Expression of E2 (Gp 55) Glycoprotein of Classical Swine Fever Virus in Lymphoid Tissue and Brain of Experimentally Infected Piglets with Different Immunological Status

Classical swine fever (CSF) is a highly contagious viral disease of domestic swine and wild boars. The aim of the study was to examine samples of lymphoid tissues and brain for the presence of Classical Swine Fever Virus (CSFV) antigen in piglets that originate from vaccinated and unvaccinated sows, in order to compare the intensity of pathological lesions in conditions of different immunological status. A total of 20 crossbreed piglets of both sexes, aged 45 days were divided in three groups (G1, G2 and G3). Piglets of G1 originated from sows vaccinated with a live vaccine containing attenuated C strain CSFV. Piglets of G2 originated from unvaccinated sows. Two piglets of G3 originated from vaccinated and two piglets from unvaccinated sows and they served as the control group. All the piglets from G1 and G2 were intramuscularly inoculated with 2×10⁵ TCDI/₅₀ of CSFV, Baker strain and they died by the 22^nd day post inoculation. Immunohistochemistry was applied for immunolabeling E2 (gp55) glycoprotein of CSFV in the tonsils, mandibular lymph nodes, ileocecal valve and brain of all tested piglets. Differences were observed in the severity of lesions in the lymphoid tissue and the brain between G1 and G2 piglets. The present level of colostral antibodies was not able to protect piglets in G1 from the fatal outcome of the disease. Among others, this finding may also have an impact on vaccination policy in the future. Having in mind that vaccination of all domestic pigs with attenuated C-strain vaccine is still a mandatory control measure for CSF in Serbia, soon a non-vaccination policy should be harmonized with EU directives.