Animal viral diseases and global change: bluetongue and West Nile fever as paradigms

Jiménez-Clavero, Miguel Á

As already mentioned, in the first half of the twentieth century WNF was considered of little importance due to the benign pathology it caused in endemic areas in equatorial Africa, where it was first isolated and diagnosed. However, after 1951 this concept began to change, as WNV was associated to severe cases of encephalitis, some fatal, in the first epidemic of WNV outside Africa, which occurred in Israel between 1951 and 1957 (Paz, 2006) . The virus circulated in Egypt in the same period, where the first eco-epidemiological studies on WNV were carried out. These studies characterized the enzootic cycle of WNV between birds and mosquitoes, identifying men and horses as susceptible to the disease but not transmitting the infection (Taylor et al., 1956) . Between 1962 and 1965 there were several outbreaks of severe illness due to WNV in the Camargue, France, affecting both horses and humans. In 1971, WNV was isolated from mosquitoes in southern Portugal, in the course of an epidemiological study starting after an outbreak of encephalitis in horses, in which 29% of the surviving horses showed seropositivity against WNV. These sporadic outbreaks occurred not only in Mediterranean countries, but also in South Africa, Russia, Romania, and India. After that, WNV in Europe remained silent for almost three decades. Its re-emergence took place almost simultaneously in the western Mediterranean (Algeria, 1994; Morocco, 1996; Tunisia, 1997; Italy, 1998 Italy, , 2008 France, 2000; and Portugal, 2004) , in central and eastern Europe (Romania, 1996; Czech Republic, 1997; Russia, 1998; Hungary, 2004; and Austria, 2008) , and in the Middle East (Israel, 1998; revisions Hubalek and Halouzka, 1999; Murgue et al., 2001; Sotelo et al., 2011a) . Very recently, another lineage of WNV (lineage 2) was detected in central Europe (Hungary, 2004) , extended to Austria (2008) and reached the Balkans and Greece in 2010, where it continues its spread (Bakonyi et al., 2006; Papa et al., 2011; Wodak et al., 2011) . Almost simultaneously, in Russia (Volga basin) a new epidemic caused by a lineage 2 WNV which is genetically different from the variant affecting central Europe, was observed, causing an increasing number of human cases since 2004 to date (Platonov et al., 2008) . This virus has extended westward reaching Romania in 2010 (Sirbu et al., 2011) .