Research Article: Comparative studies on the pathogenicity and tissue distribution of three virulence variants of classical swine fever virus, two field isolates and one vaccine strain, with special regard to immunohistochemical investigations

Date Published: September 5, 2008

Publisher: BioMed Central

Author(s): Katinka Belák, Frank Koenen, Hans Vanderhallen, Christian Mittelholzer, Francesco Feliziani, Gian Mario De Mia, Sándor Belák.

http://doi.org/10.1186/1751-0147-50-34

Abstract

The aim of this study was to compare the tissue distribution and pathogenicity of three virulence variants of classical swine fever virus (CSFV) and to investigate the applicability of various conventional diagnostic procedures.

64 pigs were divided into three groups and infected with the highly virulent isolate ISS/60, the moderately virulent isolate Wingene’93 and the live attenuated vaccine strain Riems, respectively. Clinical signs, gross and histopathological changes were compared in relation to time elapsed post infection. Virus spread in various organs was followed by virus isolation, by immunohistochemistry, applying monoclonal antibodies in a two-step method and by in situ hybridisation using a digoxigenin-labelled riboprobe.

The tissue distribution data are discussed in details, analyzing the results of the various diagnostic approaches. The comparative studies revealed remarkable differences in the onset of clinical signs as well as in the development of the macro- and microscopical changes, and in the tissue distribution of CSFV in the three experimental groups.

The present study demonstrates that in the case of highly and moderately virulent virus variants the virulence does not affect the pattern of the viral spread, however, it influences the outcome, the duration and the intensity of the disease. Immunohistochemistry has the advantage to allow the rapid detection and localisation of the virus, especially in cases of early infection, when clinical signs are still absent. Compared to virus isolation, the advantage of this method is that no cell culture facilities are required. Thus, immunohistochemistry provides simple and sensitive tools for the prompt detection of newly emerging variants of CSFV, including the viruses of very mild virulence.

Partial Text

Classical swine fever (CSF) is a highly contagious viral disease of swine and wild boars, causing severe economic losses mainly in countries with dense pig populations. The causative agent is classical swine fever virus (CSFV), a small enveloped, positive-stranded RNA virus that belongs to the genus Pestivirus in the Flaviviridae family [1,2]. The genus also comprises bovine viral diarrhoea virus (BVDV) and border disease virus (BDV) of sheep.

Although CSF is registered as one of the most important Transboundary Animal Diseases (TADs), notifiable to OIE, the regular re-occurrence of the outbreaks in various regions of the world indicates that many questions are still poorly answered concerning the biology of this devastating disease. One of the problems is that CSF has an increasing tendency to appear and re-appear in a clinically very mild or in a completely unapparent form. By being unnoticed for a time, such mild infections may spread to large populations of pigs, causing serious epizootiological and economic consequences.

The in vivo studies and the accompanied diagnostic approaches provided useful data on the comparative pathology of three virulence variants of CSFV. The experiments confirmed the previous expectations that the three variants represent various levels of pathogenicity. Data have been obtained concerning comparative aspects of clinical manifestations, development of pathological signs and tissue distribution of CSFV variants. These data have practical importance when discussing the pathobiology of classical swine fever in the host species. The observations are useful for the early diagnosis of classical swine fever, with special regard to the detection and identification of the very mild or inapparent clinical manifestations. The present study demonstrates that in the case of the highly and moderately virulent virus variants the virulence does not affect the pattern of the spread in a pig, but influences the onset, intensity, duration and outcome of the disease. As far as diagnostic tools are concerned, IHC provides useful means of early virus detection and it indicates the localisation of the virus spread in tissues, supporting the determination of the pathogenicity levels of newly emerging viruses.

The authors declare that they have no competing interests.

KB performed the histopathological, immunohistochemical and in situ hybridisation studies, participated in the evaluation and summarizing of the findings and wrote the draft of the manuscript. FK applied for funding of the project, participated in the design of the study and performed the second animal experiment inclusive virus isolation as well as participated in the evaluation of the findings and had a major impact on the manuscript. HV participated in the design of the study and performed and evaluated the second animal experiment inclusive virus isolation. CM participated in the design and performing of the in situ hybridisation study, evaluated the findings and influenced the manuscript. FF participated in performing the second and third animal experiments inclusive virus isolation and evaluating the results. GMDM participated in the design of the study, participated in performing the second and third animal experiments inclusive virus isolation, evaluated the findings and influenced the manuscript. SB applied for funding of the project, participated in the design of the study and had a major impact on the manuscript. All authors read and approved the final manuscript.

 

Source:

http://doi.org/10.1186/1751-0147-50-34

 

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