A commercial porcine circovirus (PCV) type 2a-based vaccine reduces PCV2d viremia and shedding and prevents PCV2d transmission to naïve pigs under experimental conditions

Abstract

Porcine circovirus type 2 (PCV2) vaccination has been effective in protecting pigs from clinical disease and today is used extensively. Recent studies in vaccinated populations indicate a major PCV2 genotype shift from the predominant PCV2 genotype 2b towards 2d. The aims of this study were to determine the ability of the commercial inactivated PCV2a vaccine Circovac® to protect pigs against experimental challenge with a 2013 PCV2d strain and prevent transmission. Thirty-eight pigs were randomly divided into four groups with 9–10 pigs per group: NEG (sham-vaccinated, sham-challenged), VAC (PCV2a-vaccinated, sham-challenged), VAC + CHAL (PCV2a-vaccinated and PCV2d-challenged), and CHAL (sham-vaccinated, PCV2d-challenged). Vaccination was done at 3 weeks of age using Circovac® according to label instructions. The CHAL and VAC + CHAL groups were challenged with PCV2d at 7 weeks of age and all pigs were necropsied 21 days post-challenge (dpc). The VAC-CHAL pigs seroconverted to PCV2 by 21 days post vaccination (dpv). At PCV2d challenge on 28 dpv, 3/9 VAC and 1/9 VAC + CHAL pigs were seropositive. NEG pigs remained seronegative for the duration of the study. Vaccination significantly reduced PCV2d viremia (VAC + CHAL) at dpc 14 and 21, PCV2d fecal shedding at dpc 14 and 21 and PCV2d nasal shedding at dpc 7, 14 and 21 compared to CHAL pigs. Vaccination significantly reduced mean PCV2 antigen load in lymph nodes in VAC + CHAL pigs compared to CHAL pigs. When pooled serum or feces collected from VAC + CHAL and CHAL pigs at dpc 21 were used to expose single-housed PCV2 naïve pigs, a pooled fecal sample from CHAL pigs contained infectious PCV2 whereas this was not the case for VAC + CHAL pigs suggesting reduction of PCV2d transmission by vaccination. Under the study conditions, the PCV2a-based vaccine was effective in reducing PCV2d viremia, tissue loads, shedding and transmission indicating that PCV2a vaccination should be effective in PCV2d-infected herds.

Free to Circulate: An Update on the Epidemiological Dynamics of Porcine Circovirus 2 (PCV-2) in Italy Reveals the Role of Local Spreading, Wild Populations, and Foreign Countries

“…While the efficacy of currently available PCV-2a-based commercial vaccines to protect against clinical sign onset was demonstrated in several experimental trials [30,35,36], differences have been highlighted in terms of immune response and viremia. In fact, homologous vaccines can guarantee a better (or complete) viremia control and higher neutralizing antibodies [31,37,38] compared to heterologous ones. PCV-2 vaccines have sometimes been considered a "leaky vaccine" [36], meaning they tend to decrease transmission and infection rates in controlled situations such as in a vaccine trial or in the presence of good farm conditions, but they may not confer full protection under conditions of repeated exposure and in the presence of other cofactors [39].…”

The prevalence and genetic characteristics of porcine circovirus type 2 and 3 in Korea

“…1 ). Opriessnig et al [ 46 ] reported that the current PCV2 vaccines, which were developed based on PCV2a, can prevent PCV2d transmission to naive pigs and the vaccinated pigs showed reduced levels of PCV2d viraemia. Because mass vaccination with PCV2a-based inactivated vaccines are applied to 3–4-week-old piglets and sows in Korean farms, it was concluded that the current PCV2 vaccines reduce clinical symptoms and lesions caused by PCV2d but do not provide sterile immunity against PCV2d infection.…”

Genetic diversity and different cross-neutralization capability of porcine circovirus type 2 isolates recently circulating in South Korea

“…Nevertheless, experimental evidence from the controlled studies also supported that a viremia was effectively decreased by homologous vaccine more than heterologous vaccine in a concurrent PCV2a and PCV2d challenge [21]. Besides, viremia and shedding of virus were still observed in PCV2avaccinated pigs, although the viral load was decreased after the PCV2d challenge [22], which was observed from the studies using challenging viruses of other genotypes [12,[22][23][24]. Moreover, mutant PCV2b (PCV2d) was isolated from vaccinated farms [4,10].…”