Symptoms include high fever, neck stiffness, stupor, disorientation, tremors, convulsions, severe muscle weakness, paralysis and coma. Less than 1% (about 1/150) of infected individuals develop neuroinvasive disease which typically presents as meningitis, encephalitis or acute flaccid paralysis. Most uncomplicated infections resolve in 3 to 6 days. This may include lymphadenopathy and a maculopapular or morbilliform rash on the neck, trunk, arms or leg. While most infected people are asymptomatic, the majority of clinical cases are mild and present with a sudden onset of influenza-like illness (fever, headache, myalgia). The incubation period is typically 2 to 6 days, but ranges from 2 to 14 days, and up to 21 days in immunocompromised people. People over the age of 50 are more likely to develop severe disease and about 10% of neurological infections are fatal. However, a small proportion (less than 1%) of those infected will develop more severe disease – usually encephalitis, meningitis or meningo-encephalitis. In those who develop symptoms, patients mainly present with a mild flu-like febrile illness, sometimes called West Nile fever. Most infections in humans are asymptomatic (80%). Map showing known distribution of Culex modestus mosquitoes in south-east England. modestus has not been detected elsewhere in England. Surveillance of other parts of the UK is ongoing but to date C. Mosquito surveillance activities indicate that they are now established on the land adjoining either side of the Thames estuary. The map below shows where these mosquitoes have been detected. This finding may increase the risk of WNV being transmitted in the UK. This mosquito species is the principle bridge vector (responsible for transmission between birds, horses and humans) for WNV in Southern Europe. However, in 2010 the mosquito Culex modestus was detected in the UK for the first time since 1944. Historically, therefore, the main risk of WNV for UK residents has been for those travelling abroad. To date, locally acquired WNV infection has not been reported in the UK, although there have been occasional cases of travel-associated infection. Between 19, there were more than 45,000 cases and over 2,000 deaths. In 1999, WNV spread to North America and has subsequently been detected there in all states except Alaska and Hawaii. Cases have been identified in several countries across Europe including France, Italy, Portugal and Spain. WNV was first detected in the West Nile district of Uganda in 1937 and the first large outbreak in Europe occurred in Romania in 1996. WNV belongs to the genus Flavivirus within the Flaviviridae family, along with other viruses such as dengue and yellow fever.Īlthough the reservoir of WNV is birds, the virus can be transmitted to humans and horses via mosquitoes, mainly Culex species. West Nile virus ( WNV) belongs to a group of viruses known as arboviruses which are transmitted by arthropods.
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