibody is not permanent, it could lead to complications in shipping the horse.