West Nile virus: Recognizing symptoms and protecting yourself against this mosquito-borne illness

West Nile virus is a mosquito-borne illness that can cause flulike symptoms. Most people recover, but in rare cases a West Nile virus infection can be life-threatening.

West Nile virus is found worldwide, including in the U.S., and is most commonly spread by the Culex species of mosquito. Mosquitoes carrying West Nile virus were first discovered in the U.S. in 1999. The virus is more common in the summer and fall.

What is West Nile virus and how is it transmitted?

West Nile virus is spread through a bite from an infected mosquito. Mosquitoes get the virus when they feed on birds who have the virus circulating in their bloodstream. They then spread the virus to people and other animals, including horses and dogs, when they bite them.

Most people who get West Nile virus do not have any symptoms and may not even know they have it. However, about 20% of people infected with West Nile virus will have symptoms. Most recover completely, although they may feel tired and weak for weeks afterwards.

Fewer than one in 150 people infected with West Nile virus will get seriously ill if the virus spreads to their brain. This is more common in people over age 60, and in those with health conditions that affect their ability to fight infections.

You can't get West Nile virus from another person through coughing, sneezing, or touching them. In rare cases, the virus can be transmitted from mother to fetus during pregnancy or from mother to baby during breastfeeding. Extremely rarely, it also can be transmitted through a blood transfusion or organ transplant, although blood and certain organ donations are screened for West Nile virus.

Symptoms of West Nile virus

When symptoms of West Nile virus do occur, they typically include fever, headache, body aches, weakness, and fatigue. Some people may also experience nausea, vomiting, diarrhea, rash, or swollen lymph glands.

The most worrisome complication from a West Nile virus infection is if it spreads to the central nervous system, which can cause encephalitis, meningitis, or both. Encephalitis is inflammation of the brain that can lead to brain swelling. It can be caused by infection. Meningitis refers to infection and inflammation of the membranes and cerebrospinal fluid that surround the brain and spinal cord. Doctors refer to these manifestations as West Nile virus neuroinvasive disease.

Symptoms of neuroinvasive disease include fever above 102° F, headache, stiff neck, feeling disoriented or confused, muscle jerks or convulsions, muscle weakness, numbness, and paralysis. People with any of these symptoms need immediate medical attention. In rare cases, infection with West Nile virus can cause death.

West Nile virus can invade other organs, such as the

• eye, causing blurry vision or partial vision loss, which may be temporary or permanent
• heart, leading to inflammation and possible heart failure symptoms
• liver or pancreas, with inflammation that may only be detected with blood tests.

People with neuroinvasive disease can have long-lasting symptoms for many months or even years after the infection is gone. These symptoms include persistent fatigue, memory and other cognitive problems, headache, and impaired balance.

Risk factors

You may have a higher risk of getting West Nile virus if you live in an area where the virus has been found in large numbers in humans, birds, horses, or mosquitoes. Climate change has resulted in warmer weather patterns and changes in precipitation, which in turn impact bird migration and mosquito populations.

People more likely to develop West Nile virus neuroinvasive disease:

• are over the age of 60
• have a compromised immune system due to an underlying illness, or the need to take medication that alters immune system function.

Preventing West Nile virus

There is no vaccine to prevent West Nile virus.

The best way to keep from getting sick is to protect yourself from mosquito bites:

• Use an EPA-registered insect repellent on exposed skin, avoiding areas near the eyes and mouth.
• Wear long-sleeved shirts and pants.
• Spray clothing and shoes (but not skin) with permethrin, a pesticide that kills mosquitoes and ticks.
• Cover strollers and baby carriers with mosquito netting.
• Avoid swamps and ponds, where mosquitoes commonly breed.
• Stay indoors between dusk and dawn, when mosquitoes are most active.
• Avoid having standing water around your home from buckets, planters, or birdbaths.
• Repair holes in window and door screens to keep mosquitoes out.

Treating West Nile virus

There are no antiviral drugs that kill West Nile virus. Getting rest, staying well hydrated, and taking over-the-counter medications such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) can help ease fever and body aches.

People who are severely ill may need to be hospitalized.