0
It is accepted that PCV1 is nonpathogenic to pigs. However, PCV1 has been isolated from cases of congenital tremors and stillborn piglets. Up till now, nothing is known about the outcome of PCV1 infections in porcine foetuses. In the present study, virus replication and pathology were examined in porcine foetuses, inoculated with two PCV1 strains at 55 days of gestation.
Three conventional sows were submitted to laparotomy at 55 days of gestation. Three foetuses of each sow were inoculated: one foetus with PCV1 cell culture strain ATCCCCL33; one with PCV1 field isolate 3384 and one foetus with medium. All foetuses were examined for gross lesions and tissue samples from various organs were taken for histopathology, virus isolation and titration on PK-15 cells and for localization of PCV1 antigens by indirect immunofluorescence staining. DNA was extracted from organs of PCV1-inoculated and adjacent foetuses and PCV1 PCR was performed.
All 6 PCV1-inoculated foetuses had a normal external appearance. Microscopic lesions include severe haemorrhages in the interlobular regions were observed in the lung tissues of two foetuses inoculated with PCV1 strain, CCL33. Microscopic lesions were not present in the other four PCV1-inoculated foetuses. High PCV1 titres (102.9, 104.6 and 104.7 TCID50/g tissue) were found in the lungs of CCL33-inoculated foetuses. All other organs were negative (<101.7 TCID50/g tissue) by virus isolation. All collected organs from 3384-inoculated foetuses were negative by virus isolation. PCV1-positive cells (28 to 121 for CCL33-inoculated and 1 to 13 for 3384-inoculated foetuses / 10 mm2 tissue) were observed in the lungs of all PCV1- inoculated foetuses. In general, heart, lungs, spleen, liver, kidney, thymus, tonsils and ileum of all PCV1-inoculated foetuses were positive by PCR. PCR and DNA sequencing recovered pure CCL33 and pure 3384 sequences from CCL33- and 3384-inoculated foetuses, respectively. All adjacent foetuses of PCV1-inoculated foetuses were negative by PCR. All mock-inoculated foetuses and their adjacent foetuses were also negative by PCR. All PCV1- inoculated foetuses had a low anti-PCV1 Ab titre of 10 to 40, except one foetus inoculated with CCL33, which had a titre of 160.
In this study, PCV1 strain CCL33 was found to be pathogenic to porcine foetuses inoculated at 55-days of foetal life. Severe haemorrhages were present in the lungs of CCL33 inoculated foetuses. These lesions were correlated with high titres (up to 104.7 TCID50 / g tissue) in the lungs. This study also shows that the lung tissue is the main target organ of CCL33. On the other hand, the field strain 3384 remained non-pathogenic to porcine foetuses. A high PCV1 load could be essential to induce pathology. From this study, it can be concluded that cell culture PCV1 replicates efficiently and produces pathology in the lungs of porcine foetuses inoculated at 55-days of foetal life.
D. Saha et al. Outcome of porcine circovirus type 1 (PCV1) infections in mid-gestational porcine foetuses. 6th International Symposium on Emerging and Re-emerging Pig Diseases: 40