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Hot topic - West Nile virus explained29 July 2004 - written by Bupa's Health Information Team In recent years, West Nile virus has spread to North America and parts of Europe, and there are concerns that it could eventually reach the UK. How concerned should we be? What is West Nile virus?West Nile virus is a virus that mainly affects birds and mosquitoes. It can also be passed from mosquitoes to humans. How do people catch West Nile virus?People can catch West Nile virus via mosquito bites. If a bird is infected, the virus is present in its blood. If a mosquito takes blood from an infected bird, it may take up the virus as well. People can become infected with West Nile virus if they are bitten by an infected mosquito. The mosquitoes involved in the transmission of West Nile virus usually prefer to take blood from birds, but sometimes take blood from humans or other animals. What are the symptoms?In 80 percent of people with West Nile virus, there are no symptoms. About 20 percent of infected people get mild flu-like symptoms, such as a high temperature, headache and body aches. There may also be a rash or swollen lymph glands. This is called West Nile fever. Less than one percent of people with West Nile virus get a severe infection. They may develop encephalitis (inflammation of the brain) or meningitis (inflammation of the membrane surrounding the brain and spinal cord) or both. Symptoms can include headache, high temperature, stiff neck, muscle weakness and paralysis, sore eyes, disorientation, fits and coma.³ How long after a bite from an infected mosquito do symptoms develop?The incubation time is usually between three and 15 days. How long do symptoms last?Symptoms usually last a few days, although they can last several weeks. ³ Symptoms of severe disease (encephalitis or meningitis) may last several weeks, although some effects of the disease on the brain may be permanent. ³ What's the treatment for West Nile virus?There is no specific treatment for West Nile virus. Most people with West Nile virus get better by themselves. The flu-like symptoms West Nile fever, such as headache and body aches, can be treated with normal painkillers such as paracetamol. However, if anyone in the UK develops West Nile virus, they must se their GP who may recommend that they go to hospital as a precaution. People with severe West Nile virus often need hospital treatment, such as IV fluids or help with breathing.³ Is it life-threatening?Very occasionally, people with severe West Nile virus infection can die. Who is most at risk of dying from West Nile virus?Most deaths from West Nile disease have been reported in people over the age of 50, who generally suffer more severe disease. Can it be passed from person to person?No. West Nile virus cannot be passed directly from one person to another by close contact, including cuddling, kissing, sneezing or coughing. West Nile virus is usually only passed on via infected mosquitoes. But even if a mosquito bites someone who has West Nile virus and then bites someone else, its unlikely to spread because people rarely develop high enough virus levels in their blood to infect mosquitoes. A very small number of cases have been reported following blood transfusion and organ transplantation in North America. All donated blood in North America is now screened for West Nile virus. Could I get West Nile virus from a blood transfusion in the UK?The risk of transfusion-related West Nile virus in the UK is very low. People who have travelled to the US or Canada cannot donate blood for 28 days after the time they leave. Blood donated by anyone who travelled to the US or Canada during the summer and autumn will also be tested for West Nile virus before it is used for patients.¹ Do we have West Nile virus in the UK?There have been no reported cases of West Nile virus in people in the UK. No active cases have been found in UK birds either. However, certain species of birds in the UK may have been exposed to the virus (for example, birds that have migrated to the UK from other countries). What is the risk of West Nile virus affecting people in the UK?The risk of West Nile virus causing human cases in the UK is low. For many centuries, birds from areas of Africa with West Nile virus have been migrating to Europe, and despite this, West Nile virus infection in people in Europe is rare. The species of mosquito that transmit West Nile virus are present in the UK, but probably not in high enough numbers for transmission to humans to be likely. Where is West Nile virus found in the world?West Nile virus has been found in insects, animals and people in many countries, including those in Africa, Asia and the Middle East. In the 1990s outbreaks in people were reported in Europe (eg Romania, Russia, France and Italy). West Nile virus was then found in people in North America (New York) in 1999. In 2002, 4156 people were reported as infected with West Nile virus, and 284 people died as a result.² Why did West Nile Virus spread to North America?It is not clear why West Nile virus spread to North America, but it may be the result of infected birds or mosquitoes being imported. Another possibility is that the spread resulted from environmental changes, including climate and land use. These might have increased mosquito populations to levels high enough allow transmission to humans. Is West Nile disease related to season?West Nile disease is transmitted all year round in hot climates such as African and Middle Eastern climates. In temperate climates such as northern North America and Russia, West Nile encephalitis cases tend to happen in late summer or autumn, which are usually much hotter than the UK. Should I take any precautions in the UK?There is no need to take any particular precautions in the UK. However, the UK Chief Medical Officer has drawn up a plan in case a person in the UK is found to be infected.¹ Advice about precautions may change in that case. Could I get West Nile disease when travelling abroad?The risk is low, but it is possible. If you are bitten by mosquitoes infected with West Nile virus, you could become infected. Two people in Ireland have been found to have caught West Nile disease after travelling to the Algarve in Portugal. Should I take any precautions when I travel abroad?The UK Health Protection Agency recommends that if you are travelling to areas where mosquitoes are a problem, including North America and Europe, you should take anti-mosquito precautions. This is particularly important for people over 50. The HPA advice for travellers4:
Further informationBupa resources:
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