West Nile virus

West Nile virus is a viral infection carried by mosquitoes. It belongs to a group of viruses called flaviviruses. West Nile virus/Kunjin is a strain of the virus that is found in some regions of the world.

The virus has been detected in birds, mosquitoes and people in some areas, but human disease from the Kunjin strain is considered rare.

Many infected people have no symptoms#

Many people who are infected never feel unwell. About 20% of those infected develop mild, flu-like illness.

The Kunjin strain is less virulent (less severe) than other strains of West Nile virus. Symptoms, when they occur, can appear from 7 to 28 days after a person becomes infected.

People who have developed antibodies to the Kunjin strain may be immune to further West Nile virus infection.

Symptoms#

If symptoms do occur, they can include:

• Fever
• Headache
• Muscle aches
• Lethargy or fatigue

In very rare cases (less than 1%), the infection can lead to serious complications. These include meningitis (infection or inflammation of the membranes surrounding the brain) and encephalitis (inflammation of the brain). These conditions can result in death or serious disability.

Warning signs that need urgent medical attention include:

• Severe headache
• Neck stiffness
• Sensitivity to bright light (photophobia)
• Seizures or fits (especially in young children)
• Drowsiness or confusion

If any of these occur, seek medical attention immediately.

How it spreads#

People become infected when they are bitten by a mosquito carrying the virus. Culex annulirostris is the most important mosquito species known to carry it. This mosquito breeds in fresh water and is most active at dusk and dawn.

Mosquitoes pick up the virus when feeding on water birds such as herons. There is no evidence that the virus spreads directly from one person to another.

Diagnosis and treatment#

Blood tests can show whether a person has been infected with West Nile virus recently or in the past.

There is no specific treatment. Care aims to support the patient and ease symptoms while the body fights the infection. Some people may need hospital care, depending on how severe the infection is and whether complications develop.

Preventing infection#

There is no preventive vaccine, so your best protection is to avoid mosquito bites. To reduce your risk:

• Wear long, loose-fitting, light-coloured clothing.
• Use effective insect repellents containing DEET or Picaridin, applied regularly according to the manufacturer’s instructions.
• Avoid mosquito-prone areas, especially at dusk and dawn when mosquitoes are most active.
• Fit fly screens properly to windows and external doors.
• Reduce mosquito breeding sites around your home by removing stagnant water.
• Empty and wash water-holding containers regularly.

Key points#

• A person infected with the virus may have no symptoms.
• About 20% of people infected develop mild flu-like symptoms.
• Symptoms can appear from 7 to 28 days after becoming infected.
• Many people infected with the Kunjin strain never develop symptoms.
• There is no specific treatment or vaccine, so avoiding mosquito bites is the best protection.

Where to get help#