West Nile virus infections spike in southern and central Europe

West Nile virus (WNV) infections have sharply increased in 2018 as compared to the previous 4 years. This is largely due to the early start of the 2018 transmission season in the WHO European Region, which normally lasts from July to October. This year’s season has been characterized by high temperatures and extended rainy spells, followed by dry weather. Such weather conditions have been conducive to mosquito breeding and propagation.

A total of 401 autochthonous human WNV infections have been reported by European countries this year, as of 16 August, including 22 deaths, according to data from the European Centre for Disease Prevention and Control (ECDC). The most affected countries include Serbia (126 cases), Italy (123), Greece (75), Hungary (39) and Romania (31). These areas have all been affected by WNV in the past.

Who is at risk?

Residents of or travellers to WNV-affected areas are at risk of WNV infection. Only 20% of infected individuals will show WNV symptoms. Certain population groups (e.g. the elderly, pregnant women, immunocompromised people) are at higher risk of developing a neuroinvasive form of the disease.

Given the favourable weather conditions this season, the virus may spread to new areas, thus affecting new populations never exposed to the virus before. In these areas, low general awareness about WNV among the public and both human and animal health professionals might challenge early detection of cases.

Protect yourself with the “4 D’s”

Currently, there is no human vaccine against WNV. To prevent infection, people in affected areas should follow the “4 Ds” of WNV prevention:

  1. Dusk – This is the prime feeding time for mosquitos and therefore when people are most likely to get bitten. Avoid outdoor activity at peak biting times.
  2. Dress – Wear light-coloured long-sleeved shirts and trousers.
  3. DEET – Use insect repellent that contains DEET (diethyltoluamide), strictly following the user instructions on the package.
  4. Drainage – Make sure mosquito breeding sites (flower pots, water dishes, bird baths and children's swimming pools) are drained so that they do not become breeding grounds for mosquitos.

In addition, people are advised to wear gloves and other protective clothing while handling sick animals or their tissues, and during slaughtering and culling procedures.

About WNV

WNV infection is transmitted to humans through the bite of an infected mosquito, primarily of Culex genus. Infection can also happen through blood transfusion or organ/tissue/cell transplants. In addition to humans, WNV can also cause severe disease and death in horses and donkeys. Birds are the natural reservoir hosts of the virus.

Although 80% of infected people will show no symptoms, in 20% of cases the virus will develop into West Nile fever (WNF) – a febrile, influenza-like illness characterized by an abrupt onset of moderate to high fever with headache, sore throat, muscle and joint pain, backache, fatigue, nausea and diarrhoea.

There is no specific treatment for WNF in humans other than symptomatic therapy. This often involves hospitalization, intravenous fluid therapy and respiratory support. Recovery is rapid in children and slower in adults, but usually complete, and is often accompanied by long-term muscle pain and weakness.

Less than 1% of infected people present with severe symptoms, such as meningitis or encephalitis. Of patients developing the neuroinvasive form of the disease, 4–14% will die.

Since human WNV infection was first described in Europe in the 1950s, many outbreaks have been reported in the European Region. The most serious European outbreak of WNV thus far occurred in Romania in 1996–1997.

WHO’s public health advice and support

WHO works with countries to reduce the risks of WNV and other vector-borne infectious diseases. It supports them in providing public health advice to citizens at risk, and implementing prevention, surveillance and control activities, as well as effective management of cases and outbreaks.

The implementation of the Regional Framework for Surveillance and Control of Invasive Mosquito Vectors and Re-emerging Vector-borne Diseases 2014–2020 will be discussed at the 68th session of the WHO Regional Committee for Europe, to be held in Rome, Italy on 17–20 September 2018.