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West Nile Information

What is West Nile?

West Nile is one of several arboviruses. An arbovirus (acronym ARthropod BOrne) is a virus transmitted by the bite of an infected arthropod. Mosquitoes are arthropods because they are invertebrates with an exoskeleton, segmented body parts, and jointed appendages, or legs. Several different species of mosquitoes are known to transmit the disease, but the most common mosquito vector here in North Texas is the Southern House Mosquito, known scientifically as Culex quinquefasciatus.

Southern House mosquito.jpg Female Culex Quinque laying eggs.jpg
Culex quinquefasciatus taking a blood meal Culex quinquefasciatus laying eggs

Where did the disease originate from?

West Nile was first discovered in Uganda in 1937. The disease first appeared in the eastern U.S. in the early summer of 1999 when a large bird die-off was noticed and testing showed they were positive for West Nile. The largest outbreaks have occurred in Greece, Israel, Romania, Russia and USA. These outbreak sites have coincided with major bird migratory routes. In its original range, West Nile virus was prevalent throughout Africa, parts of Europe, Middle East, West Asia, and Australia. Since its introduction in 1999 into USA, the virus has spread and is now established world wide.

How does the mosquito transmit it?

People become infected when bitten by a mosquito carrying the virus. Mosquitoes become infected when they bite a bird infected with the virus. The virus enters the mosquito's blood circulates and eventually gets into the salivary glands where it can be introduced to a susceptible host when the mosquito feeds on them. The Culex quinquefasciatus is a primary vector of West Nile because it prefers to feed on birds so the chances are greatly increased of picking up the West Nile virus from an infected bird, however, it will also readily take a blood meal from people and other animals if birds are unavailable thereby completing the cycle of transmission.

Can mosquitoes transmit West Nile by biting an infected person and then biting someone who is not infected with West Nile?

No, people are dead end hosts meaning that they do not achieve the necessary levels of high viremia  for the mosquito to become infected. High viremia means that the virus has entered the bloodstream in such high numbers it can now be picked up by a blood feeding vector capable of transmitting it. People and horses can still be affected by West Nile and become ill with the disease, but cannot infect mosquitoes. Infected birds can transmit the West Nile virus to mosquitoes who feed on them because birds can sustain very high levels of viremia in their system.

CDC image explaining the transmission cycle of West Nile virus

Can you get West Nile from other ways besides from the bite of a mosquito?

In a very small number of cases, West Nile virus has been spread through blood transfusions, organ transplants, and from mother to baby during pregnancy, delivery, or breastfeeding.

Besides people and birds does West Nile make other animals sick?

Birds - West Nile is primarily a zoonotic disease of birds, where people and other animals can become accidental  "dead end"  hosts, but can show signs and symptoms of the disease. Crows and blue jays appear most susceptible to the virus, but it can severely affect other bird species as well. 

Animals other than horses - Domestic animals such as dogs, cats, rabbits and wildlife such as skunks, bats, and squirrels can become infected, but rarely get sick.

Horses - Horses can become severely ill from West Nile. A vaccine is approved for use on horses only and a veterinarian should be consulted about administering the vaccine.

If you are bitten by an infected mosquito how long does it take till you become sick?

The majority of people are asymptomatic, but if a person does exhibit signs of the disease the incubation period, meaning the period of time from when a person was bitten till symptoms of illness begin to show is variable and can range between
2-14 days. 

What are symptoms of the disease?

According to the CDC the majority of people (70-80%) who contract West Nile will not have any symptoms and are asymptomatic.

Some people may develop flu-like symptoms with a headache, fatigue, joint pains, rash, and weakness.
A few people will experience the most severe neuroinvasive form of the disease characterized  by high fever, neck stiffness, disorientation, coma, tremors, seizures, encephalitis (acute inflammation of the brain), paralysis, and even death.

For those who show symptoms of the disease, recovery can take several weeks to several months with some neurological conditions being permanent.

If you think you may have West Nile see a doctor as only a healthcare provider can make the determination by evaluating clinical signs and symptoms and ordering confirmatory lab tests.

Is there any treatment for West Nile?

There is no specific medication to treat West Nile or a vaccine to prevent it. Treatment is mainly supportive with over-the-counter analgesics to relieve mild symptoms, those with severe symptoms may require hospitalization.

Who is at risk for West Nile?

People who work or spend a great deal of time outdoors may be more susceptible to the disease because of the increased exposure to mosquitoes. People over the age of 50 may also be more at risk to the severe form of the disease.

What can I do to lessen the chances of becoming infected with West Nile?

  • Drain, or remove all standing water from your yard or property to keep mosquitoes from breeding.
  • Keep your property maintained with shrubs, bushes, and grass trimmed to avoid providing shelter for adult mosquitoes.
  • Wear an approved mosquito repellent when outdoors especially one with DEET as the main ingredient.
  • Wear light colored, loose, long sleeved shirts and pants when outside, weather permitting.

What do I do if I see a dead bird?

The state is not testing birds at this time so the bird does not have to be submitted for testing. It is also important to remember that bird die-offs can be attributed by many different reasons such as natural causes, accidents, predators, diseases other than West Nile, severe weather, chemical spills, and pesticides. 

Do not handle a dead bird or any dead animal with your bare hands. If you are going to dispose of it wear gloves when handling it, or pick it up with a dust pan and broom put it in a plastic bag and place it in waste receptacle, or you can call Farmers Branch Animal Services to pick it up at 972.919.8770.

For further information on West Nile and West Nile statistical data click on the following links: