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Home Eurosurveillance Weekly Release  2004: Volume 8/ Issue 32 Article 1
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Eurosurveillance, Volume 8, Issue 32, 05 August 2004

Citation style for this article: Two linked cases of West Nile virus (WNV) acquired by Irish tourists in the Algarve, Portugal. Euro Surveill. 2004;8(32):pii=2517. Available online:

Two linked cases of West Nile virus (WNV) acquired by Irish tourists in the Algarve, Portugal

Jeff Connell1, Paul McKeown2(, Patricia Garvey2, Suzanne Cotter2, Aileen Conway1, Darina O’Flanagan2, Brian P. O’Herlihy3, Dilys Morgan4, Angus Nicoll4 and Graham Lloyd5

1National Virus Reference Laboratory, Dublin, Ireland
2National Disease Surveillance Centre, Dublin, Ireland
3Department of Public Health, Eastern Regional Health Authority Dublin (ERHA), Ireland
4Health Protection Agency Communicable Disease Surveillance Centre, London, England
5Health Protection Agency, Porton Down, Wiltshire, England

On 21 July 2004, Ireland’s National Virus Reference Laboratory (NVRL) reported two suspected cases of West Nile virus (WNV) infection to the National Disease Surveillance Centre (NDSC). It is thought that both patients were exposed in the Algarve region of Portugal during a holiday stay between 26 June and 10 July. The patients developed influenza-like symptoms at the end of their holiday. One of them subsequently developed symptoms and signs of mild encephalitis. Both are recovering well.

Initial diagnosis was based on detection, at the NVRL, of IgM specific to WNV in the sera of both cases. Analysis of the second samples, collected seven days after the first samples confirmed high levels of IgM in one patient and a significant rise in IgM in the second patient. Testing at the Health Protection Agency, Porton Down, confirmed WNV infection.

These cases are the first reported cases of imported WNV infection in Ireland or in northwest Europe. Countries around the Mediterranean have seen sporadic WNV activity over the last 40 years [1,2] involving human, mammalian, avian and vector infection [3]. Autochthonous European cases appear occasionally, most recently in France [4]. Results of studies during the 1960s and 1970s suggest there may have been low level transmission of the virus in Portugal in the past [5], although these are the first reported clinical cases of WNV disease acquired in Portugal.

Portuguese authorities were notified of the initial diagnosis and have started a national action plan, which involves strengthening the mechanisms of vigilance related to human and animal health and mosquitoes.

In Ireland and the United Kingdom, information has been produced for travellers to any area (including Southern Europe) where there is a risk of encountering mosquitoes. This emphasises the possible but low risk of WNV and other vectorborne diseases in the region and advises on reducing the risk of exposure (see and

  1. Murgue B, Murri S, Triki H, Deubel V, Zeller HG. West Nile in the Mediterranean basin: 1950-2000. Ann N Y Acad Sci. 2001;951:117-26. ( [abstract]
  2. Hubalek Z. European experience with the West Nile virus ecology and epidemiology: could it be relevant for the New World? Viral Immunol 2000; 13(4):415-26.
  3. Hubalek Z, Halouzka J. West Nile fever--a reemerging mosquito-borne viral disease in Europe. Emerg Infect Dis 1999; 5(5): 643-50. (
  4. Mailles A, Dellamonica P, Zeller H, Durand JP, Zientara S, Goffette R, et al. Human and equine West Nile virus infections in France, August – September 2003. Eurosurveillance Weekly 2003; 7(43): 23/10/2003. (
  5. Filipe AR. Isolation in Portugal of West Nile virus from Anopheles maculipennis mosquitoes. Acta Virol 1972; 16(4):361

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