[Analysis of bulk milk samples using polymerase chain reaction: an additional tool for bovine viral diarrhea monitoring]. / Untersuchung von Sammelmilchproben mittels Polymerasekettenreaktion: Eine ergänzende Methode für die BVD-Uberwachung.

Programmes for the eradication and control of infections with bovine viral diarrhea virus (BVDV) concentrate on the identification and elimination of persistently infected (PI) animals. The identification of these animals is mainly based on the detection of viral antigen using ELISA techniques. Protocols detecting viral nucleic acid using RT-PCR have been described recently. Due to high costs the German model recommends screening of animals of 9 up to 36 months of age. Screening of bulk milk samples using RT-PCR technology would allow a system independent of age. The aim of the present study was to test whether bulk milk samples (1433 including max. 50 animals each) collected in four counties of Lower Saxony are suitable for a complementary identification of PI animals via RT-PCR. Thirty-one bulk milk samples derived from 27 dairy herds were BVDV positive, corresponding to 2.3 % of the herds analysed in this study. Two samples first scored doubtful. Follow up tests revealed lactating PI animals in most cases (18). In other cases the epidemiological status of the herd, i.e. high sero-prevalence and/or presence of PI animals among non-lactating cattle, suggested a transient infection detected in the first bulk milk sample. These results demonstrate that monitoring of lactating cattle of any age using RT-PCR is a very sensitive, economically effective additional method for the identification of PI animals.

Pestiviruses: a review.

Pestiviruses comprise a group of economically important animal pathogens, namely hog cholera, bovine viral diarrhoea and border disease viruses. The viruses are serologically closely related and share a common host spectrum, i.e. pigs and numerous domestic and wild living ruminants. Interspecies transmissions occur frequently. Despite some common features in their natural hosts, pathogenesis of pestivirus-induced disease is complex; especially some aspects of highly fatal mucosal disease of cattle are still enigmatic. Pestiviruses are amongst the smallest enveloped single-stranded RNA viruses with an icosaeder-shaped nucleocapsid. They are currently classified as Togaviridae. However, based on recent progress in the molecular characterisation of the viruses their taxonomic real-location seems inevitable. Viral RNAs studied so far display one large open reading frame and in infected cells no subgenomic RNA is demonstrable. Structural proteins are coded for by genes located at the 5' end of the RNA. The majority of the genome codes for 2-3 nonstructural proteins. Virions are composed of a major and one minor envelope glycoprotein with molecular weights of 53 and 48 kD respectively. The core is composed of a small protein with a molecular weight of 20 kD. Analysis of viral proteins with monoclonal antibodies has yielded detailed information about the antigenic composition of both structural and nonstructural proteins.

Most alphaviruses share a conserved epitopic region on their nucleocapsid protein.

Fourteen hybridoma cell lines secreting antibodies against the Semliki Forest virus nucleocapsid protein were established and employed for identification of conserved epitopes among 27 alphavirus types and subtypes. Using an antibody capture test, the antibodies were found to cross-react to variable degree with alphaviruses belonging to the Semliki Forest, western encephalitis and eastern encephalitis complexes, as well as Middelburg and Ndumu. None of the antibodies reacted with either Venezuelan equine encephalitis or Barmah Forest virus. Due to their reactivity with Fort Morgan, Y62-33, Whataroa and chikungunya, the monoclonal antibodies were divided into six reactive types. Competition assays showed that the epitopes for all the types were either identical or clustered on a single domain of the nucleocapsid protein.