Molecular epidemiology of Bluetongue virus in Portugal during 2004–2006 outbreak

Laboratório Nacional de Investigação Veterinária, Estrada de Benfica 701, 1549-011 Lisboa, Portugal.
Veterinary Microbiology (Impact Factor: 2.51). 10/2007; 124(1-2):25-34. DOI: 10.1016/j.vetmic.2007.04.014
Source: PubMed


After 44 years of epidemiological silence, bluetongue virus (BTV) was reintroduced in Portugal in the autumn of 2004. The first clinical cases of bluetongue disease (BT) were notified in sheep farms located in the South of Portugal, close to the Spanish border. A total of six BTV, five of serotype 4 and one of serotype 2 were isolated from sheep and cattle during the 2004-2006 epizootics. The nucleotide sequence of gene segments L2, S7 and S10 of BTV-4 prototype strain (BTV4/22045/PT04) obtained from the initial outbreak and of BTV-2 (BTV2/26629/PT05) was fully determined and compared with those from other parts of the world. The phylogenetic analysis revealed that BTV4/22045/PT04 is related to other BTV-4 strains that circulate in the Mediterranean basin since 1998, showing the highest identity (99%) with BTV-4 isolates of 2003 from Sardinia and Corsica, whereas BTV2/26629/PT05 is almost indistinguishable from the Onderstepoort BTV-2 live-attenuated vaccine strain and its related field strain isolated in Italy. Since live-attenuated BTV-2 vaccine was never used in Portugal, the isolation of this strain may represent a natural circulation of the vaccine virus used in other countries in Mediterranean Europe.

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    • "However, the arrival of BTV-2, BTV-4, BTV-9 and BTV-16 in Italy within a short span of time led the Italian authorities to consider that the risks were outweighed by the cost of not vaccinating, and wide-scale use of live attenuated BTV vaccines in Italy began in 2001. During this vaccination campaign several of the above concerns were confirmed, including the re-assortment of attenuated vaccine strains with other strains in co-infected hosts (Batten et al. 2008) and the transmission of the vaccine strains in the field (Ferrari et al. 2005; Barros et al. 2007). Subsequent experimental work also confirmed the potential for attenuated BTV vaccine strains to be transmitted by Culicoides under laboratory conditions (Venter & Paweska 2007), and to generate clinical signs in European breeds of sheep (Veronesi et al. 2005). "
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