05 August 2004
Two linked cases of West Nile virus (WNV) acquired by Irish
tourists in the Algarve, Portugal
Jeff Connell1, Paul McKeown2(Paul.McKeown@ndsc.ie),
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),
4Health Protection Agency Communicable Disease Surveillance Centre, London,
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 . Autochthonous European cases appear occasionally,
most recently in France . Results of studies during the 1960s and 1970s
suggest there may have been low level transmission of the virus in Portugal
in the past , 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
- 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.
- 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.
- Hubalek Z, Halouzka J. West Nile fever--a reemerging mosquito-borne viral
disease in Europe. Emerg Infect Dis 1999; 5(5):
- 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.
- Filipe AR. Isolation in Portugal of West Nile virus from Anopheles maculipennis
mosquitoes. Acta Virol 1972; 16(4):361
back to top