Porcine circovirus type 2 (PCV2) infection decreases the efficacy of an attenuated classical swine fever virus (CSFV) vaccine

The Lapinized Philippines Coronel (LPC) vaccine, an attenuated strain of classical swine fever virus (CSFV), is an important tool for the prevention and control of CSFV infection and is widely and routinely used in most CSF endemic areas, including Taiwan.

The aim of this study was to investigate whether PCV2 infection affects the efficacy of the LPC vaccine. Eighteen 6-week-old, cesarean-derived and colostrum-deprived (CDCD), crossbred pigs were randomly assigned to four groups.The pigs in groups 1 and 2 were intranasally inoculated with 0.5 mL of PCV2 in each nostril and were intramuscularly injected with 1 mL of PCV2 at 0 dpi (a total dose of 10^5.3 TCID₅₀ per pig). The pigs in groups 1 and 3 were intramuscularly injected with 1 dose of LPC vaccine/pig at 12 dpi. Therefore, all pigs were challenged with 1 mL of CSFV (ALD strain)/pig by intramuscular injection at 27 dpi (a total dose of 10^6.8 TCID₅₀ per pig). Clinical monitoring was recorded daily, and rectal temperature and sample collection of blood, saliva, and feces were taken every 3 days until 45 dpi. All surviving pigs were necropsed at 45 dpi.

Following CSFV challenge, the LPC-vaccinated pigs pre-inoculated with PCV2 showed transient fever, viremia, and viral shedding in the saliva and feces. The number of IgM+, CD4+CD8-CD25+, CD4+CD8+CD25+, and CD4-CD8+CD25+ lymphocyte subsets and the level of neutralizing antibodies against CSFV were significantly higher in the animals with LPC vaccination alone than in the pigs with PCV2 inoculation/LPC vaccination. In addition, PCV2-derived inhibition of the CSFV-specific cell proliferative response of peripheral blood mononuclear cells (PBMCs) was demonstrated in an ex vivo experiment.

These findings indicate that PCV2 infection decreases the efficacy of the LPC vaccine. This PCV2-derived interference may not only allow the invasion of wild-type CSFV in pig farms but also increases the difficulty of CSF prevention and control in CSF endemic areas.

Yu-Liang Huang, Victor Fei Pang, Chun-Ming Lin, Yi-Chieh Tsai, Mi-Yuan Chia, Ming-Chung Deng, Chia-Yi Chang and Chian-Ren Jeng. Porcine circovirus type 2 (PCV2) infection decreases the efficacy of an attenuated classical swine fever virus (CSFV) vaccine. Veterinary Research 2011, 42:115. doi:10.1186/1297-9716-42-115