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Type 2 porcine circovirus (PCV2) is now associated with several diseases, including postweaning multisystemic wasting syndrome (PMWS), reproductive disorders, porcine dermatitis and nephropathy syndrome (PDNS) and porcine respiratory disease complex (PRDC).1

It’s well known that PRRS virus is also a major contributor to PRDC. If commercial PRRSV vac-cines are administered to healthy pigs fi ve weeks prior to exposure, they are generally eff ective in decreasing the severity of clinical disease and PRRSV-induced lesions and will enhance aver-age daily gain as compared to non-vaccinated pigs. But what if pigs are vaccinated at the same time a viral infection is compromising immune response?

Few studies have been conducted investigating the eff ect of PCV2 infection on vaccine effi cacy. So Patrick Halbur, DVM, and Tanja Opriessnig, DVM, both with Iowa State University’s Veteri-nary Diagnostic Laboratory, looked at the eff ect of acute PCV2 infection on effi cacy of PRRSV vaccine to protect pigs against PRRSV-induced clinical disease and lesions.

In the study, specifi c-pathogen-free pigs were vaccinated with 2 ml of a MLV PRRS vaccine – Ingelvac® PRRS ATP – according to label instructions. All vaccinated pigs seroconverted to PRRS virus prior to challenge. Average daily gain was signifi cantly increased in both the vacci-nated/PRRSV-challenged group and the PCV2-infected/PRRS-vaccinated/PRRS-challenged groups, compared to the unvaccinated/PRRSV-challenged (see table above).

Th e PRRSV-infected non-vaccinated group had pigs with severe macroscopic and microscopic lesions consistent with PRRSV infection. Th e PRRSV-vaccinated/PRRSV-challenged group had signifi cantly less severe gross lung lesions than the unvaccinated/PRRSV-challenged group.

Th ose pigs infected with PCV2 prior to PRRSV vaccination (PCV2 infected/PRRSV vaccinated/PRRSV challenged) did have signifi cantly more severe lung lesions than the PCV2-naive/PRRSV-vaccinated/PRRSV-challenged group.

Th is work, according to the authors, provides evidence that the effi cacy of PRRSV and other respiratory vaccines, as well as control of PRDC and related diseases, may be impacted when administered to pigs at the time of PCV2 infec-tion.2 As a result, the study suggests that timing the administration of PRRS and other vaccines in advance of PCV2 challenge is important in achieving the maximum benefi t of vaccination.

VACCINE TIMING, TYPE

In addition, studies in several countries show that both the timing of swine vaccinations and the type of vaccine used can aff ect the severity of PCV2-associated disease.

Antigen carried in the vaccine’s adjuvant appears to initiate potentiation by activating immune cells, explains John Kolb, DVM, senior biologics veterinarian with Boehringer Ingelheim Vetmedica, Inc. Th is activation makes cells vulnerable to the PCV2 virus.

Firm evidence from Halbur and others show the wrong time to use some adjuvanted vaccines is when pigs are starting to circulate circovirus. According to Halbur, vaccines should be ad-ministered 2 to 4 weeks prior to PCV2 exposure, which typically happens from 6 to 8 weeks of age. Th e most common adjuvanted vaccine for pigs is mycoplasma, so producers should pay particular attention to timing with regard to PCV2 when using a mycoplasmal pneumonia vaccine.

Vaccines using mineral oil-in-water-based adjuvants have been targeted as the culprits in triggering a PCV2 reaction. Th is is signifi cant since about half of mycoplasma vaccines use mineral-oil adjuvants. Th e adjuvant is a compo-nent of many vaccines that enhances immune response to the vaccine’s antigen. Most adjuvants carry antigens in either a water-based solution or oil-based emulsion.

Of the commercial vaccines tested in a study presented at this year’s American Association of Swine Veterinarians (AASV) meeting, only one product (adjuvanted with Amphigen) potentiated PMWS.3 Previous studies have shown another vaccine containing mineral oil can stimulate PCV2 to grow to higher levels.4 Ingelvac® M. hyo does not contain mineral oil and is proven not to trigger a PCV2 reaction.3

Producers who vaccinate for mycoplasma and are concerned with the risk of PCV2-related diseases should consider Halbur’s observations on the eff ect of adjuvants: • Oil-in-water products appear to be more likely to enhance PCV2-associated lesions. • Differences likely exist among oil-in-water products (mineral oil vs. non-mineral oils). • Practitioners must weigh the negative eff ect of not controlling coinfections vs. the potential negative eff ect of vaccination. • M. hyo infection signifi cantly enhances PCV2 replication, severity of PCV2-associated lesions, and incidence of PMWS in PCV2-infected pigs. • Vaccines also may vary in effi cacy of control of mycoplasmal pneumonia.