West Nile Virus - Situation in Austria

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Changed on: 26.08.2019

West Nile Virus - Situation in Austria

The risk of getting a West Nile Fever infection in Austria is very low at present. A total of 17 West Nile Virus cases of local infections were recorded in Austria to date (as of May 2017). Deaths have not been reported to date.

The first cases of local West Nile Fever infections recorded in Austria in three patients (two in 2009, one in 2010) were documented in the course of a retrospective examination in 2012 [Aberle S, Heinz FX (2012) West Nile Virus Infections in Austria. virus epidemiologic information No. 12/12. Available at: http://www.virologie.meduniwien.ac.at/fileadmin/virologie/files/Epidemiologie/2012/1212s.pdf, query from: 9th May, 2017]. Two cases “imported” from Serbia were documented in 2012. There were no human infections with West Nile Fever in Austria in 2011 and 2013.

The West Nile Virus was diagnosed for the first time in a blood donor in 2014. Eight cases, including five blood donors, were found in 2015 [Céline M Gossner CM, Laurence Marrama L, Marianne Carson M, Franz Allerberger F, Paolo Calistri P, Dimitrios Dilaveris D, Sylvie Lecollinet S, Dilys Morgan D, Norbert Nowotny N, Marie-Claire Paty M-C, Danai Pervanidou D, Caterina Rizzo C, Helen Roberts H, Friedrich Schmoll F, Wim Van Bortel W, Andrea Gervelmeyer A. West Nile virus surveillance in Europe: moving towards an integrated animal-human-vector approach. Eurosurveillance, Volume 22, Issue 18, 04 May 2017. Available at: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=22789, query from 9th May, 2017]. Six human infections, including four in blood donors, were recorded in 2016.

The first time that a West Nile Virus lineage 2 infection was detected in birds of prey in Austria was in Lower Austria in August 2008. The first clinical case of horse encephalomyelitis caused by the WNV was recorded in Vienna in August 2016. An investigation in the same stables also found evidence of the virus in the mosquitoes examined. The main symptoms found in horses are fever and neurological symptoms, such as diffuse encephalitis and encephalomyelitis in combination with ataxia and paresis. This is often followed by coma and death. The morbidity rate in horses is relatively high. About 20-43 % of infected horses show neurological symptoms. Approximately 25–45 % of  the infected animals may die. The first fatal case in a horse was recorded in Lower Austria autumn 2016.

Prophylactic measures for stables:

  • Mosquitoes are particularly active at dawn and dusk. Thus, the horses should be taken to the stables during that time. 
  • Seal windows with mosquito nets, keep stable doors closed at night and dawn. 
  • Reduce the number of mosquitoes: mosquitoes deposit their eggs in standing water. Thus, cover rain barrels and clean out troughs on a daily basis, to avoid proliferation. 
  • Keep the washing area dry: make sure that the water flows into the drain at the animals‘ washing areas.
  • Vaccines for horses: there are a number of authorised vaccines. Horses should be inoculated twice at an interval of three to five and four to six months, followed by an annual jab.

Cats and dogs usually show no symptoms when infected. The only available vaccine is for horses. There is no vaccine for humans that can be used for prevention. Avoiding mosquito bites is the easiest way to prevent WNV infections.

Number of Detected West Nile Virus Cases in Austria, 2010-2016

Detection of WNV in: 2010 2011 2012 2013 2014 2015 2016
Humans 1 0 0 0 2 8 6
Horses 0 0 0 0 0 0 2
Birds 0 0 0 1 1 2 0
Mosquito Pools 0 1 1 0 2 3 2

Mosquitoes as Vectors

The West Nile Virus is transmitted by an unusually large number of mosquito species for Flaviviruses. Possible vectors include a multitude of different mosquito species, in particular Culex, Aedes and Ochlerotatus. ). Within the genus Culex, these are most notably Culex pipiens, C. quinquefasciatus, C. molestus, C. restuans, C. salinarius und C. tarsalis. There is repeated evidence of local mosquitoes transmitting West Nile Fever in Austria. [Kolodziejek J, Seidel B, Jungbauer C, Dimmel K,  KolodziejekM, Rudolf I, Hubálek Z, Allerberger F, Nowotny N. West Nile Virus Positive Blood Donation and Subsequent Entomological Investigation, Austria, 2014. PloS One. 2015; 10(5): e0126381. Available at:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4427133/, query from 9th May, 2017].

Culex pipiens, as a parasite vector in birds and humans, is the most important vector in the transmission chain between birds and humans in Austria. The virus can survive the winter in this common mosquito and begins its reproduction cycle inside the insect the following spring. Mosquitoes of the Culex genus spend the entire winter in sheltered spaces, such as basements, barns, tunnels and caves. The West Nile Virus is transferred via a mosquito bite, following an incubation period of 10-15 days in the female mosquito. One of the most important factors for the presence of the virus are higher temperatures: while the virus titre increases only very gradually in the insect at 18 °C, the virus proliferates rapidly at 30 °C and the probability of a transmission is high. 

Isolated for the first time in a female patient with fever in Uganda’s West Nile District in 1937, the West Nile Virus was only present in Africa and parts of Asia and Southern Europe before 1999. Additionally, the first cases of encephalitis caused by the West Nile Virus lineage 1 in humans, cats, dogs and horses in North America also appeared in 1999. Since then, the virus has spread across the entire North American continent. It has been isolated in the USA, Canada, Mexico, the Caribbean and in Central and South America, to date.

The dominant West Nile Virus genotype in Europe is lineage 2. There have only been a few larger local outbreaks, in addition to the sporadic infections recorded in Southern, Central and Eastern Europe, such as in Bucharest (393 infections, 17 fatalities) in 1996, in Volgograd (826 infections, 40 fatalities) in 1999 and in Northern Greece (292 infections and 35 fatalities) in 2010.

The Disease: West Nile Fever

About 80 % of infections are asymptomatic. Only 20 % of patients show influenza-like symptoms with sudden, high fever (= mild West Nile fever), muscle pain, headaches, gastrointestinal symptoms, possible cold symptoms, swollen lymph nodes and rashes. The incubation period is 2-8 days. The most prominent symptoms will subside within 7-10 days. 

West Nile meningitis or encephalitis may follow in individual cases (0.7 %). Neuroinvasive disorders with disorientation, coordination disorders, swallowing problems, extreme fatigue and dizziness combined with altered behaviour and mental states are all typical signs. These are followed by hepatitis, myocarditis (inflammation of the heart muscles), nephritis (inflammation of the kidneys), pancreatitis (inflammation of the pancreas) and splenomegaly (enlarged spleen), coupled with a long period of recovery. Patients with compromised immune systems and individuals aged over 50 have a higher risk of developing the severe form of the disease. In places where West Nile fever outbreaks have occurred abroad, it has been observed that individuals over 50 years and people who spend large amounts of time outdoors suffered above average infection Levels.

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This is how you can help contain mosquitoes.
[Translate to English:] Behälter, in denen sich Wasser sammeln kann, kippen oder unter Dach lagern (Töpfe, Kübel, Autoreifen etc.); Regentonnen abdecken; Blumenuntersetzer vermeiden; Kinderplanschbecken wöchentlich entleeren; Dachrinnen auf Verstopfung kontrollieren; Behälter, in denen sich Wasser sammeln kann, nicht im Freien stehen lassen.

How do I avoid mosquito bites

The common mosquito is a so-called synanthrope (wild animals that benefit from an association with humans and the artificial habitats created by them) with their breeding grounds very close to human habitats. Adult mosquitoes remain within a radius of 200 metres. This is also the point where the first step of fighting them begins: everyone can help prevent the mosquitoes from creating their nests. Rain barrels, dog bowls filled with water, flower pot saucers, basically all containers with water provide ideal breeding grounds for mosquitoes. The mosquito population can be reduced by taking away these containers. The folder “Helfen Sie mit, die Gelsen einzudämmen” (Help in containing mosquitoes) illustrates simple but effective ways to help fight mosquitoes. Mosquitoes not only have painful bites and are annoying, they are also disease vectors: However, the infection risk in Austria is very low, although it can rise when going on holiday abroad. As a result, prophylactic measures should be used on journeys.

  • Apply insect repellent when outdoors: sweat and carbon dioxide (on breath) attract mosquitoes. 
  • Wear long-sleeved clothes when there are lots of mosquitoes around. This applies especially during dawn and dusk, when many mosquito species are active.
  • Seal windows and doors with mosquito nets. Additional mosquito nets over the bed help when there are vast numbers of mosquitoes. Leave the bedroom windows closed overnight, if necessary. 
  • Mosquitoes deposit their eggs in any accumulation of water. You can reduce the number of mosquitoes in your own vicinity by covering rain barrels and changing the water in bird baths and dog bowls at least once every week.
  • The mosquito problem should always be part of considerations when building. Badly planned building and water management projects may lead to a mass proliferation of mosquitoes.
  • Measures to mitigate the reproduction of mosquitoes, such as reducing their breeding places or – in special situations – the targeted application of substances that prevent the growing of the larvae in water reservoirs, are sensible in the field of landscape planning.

Information for Animal Owners: What Can I do to Avoid Mosquito Bites?

Links

• AGES Folder “West Nile Virus“ (2016)
• AGES Folder „Helfen Sie mit, die Gelsen einzudämmen“(Help in containing mosquitoes)
• AGES Video „Helfen Sie mit, die Gelsen einzudämmen" (Help in containing mosquitoes)
• AGES Information on the West Nile Virus pathogen 
• BMGF Information on the West Nile Virus
• Kommunikationsplattform VerbraucherInnengesundheit (Communications Platform Consumer Health)
• National Reference Center for Flavivirus Infections in Humans at the MedUni Vienna
• National Reference Laboratory for Equine Encephalomyelitis Viruses and Reference Activities West Nile Fever in Animals at AGES
• European Centre for Disease Prevention and Control (ECDC) on West Nile Fever 

 

 


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