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Biology

West Nile Virus Information

May 21, 2012 by CouesWhitetail in Biology with 1 Comment

Background

What is West Nile virus?

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

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 clinical signs are associated with West Nile virus infection?

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 toe dragging. In extreme cases, paralysis may follow. Fever is sometimes evident, as are depression and fearfulness. Approximately 40% of cases of West Nile encephalitis in horses proved fatal during the 1999 outbreak.

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 highest among the elderly.

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, prevention of secondary infections, and good nursing care) while the affected individual’s immune system responds to the infection.

Can you get West Nile virus directly from birds?

There is no evidence that a person can get the virus from handling live or dead infected birds. However, persons should avoid barehanded contact when handling any dead animals and use gloves or double plastic bags to place the carcass in a garbage can.

How many types of animals have been found to be infected with West Nile virus?

Although the vast majority of infections have been identified in birds, West Nile virus has been shown to infect horses, cats, bats, chipmunks, skunks, squirrels, and domestic rabbits.

What is the incubation period in humans (i.e., time from infection to onset of disease symptoms) for West Nile encephalitis?

Usually 3 to 14 days.

Prevention

Can West Nile viral encephalitis be prevented?

A vaccine is now available for horses. For other species, 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 repellents 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 following the manufacturer’s directions for use.
  • Eliminate stagnant water from any receptacles in which mosquitoes might breed.

Is DEET safe?

Yes, products containing DEET are very safe when used according to the directions. Because DEET is so widely used, a great deal of testing has been done. When manufacturers seek registration with the U.S. Environmental Protection Agency (EPA) for products such as DEET, laboratory testing regarding both short-term and long-term health effects must be carried out. Over the long history of DEET use, very few confirmed incidents of toxic reactions to DEET have occurred when the product is used properly.

Is there a vaccine against West Nile encephalitis?

No, but several companies are working towards developing a vaccine.

Risk To Humans

Are game hunters at risk for West Nile virus infection?

Because of their outdoor exposure, game hunters may be at risk if they become bitten by mosquitoes in areas with West Nile virus activity. The extent to which West Nile virus may be present in wild game is unknown. It appears that birds often die within 48 hours of exposure so birds that are acting normally pose essentially no risk to hunters.

What should wild game hunters do to protect against West Nile virus infection?

Hunters should follow the usual precautions when handling wild animals. If they anticipate being exposed to mosquitoes, they should apply insect repellents to clothing and skin, according to label instructions, to prevent mosquito bites. Hunters should wear gloves when handling and cleaning animals to prevent blood exposure to bare hands and meat should be cooked thoroughly.

Who is at risk for getting West Nile encephalitis?

All residents of areas where virus activity has been identified are at risk of getting West Nile encephalitis; persons over 50 years of age have the highest risk of severe disease. It is unknown if immunocompromised persons are at increased risk for West Nile virus disease.

Additional Information

Arizona Department of Health Services 24 Hour phone line:
Phoenix Area – 602-364-4500
Elsewhere in Arizona – 800-314-9243

Informational web sites:
Center for Disease Control (CDC) – www.cdc.gov
American Veterinary Medial Association (AVMA) – www.avma.org
Arizona Department of Health Services (ADHS) – www.hs.state.az.us

What You Should Know About West Nile Virus Brochure (PDF, 800 kb)

[highlight1 variation="orange" textColor="#191919"]Attention Hunters: Doves Do Not Transmit West Nile Virus[/highlight1]

West Nile Virus (WNV) is a mosquito-borne virus that was first detected in the United States in 1999. The majority of people and animals that are infected with WNV have no symptoms or only a mild illness, such as a fever or headache. The Arizona Game and Fish Department has put this information sheet together to inform and educate dove hunters about WNV. All information contained on this sheet was taken from the Arizona Department of Health Services – West Nile Virus Fact Sheet. Here are some facts to keep in mind as you go out into the field:

  • People become infected with WNV only from the bite of an infected mosquito. Birds (including doves) and other animals CANNOT transmit WNV to people.
  • WNV is not spread by direct person-to-person or person-to-animal contact. To be fully safe, wear protective gloves when handling or cleaning your dove.
  • The most severe illnesses have been seen in crows, jays, ravens and horses, NOT doves.
  • Avoid standing water where mosquitos may be living. Avoid being bitten by mosquitos by using insect repellent (35% DEET) and/or wearing lightweight clothing that covers the arms and legs.
  • Proper cooking kills the WNV. Consequently, there is no danger associated with eating birds that have been properly cooked.

Other Resources

 

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One Comment

  1. Diseases of Coues DeerMay 21, 2012 at 1:12 am

    [...] West Nile Virus [...]

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