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

Jiménez-Clavero, Miguel Á

This new wave of WNV in Europe differed from the former in several aspects. Firstly, its duration: this wave has extended further in time, to the point that it is still ongoing with increasing intensity, Since the late 1990s sporadic outbreaks have occurred in the same locations in consecutive years. For example, in the Camargue, France, after the first outbreak of 2000, new outbreaks occurred in (Zientara et al., 2009 , and virus isolates available from these outbreaks were very closely related phylogenetically (Sotelo et al., 2011b) . This fact supports that the virus is circulating endemically in the area since 2000 or before. In Morocco, an outbreak occurred in 2003 affecting horses, similar to that produced in 1996, and again, WNV isolates from both outbreaks show a striking similarity at the genetic level (Sotelo et al., 2011b) . In Italy an outbreak occurred in horses in Tuscany in 1998, and 10 years later, in 2008, a serious epidemic took place in the Po river delta, which affected hundreds of horses and produced some human cases. Since then the same area has been affected by epidemic waves of WNF every year to date, and again, the viruses isolated in consecutive years are genetically closely related (Sotelo et al., 2011b) . In Spain the first WNV isolation took place in 2007 from golden eagles . Later, an outbreak affecting horses and humans occurred in 2010, which continued in 2011 (OIE, 2010) . Apparently, all the viruses isolated since 1996 from western Mediterranean countries (France, Italy, Morocco, Portugal, and Spain), have a close phylogenetic relationship, which, as noted above, supports a single introduction in the area of a virus which has been able to remain endemic and spread in the area during all these years (Sotelo et al., 2011b) . Secondly, the affected territory is more extended in the present epidemic wave than in the previous one. In fact there are more countries affected than ever in Europe. Moreover, the number of clinical cases is higher (Sotelo et al., 2011a) . Exceptionally severe, with unusually high mortality in humans, were the epidemics on an "urban cycle" that occurred in 1996 in Bucharest, Romania (about 1,000 human cases, 396 severe, 17 deaths), in 1999 in Volgograd, Russia (approximately 1,000 human cases, 40 deaths), in [1998] [1999] in Israel (about 400 human cases, 35 deaths) and in Greece in 2010-2011 (336 human cases, 40 deaths; Anonymous, 2011) . Finally, the range of WNV variants circulating in Europe is presumably higher than in the previous wave: While all isolates analyzed from European outbreaks occurring between 1951 and 1971 belonged to lineage 1, more recent European outbreaks have revealed not only two"classic"WNV lineages (1 and 2), but also up to three "unusual" WNV variants, including Rabensburg strain or lineage 3, Krasnodar strain or lineage 4 and putative lineage 7 from Spain.