West Nile Virus Update
Overview
West Nile virus is one of the fastest-growing health threats in the U.S. today. Since its discovery in 1999, this mosquito-borne disease has spread quickly throughout the U.S. Many experts expect that West Nile will soon become a threat coast to coast. The disease can be serious for humans, espeically the elderly or those suffering from other illnesses.
In addition to humans, the disease threatens horses, dogs, cats and birds. Of this group, horses and birds appear to be the most endangered by West Nile Virus.
Poultry does not seem to be seriously affected by the West Nile Virus. Although there is little evidence that pet birds have become ill from the virus, infections without symptoms are possible. It is prudent to protect pet birds from biting mosquitoes.
In general, the risk to dogs and cats is very slim because those animals develop natural antibodies against the virus. Pet owners may use mosquito repellent on dogs because mosquitoes also spread heartworm. Cats may be sensitive to repellent.
A relatively new vaccine for West Nile virus is available for horses, which are susceptible to a number of types of encephalitis.
Symptoms
Sick animals may have fever, weakness, poor muscle coordination, muscle spasms and neurological disorders such as seizures or a change in temperament. Horses exhibit somewhat different symptoms and may not have a fever. Look for listlessness, stumbling, lack of coordination, ataxia, or partial paralysis.
If your animal is sick, contact a veterinarian. The veterinarian will evaluate the animal, provide treatment and collect samples for laboratory analysis to determine the cause.
All pet, horse and other animal owners are advised to contact local their local and/or state health officials for the latest information on their areas. State and local health departments, university extension offices and veterinarians are excellent sources for localized information. Web sites are available from many of these sources.
Human Risk from Pets
Pets and other animals do not appear to be a threat to humans as carriers. West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person, animal-to-animal, or animal-to-person transmission of West Nile virus. However, veterinarians should take normal infection control precautions when caring for an animal suspected to have this or any viral infection.
Infection from means other than mosquitoes bites are not documented, but health officials advise caution. It is possible that dogs and cats could become infected by eating dead infected animals such as birds, but this is unproven. There is no reason to destroy a pet or horse because it has been infected with West Nile virus. At least for dogs and cats, full recovery from the infection is likely. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.
Although there is no evidence of human infection from handling infected animals, the federal Centers for Disease Control and Prevention recommends that anyone handling sick or dead animals avoid bare-hand contact. Hunters should use gloves when cleaning game animals and persons disposing of dead birds should use a shovel, gloves or double plastic bags to place carcasses in a garbage can. After disposing of the carcass, the hands must be thoroughly washed with soap and warm water. Veterinarians should use normal veterinary infection control precautions when caring for a horse suspected to have West Niles Virus. Proper cooking kills West Nile Virus, so there is no danger from eating wild game that may be infected.
Prevention and Warning
Although widely publicized, everyone is reminded of the need to report any dead crow, bluejay or raptor found between May 1 and the end of October that appears to have died of natural causes. These should be reported to your local health department. The bird will be collected and sent for laboratory for testing. The information from such remains help determine the extent and locations of West Nile infections.
The best way to prevent West Nile encephalitis and other mosquito-borne disease is to reduce the number of mosquitoes around the home and neighborhood.
During summer, mosquitoes can develop in any standing water lasting more than seven to ten days. Ponds or streams where fish are present or the water is disturbed by current or wave action do not produce many mosquitoes. Mosquito larvae or "wrigglers" must live in still water for five or more days to complete their growth before changing into adult mosquitoes. Hundreds of mosquitoes can be generated by one discarded tire full of water.
You can protect your family and pets from biting mosquitoes by reducing the amount of standing water available for mosquito breeding in or near your property:
• Repair failed septic systems.
o Keep grass cut short and shrubbery trimmed so adult mosquitoes cannot hide there.
• Dispose of old tires, cans, plastic containers, ceramic pots or other unused containers that can hold water. Drill a hole in the bottom of any tire used as a swing, so it cannot hold water. Do not overlook containers that have become overgrown by vegetation.
• Fill in or drain any low places that can collect water, such as puddles or ruts.
• For those containers that must remain on your property, such as birdbaths and wading pools, change the water at least once per week.
• Fill in tree holes and hollow stumps that hold water.
• Cover trash containers to keep out rainwater. Drill holes in the bottom of recycling containers that must be left outdoors. If holes are drilled in the sides of the containers sufficient water will collect to support mosquito breeding.
• Clean clogged roof gutters, particularly if leaves tend to plug up the drains. Flooded roof gutters are easily overlooked but can produce thousands of mosquitoes in a season.
• Repair leaky water pipes and outside faucets.
• Turn over wheelbarrows and plastic wading pools when not in use.
• Store boats either covered or inverted, or else remove the water after each rain.
• Aerate ornamental pools or stock them with predatory fish. Water gardens may be fashionable, but they are major mosquito producers if the water stagnates.
• Clean and chlorinate swimming pools even if they are not being used. Mosquitoes can also breed in the water that collects on swimming pool covers.
• Keep drains, ditches and, culverts free of grass clippings, weeds and trash so water will drain properly.
Report other area mosquito breeding sites to your local health department. Some communities conduct community-wide mosquito abatement programs. Whenever possible, the primary effort of such programs should be identification of mosquito-breeding sites, followed by draining of the sites or treatment with an insecticide to destroy mosquito in the larval stage.
Water may also collect in old tires, tin cans, plastic containers, ceramic pots, or similar containers. Remember to clean roof gutters so they drain properly in the spring and fall, clean and chlorinate swimming pools, outdoor saunas and hot tubs, and if not in use, keep empty and covered. Drain water from pool covers. Change the water in birdbaths at least once a week, turn over plastic wading pools, and wheelbarrows, etc. when not in use. Non-toxic products such as mosquito dunks can be used to prevent maturation of the mosquito larvae in standing water that cannot be readily eliminated.
Horse Vaccine
The USDA has recently approved a conditional license for a West Nile Virus vaccine for equids, including horses. The vaccine is made with a killed virus and has limited efficacy data, however, a similar vaccine for Japanese Encephalitis virus, which is closely related to West Nile Virus, has been used for many years. The efficacy of the Japanese Encephalitis vaccine has been reported at nearly 80 percent. Cases of West Nile Virus in horses occurred as late as October in 2000 in the eastern US. Therefore, internists at The Ohio State University, College of Veterinary Medicine recommend that if the vaccine is available, horses should be vaccinated twice this fall. The vaccine requires an initial dose and a second dose three to six weeks later. Horse owners who are interested in vaccinating their horses should contact their local veterinarian. Veterinarians are being encouraged to place orders so the company will have some indication of the demand for the vaccine. Studies have indicated the vaccination is largely effective and safe.
Horse owners planning to export their animals should be aware that vaccinated animals may not meet the import requirements of receiving countries due to the presence of anti-West Nile Virus antibodies in blood. While these antibodies are present transiently, presence of the antibody when the horse is due to be exported could result in denial of permission to import.
In horses that do become clinically ill, the virus infects the central nervous system and causes signs of encephalitis. Clinical signs of encephalitis in horses include loss of appetite and depression, in addition to any combination of the following: fever, weakness or paralysis of hind limbs, impaired vision, ataxia (incoordination), head pressing, aimless wandering, convulsions, inability to swallow, circling or coma.
Canine Update
According to an Associated Press news article, dogs may be in more danger from West Nile Virus than originally suspected.
Four dogs with encephalitis-symptoms had the West Nile virus, state officials said in one of the first signs the disease may be becoming more widespread in animals.
Three of the dogs died. They had symptoms that included seizures, trouble walking, "stargazing," and flinching at a gentle touch. The virus may not have caused the disease, but veterinarians should consider West Nile as a possible cause of brain or central nervous system trouble in dogs. For additional information visit American Veterinary Medical Association: or CDC.
