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West Nile virus

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VOL: 101, ISSUE: 26, PAGE NO: 28

What is it?

What is it?
- West Nile virus (WNV) originates in birds and can be transmitted to humans through mosquito bites.

- It has not been reported in any insect, animal or person in the UK. However, some UK birds migrate from areas of WNV activity, and mosquitoes capable of carrying WNV exist in the UK. However, the mosquito population is not considered large enough to cause an outbreak.

- There were WNV outbreaks in Romania, Volgograd in Russia, New York city and Israel in the late 1990s, and an outbreak in the Camargue, France, in 2004.

- Travellers to the US or mainland Europe should be advised about prevention.

Causes
- WNV is transmitted to humans through mosquito bites.

- Potentially, WNV can be transmitted via blood transfusion and organ transplants.

Diagnosis
- The Health Protection Agency recommends that patients over 50 who develop encephalitis or viral meningitis of unknown origin between July and September be tested for WNV.

- Microbiologists may wish to consider WNV in patients with otherwise unexplained neurological or other symptoms.

Symptoms
- Symptoms can develop 3-15 days after the person is bitten by the infected mosquito.

- WNV can be asymptomatic or cause a mild flu-like illness.

- There may be longer-term symptoms such as movement disorders and sensory symptoms.

Incidence
- Since 2001 the Health Protection Agency has had WNV under surveillance in the summer.

- Symptoms and severe illness are more common in the elderly.

- WNV is more likely to be fatal in those over 50 years of age.

- More than half of encephalitis cases in England do not have known causes. There is not enough information to eliminate WNV as a potential cause.

Prognosis
- West Nile fever lasts for three to six days.

- Fewer than one per cent of infections lead to severe illness.

- Fewer than one in 1,000 of those infected with WNV will die.

Complications
- Encephalitis.

- Meningoencephalitis.

- Aseptic meningitis.

- Acute flaccid paralysis.

- Guillain-Barre syndrome.

Prevention
- No effective vaccine has been developed for WNV.

- Prevention advice includes:

- Stay indoors in warm weather from dusk to dawn (peak hours for bites from many mosquito species);

- Cover up when outdoors (wear long-sleeved shirts, full-length trousers and socks);

- Use insect repellent containing DEET (N,N-diethyl-m-toluamide);

- Eliminate all standing water where mosquitoes can lay their eggs.

Treatment
- There is no cure for WNV.

- In mild cases of a flu-like illness, the symptoms will eventually resolve.

- In more severe cases the patient will require urgent hospitalisation.

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