Clinical, virological, immunological and pathological evaluation of four porcine circovirus type 2 vaccines.

The objective of this study was to rigorously compare the efficacy of four porcine circovirus type 2 (PCV2) vaccines of varying antigen type and dose under experimental conditions based on well-defined clinical (average daily weight gain [ADWG]), virological (evidence of viraemia), immunological (presence of PCV2-specific neutralising antibodies [NA], interferon-γ-secreting cells [IFN-γ-SCs], and CD3(+) and CD4(+) T cell subsets), and pathological (lymphoid lesion and PCV2 antigen score) criteria. A total of 60, 3-week old piglets were assigned to six groups of 10/group and were vaccinated either with 1/4 commercially available one-dose vaccines or were not vaccinated. At 7 weeks of age, vaccinated and control animals were inoculated intranasally with 2 mL of PCV2b. All pigs were euthanased and subjected to post-mortem examination at 25 weeks of age. From 9 to 16 weeks of age, the ADWG of vaccinated animals was significantly higher than that of non-vaccinates. Significant (P<0.05) differences were observed between vaccinated and positive control groups in the quantity of log-transformed PCV2b DNA in the blood and nasal swabs, log-transformed NA titres, and PCV2-specific IFN-γ-SCs at 0, 7, 14, 21, and 42 days post challenge (dpc). The proportion of CD4(+) cells at 7 and 14 dpc was also significantly different between vaccinated and control pigs (P<0.05). The histopathological lesions and PCV2-antigen scores in the lymph nodes were significantly lower (P<0.05) in vaccinated animals. All four vaccines were found to be highly efficacious in controlling experimental PCV2 challenge based on this range of criteria.