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West Nile Virus - Concerns for Humans, Dogs, and Cats

As "alarming" news of an increasing number of cases of West Nile Virus (WNV) in wild birds, horses, pets, and humans are reported across the country; nearly everyone is concerned about keeping their "entire family" safe. The potential magnitude of this national problem given an estimated population of 310 million people in addition to another 52 million dogs and 48 million cats is staggering. While the actual threat of WNV reaching epidemic proportions seems remote, the remedy for this problem - the use of toxic insect repellants - maybe introducing an even greater hazard. In addressing this issue - namely the use of insect repellants with potentially harmful ingredients - answers to the following questions are vital.

Bug N' Out Natural Insect Repellent for Pets

1. What is West Nile Virus?

West Nile virus (WNV) is an "arbovirus" that causes encephalitis (inflammation to the brain). Blood-feeding insects such as mosquitoes transmit these viruses. Mosquitoes draw the virus from infected birds and transmit it to animals and humans through bites. West Nile viral encephalitis develops in animals and humans when the virus multiplies and crosses the blood brain barrier. Most infections with WNV have been identified in wild birds, but the virus can also infect horses, dogs, cats, domestic rabbits, domestic birds and humans. The WNV, which originated in Uganda, was discovered in North America in 1999. Since that time the West Nile Viral Encephalitis has spread to 37 states and the Distinct of Columbia.

2. What is the Risk of Contracting West Nile Virus?

The risk of becoming ill with WNV from a single mosquito bite is extremely low. Transmission of WNV is almost exclusively by mosquitoes that pick up the virus from infected birds, and then bite another animal or person. In all the intensive research and surveys that have been done, there are no reports of transmission from person to person, or from animals directly to humans, or another animal.

For humans, the risk associated with WNV is highest in those over 50 years of age. It is unknown if immunocompromised persons are at increased risk for WNV disease. In areas where mosquitoes carry the virus, fewer than 1% of the people bitten, and subsequently, infected become severely ill. As of August 9, 2002 this year out of 135 reported cases nationwide only seven deaths have been recorded.

Dogs or cats become infected the same way humans become infected - by the bite of infectious mosquitoes. The virus is located in the mosquito's salivary glands. During blood feeding, the virus is injected into the animal. The virus then multiplies and may cause illness. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. It is possible that eating dead infected animals such as birds could infect dogs and cats, but this is unproven.

WNV affects horses more often than other domestic animals. Many horses infected with WNV do not develop any illness, but of the 85 that did become ill in the 1999 or 2000 outbreak, 32 (38 percent) died or were euthanized. As of July 25, there were 47 confirmed cases of WNV in horses in 2002. Of the 47, seventeen either died or were euthanized.

Other animals including wild birds infected with WNV in the United States are most often found dead; therefore descriptions of clinical signs in wild birds are not readily available. Clinical signs associated with West Nile virus infection in dogs, cats, bats, chipmunks, skunks, squirrels, domestic rabbits, and domestic birds are not well described. It appears, however, that, although they may be infected, many of these latter species may not develop clinical signs of disease.

3. Identifying and Treating West Nile Virus?

The WNV infections in humans are relatively mild with flu like symptoms including fever, headache, body aches, and sometimes swollen glands or rash. Severe signs include high fever, neck stiffness, muscle weakness, and convulsions. Although no cases have been reported among dogs and cats, the disease can occur. If so, one could assume at least some symptoms are similar to those in people.

West Nile Virus has been reported only in the eastern half of the U.S. and is expected to spread to the northwest. Fortunately, with this type of virus, birds, horses, humans and other animals quickly develop immunity and the infection rate is expected to peak and then decrease to a persistent, but low level.

Horses are definitely susceptible. For horses the most common sign is weakness. Weakness may be indicated by a widened stance, stumbling, leaning to one side and toe dragging. In extreme cases paralysis may follow. Approximately 40% of cases of WNV encephalitis in horses proved fatal during the 1999 outbreak in the U.S. Other livestock and poultry do not commonly show wellness if infected with WNV. Diagnosis of WNV encephalitis is based on a history of exposure, clinical signs and results of diagnostic blood tests. As for all viral diseases, treatment consists of providing support while the affected individual's immune system responds to the infection.

4. Preventing West Nile Virus?

Given that mosquitoes are associated with WNV transmission, the key to preventing or controlling future outbreaks of WNV among horses and other animals is to control mosquito populations and to prevent horses from being exposed to any adult mosquitoes that may be present. Because pets could be infected the same way people are, the key to prevention is to prevent mosquito bites. Products to prevent fleas and ticks have no effect on mosquitoes. There are over the counter products, however, available to repel mosquitoes. Similar recommendations would apply for other pets, livestock, or poultry should illness due to WNV in those types of animals come to be commonly recognized. Generally accepted responses are:

  • Reduction of Mosquito Breeding Habitat by reducing sources of standing or stagnant water to minimize breeding places.
  • Decrease Human and Pet Exposure to Adult Mosquitoes including:
  • Maintaining the integrity of screened housing to provide mosquito free areas.Use insect repellent in conjunction with other measures and use of safe ingredients. While the use of DEET is highly recommended for use in repelling mosquitoes, both the CDC and EPA have issued extensive cautions about its use.*
  • Limit outdoor exposure particularly at dawn and dusk time of day when mosquitoes are generally most active.
  • Cover up with protective clothing in conjunction with other protective measures.
  • Vaccination is now available as an option for horses:
  • In 2001 a license was issued by the USDA-APHIS Center for Veterinary Biologics for an equine WNV vaccine.


* For more information contact the National Pesticide Information Center (NPIC) at 1.800.858.7378 or 1.800.222.1222 for information on nearest the Poison Control Center to you.] Repellents should be used according to their label instructions regarding appropriate species, method of application and other precautions. Some repellents contain permethrin as their active ingredient. Topical application of a product containing a synthetic permethrin compound as the active ingredient may offer the best combination of safety and efficacy. While these sprays do prevent some mosquitoes from biting, others will penetrate. Warning: Permethrin sprays are deadly if used on cats.

There are a few all natural products using citronella which are effective and safe in repelling mosquitoes and do not have the same side effects that deet can have. For information on an all natural, deet free repellent for people see Bug N' Out. For an all natural, deet free repellent for dogs and cats see Bug N' Out for Pets.



Published Summer 2001

 

 


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