08/03/2001 12:00AM

Just in time: A vaccine for West Nile virus

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LEXINGTON, Ky. - This week, the United States Department of Agriculture announced that it has issued a conditional one-year license for a vaccine against West Nile virus. News of the vaccine, which is made by Fort Dodge and available to veterinarians in states that approve its use, came even as officials at the Centers for Disease Control reported that the virus has spread into new territory.

The mosquito-borne virus has killed nine people and at least 32 horses since it first emerged in the Western Hemisphere in 1999. It first became known in New York, where the nine fatalities occurred, but since its arrival has spread south and west as infected birds carried it along migratory paths. Mosquitoes feeding off the birds become carriers who can infect both horses and humans.

This week, the CDC reported its first indication that West Nile virus had arrived in Ohio: a dead bird, a non-migratory blue jay found near Cleveland, tested positive for the virus and set a new westward border for the disease's presence. Earlier, one man and three horses in Florida also tested positive for West Nile.

In horses, the disease's symptoms can include lack of coordination, muscle weakness, stumbling, and twitching muscles.

The disease's spread appears inevitable, but there are some management steps that horse owners and trainers can take to minimize risk. An aggressive mosquito-control program is at the top of the list, and both veterinary and human-health officials recommend avoiding or eradicating standing pools of water where mosquitoes are likely to breed.

Recommendations issued by the USDA's Animal and Plant Health Inspection Service note that mosquitoes can breed in any puddle that lasts more than four days. In addition to recommending elimination of stagnant water, the guidelines call for horsemen to clean water troughs thoroughly every month and to dispose of or drill holes in the bottom of containers that collect water.

The USDA also recommends the use of insect repellents to help prevent exposure to adult mosquitoes who may be carrying West Nile.

Horsemen considering the Fort Dodge vaccine should note that vaccinated horses temporarily will test positive for antibodies to the virus. Though the USDA emphasizes that the presence of the antibodies is temporary, horsemen should be aware that they may hamper attempts to ship the horse to countries with import restrictions regarding West Nile virus.

Preserving lines through science

Last month, researchers at Colorado State University in Fort Collins produced the first foals ever born from eggs that had been collected months earlier from a mare, frozen in liquid nitrogen, and then thawed before breeding.

The successful foaling of a colt and a filly raises some interesting possibilities for the preservation of female genetic lines, says Dr. Lisa Maclellan, an Australian researcher who headed up the program at CSU's Animal Reproduction and Biotechnology Laboratory.

"We can preserve an egg from a mare with infertility problems, due perhaps to age, put them in a surrogate mare later, and breed the surrogate," Maclellan said. "We have [artificially] inseminated the recipient of the eggs, but you can do it by live cover."

In theory, that means a breeder could "harvest" eggs from mares in training - or even upon a mare's death - and preserve their genetic material for later use, effectively making it possible for the mare to "produce" a foal some years past her natural breeding life.

For Thoroughbred breeders, the concept is likely to remain just theory, as Maclellan acknowledges, because the American Stud Book administered by The Jockey Club requires a "natural gestation" in order for a foal to be registered.

"It's just a dream for Thoroughbreds, but wouldn't it be exciting to preserve some of those great female lines?" she asked.

Maclellan may be more aware of the tantalizing possibilities, however unrealistic in today's Thoroughbred world, than most researchers. From a family of Australian Thoroughbred breeders, she is the great-grandaughter of W.S. Cox, for whom Australia's Grade 1 Cox Plate in named.