Laboratory decision-making during the classical swine fever epidemic of 1997-1998 in The Netherlands

The National Reference Laboratory for classical swine fever (CSF) virus in the Netherlands examined more than two million samples for CSF virus or ser um antibody during the CSF epizootic of 1997-1998. The immense amount of sa mples and the prevalence of border disease (BD) virus and bovine viral diar rhoea (BVD) virus infections in Dutch pig herds necessitated the diagnostic efforts of the laboratory to be focused on generating CSF specific test re sults throughout the eradication campaign. Detection of 82% of the 429 outbreaks was achieved through the combined use of a direct immunofluorescence and peroxidase assay (FAT/IPA) with samples (tonsils) collected from clinically-suspected pigs. This suggests that in the majority of the outbreaks, the pigs had clinical signs that were recogn ised by the farmer and/or veterinarians, indicating the presence of CSF vir us in a pig herd. A positive diagnosis of 74% of all the tissue samples (to nsils) collected at infected pig holdings was established by FAT. More than 140,000 heparinised blood samples were examined by virus isolation, result ing in the detection of 4.5% of the infected herds. CSF virus was isolated in approximately 29% of all the blood samples collected from pigs at infect ed or suspected farms. Several serological surveys - each done within a different framework - led to the detection of 13.5% of the total number of outbreaks. The detection o f CSF virus antibody in serum was carried out by semi-automated blocking EL ISA. Approximately 28.5% of the sera which reacted in the ELISA were classi fied as CSF virus-neutralising antibody positive and 26.5% as positive for other pestiviruses following the virus neutralisation test (VNT). We concluded that two of the CSF laboratory diagnostic methods described we re determinative in the eradication campaign first, the FAT for the screeni ng of diseased pigs; and second, the ELISA and VNT when millions of predomi nantly healthy pigs needed to be screened for the presence of CSF serum ant ibody. Decision-making on the basis of results generated by either method c an, however, be seriously hindered when samples are examined from pig herds with a high prevalence of non-CSF pestiviruses. (C) 1999 Elsevier Science B.V. All rights reserved.