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Summary
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Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) are the major causes of porcine respiratory disease complex (PRDC) and lead high mortality in nursery-to-finish pig herds. In order to study the susceptible age of PCV2 and PRRSV and pathogenesis of PCV2- and PRRSV-induced PRDC, we collected serum samples of various ages from 5 herds to assay susceptible age of PCV2 and PRRSV and collected 50 lung tissues of PRDC to assay the cytokine regulation. The titer of anti-PRRSV neutralizing antibody was lowest between 6 and 8 week-olds and was significantly raised after 14 week-olds. On the contrary, the morbidity of PRRSV reached peak at 8 week-olds and then gradually decreased over time. The titer of PCV2 ORF2 antibody in 3 herds without PCV2 vaccination was gradually decrease over time, however, the morbidity of PCV2 in various age among 3 herds was significantly different and was positive correlation with the mortality in nursery-to-finish pig herds. In addition, more than 80% PRDC cases were caused by PCV2 and/or PRRSV. These results indicated that PCV2 and PRRSV infections are also the major problem in pig herds of Taiwan.
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