Reproduction of PMWS in immunostimulated SPF piglets transfected with infectious cloned genomic DNA of type 2 porcine circovirus

Abstract

-Postweaning multisystemic wasting syndrome (PMWS) is a recently emerged disease affecting pigs. Type 2 porcine circovirus (PCV2) has been associated with this syndrome although other factors are required in association with this virus for PMWS expression. The aim of this study was to investigate whether general immunostimulation (injections of keyhole limpet hemocyanin emulsified in incomplete Freund adjuvant and of thioglycollate medium) could strengthen the severity of PMWS in six-week-old specific-pathogen-free (SPF) piglets transfected with pure tandem-cloned PCV2 DNA by the intramuscular route. Non-immunostimulated piglets transfected with the viral clone did not present clinical signs but only mild pathological microlesions characteristic of PMWS. These piglets seroconverted and high viral genome loads and infectious titers were detected in the lymphoid organs at the end of the trial. Mild-to-moderate forms of PMWS were generally observed in the immunostimulated transfected piglets, as well as one severe form for a piglet (8003) which died. These piglets with mild-to-moderate forms had higher DNA loads than the transfected-only animals. Thus, viral replication was enhanced by immunostimulation. This is the first time that clinical PMWS has been reported in an SPF immunostimulated piglet infected with a pure inoculum consisting of tandem-cloned PCV2 DNA. This result confirms that PCV2 is the agent of PMWS and that immunostimulation could enhance PMWS in SPF piglets transfected with a PCV2 DNA clone. porcine circovirus type 2 / immunostimulation / tandem-cloned DNA / PMWS

Quantification of porcine circovirus type 2 (PCV-2) within- and between-pen transmission in pigs

“…Infection of SPF pigs by PCV-2 without immune enhancement [9,14] or coinfection [2,10,13] is known to lead to subclinically infected animals with mild symptoms and lesions as we observed in this study. However, even if no disease was reproduced as expected, the infection was successful and led to a similar genome load as observed in field conditions, in naturally sub-clinically infected animals [8,30].…”

“…The PCV-2 statuses of the inoculated and contact pigs were monitored once and twice a week respectively until 42 days post-inoculation (dpi) using real-time PCR [9] in sera to assess the PCV-2 genome load. Pigs were declared as infected as soon as PCV-2 genome load was detected in the serum.…”

“…The number of PCV-2 genome copies was assessed by a real-time PCR based on TaqMan technology as described previously [9]. For each PCR run, a positive control obtained from lymph node tissue from PCV-2-infected pigs, was included.…”

“…This algorithm relies on a SEIR (Susceptible, Exposed, Infectious, Recovered) model with a constant latent period E of six days (infected but not infectious), according to the results of an immunoperoxydase monolayer assay (IPMA) [9] on sera taken from inoculated pigs at 4 and 7 dpi (data not shown). Briefly, sera were tested for infective particles in cell cultures (PK15 monolayer).…”

The comparative profile of lymphoid cells and the T and B cell spectratype of germ-free piglets infected with viruses SIV, PRRSV or PCV2

“…Microscopic lesions consist of hepatitis, nephritis, damage of lymphoid tissue, and extensive lymphopenia [16][17][18]. Full expression of PMWS appears to require secondary factors such as coinfection, vaccination or other factors that activate the immune system [17][18][19]. Lymphopenia may predispose the host to immunosuppression leading to further complications in the form of co-infections with bacterial and viral pathogens.…”