MISSISSIPPI STATE -- West Nile Virus made its first appearance in the state in 2001, and Mississippians will likely need to take precautions from it for many years to come.

After entering the northeast United States in 1999, West Nile Virus made its first appearance in Mississippi's bird and horse populations in 2001. This year, it has recurred in those animal populations and is taking a human toll as well. No deaths are expected in other species, such as dogs or cats.

As of Aug. 1, Mississippi had 14 confirmed cases in horses in 11 counties. The Centers for Disease Control and Prevention have confirmed five human cases in three Mississippi counties and identified three more probable cases in three additional counties.

"There are several things people need to do to protect themselves and their horses from West Nile Virus," said Dr. Stanley Robertson, veterinarian with Mississippi State University's Extension Service. "As much as possible, remove standing water that mosquitoes will use for breeding grounds. Even small pools of standing water, such as is often found in discarded tires, can become mosquito breeding grounds."

People should use a mosquito repellent containing DEET at times and in places where they are more likely to encounter mosquitoes.

"For horses, try to limit the time they are turned out during early morning and late afternoon, when mosquitoes are most active," Robertson said. "Use of fans, screened enclosures and insect repellents can also limit exposure to mosquitoes."

Dr. Michael Brashier, equine veterinarian at MSU's College of Veterinary Medicine, said horse owners should include the West Nile Virus vaccine in their annual vaccination plan.

"The best time to vaccinate a horse is the spring, usually April and May, before mosquito season begins," Brashier said. "The peak time for West Nile Virus infection is July through September, so horses should have immunity before this time. The vaccine, which is available from veterinarians, requires two shots administered three to four weeks apart."

This vaccine, which has just been out since August 2001, is conditionally licensed, meaning it is safe, and there is a reasonable expectation it will be effective.

"Currently, we don't know if annual boosters will be adequate for horses in Mississippi, especially on the Gulf Coast," Brashier said. "Only testing and experience will determine if the West Nile Virus vaccine will need to be given more frequently than once a year."

Robertson said if a horse is exhibiting signs of neurological disease, it is important to contact a local veterinarian for a diagnosis. They base West Nile Virus diagnosis on clinical signs and laboratory tests. Some horses infected with the virus will never show signs of illness. 

Clinical signs of West Nile Virus range from fever, mild instability on their feet or muscle twitching, to severe instability, lying down, convulsions and death. About 25 percent of the sick horses die or require euthanasia. Since several equine diseases can cause these clinical signs, it is important to also have blood samples sent to the laboratory to aid in the diagnosis.

West Nile Virus is spread in mosquitoes' salivary glands. It cannot be passed from an animal to humans.