Studies on the Virulence of Two Field Isolates of the Classical Swine Fever Virus Genotype 2.3 Rostock in Wild Boars of Different Age Groups

Abstract

The virulence of two isolates of the classical swine fever virus (CSFV) was studied in experimentally infected wild boars of different ages. The isolates, originating from wild boars shot in Mecklenburg-Western Pomerania (isolate '1829-NVP') and in Rhineland-Palatinate (isolate '11722-WIL'), belong to the genetic subgroup 2.3 Rostock. Clinical picture, transient viraemia, virus excretion and gross lesions at necropsy as well as a failure of virus detection at the end of the experiment revealed that this virus subtype was only moderately virulent. Whereas one subadult wild boar and both 7-week-old wild boar piglets infected intranasally became sick and died, only one of three 8-week-old animals which survived after contact infection remained CSFV positive until the end of the experiment [34 days post infection (dpi)], although neutralizing antibodies were present. This underlines the role of young boars in CSF epidemics. The isolate '11722-WIL' was shed by an infected adult wild boar and was transmitted to susceptible piglets. Interestingly, all animals which became sick and died also were found to be infected with a secondary pathogen. Therefore, we assume that after infection with moderately virulent CSFV simultaneous infections with other pathogens may be important for the clinical course and the outcome of the disease as well as for a spread of the virus in field.

Effect of strain and inoculation dose of classical swine fever virus on within-pen transmission

“…At the start of the experiment, three pigs were removed from each group and intranasally inoculated. After 24 h [3,12,23], the inoculated pigs were returned to their original groups, allowing contact exposure of the remaining seven pigs. Each group was inoculated with a different virus strain or dose.…”

“…Serum and EDTA-blood samples were collected from each pig at days 0, 3,5,7,10,12,14,17,19,21,24,28, and 35 p.i. Serum samples were stored at À70°C until testing for antibodies in the ELISA and NPLA (neutralization peroxidase-linked assay).…”

“…Oropharyngeal fluid and faeces were collected at days 0, 3,4,5,6,7,8,10,11,12,13,14,15,17,19,21,24,26,28,31, 33, and 35 p.i. Oropharyngeal fluid was obtained with a gauze tampon held by a 30 cm long forceps, which was scrubbed against the dorsal wall of the pharynx behind the soft palatum.…”

Application of a Commercial Real-Time RT-PCR Assay for Surveillance of Classical Swine Fever: Evaluation by Testing Sequential Tissue and Blood Samples

“…This virus strain was originally isolated from a wild boar in Rhineland-Palatinate (Germany) and belongs to the genotype 2.3 (Rostock type) [8]. The inoculum, consisting of the original isolate passaged twice in porcine kidney cell cultures (PK 15 ), was kindly provided by Dr. V. Kaden (Friedrich-Loeffler-Institut, Germany).…”

“…Such a clinical picture is encountered with moderate to low virulent CSFV strains, like those isolated from outbreaks in wild boar and domestic pigs in Europe from the 1990s onwards [6][7][8]. In such situations, laboratory diagnostics based on virus isolation (VI) or on the detection of viral antigen, genome or specific antibodies are essential to confirm suspicious cases [9][10][11].…”