Application of genetic methods to study the relationship between classical swine fever outbreaks.

Eleven viruses isolated between 1993 and 1997 from outbreaks of classical swine fever in the neighbouring countries of Slovakia, The Czech Republic and Austria were compared after partial sequencing of the NS5B and E2 genes. Viruses collected from South-Central and West Slovakia were indistinguishable during a period of four years, even when associated with outbreaks of variable severity. Outbreaks that occurred in the Czech Republic in 1996 involved two types of virus, one of which was related to the Slovakian outbreaks, and the other to Austrian outbreaks. The results show that the molecular-genetic approach can reveal epizootiological relationships between outbreaks that would not otherwise be apparent. Furthermore, the relative genetic stability of the classical swine fever virus in the field, means that quite small sequence differences can have epizootiological significance.