Pathologic and virologic findings in mid-gestational porcine foetuses after experimental inoculation with PCV2a or PCV2b

Two major genotypes of porcine circovirus type 2 (PCV2) have been described: PCV2a and PCV2b. Previous studies mainly used PCV2a to experimentally reproduce reproductive failure in sows. This study aims to determine the clinical and virological outcome of surgical inoculation of 55-day-old immuno-incompetent porcine foetuses with PCV2a or PCV2b. Twelve foetuses were inoculated with PCV2: three with the post-weaning multisystemic wasting syndrome (PMWS)-associated PCV2a strain Stoon-1010, three with the reproductive failure-associated PCV2a strain 1121, three with the PMWS-associated PCV2b strain 48285 and three with the porcine dermatitis and nephropathy syndrome-associated PCV2b strain 1147. Four foetuses were mock-inoculated with cell culture medium. At 21 days post-inoculation eleven out of twelve PCV2-inoculated foetuses were oedematous and had distended abdomens, whereas one had a normal external appearance. All PCV2-inoculated foetuses had haemorrhages and congestion in internal organs and an enlarged liver. High PCV2 titres (>104.5 TCID50/g tissue) were found in all PCV2-inoculated foetuses, especially in the heart, spleen and liver. High numbers of PCV2-infected cells (>1000 infected cells/10 mm2 tissue) were observed in the hearts. PCR and DNA sequencing of the capsid gene recovered pure PCV2a and pure PCV2b sequences from PCV2a- and PCV2b-inoculated foetuses, respectively. All mock-inoculated and the remaining foetuses were normal in appearance and were PCV2 negative in virus titrations and indirect immunofluorescence stainings. The present study shows that PCV2a and PCV2b induce similar gross pathological lesions and replicate to similar high titres in organs of 55-day-old immuno-incompetent porcine foetuses.