West Nile Virus Found in North Florida

The West Nile Virus has now been found in several locations in North Florida including neighboring Duval County. Many local residents have questions and concerns regarding what can be done to protect themselves from this threat.

West Nile is a virus that is transmitted by mosquitoes to humans, birds, and horses. The virus can lead to a disease known as encephalitis which can be severe in the elderly, but is usually mild in healthy adults and children.

The West Nile Virus was first reported in Central Africa in 1937. There has been several outbreaks around the world since then. It was first reported in

New York in 1999 and has since been located in several northeastern states. The virus is spread by mosquitoes which get it by feeding on infected birds. The virus is then passed along to humans when an infected female mosquito takes a second blood meal from a human instead of a bird. As they are feeding on human blood, they release saliva that contains the virus. The saliva then enters the human bloodstream carrying the virus with it.

Many birds, in particular crows, are susceptible to infection with West Nile Virus and experience high mortality. If you find a dead bird you are asked to report it to the Florida Fish and Wildlife Conservation Commission or contact the Baker County Health Department at 259-6291. It is important to provide the correct address and contact information in case the bird is to be picked up for testing.

There is now an experimental vaccine to protect horses from West Nile Virus but for humans the best defense  against this disease is personal protection and avoiding mosquitoes. Make sure screens are in good repair to prevent mosquitoes from entering homes. If you must enter areas where there is a threat of encountering infected mosquitoes, wear protective clothing.

Finally, use a personal insect repellent that provides a reasonable Complete Protection Time (CPT). The CPT is the total time following repellent application that the treated individual will remain bite free. For example, under normal conditions the CPT for a 5% formulation of DEET (diethyl toluamide, presently the most effective insect repellent) is approximately 2 hours. The CPT for a 24% DEET formulation is more than 4 hours.

West Nile Virus & Horses

Horse owners should take extra precautions to protect their animals from exposure to mosquitoes with the finding of West Nile Virus in Florida. Horses can become infected with the virus from mosquito bites.West Nile Virus is a form of encephalitis which can affect horses, birds and people. Like other forms of encephalitis such as Eastern Equine Encephalitis and St. Louis Encephalitis, West Nile is transmitted by mosquitoes. A mosquito who has been feeding on the blood of an infected bird can spread the virus. A birds metabolism allows a sufficient population of the virus to build up in its bloodstream for the mosquito to become a vector of the disease. The mosquito then bites a person or horse who is infected. People and horses are called dead-end hosts since the virus cannot build up enough in their blood to allow it to be transmitted from them to another victim.

For horses, the time between the bite from an infected mosquito and the appearance of symptoms is between 5 and 15 days. Symptoms can include listlessness, stumbling and incoordination, weakness of limbs, partial paralysis, and death. Other signs may be impaired vision, head tilt, convulsions, inability to swallow, circling, hyper excitability, or coma. In the New York outbreak of 1999, 25 horses showed signs of infection, 9 of those died and the remaining 16 recovered. Another 35 had the antibodies in their system but never showed signs of the illness, so the virus can be fatal but the majority of horses do recover. If you see symptoms, contact your veterinarian immediately. Horse owners should do everything possible to prevent exposure of animals to mosquitoes. Remove potential mosquito breeding sites such as water-holding containers, clean watering troughs every 1-3 days, keep horses stabled during peak feeding times, and use approved mosquito repellents for horses (not DEET).

An experimental vaccine has just been released which will allow horse owners to protect their horses against West Nile Virus. Florida Agriculture Commissioner Charles Bronson announced on August 3, 2001 that the newly developed vaccine would be available for private veterinarians. The vaccine has been under development for several years and has just completed field trials. Supplies will be limited as plans call for distribution first in the counties with West Nile Virus positive tests in birds and horses, then working outward to the rest of the state. Current recommendations are for two doses of vaccine, three to six weeks apart. The new vaccine for West Nile Virus is separate and should be in addition to the current vaccination for Eastern Equine Encephalitis that all horse owners should be familiar with.

West Nile Resources for Florida Residents

The Florida Medical Entomology Laboratory Encephalitis Information System (EIS) provides updated information on the current status of mosquito-borne Encephalitis in Florida with risk maps highlighting counties in Florida with reported virus transmission. 

Residents can report dead birds directly to the Florida Fish and Wildlife Conservation Commission .  It is important to provide the correct address and contact information in case the bird is to be picked up for testing.