Porcine circovirus type 2 (PCV2)-infection and re-inoculation with homologous or heterologous strains: virological, serological, pathological and clinical effects in growing pigs

Abstract

Long-term PCV2 infection and/or concurrent infection with genotypes PCV2a and PCV2b may play a role in the development of clinical porcine circovirus-associated disease (PCVAD). To evaluate this premise, 24 11-week-old specific pathogen-free (SPF) pigs were randomly assigned to 1 of 4 treatments: negative controls, a single inoculation with PCV2a, single inoculation followed by re-inoculation with a homologous PCV2a strain, or repeated inoculations with heterologous strains (PCV2a, PCV2b). Pigs were evaluated for clinical signs daily through 140 days post inoculation (dpi). Serum samples were collected every other day from dpi 0 through 14 and weekly thereafter. PCV2-inoculated pigs were viremic by dpi 2 and 13 of 18 pigs remained viremic at 140 dpi. No statistical differences in the onset, level, or duration of PCV2 viremia were detected among treatment groups. Anti-PCV2 antibodies were detected between 14 and 28 dpi and were present through 140 dpi without statistical differences in antibody response among treatment groups. In the current study, pigs had extended viremia combined with detectable tissue PCV2 antigen levels despite the presence of high levels of anti-PCV2 antibody; however, no clinical disease was observed.

Current State of Knowledge on Porcine Circovirus Type 2-Associated Lesions

“…In experimentally infected pigs, the peak of viral replication in most tissues, independent of clinical outcome, appears to be around 14 days after exposure, 124 which corresponds also to the peak levels of PCV2 DNA in serum. 77,87 The following provides a detailed description of PCV2-associated lesions that have been reported for different organ systems ( Fig. 1).…”

Concurrent porcine circovirus type 2a (PCV2a) or PCV2b infection increases the rate of amino acid mutations of porcine reproductive and respiratory syndrome virus (PRRSV) during serial passages in pigs

“…DNA from all serum samples was extracted by using a commercially available kit (QIAamp ® DNA Blood Kit; Qiagen, Valencia, CA, USA) according to the manufacturer's specifications. PCV2 DNA was detected using previously described primers and probes targeting a signature motif located in the ORF2 capsid gene of PCV2 capable of differentiation between PCV2a and PCV2b (Opriessnig et al, 2010) with a total reaction volume of 25 l consisting of 12.5 l of commercially available master mix (TaqMan ® Universal PCR master mix), 2.5 l of DNA, 0.4 M of each primer, and 0.2 M of each probe. The cycling conditions were as follows: one cycle of 2 min at 50 • C, one cycle of 10 min at 95 • C, followed by 40 cycles of 15 sec at 95 • C and 1 min at 60 • C. A sample with a C T value greater than 40 was considered negative.…”

Genetic Characterization of Porcine Circovirus Type 2 from Pigs with Porcine Circovirus Associated Diseases in Argentina

“…A study has highlighted the importance of the order of infection in which gnotobiotic pigs inoculated with PCV-2b seven days after a PCV-2a infection, but not vice versa, cause PMWS [29]. However, when SPF instead of gnotobiotic pigs was used, results were negative [31]. Unfortunately, sequence studies with PCV-2a followed with PCV-2b in conventional pigs are still lacking.…”