West Nile Virus

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West Nile Virus
West Nile virus EM PHIL 2290 lores.jpg

West Nile Virus

Classification : Viruses
Area : Riboviria
Empire : Orthornavirae
Phylum : Kitrinoviricota
Class : Flasuviricetes
Order : Amarillovirales
Family : Flaviviridae
Genre : Flavivirus
Type : West Nile Virus
Taxonomic characteristics
Genome : (+) ssRNA linear
Baltimore : Group 4
Symmetry : icosahedral
Cover : available
Scientific name
West Nile virus
Short name

The West Nile virus ( scientifically West Nile virus , WNV ) is an enveloped RNA virus of the type ss (+) -RNA from the Flaviviridae family known since 1937 , which occurs in both tropical and temperate areas. The virus mainly infects birds , but can also spread to humans , horses and other mammals . WNV infection in humans is symptom-free in the majority of cases (approx. 80%). The clinical symptoms are called West Nile fever .


The virus is transmitted from one host to the next by mosquitoes . A large number of different species of mosquito, especially of the genera Culex , Aedes and Ochlerotatus, are possible carriers (or vectors ) . In terms of human medical significance, however, species that transmit the virus from their reservoir hosts (i.e. mostly birds) to humans (so-called bridge vectors) are particularly important. In the genus Culex , these are mainly species from the Culex pipiens complex ( Culex pipiens / molestus and Culex pipiens / quinquefasciatus ). Another possible bridge vector is the Asian tiger mosquito ( Aedes albopictus ). This spreads as a neozoon in Europe and stings both humans and birds.

In a study published in January 2006 in the Journal of Experimental Medicine , the assumption is made that a mutation in the CCR5 gene called CCR5Δ32 (CCR5-Delta32) massively increases a person's susceptibility to the West Nile virus. This assumption was confirmed in 2008 by a meta-analysis of the serum samples from cases of West Nile fever outbreaks in 2005 and 2006 in the USA. The linked with the gene mutation elimination of 32 base pairs causes also a limited resistance against at ordinary CCR5 receptors docking end HIV . Since its discovery in 1996, this mutation has therefore formed the basis for the development of new CCR5 fusion inhibitors in the fight against AIDS . No negative effects have been known to date. It has not yet been clarified whether the CCR5Δ32 mutation affects not only susceptibility but also the severity of the course of the disease after infection with the West Nile virus. The WNV binds to integrin β-3 .

West Nile fever

West Nile fever is an infectious disease caused by the West Nile virus that occurs mainly in birds but occasionally also in mammals (including humans ).

Clinical picture in humans

The majority of WNV infections are symptom-free . About 20 percent of those infected develop flu-like , febrile symptoms with an abrupt onset that lasts for about 3–6 days. The period between infection and the onset of symptoms is 2–14 days.

Only one in 150 infected people becomes seriously ill. Older and previously ill people are usually affected by the severe course . Meningitis occurs in only some of the seriously ill and is usually benign. In rare cases, encephalitis develops , which can lead to late effects (in 50% of encephalitis cases ), inflammation of the heart or inflammation of the liver .

West Nile fever usually heals without complications.


West Nile fever is treated symptomatically . There is no specific antiviral therapy. Isolation of the sick is not necessary. If the disease is severe, it makes sense to be monitored in the hospital in order to be able to react quickly if complications arise.

History and epidemiology

Worldwide occurrence of the West Nile virus in 2006 according to the Centers for Disease Control and Prevention

During periods of drought and hot weather, the spread can increase dramatically, as the lack of flushing in the sewer system and river beds means that there is more stagnant water, e.g. B. in the form of puddles, which are used by mosquitoes as breeding water. As a countermeasure, attempts are being made to control mosquitoes, which carry the virus, with pesticides . The use of insecticides in the cargo and passenger areas of intercontinental aircraft before landing has also increased significantly worldwide.

First record (1937)

The West Nile virus was isolated for the first time in 1937 in the West Nile District of Uganda in a sick elderly woman, hence the name. It appeared in Israel in 1957 and has continued to be found in horses in France and Egypt since 1960 .

In recent years there have been epidemic clusters of encephalitis caused by the West Nile virus in Algeria (1994), Romania (1996/97), the Czech Republic (1997), the Democratic Republic of the Congo (1998), Russia (1999) and Israel (2000) have been documented. It was detected in Hungary in 2004 and in Austria in 2008 .

USA (since 1999)

With the first appearance of the West Nile virus in North America in 1999, the topic moved into the media spotlight. In the United States, the virus outbreak began in the New York City area . The first signs were birds falling dead from the trees in Central Park . Soon afterwards, the elderly in the area became infected and fell ill. Deborah Asnis (1956–2015), a doctor from the New York Bronx with experience of the tropics, believed she recognized West Nile fever and contacted USAMRIID military researchers who were able to confirm the suspicion. It has since spread across the North American continent. In the United States, which continues to be hardest hit in North America, the virus reached the west coast in annual waves until 2004. Large regional outbreaks occurred particularly in the central states in 2002 and in the Rocky Mountain states in 2003. Between 2004 and 2011, many smaller and some larger regional outbreaks with strong fluctuations were recorded, with the number of cases being interpreted as tending to decrease. However, in 2012 there was again an unexpectedly large epidemic, which particularly affected Texas with almost 40% of all cases, especially in Dallas and the surrounding area. With 236 deaths, the epidemic is considered to be the one with the most deaths to date. In addition, about half of all cases were neuroinvasive.

Statistics USA

The Centers for Disease Control and Prevention has documented the following numbers for infections and deaths in humans since 1999:

year 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Infections 62 21st 66 4156 9862 2539 3000 4269 3630 1356 720 1021 712 5674 2469 2205 2175 2149 2097
dead 7th 2 10 284 264 100 119 177 124 44 32 57 43 286 119 97 146 106 146
Source: Centers for Disease Control and Prevention

Europe (since 1960)

According to the first evidence in Europe since 1960 ( see section above ), the virus caused a total of 33 deaths in 197 people in Greece in 2010 and reappeared in other parts of the country in the following year 2011. An increase in infections was also observed in Romania in 2010, with 5 deaths in 50 documented diseases. In July and August 2012, cases of West Nile fever reappeared in Greece. There were three fatalities, 44 other people fell ill.


In 2018, the virus was able to spread again in some EU countries; in August, eleven deaths occurred within a week. In Serbia , 21 deaths have been confirmed since the beginning of the year, the authorities announced. There is a risk of infection there, especially in the capital Belgrade . In Greece , the number of people who died rose by 5 to 16 within a week, as the Keelpno authority told the ANA-MPA news agency. Most of the cases were recorded in the Peloponnese peninsula and in the rural areas around Athens and in the area around the port city of Thessaloniki. In Italy there were ten deaths between the beginning of June and August 23, according to the health authority Istituto Superiore di Sanità . The north and parts of Sardinia are particularly hard hit. A total of around 400 other infections were detected in the three countries.

In Italy, however, according to the health authority, the pathogen spreads to the nervous system in a relatively large number of patients . In total, 103 of the 255 confirmed infections were severe. For comparison, according to the Ansa news agency, only 55 infections were recorded in Italy in 2017, 27 with severe course. A person there died of the infection that year. 26 people died across Europe at the time.

In total, the EU health authority registered more than 1,460 human infections across Europe by the end of October 2018, at least 170 people died (all of 2017: 200 infections, 25 deaths); In addition, the pathogen was detected in birds and horses for the first time in Germany in 2018 ( see following section ).


Since the start of the 2019 broadcast season, 33 human cases have been reported in EU member states. Three of them with fatal outcome. For the first time a case became known in France. Three cases have been reported in horses in the same area. In neighboring EU countries, no infections were known until they became known in Germany in September 2019.

Germany (since 2018)


In Germany, the virus was first detected at the end of August 2018 in three bearded owls from an aviary in the Halle (Saale) zoo , one of which did not survive the infection. After the virus was detected, experts began collecting mosquitoes there. According to the Friedrich Loeffler Institute, mosquito traps with attractants were set up and water surfaces were searched for eggs and mosquito larvae. In Bavaria, the West Nile virus was detected in mid-September 2018 - also in a dead great gray owl - in a wildlife park in Poing in the Upper Bavarian district of Ebersberg . The virus was also detected in a goshawk kept in Bad Düben ( Saxony ) in mid-September 2018, as well as in a snowy owl and several thrushes in Berlin . In Plessa ( Brandenburg ), the virus was discovered in several horses in mid-September 2018 and in the Rostock district ( Mecklenburg-Western Pomerania ) at the end of September 2018 in a dead thrush. The probability of being infected as a person in Germany is low. The Federal Ministry of Health considers it possible that the West Nile virus will occur seasonally in humans in Germany in the future (as of 2018).


In the summer of 2019, the virus was repeatedly detected in various birds and horses in the eastern federal states; two sick horses were also detected in Bavaria in September 2019. At the end of September 2019, the first case of a human infection acquired in Germany became known. "Apparently the unusually warm summers of the last two years caused by climate change have contributed to the West Nile virus establishing itself north of the Alps," said Jonas Schmidt-Chanasit, head of virus diagnostics at the Bernhard Nocht Institute .

Reporting requirement

The occurrence of birds or horses is a notifiable animal disease in Germany . Since 2016, according to Section 7 of the German Infection Protection Act , direct or indirect pathogen detection in humans has to be reported to the health department by name if the evidence indicates an acute infection.

In Austria, illnesses and deaths are subject to reporting.

In Switzerland, the positive laboratory analysis findings for is West Nile Virus a notifiable disease and that after the Epidemics Act (EpG) in connection with the epidemic Regulation and Annex 3 of the Regulation of EDI on the reporting of observations of communicable diseases of man .

Consequences for blood donation

West Nile virus can be transmitted through blood products that have not been virus- inactivated . In individual cases, a low virus concentration in the blood products is sufficient.

In order to prevent the pathogen from being transmitted via blood products, measures must be taken by the pharmaceutical company that extracts the blood product. Infected people are not allowed to donate blood . People who have returned from a risk area for the transmission of the WNV in the last 28 days must be deferred. Alternatively, the donated blood of such persons can be tested for the pathogen or a pathogen-inactivating measure can be carried out.


Web links

Commons : West Nile Virus  - Collection of pictures, videos and audio files
Wiktionary: West Nile Virus  - explanations of meanings, word origins, synonyms, translations
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