West Nile Virus

West Nile virus is typically transmitted by mosquitoes. It first appeared in the US in 1999. It has been found most often in Africa, Asia, the Middle East, and Europe. Most infections with this virus cause no illness at all. However, about 1/5 of people infected with the virus suffer flu-like symptoms including:

• Fatigue
• Fever
• Headache
• Nausea
• Vomiting

About 1/150 people infected with the virus develop neurologic symptoms including:

• Encephalitis —inflammation of the brain
• Meningitis —inflammation of the membrane covering the brain and spinal cord
• Poliomyelitis —paralysis combined with fever and meningitis

West Nile infection is caused by a virus. Most cases occur after a bite from an infected mosquito. The mosquito picks up the disease from biting an infected bird. It then passes the virus on when it bites a person, horse, dog, or some other animal. An increase in dead birds may signal an increased risk for the transmission of this virus.

West Nile virus may also be passed through blood transfusions or organ transplants. Infected donors may not have any symptoms. Tests to screen blood for this virus may be used.

In one case, West Nile virus was passed through breast milk. Experts are studying this possible route. Breastfeeding women who feel ill or suspect that they have West Nile should talk with their doctors.

Being bitten by an infected mosquito poses the greatest threat. A small risk is associated with the following:

• Receiving a blood transfusion
• Receiving an organ transplant

Risk factors for a more severe case of the disease include:

• Having a condition that weakens the immune system, such as diabetes or HIV infection
• Age: over 50

Most people who become infected with West Nile virus have no symptoms. About 20% develop a mild condition called West Nile fever. It lasts about 3-6 days. One in 150 people develop a serious neurologic disease. It may last for weeks. Some effects, such as fatigue, memory loss, difficulty walking, or muscle weakness may be permanent. About 12% of hospitalized patients do not survive.

The majority of cases develop in late summer and early fall.

Seek medical care immediately if you develop any symptoms.

Symptoms of West Nile fever include the following:

• Body aches
• Eye pain
• Fever
• Generally not feeling well
• Headache
• Lack of appetite
• Muscle pain
• Nausea
• Rash
• Swollen lymph nodes
• Vomiting

Symptoms of serious neurologic disease include the following:

• A change in mental status
• Confusion or disorientation
• High fever
• Paralysis
• Severe muscle weakness
• Stiff neck
• Stupor

The doctor will ask about your symptoms and medical history. A physical exam will be done. He or she may inquire about:

• Outdoor activities
• Recent mosquito bites
• Travel to areas where West Nile is present
• Use of insect repellent

Some symptoms of this disease may be due to other conditions. Tests help determine the cause of the symptoms. Tests may include those listed here:

• Blood tests—for antibodies to the virus and to check for abnormalities associated with West Nile infection
• Electroencephalogram (EEG) —a test that records the brain's activity by measuring electrical currents through the brain
• Electromyography and nerve conduction studies—electrical current is measured in a muscle or passed through a nerve to determine the condition of that nerve and to determine the reason for muscle weakness
• Lumbar puncture (spinal tap) —removal of a small amount of fluid from the spinal column to check for signs of infection
• MRI scan of the head—a test that uses magnetic waves to make pictures of the inside of the head; in this case to look for abnormal areas in the brain

No definitive treatment exists for West Nile infection. The treatment given is supportive. Severe cases it may need a machine to help with breathing. Care includes IV fluids and preventing other infections. Two drugs are being studied to see if they can shorten the length of symptoms or decrease the disease’s severity. These drugs are:

• Ribavirin
• alpha-interferon

The best preventive measure is to avoid mosquito bites. Tips to do so include the following:

• Avoid going outdoors at dawn or dusk.
• Clean clogged gutters to remove pooled water.
• Remove standing water, such as birdbaths, to prevent mosquito breeding.
• Repair screens to prevent mosquitoes from entering the house.
• Use an insect repellent with the chemical DEET (N,N-diethyl-3-methylbenzamide).
• Wear long pants and long-sleeve shirts when outdoors.

Other prevention tips include the following:

• Do not donate blood if you are feeling ill or have a fever.
• Do not touch dead birds unless you are wearing disposable gloves.
• Donate your own blood before elective surgery.
• Notify the public health department if you find a dead bird.

Researchers are developing a vaccine for people at high risk.