Outcome of experimental porcine circovirus type 1 infections in mid-gestational porcine foetuses

Abstract

BackgroundPorcine circovirus type 1 (PCV1) has been described as a non-cytopathic contaminant of the PK-15 cell line. Several experimental infections with PCV1 failed to reproduce disease in pigs. Therefore, PCV1 is generally accepted as non-pathogenic to pigs. To our knowledge, nothing is known about the outcome of PCV1 infections in porcine foetuses. This was examined in the present study.ResultsNine foetuses from three sows were inoculated at 55 days of gestation: three with 104.3 TCID50 of the PCV1 cell culture strain ATCC-CCL33, three with 104.3 TCID50 of the PCV1 field strain 3384 and three with cell culture medium (mock-inoculated). At 21 days post-inoculation, all 6 PCV1-inoculated and all 3 mock-inoculated foetuses had a normal external appearance. Microscopic lesions characterized by severe haemorrhages were observed in the lungs of two foetuses inoculated with CCL33. High PCV1 titres (up to 104.7 TCID50/g tissue) were found in the lungs of the CCL33-inoculated foetuses. All other organs of the CCL33-inoculated foetuses and all the organs of the 3384-inoculated foetuses were negative (< 101.7 TCID50/g tissue) by virus titration. PCV1-positive cells (up to 121 cells/10 mm2 in CCL33-inoculated foetuses and up to 13 cells/10 mm2 in 3384-inoculated foetuses) were found in the heart, lungs, spleen, liver, thymus and tonsils. PCR and DNA sequencing of Rep recovered CCL33 or 3384 sequences from CCL33- or 3384-inoculated foetuses, respectively.ConclusionsFrom this study, it can be concluded that cell culture PCV1 can replicate efficiently and produce pathology in the lungs of porcine foetuses inoculated at 55 days of foetal life.

Origin of porcine circovirus type 2 (PCV2) from swine affected by PCV2‐associated diseases in Croatia

“…How PCV2 is involved in the pathogenesis of PCVDs remains unclear. Koch's postulates establishing PCV2 as the causative agent have been partially satisfied for only PCV2-SD and PCV2-RD (Ellis and others 1998, Krakowka and others 2001, Saha and others 2011). …”

Identification of three new type-specific antigen epitopes in the capsid protein of porcine circovirus type 1

“…PCV1 has therefore been considered non-pathogenic to pigs. But recently, PCV1 has also been described as pathogenic to porcine foetuses [14].The PCV1 genome consists of a circular single-stranded DNA of 1759 nt [13]. It has a genomic organization similar to that of PCV2, containing two major open reading frames (ORFs): ORF1, which encodes two proteins (Rep and Rep 0 ) that are involved in virus replication [11,12], and ORF2, whose product is the major structural capsid protein.…”

“…PCV1 has therefore been considered non-pathogenic to pigs. But recently, PCV1 has also been described as pathogenic to porcine foetuses [14].…”

Studies on transmission of porcine circovirus type 2 (PCV2)

“…antigen was detected in the fetal myocardium. As only fetal heart tissues were investigated in the current study, the tissue tropism of PCV1-2 is unknown, and PCV1 has been previously identified in fetal lung tissues (20), PCV1-2, although unlikely, could have been present elsewhere in the fetal tissues. As a PCV1-2 chimeric virus was identified in Canadian swine herds, the risks of introduction of a live-attenuated PCV2 vaccine for use in breeding age females needs to be seriously considered before approval.…”

“…Recently, PCV1 has been associated with hemorrhages in lung tissues of fetuses experimentally inoculated with the PK-15 cell-derived PCV1 isolate but not a field isolate of PCV1 (20).…”