West Nile virus

A mosquito bite can turn into something much more severe if you are infected with West Nile virus. Mosquitoes transmit this virus after they bite an infected bird and then bite a person. While not all people with infected mosquito bites will get the disease, it can be a very severe occurrence for those with weakened immune systems and the elderly. If it is diagnosed and treated quickly, the outlook for West Nile virus recovery is good, according to the National Institutes of Health.

West Nile infection is caused by a virus transmitted by mosquitoes. Most people infected with West Nile virus don't experience any signs or symptoms, or may experience only minor ones, such as fever and mild headache. However, some people who become infected with West Nile virus develop a life-threatening illness that includes inflammation of the brain.

Mild signs and symptoms of a West Nile virus infection generally go away on their own. But severe signs and symptoms — such as a severe headache, fever, disorientation or sudden weakness — require immediate attention.

Exposure to mosquitoes where West Nile virus exists increases your risk of getting West Nile virus infection. Protect yourself from mosquitoes by using mosquito repellent and wearing clothing that covers your skin to reduce your risk.

Mild infection signs and symptoms

About 20 percent of people develop a mild infection called West Nile fever. Common signs and symptoms of West Nile fever include:

  • Fever
  • Headache
  • Body aches
  • Fatigue
  • Back pain
  • Skin rash (occasionally)
  • Swollen lymph glands (occasionally)
  • Eye pain (occasionally)

Serious infection signs and symptoms

In less than 1 percent of infected people, the virus causes a serious neurological infection. Such infection may include inflammation of the brain (encephalitis) or of both the brain and surrounding membranes (meningoencephalitis). Serious infection may also include infection and inflammation of the membranes surrounding the brain and spinal cord (meningitis), inflammation of the spinal cord (West Nile poliomyelitis) and acute flaccid paralysis — a sudden weakness in your arms, legs or breathing muscles. Signs and symptoms of these diseases include:

  • High fever
  • Severe headache
  • Stiff neck
  • Disorientation or confusion
  • Stupor or coma
  • Tremors or muscle jerking
  • Lack of coordination
  • Convulsions
  • Pain
  • Partial paralysis or sudden muscle weakness

Signs and symptoms of West Nile fever usually last a few days, but signs and symptoms of encephalitis or meningitis can linger for weeks, and certain neurological effects, such as muscle weakness, may be permanent.

Causes

Typically, West Nile virus spreads to humans and animals via infected mosquitoes. Mosquitoes become infected when they feed on infected birds. You can't get infected by touching or kissing a person with the virus.

Most West Nile virus infections occur during warm weather, when mosquito populations are active. The incubation period — the period between when you're bitten by an infected mosquito and the appearance of signs and symptoms of the illness — ranges from three to 14 days.

West Nile virus is present in areas such as Africa, parts of Asia and the Middle East. It first appeared in the United States in the summer of 1999 and since then has been found in all 48 contiguous states.

Other possible routes of transmission

In a few cases, West Nile virus may have been spread through other routes, including organ transplantation and blood transfusion. However, blood donors are screened for the virus, substantially reducing the risk of infection from blood transfusions.

There have also been reports of possible transmission of the virus from mother to child during pregnancy or breast-feeding, but these have been rare and not conclusively confirmed.

Risk factors

Your overall risk of getting West Nile virus depends on these factors:

  • Time of year. The majority of cases in the United States have occurred between the months of July and September.
  • Geographic region. West Nile virus has been reported in most of the United States, but Midwestern and Southern states have recently had the highest incidence rates.
  • Time spent outside. If you work or spend time outdoors, you have a greater chance of being bitten by an infected mosquito.

Risk of serious infection

Even if you're infected, your risk of developing a serious West Nile virus-related illness is extremely small — less than 1 percent of people who are infected become severely ill. And most people who do become sick recover fully. You're more likely to develop a severe or fatal infection based on:

  • Age. Adults older than age 50 are at higher risk of infection.
  • Health. Those who have a weakened immune system, such as after receiving an organ transplant with anti-rejection medication, are at greater risk of infection.
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