West Nile virus (WNV) has been recognised since 1937 when it was first isolated in Uganda. It is primarily transmitted in birds through mosquito bites while humans are incidental hosts. Incidental infection may also occur in other mammals including horses, cats, and domestic mammals. The virus is widely distributed throughout Africa, Western Asia, Europe and Australia. Recent attention has been drawn to WNV in the USA and Canada, where this virus has caused epidemics throughout the summer months since 1999. The time course of these epidemics has paralleled the life-cycle of the mosquitoes, with a regular increase in the outbreaks from 1999 to 2002. In US, during the year 2002, 4,156 human cases and 284 deaths of WNV-caused were reported. Data available for the US 2003 indicate even an increased epidemic course in 2003. Although most people infected with WNV remain asymptomatic (~80-85%), approximately 15-20% will develop mild symptoms, which are often indistinguishable from other viral infections. These symptoms may include fever, headache, body aches, gastrointestinal complaints, eye pain, or occasionally a generalized rash, or swollen lymph nodes. It is estimated that 1 in 150-200 persons infected with WNV may develop a more severe form of the disease, with fatal encephalitis, in the worst cases, in about 1 in 1000 infections. Currently there is no specific therapy for WNV and the treatment is supportive. At the moment no vaccination is available for humans.

The rising concern of the potential for WNV spreading in Europe and the risk linked to the possibility of its transmission by blood and organs prompted the Commission to seek scientific opinions.

The Scientific Committee on Veterinary Measures relating to Public Health was asked to review the present knowledge on the WNV epidemiological situation in Europe. Their scientific opinion was adopted on 15 April 2003.

The Scientific Committee on Medicinal Products and Medical Devices was asked to give an opinion concerning the potential impact of WNV and other arthropod-borne viruses that cause encephalitis, on the safety of blood for transfusion and organs used for transplantation in the European Union. This scientific opinion was adopted on 16 October 2003.

The Scientific Committee on Emerging and Newly Identified Health Risks adopted on 17 February 2005 an updated Opinion on: 'The Safety of Human Blood and Organs with Regard to West Nile Virus'.

To strengthen and to update the knowledge of the WNV and of the other arthropod-transmitted viruses that cause acute encephalitis, the European Commission organised on 20-21 January 2003 an international seminar on 'Arboviral infections (including West Nile Virus) and their impact on public health in Europe' where international experts were invited to discuss the epidemiology of the disease and to agree key actions for the future.

Around the Mediterranean area there has been evidence that the transmission of WNV is occuring.

During October 2003, WNV infections were identified in humans and horses in France. This fact raised concern about the possibility of WNV re-emerging in some part of the European Mediterranean coast. Through the EU Early Warning and Response System (EWRS) the available information on this event was circulated in real time to all the National health authorities in the Member States in order to facilitate the identification of the potential source of the infection and to strengthen the response. The National Health Authorities responded promptly and France identified the occurrence of two human cases (one confirmed and one probable) and three equine cases (one confirmed and two probable), strongly suggesting that the infections were acquired in the Var Department (France). The up-dated information was circulated to the public through the web-site of Eurosurveillance, a European Union funded project, which aims to promote the diffusion of information on communicable diseases surveillance, prevention and control.

This confirmed that, although the incidence of certain diseases is low, rapid response in investigating potential outbreaks is an important element in controlling emerging communicable diseases in the European Union, and that a shared approach is fundamental to strengthening the capability of controlling the spread of diseases.

The concern in Europe was that the plasma derived products could contain WNV. For this reason the European Agency for the Evaluation of Medicinal Products delivered a position statement on plasma derived medicinal products on 25 July 2003.

Moreover the risk of WNV being transmitted through blood transfusion can be attributed not only to the possibility of its indigenous transmission but also to the chance that the potential donor 'pool' for many countries could include individuals with a history of recent travel during the summer months to endemic areas in North America. Measures to ensure the safety of blood in the European Union are set out in Directive 2002/98/EC which requires Member States to introduce technical requirements related to the deferral of blood donors and the testing of blood donations. These include additional tests for particular epidemiological situations. 

More information on equine animals or 'equidae' in an enlarged European Union can be found at this Animal Health and Welfare web page.