West Nile
by Dr. Keith Ratcliff, D.V.M.

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  What you need to know to keep your family and pets safe this summer!

 

Summertime has arrived, and with it comes the typical list of heat-related maladies to which our pets are vulnerable.  The list includes (but is not limited to ):
 

Fortunately most of the above problems are avoidable by using common sense and/or preventative medications currently available from your veterinarian.

As if that weren’t enough, we now have a newcomer to add to the list – the West Nile virus.  The purpose of this article is to give pet owners the most current information on the virus and some simple steps to limit their pets’ exposure to it.
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            What is West Nile virus?                    

                        West Nile virus is an arbovirus (short for arthropodborne virus) that causes encephalitis (inflammation of the brain).  Arboviruses, including West Nile virus, are transmitted by blood-feeding insects such as mosquitoes.  Most infections with West Nile virus have been identified in wild birds, but the virus can also infect horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic rabbits, domestic birds and humans.

            Where did West Nile virus come from? 

                        West Nile virus was first identified in the West Nile district of Uganda in 1937, and has since been found in Africa, Eastern Europe, West Asia, the Middle East and the United States.  The strain of virus found in the United States most closely resembles that found in the Mediterranean and Middle East.

            How is West Nile virus transmitted? 

                        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.  West Nile virus is not transmitted directly from person to person, animal to person, person to animal, or animal to animal.  Ticks infected with the virus have been found in Asia and Africa; however, there are no verified reports of ticks spreading the virus and their role in transmission has not been determined.
 

            What is the risk of a person contracting West Nile virus? 

                        The risk of becoming ill from a single mosquito bite is extremely low.  In areas where mosquitoes carry the virus, less than 1% are actually infected.  Even if mosquitoes are infected, less that 1% of people bitten and infected by those mosquitoes become severely ill.

 
            What clinical signs are associated with West Nile virus infection? 

                        Humans Most infections in humans are relatively mild, with flu-like symptoms including fever, headache, body aches and, in some cases, skin rash and swollen lymph glands.  Signs of more severe infections include high fever, neck stiffness, muscle weakness, convulsions and paralysis.  Death rates associated with severe infection range from 3% to 15% and are the highest among the elderly and those with weakened immune systems. 

Horses The most common sign is weakness, usually in the hindquarters.  Weakness may be indicated by a widened stance, stumbling, leaning to one side and to dragging.  In extreme cases, paralysis may follow.  Fever is sometimes evident, as are depression and fearfulness.  Approximately 40% of cases of west Nile viral encephalitis in horses proved fatal during the 1999 outbreak in the U. S. 

                        Other animals Wild birds infected with West Nile virus in the United States are most often found dead; therefore, descriptions of clinical signs in wild birds are not readily available.  Nor have clinical signs associated with West Nile virus infection in dogs, cats, bats, chipmunks, skunks, squirrels, domestic rabbits and domestic birds been well described.  It appears that, although they may be infected, many of these latter species may not develop clinical signs of disease.
 

            How is West Nile viral encephalitis diagnosed and treated? 

                        Diagnosis of West Nile viral 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 (e.g., hospitalization, intravenous fluids, respiratory support and prevention of secondary infections) while the affected individual’s immune system responds to the infection.

            Can West Nile viral encephalitis be prevented? 

                     A vaccine is now available for horses.  For humans and other animals, limiting exposure to mosquitoes is considered effective prevention.  The following actions may reduce the risk of mosquito bites and possible exposure to West Nile virus: 

• Check the integrity of screens around your home, porch and patio.
   
• During warm months, avoid outdoor activities at dusk and dawn.
   
• If you must be outdoors during hours when mosquitoes are most active, cover up with shoes, socks, long pants and long-sleeved shirts.
   
• Use mosquito repellant on exposed skin and spray clothing with repellants containing permethrin or 35% DEET (N,N-diethyl-meta-toluamide) since mosquitoes may bite through thin clothing.  When using insecticides or insect repellants, be sure to read and follow the manufacturer’s directions for use.
   
• Eliminate stagnant water from any receptacles in which mosquitoes might breed, including house gutters, birdbaths, old tires or swing sets, wheelbarrows, etc.
   
• Eliminate nesting sites for birds in barns and stables and around the house.
   
• Maintain the health of your pet.  Animals whose health is compromised are at far greater risk of developing disease.
   
• If purchasing an exotic bird or other pet, make sure you are buying from a reputable dealer.

There are several products currently available which claim to repel mosquitoes away from pets.  Efficiency is unproven and you should always read the label and apply only as directed.  Currently, products containing synthetic pyrethroids such as permethrin, allethrin or phenothrin seem to be effective.  Be extremely cautious when applying any pesticide to cats.   

Some experts claim that a dilute mixture of Avon® Skin So Soft misted on pets before going outside is safe and effective, but unproven by scientific studies. 

The Doctors and staff of Ratcliff Animal Hospital want all pet owners to be aware that West Nile virus is a threat to the health of all residents and pets in our area.  The most effective defense against the virus at this time is to:

• Reduce the mosquito population around your home using the previously mentioned steps

• Maintain healthy pets

• Heartworm / intestinal parasite prevention

• Flea and tick control

• Vaccination against common diseases

• High quality diet

• Regular veterinary examinations

A healthy pet is much better prepared to resist any infection, particularly West Nile virus.                                                            

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