Background: The West Nile Virus (WNV) is a Flavivirus which is transmitted to man by means of different species of mosquitoes and causes outbreaks and sporadic cases of illness in different regions of the Old World, including the Mediterranean Basin. Europe's wetlands which comprise a stopping-off point for birds migrating from Africa are high-risk areas as regards this infection, as well as other arthropod-borne virus infections.
Methods: For the purpose of researching the prevalence of the WNV infection and other viruses transmitted similarly among the human population of the Ebro Delta, 1037 samples of serum taken in 10 towns in this area were analyzed to detect the presence of WNV antibodies and antibodies of another 12 arthropod-borne viruses (3 Alphaviruses, 8 Flaviviridae and 1 Bunyaviridae) by means of titration by inhibition of hemagglutination (HAI). In some cases, the presence of HAI-specific IgM was analyzed after breaking down the serum by centrifuging into sucrose gradients.
Results: In all, a significant degree of reaction was found to some of the viruses tested in 130 cases (12.5%; 4.1% to Alphavirus; 8% to Flaviviridae and 0.4% to Bunyaviridae). The analysis of the antibody titers revealed significant percentages of samples showing high was titers to WNV and other types of antigens. The spread for the antibody prevalence was highly uneven, being focused mainly in 3 localities located in land on the Delta (Ampolla, San Jaime and Montells), where the prevalence of Flaviviridae antibodies totaled as high as 30%, with residual levels of WNV-related IgM having been found in some serum samples.
Conclusions: These results and those obtained previously in other parts of the Iberian Peninsula suggest that the WNV is moving throughout the human population in the areas where this risk is found to exist and periodically gives rise to epidemic outbreaks. Bearing in mind the high percentage of neurological complications found to exist in the most recent outbreaks of WNV infections recorded in the Mediterranean Basin (Bucharest, Algeria), it can be thought that the WNV plays some role in the factors contributing to viral meningitis and encephalitis which occur within the population of the areas at risk within Spain.