West Nile Virus

West Nile virus (WNV) is a virus spread by mosquitoes that is found in many countries around the world.

Most cases of WNV are not serious and many people have no symptoms or only mild flu-like symptoms, such as headaches, muscle aches and a high temperature (fever).

Serious problems occur in fewer than 1 in 100 people infected with the virus, but can include infection of the brain (encephalitis), spinal cord, and tissues surrounding the brain and spinal cord (meningitis), which can be fatal.

Signs of a severe infection can include muscle weakness, disorientation, seizures (fits) and loss of consciousness.

You should seek medical advice as soon as possible if you develop symptoms of WNV while you are travelling or after you return home. Make sure you tell the health practitioner where you have been travelling.

Where is WNV found?

Despite its name, WNV is found in many parts of the world, including:

Africa
west and central Asia
The Middle East
Europe, particularly southern Europe
North, Central and South America
The Caribbean
Australia

In tropical countries, it's possible to catch WNV all year round. In places with changing summer and winter seasons, such as North America, WNV is usually more common during summer and autumn.

For more information about the area you are visiting, check the Fit for Travel website.

There have been no confirmed cases of WNV originating in the UK, and cases affecting travellers returning to the UK are very rare.

Since 2002, there have only been four cases confirmed in the UK – three in people returning from North America and one in a person returning from the Middle East.

WNV is spread through the bites of infected mosquitoes. Mosquitoes become infected when they feed on infected birds. They can then spread the virus to humans and other animals they bite.

The virus cannot be spread from close person-to-person contact – for example, by kissing someone who is infected.

Symptoms

In around 4 out of 5 people, West Nile virus (WNV) does not cause any symptoms.

In some people, the virus causes mild flu-like symptoms which may include:

high temperature of 38C (100.4F) or over
headache
backache
muscle aches
sore throat
nausea
vomiting
diarrhoea
swollen lymph nodes in your neck - lymph nodes are small oval glands that form part of your immune system
a rash on your stomach, back and chest

These symptoms usually appear 3-15 days after you have been bitten by an infected mosquito, and can last for several days or weeks.

Severe symptoms

In less than 1 in 100 infected people, WNV can cause a more serious infection of the brain and nervous system, which may take the form of:

encephalitis - inflammation of the brain
meningitis - inflammation of the membranes that surround the brain and spinal cord
paralysis - loss of the ability to move one or more muscles of the body

Symptoms include:

a high temperature
headache
stiff neck
sore eyes
disorientation
shaking
seizures or fits
stupor or coma
muscle weakness

People over 50 years of age have an increased risk of developing serious symptoms of WNV if they become infected.

Causes

You can get West Nile virus (WNV) if you are bitten by a mosquito carrying the infection. The mosquitoes become infected when they bite infected birds.

Mosquitoes that carry WNV are most active at dusk and dawn, although they may also bite during the day. Read more about preventing mosquito bites.

Rarely, WNV can also be spread through:

blood transfusions
organ transplants
breastfeeding
pregnancy

However, only a small number of cases have occurred in these ways.

WNV cannot be spread from close person to person contact - for example, by kissing someone who is infected.

At risk areas

WNV is found in:

Africa, including Egypt
Asia
Australia
the Middle East, including Israel

Outbreaks of WNV have also occurred in the following European countries:

Albania
Austria
Czech Republic
France
Greece
Hungary
Italy
Poland
Portugal
Romania
Slovakia
Spain

In 1999, the virus appeared in New York. It has since spread rapidly throughout North America and more recently to:

Canada
Central and South America, including Mexico
the West Indies

The increase in cases of WNV in mainland Europe and America has led to fears that it may soon arrive in the UK. However, so far there has not been any reported case of WNV affecting someone in the UK who has not travelled abroad.

Seasonal changes

In tropical countries, it is possible to catch WNV all year round. In countries with changing summer and winter seasons, such as North America, WNV is usually more common during summer and autumn.

Diagnosis

WNV can usually be diagnosed with a blood test. If meningitis is suspected, a sample of cerebrospinal fluid (the fluid surrounding your brain and spinal cord) will be removed during a lumbar puncture and tested.

There is no specific treatment for the infection. If your symptoms are mild, they will usually get better without treatment in a few days and you won't normally experience any long-term side effects.

If your symptoms are more severe, you will need to go to hospital. Treatment may include intravenous fluids (given through a drip in your arm), medication to control seizures, and help with breathing.

Even with treatment, severe WNV can lead to long-term problems such as fatigue (extreme tiredness), muscle weakness and memory problems.

If you have symptoms of West Nile virus (WNV) while travelling, contact a doctor, local hospital or health worker as soon as possible, particularly if your symptoms are severe.

If you are travelling in a remote area, move to a more built up area as soon as possible, where you are more likely to find a doctor and medical care.

Medical history and tests

If a doctor suspects WNV, they will ask about your medical history. For example, they may ask:

where you have been travelling
whether you have been bitten by mosquitoes
what symptoms you have experienced

Blood tests

A sample of your blood may be tested for antibodies. Antibodies are special proteins produced by the immune system (the body’s natural defence) to fight infections. If antibodies are found in your blood, you may have further tests to confirm the results.

Lumbar puncture

If your symptoms are severe, you may need a lumbar puncture (also known as a spinal tap). This is a procedure to take a sample of cerebrospinal fluid (CSF), which surrounds your brain and spinal cord.

The fluid will be checked for antibodies and signs of infection, and can also be used to diagnose meningitis (inflammation of the membranes that surround the brain and spinal cord).

Imaging scans

In some cases, imaging scans of your head may be taken to rule out other conditions, such as meningitis or encephalitis (brain inflammation) caused by the herpes simplex virus. Possible imaging scans include:

Treatment

There is no specific treatment for West Nile virus (WNV).

If you have mild WNV, your symptoms will usually get better without treatment after several days or weeks.

If your symptoms are more severe, you will need to go to hospital. You may be admitted and given supportive treatments such as:

intravenous fluids, through a drip in your arm
help with breathing
nursing care

Success of treatment

If you have mild symptoms of WNV, such as a high temperature, a headache and aching muscles, you can expect a complete recovery with no long-term side effects.

If your symptoms develop into encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes surrounding the brain and spinal cord), the outlook is less good. These conditions can lead to brain damage and, in some cases, may be fatal.

See how encephalitis is treated and how meningitis is treated for more information about treating these conditions and possible complications

Preventing WNV

As there is no specific treatment or vaccine for WNV, it's best to avoid being bitten by mosquitoes when visiting affected areas. The mosquitoes that carry WNV are most active around dusk and dawn.

You should follow the advice below while you are away:

Wear loose-fitting, long-sleeved tops and long trousers that cover up your skin as much as possible.
Use an insect repellent on exposed skin, taking care to avoid your eyes. Repellents containing 50% diethyltoluamide (DEET) are thought to be the most effective.
Insect-proof screens on windows and doors and mosquito nets impregnated with insecticide over the bed will reduce mosquito bites inside. Air conditioning in the room may also help.
Avoid areas where there are likely to be large numbers of mosquitoes, such as near stagnant pools of water.

If you are travelling to areas where West Nile virus (WNV) is present, you should be aware of the risks and take appropriate precautions.

Before you go

Make sure you are aware of potential risks, particularly if you are over 50 years of age, and take steps to protect yourself against mosquito bites.

There is no vaccine for WNV, although scientists are currently working on developing one.

Travel insurance and EHIC

Before travelling, take out adequate travel insurance for countries you will be visiting. Check your insurance policy gives information about what to do if you become seriously ill, and that it covers you for repatriation on medical grounds (returning you to the UK if you become unwell).

If you are travelling in Europe, make sure you have a European Health Insurance Card (EHIC) as well as travel insurance. An EHIC is free and could save you unnecessary costs and difficulties if you need medical help while in Europe.

While you are away

You will need to ensure you are protected from biting mosquitoes at all times as there is no treatment for WNV.

If the virus is reported to be in or near the area where you are travelling, be particularly careful and pay close attention to local news about the movement of the virus.

You should follow the advice listed below while you are away.

The mosquitoes that carry WNV are most active around dusk and dawn, but some also bite during the day. You will therefore need to protect yourself if you are outside at these times.
Wear loose-fitting, long-sleeved tops and long trousers to cover up your skin as much as possible.
Use an insect repellent on exposed skin, taking care to avoid your eyes. DEET-based insect repellents are thought most effective. Always follow the manufacturer’s instructions.
Mosquitoes can bite through thin clothing, so spraying clothes with insect repellent can help.
Insect-proof screens on windows and doors and mosquito nets over the bed will reduce mosquito bites inside. Air conditioning and spraying insecticide in the room may also help.
If necessary, mosquito coils (plugs) can be burned in enclosed areas to repel mosquitoes.
Avoid areas where there are likely to be large numbers of mosquitoes, such as near water.