West Nile Virus (WNV) is an enveloped virus, belonging to the family Flaviviridae (origin: yellow fever virus), that can cause a flu-like symptoms and in rare circumstances, a neurological illness which could lead to death. WNV was first isolated in a woman in the West Nile district of Uganda in 1937, giving the virus its name. Today, WNV is present around the globe in Africa, Europe, the Middle-East, North America and West Asia. Since a dramatic outbreak in 1999 that spread throughout the continental U.S., the importance of this insect-borne pathogen has been recognized as a major cause of public health concern globally.
Most cases of an infection with WNV are asymptomatic (approx. 80%). About 20% of infected humans will develop the West Nile fever, leading to flu-like symptoms such as fever, headache, tiredness, body aches, nausea, vomiting and swollen lymph glands. Severe cases have been observed (one out of 150 people), especially in elderly people (over the age of 50) and in immunocompromised people showing signs of encephalitis, meningoencephalitis or meningitis. Lethality ranges between 15 - 40% in elderly people2). The incubation period is usually three to 14 days1).
The main route of transmission of WNV is through mosquito bites (commonly: Culex-, Aedes- and Mansonia species). Mosquitoes become infected when they feed on infected birds that serve as a natural host of the virus. Horses and humans can get infected, but typically do not contribute to the spread of the virus. In rare cases, human infections have occurred through organ transplant, blood transfusion and breast milk. There is only one reported case of transplacental (mother to child) WNV transmission. To date, no human-to-human transmission of WNV through casual contact or to health care workers has been reported when standard infection control precautions have been put in place1).
In the absence of a vaccine for humans, the main preventive approaches aim at raising awareness of the risk factors and measures people can take to reduce exposure to mosquito bites. The use of an insect repellent is highly recommended when doing outdoor activities as well as wearing clothing that covers the body. Many mosquitoes are most active from dusk until dawn which should be taken into consideration. In addition, local health departments have issued a number of mosquito control programmes and give instructions how to dispose of dead birds, which should not be touched with bare hands3).
In conclusion, prevention of a WNV infection through standard hygiene measures is therefore limited. But, as WNV is an enveloped virus, disinfectants should meet ‘efficacy against enveloped viruses’ acc. Robert Koch-Institute (RKI) and German Association for the Control of Virus Diseases (DVV) or ‘virucidal’ acc. DVV/RKI guideline or ‘virucidal’ acc. EN 14476(4-6). Health-care workers caring for patients with suspected WNV infection should implement standard infection control precautions.
Since mid-1990s, there has been increased spread of MNV-associated illnesses which have been especially observed in the Mediterranean area, Russia, Romania, Hungary and Austria2). Outbreak sites often occur along the migratory routes of major birds. As a matter of discussion, ongoing climate changes can influence bird migratory routes and also lead to a spread of the disease.
5) Leitlinie der DVV/RKI, Bundesgesundheitsbl. 2015, 58, 493-504
6) EN 14476:2013 + FprA1:2015
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