West Nile Virus

By Wendy Innes. May 7th 2016

Largely unknown until the turn of the millennium, West Nile virus has caused quite a stir. Since it was first found in the United States in 1999, it has spread to the rest of the country causing illness in the form of West Nile fever and West Nile encephalitis.

What Is It?

West Nile virus is a disease that is spread by mosquitoes. It is part of a family of viruses called arboviruses, which is short for arthropod-borne viruses and includes any virus that is spread by the bite of a tick, mosquito or fly. More specifically, it is part of the flavivirus family of arboviruses. This particular flavivirus is in the same family as yellow fever (which is where it gets its name, flavus is Latin for yellow), dengue fever, and Japanese encephalitis.

West Nile virus made its way to the United States in 1999 when it showed up in New York, though it was discovered in Africa in 1937. Since first being identified in New York, it has since spread to the rest of the country. The virus itself can cause different problems in different people.

Mosquitoes carry the highest concentration of the virus in the late summer and early fall, which is why cases increase between August and September. Cold weather causes the mosquitoes to die off so the virus dies with them.


West Nile virus is spread to humans who have been bitten by a mosquito that is infected with West Nile Virus. A mosquito is infected when it feeds from a bird that carries the virus. Upon biting an infected bird, the mosquito picks up the disease and then passes it to any human it feeds on.

Most people who are going to get sick from it develop something called West Nile fever, which is a mild illness with flu-like symptoms, but some people develop a very serious condition called West Nile encephalitis, which is dangerous swelling of the brain that can be fatal if not treated.

Only about 1 percent of people who get West Nile virus will develop West Nile encephalitis, and of those people about 10 percent will die from it. The age of the person seems to affect the severity, as the majority of deaths have involved older people or children. Those who have a compromised immune system are also at risk.

Another, though less common, route that the virus can take causes West Nile meningitis, which affects the membrane around the brain and spinal cord. It can result in permanent damage if left untreated.

West Nile can also be spread through blood transfusions as well as from mother to child in breast milk.


The symptoms of West Nile virus vary from person to person. Some people don't know they have it and never get sick, while others become seriously ill. These are some of the more common symptoms associated with West Nile fever, the milder illness the virus can cause:

  • Abdominal pain
  • Diarrhea
  • Nausea or vomiting
  • Lack of appetite
  • Throat pain
  • Headache
  • Muscle aches
  • Swollen lymph nodes
  • Rash (about half of patients with West Nile will have a rash)

The symptoms will usually be brief, lasting from three days to about a week. They will typically resolve on their own.

More serious symptoms, which may be an indication of West Nile encephalitis or West Nile meningitis include:

  • Confusion
  • Loss of consciousness
  • Coma
  • Muscle weakness or paralysis, particularly in one area of the body
  • Neck stiffness

If any of these symptoms occur, especially in conjunction with some of the milder symptoms of West Nile virus, seek medical help immediately. If left untreated, these symptoms could lead to death, but they often do improve with treatment.


Because West Nile is a virus, and not a bacterial infection, antibiotics do not help. However, there are treatment options available.

Treatment is usually supportive, meaning that the treatment is aimed at lessening symptoms and making the person more comfortable until the virus runs its course. However, in some cases, antiviral medications may be used.

There is some evidence that points to interferon being effective at helping patients recover from West Nile virus. This drug is used for immune cell therapy, often in cancer patients, but it does show some promise in the case of West Nile encephalitis and West Nile meningitis. However, more research is still needed for this particular form of treatment.


If West Nile virus is left untreated, severe complications could result including brain damage (from West Nile encephalitis), permanent muscle weakness or paralysis (similar to polio, from West Nile meningitis), and death.

Currently there is no way to prevent someone from contracting West Nile virus, though scientists are working on creating a vaccine for humans. The best way to prevent a West Nile infection is through preventative measures to decrease the chance of a mosquito bite. Clear all standing water, avoid going outdoors when they are most active and if it is necessary to be outdoors during those times, use mosquito repellant products. Prevention goes a long way when it comes to West Nile virus.

(For more information on preventing mosquito bites, see 10 Essential Tips For Preventing Mosquito Bites.)


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