Atypical BTV
For decades, only 24 serotypes of BTV were recognized. As for the development of new molecular technologies, in the last years novel BTV serotypes such as BTV-25 (TOV strain) from Switzerland, BTV-26 from Kuwait, BTV-27 (variants 01, 02 and 03) from Corsica (France), BTV-XJ1407 from China or a BTV strain isolated from a sheep pox vaccine (SP vaccine-derived BTV), have been described by researchers.
Since these novel BTV atypical strains have not caused economic losses, restriction measures have not been implemented in the affected regions so far. In fact, EU Regulation does not consider these new atypical strains as BTV for notification and control purposes.
From the laboratory diagnostic to have fit for purpose BTV serogroup RT-PCRs targeting to different segments of the BTV genome (p.e segments 10 and 5) is recommended, since these strains are generally detected with rRT-PCRs targeting segment 10 designed for classical strains, such as Hofmann 2008a y 2008b, but not detected, or with much lower sensitivity, with rRT-PCRs targeting other segments, such as segment 5, designed for classical strains, such as Toussaint et al. 2007.
A definitive diagnostic confirmation is only possible by means molecular methods targeted to segment 2. For it, to try virus isolation using all available methods is highly recommended to get cultured virus in high concentration to carry out a definitive characterization.