Irene Greiser-Wilke

Classical swine fever (CSF) is a notifiable disease of domestic pigs and wild boar. It is caused by the highly contagious CSF virus and in its acute form the disease generally results in high morbidity and mortality. Due to the great economical impact an outbreak can cause to the pig industry it is one of the most important swine diseases worldwide. To limit the damage in the case of a new outbreak it is necessary to identify the virus as fast as possible. This information helps epidemiologists to trace the origin of the virus and to follow the virus spread. Genetic typing revealed that CSF virus genotypes, subgroups and types show a regional distribution making it an important tool for epidemiologists. Meanwhile, besides epidemiological data and nucleotide sequences from European isolates, information from isolates from South- and Central America, the Caribbean, Asia and recently from South Africa have become available. The data are stored in a database in the EU Reference Laboratory for CSF, accessible by the WWW (http://viro08.tiho-hanno ver.de). A new module was implemented that allows efficient automated genotyping.

The most widely used vaccines for the control of classical swine fever (CSF) in countries where it is endemic are live attenuated virus strains, which are highly efficacious, inducing virtually complete protection against challenge with pathogenic virus. In the European Union (EU), the combination of prophylactic mass vaccination and culling of infected pigs in endemic regions has made it possible to almost eradicate the disease. However, it is not possible to discriminate between infected and vaccinated animals, thus hampering disease control measures that rely on serology. Therefore, vaccination was banned at the end of 1990 before the internal common market was established in the EU. Vaccination is allowed only in severe emergencies. In addition, there are strict restrictions on the international trade in pig products from countries using vaccination. To circumvent these problems, marker vaccines which allow differentiation of infected from vaccinated animals (DIVA) have been developed. There are several approaches, ranging from protective peptides, single expressed proteins, naked DNA and chimeric viruses. To date, two subunit vaccines based on the E2 glycoprotein are commercially available and have been tested extensively for their efficacy. The accompanying discriminatory tests are based on an ELISA detecting another viral glycoprotein, the E^rns. The subunit vaccines were found to be less efficacious than live attenuated vaccines. In addition, the currently available discriminatory tests do not provide high enough specificity and sensitivity. Although there is an urgent need for more advanced marker vaccines and better discriminatory tests, the development of new DIVA vaccines against CSF is hampered by the small market potential for these products.

Bovine viral diarrhoea virus (BVDV) is a member of the genusPestiviruswithin the familyFlaviviridae. In this report, protein localization studies were performed to assess the mechanism for the release of mature virus particles from infected cells. Since BVDV is an enveloped virus, budding from either intra- or extracellular membranes is feasible. A prerequisite for the latter mechanism is the integration of viral glycoproteins into the host cell membrane. Using monoclonal antibodies (MAbs) directed against the viral envelope glycoproteins E2 and E^RNS, no specific signals were detected on the surface of BVDV-infected cells by indirect fluorescence, confocal microscopy or fluorescence-activated cell sorter analyses. Furthermore, biotin-labelled cell surface proteins of virus-infected and non-infected cells were not detected by immunoprecipitation using MAbs directed against E^RNSand E2 or the non-structural protein NS2-3. None of these proteins was detected on the cell surface. In addition, to analyse the intracellular localization of the two viral glycoproteins E^RNSand E2 and the non-structural proteins NS2-3 and NS3, subcellular fractionation of virus-infected cells followed by radioimmunoprecipitation with the MAbs were performed. These results led to the conclusion that the BVDV envelope glycoproteins E^RNSand E2 as well as the non-structural proteins NS2-3 and NS3 were almost quantitatively associated with intracellular membranes. These findings indicate that BVDV is released by budding into the cisternae of the endoplasmic reticulum and that there seems to be no correlation between the location and function of the analysed proteins.