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

Jiménez-Clavero, Miguel Á

In the past 15 years very significant qualitative changes have occurred with regard to the epidemiology of BT, which has reached unprecedented severity in Europe Mellor, 2008, 2009; Zientara et al., 2009) . Some important trends observed in this period are: (1) a major increase in the frequency of BTV incursion events in Europe, (2) a geographic expansion of the disease, reaching latitudes close to parallel 55 • N, i.e., 15 • beyond the classic northern distribution limit for BT in Europe, (3) an ability to overwinter in locations a priori unsuitable for known competent vectors, (4) changes in some strains with regard to their pathogenicity (BTV1 strain is highly pathogenic in sheep; unpublished observation) and host range (BTV8 strain is pathogenic in European bovine), and (5) new ways of transmission (BTV8 strain can be transmitted transplacentally, affecting fetuses and newborn cattle).