Are different courses of classical swine fever virus infection in weaner pigs influenced by breed-related factors?

Depner, K. R., Hinrichs, U., Bickhardt, K., Greiser-Wilke, I., Pohlenz, J., Moennig, V., Liess, B.


During the outbreaks of classical swine fever (CSF) in Germany between 1993 and 1995 differing clinical courses were observed, ranging from mild symptoms to severe ones "typical" of CSF, and displaying low and high mortality rates, respectively. This diversity of clinical courses and the different patterns of distribution and severity of morphological lesions suggested that CSF viruses with varying virulence were involved in the epidemic.

However, wide variations were also observed after experimental inoculation of weaner pigs with one single CSF virus isolate IVisbek/Han95/I (Depner
and others 1996). Although the pigs were of the same age three different clinical courses were found: (i) strong clinical reaction typical of acute
CSF, (ii) chronic disease and viral persistence and (iii) mild transient
infections. These results prompted us to perform a new study using weaners of different breeds, in order to elucidate whether the genetic background of pigs influences the outcome of CSF virus infection.

Development of a nucleotide sequence data base for the molecular epidemiology of classical swine fever

Haas, L., Greiser-Wilke, I., Depner, K., Moennig, V.
Prakt Tierarzt Coll Vet XXVII (1997), 60-62.

During new outbreaks of classical swine fever (CSF) it is necessary to standardize and clear up the origin of the virus. Therefore we analyse distinct parts of the genome of CSF virus. After a polymerase chain reaction to amplify a fragment of the 5�non coding region (NCR), the product gets directly and nearly automatically sequenced. With the assistance of computer programs, the sequences are compared to saved data from former outbreaks. In case, a phylogenetic analyse can be done afterwards. We report first experiences with the development of the data base which should be able to standardize CSF virus isolates more specific until now.

Experiences with the application of an ELISA for the detection of antibodies in bulk tank milk samples in a BVD control program

Greiser-Wilke, I., Frey, H.-R., Moennig, V.
Tier�rztliche Umschau 10 (1999), 582-585


A control program with the aim of eliminating BVD virus from the Swedish cattle population is in progress since 1993. The program is based on the determination of the antibody levels in bulk tank milk using an ELISA, identification and elimination of persistently infected (PI) animals, and no vaccination. According to the level of the test values in the ELISA, all herds were classified into one of four categories. For herds in categories 0 or 1 (negative or low antibody values), it is considered improbable that they had recent contacts with PI animals. In contrast, in herds of categories 2 and 3 (high antibody values), each animal in the herd has to be analysed in order to detect the PI animals, which have to be eliminated. Similar programs are being performed with success in most Scandinavian countries. Specially due to the high prevalence of BVD virus infections and the wide use of vaccination, this program can not be recommended in countries like Germany.

Application of a computer program for genetic typing of classical swine fever virus isolates from Germany

Greiser-Wilke, I., Depner, K., Fritzemeier, J., Haas, L., Moennig, V.
Journal of Virological Methods 75 (1998), 141-150.

The commercial software program HLA I SequiTyper/I (Amersham Pharmacia Biotech), originally designed for human leukocyte antigen typing, was adapted for rapid typing of classical swine fever (CSF) virus isolates. The program compares new sequence data with those stored in a database file and calculates the most probable assignment. For generating the CSF virus sequence database, 150 bp of the 5' nontranslated genomic region (5'-NTR) from 88 German classical swine fever (CSF) virus isolates from outbreaks between 1984 and 1997 were solid-phase sequenced directly after RT-PCR amplification. Sequence alignments showed that they all belonged to the previously defined genetic group 2. Within this group, six different subgroups could be distinguished, and were designated according to the geographic location where they are either still endemic or where they most commonly appeared. The advantage of using the HLA I SequiTyper/I program is that it directly reads the sequence files as generated by the ALF sequencer (Amersham Pharmacia Biotech), making any manipulations unnecessary. In addition, a constant quality control of the raw sequence data can be achieved, as more than one sequence from the same isolate can be evaluated at once. Using this approach, new CSF isolates can be typed within two days.

Evaluation of the enzyme-linked immunosorbent assay for the rapid screening and detection of classical swine fever virus antigens in the blood of pigs

Depner, K.; Paton, D.J.; Cruciere, C.; De Mia, G.M.; Muller, A.; Koenen, F.; Stark, R.; Liess, B.
Rev. Sci. Tech. 1995 Sep; 14(3): 677-89

A workshop was convened, at which seven enzyme-linked immunosorbent assays (ELISAs) were compared with virus isolation for the detection of viraemia in serial blood samples collected from six pigs at up to fourteen days after inoculation with classical swine fever virus. All ELISAs were of the double antibody sandwich type, using monoclonal and/or polyclonal antibodies to detect a variety of viral proteins in leukocytes, or in anti-coagulated blood or serum. Compared to virus isolation, specificity of the ELISA was good: only one sample found negative by virus isolation yielded a positive result in a single ELISA. Some false-negative results occurred with samples collected at up to eight days after inoculation, but all tests found samples collected between nine and fourteen days post-inoculation to be positive. The ELISAs require less-specialised facilities and can be performed much more rapidly than virus isolation. They are therefore extremely promising tools for screening large numbers of live pigs.

Large Scale Marker Vaccine Trial on Classical Swine Fever (CSF)

EU Reference laboratory for CSF, Institute of Virology, School of Veterinary Medicine, Buenteweg 17, 30559 Hannover

The Scientific Veterinary Committee concluded in the report:"The use of marker vaccines in the control of infectious diseases in particular ,classical swine fever'", adopted on 17. September 1997 that CSF Marker Vaccines could be an additional tool of disease control especially in pig dense areas. However, further research was considered necessary. The vaccine should be tested in scenarios which are likely to occur in the field and the reliability of the discriminatory test evaluated.
According to these recommendations a large scale marker vaccine trial was financed by the EU Commission and organised by the EU Reference Laboratory for CSF. The EU Commission wanted all EU Member States to have the possibility to participate in the trial. Countries which had no isolation units for pigs participated in the testing of the discriminatory tests. The trial should test the efficacy of two marker vaccines (Bayer and Intervet) used as emergency vaccination following a disease outbreak.

Influence of CSF infection on weaner pigs within three weeks post vaccination:
Groups of ten weaner piglets were vaccinated with a marker vaccine. Five of the pigs were challenged with CSF virus. In each group the challenge was administered at different times after vaccination (e.g. 7 days, 10 days, 14 days or 21 days after vaccination). The same protocol was used with each marker vaccine. The experiments with weaner piglets were shared by the National Swine Fever Laboratories of Denmark, France, Italy and Spain. Each country performed its experiment using both vaccines.
There was a shift towards the subclinical course of CSF infection in all vaccinated animals. From 10 days after vaccination the duration of viremia and the transmission of CSF virus was reduced, although it was not completely inhibited even 21 days after vaccination. A shift from the acute towards a chronic course of CSF infection could not be observed in the marker vaccinated animals. No major differences could be observed between both vaccines. The detection of the CSF infected pigs as 'CSF positive' in the discriminatory ELISAs was not reliable.

Transplacental transmission of CSF virus to foetuses in pregnant sows:
Groups of six pregnant sows were challenged at the same stage of gestation (~55 days) but at different times after vaccination. One group was challenged 14 days after vaccination and another group was challenged 14 days after a booster vaccination. The performance of the trial was shared between the National Swine Fever Laboratories of Germany, The Netherlands and Belgium.
Transplacental transmission of CSF virus in pregnant sows could not be prevented completely. Challenge with CSF virus two weeks after a booster vaccination led to infection of fetuses. Sows challenged two weeks after a single vaccination produced fewer transplacentally CSF infected fetuses compared to non vaccinated sows. In sows vaccinated with the Bayer vaccine less CSF virus positive piglets could be detected than in sows vaccinated with the Intervet vaccine.

Sensitivity and specificity of the discriminatory ELISA:
The Ceditest Marker was used in combination with the Bayer vaccine and the Chekit Marker in combination with the Intervet vaccine as recommended by the manufacturers.
Both discriminatory ELISAs are less sensitive than conventional CSF antibody ELISAs, although they varied significantly between each other. The sensitivity of the Ceditest Marker was lower than the sensitivity of the Chekit Marker. Several reference sera with a high CSF antibody titre were scored false negative. The Chekit Marker is not CSF specific and recognised many BVD antibody positive pig sera. In contrast, the specificity of the Ceditest Marker was higher. At present there is no confirmatory test available.

Veterinary epidemiology �
a key to sustainable pig production in Switzerland

Katharina D C St�rk, Swiss Federal Veterinary Office

Sustainable animal production requires a healthy production system including healthy animals producing wholesome products. Clinically infected but also clinically healthy food animals can be a risk for consumers. Epidemiology as a discipline is concerned with the occurrence of disease or disease indicators in populations as well as with fac-tors influencing the occurrence. The knowledge of such risk factors forms the basis for preventive interventions and disease eradication programmes. By providing this infor-mation, epidemiology contributes significantly to the development and maintenance of healthy livestock. This is illustrated with the example of the enzootic pneumonia eradi-cation programme of Switzerland.
An EP-free pig population does produce more efficiently and with a reduced use of an-timicrobial drugs. This is desirable from both an economical and food safety point of view. Minimal-disease herds support sustainable production by reducing adverse impact on human and ecosystem health. The example of the EP eradication programme illus-trates that applied epidemiological research supplements disease control programmes with critical information and is thus a key tool in developing sustainable animal produc-tion systems.

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