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Virologica Sinica, 29 (3) : 176-182, 2014
Research Article
Unusual outcome of in utero infection and subsequent postnatal super-infection with different PCV2b strains
1. Laboratory of Virology, Department of Virology, Parasitology and Immunology, Faculty of Veterinary Medicine, Ghent University, Belgium

2. Department of Pathology, Bacteriology and Poultry Diseases, Faculty of Veterinary Medicine, Ghent University, Belgium

3. Department of Health Care and Biotechnology, KATHO Catholic University College of South-West Flanders, Belgium

4. CODA-CERVA, Groeselenberg 99, 1180 Ukkel, Belgium

5. Ablynx nv, Technologiepark 21, 9052 Zwijnaarde, Belgium

6. Brain Tumor Research Center, Department of Molecular Neurosurgery, Harvard Medical School and Massachusetts General Hospital, 185 Cambridge Street, Boston, MA-02114, USA

7. Division of Swine Infectious Diseases, Harbin Veterinary Research Institute, The Chinese Academy of Agricultural Sciences, Harbin, China

8. Division of Experimental Therapeutics, Toronto General Hospital Research Institute, University Health Network, Toronto, Canada
 Correspondence: Hans.Nauwynck@ugent.be
VC2002, isolated from postweaning multisystemic wasting syndrome (PMWS)-affected pig, is a mixture of two porcine circovirus genotype 2b (PCV2b) viruses, K2 and K39. Preliminary experiments disclosed short-term adverse effects of K39, but not K2, on porcine foetuses. These findings led to the hypothesis that infection of immuno-incompetent foetuses with K2 confers a status of immunotolerance, and postnatal super-infection with K39 triggers PMWS. To explore this hypothesis, nine 55-day-old foetuses were inoculated in utero (three with K2-104.3TCID50, three with K39-104.3TCID50 and three with medium), and foeto-pathogenicity examined. At 21 days post-inoculation (dpi), K2 did not induce pathology, whereas pathological effects of K39 were evident. Twenty-four 45-day-old foetuses were subsequently inoculated to examine the long-term effect of K2, including six with K2-high dose-104.3TCID50, six with K2-low dose-102.3TCID50 and 12 mock-inoculated controls. Both doses resulted in five mummified foetuses and one live-born piglet each (69dpi). K2 was recovered from all mummies. K2 and K2-specific antibodies were not detected in serum of the two live-born piglets at birth, indicating full control of K2 infection. The K2-low dose-infected piglet was immunostimulated at day 2, but not the K2-high dose-infected piglet. Both non-stimulated and stimulated K2-infected piglets were super-inoculated with K39 at day 6 or 8 (taken as 0 days post super-inoculation). Low viral replication was observed in the non-stimulated K2-K39 piglet (up to 103.3TCID50/g;identified as K39). In contrast, viral replication was extremely high in the stimulated K2-K39 piglet (up to 105.6TCID50/g) and identified as K2, indicating that K2 infection is controlled during foetal life, but emerges after birth upon immunostimulation. However, none of the piglets showed any signs of PMWS.
Key Words: PCV2;  immunotolerance;  PMWS;  porcine foetuses
Received: 17 Jun 2014  Accepted: 7 Jan 2014  Published online: 1 Jun 2014
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