Efficacy of bivalent vaccines of porcine circovirus type 2 and Mycoplasma hyopneumoniae in specific pathogen-free pigs challenged with porcine circovirus type 2d

Abstract

Background: Porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae (MHP) are economically significant pathogens in the pig industry. The use of combined vaccines against PCV2 and MHP is one of the most effective ways of protecting pigs from both diseases, and it has become a part of general management.

Objectives: This study evaluated the efficacy of two new bivalent vaccines of PCV2 and MHP (Myco-X and Myco-XD) in SPF pigs. Myco-X and Myco-XD are a combined vaccine of MHP with PCV2b and PCV2d, respectively.

Methods: Sixteen pigs were divided into four groups: Myco-X-vaccinated challenged, Myco-XD-vaccinated challenged, unvaccinated challenged, and unvaccinated unchallenged. Two milliliters of Myco-X were administered intramuscularly, and 0.5 mL of Myco-XD was injected intradermally at 3 wk of age. The pigs were challenged with virulent PCV2d via the intramuscular and intranasal route 4 wk post-vaccination.

Results: All vaccinated pigs showed effective reduction of the clinical signs, the PCV2d load in the blood and nasal swab samples, as well as lung and lymphoid tissue lesions in the challenge test. Compared to unvaccinated challenged animals, the vaccinated challenged animals showed significantly higher (p < 0.05) levels of anti-PCV2 IgG, PCV2d-specific interferon-γ (IFN-γ), and anti-MHP IgG.

Conclusions: Based on clinical, microbiological, serological, and pathological assessments, this study confirmed that both combined vaccines could protect pigs against PCV2 infection caused by PCV2d. On the other hand, further research on the efficacy evaluation of these new vaccines against the MHP challenge and PCV2d/MHP co-challenge is needed.

Keywords: Mycoplasma hyopneumoniae; Porcine circovirus; bivalent vaccine.

Fig. 1. Bodyweight changes. (A) Mean body weight. (B) Average daily weight gain between 4 to 7 WPV in the different groups.

WPV, wk post-vaccination; PCV2d, porcine circovirus type 2d; G1, Myco-X PCV2d challenge (Myco-X-vaccinated); G2, Myco-XD PCV2d challenge (Myco-XD-vaccinated); 2dC, PCV2d challenge control (unvaccinated challenged); NC, negative control (unvaccinated unchallenged). ^aDifferent superscripts indicate a significant difference (p < 0.05) between groups.

Fig. 2. Quantification of PCV2 DNA. (A) Mean values of the genomic copies of PCV2 DNA in the serum samples. (B) Mean values of the genomic copies of PCV2 DNA in the nasal swab samples in the different groups.

PCV2, porcine circovirus type 2; PCV2d, porcine circovirus type 2d; G1, Myco-X PCV2d challenge (Myco-X-vaccinated); G2, Myco-XD PCV2d challenge (Myco-XD-vaccinated); 2dC, PCV2d challenge control (unvaccinated challenged); NC, negative control (unvaccinated unchallenged). ^aDifferent superscripts indicate a significant difference (p < 0.05) between groups.

Fig. 3. Immunological responses against PCV2 and MHP. (A) Mean values of the anti-PCV2 IgG levels. (B) Mean values of the anti-MHP IgG levels in the different groups.

PCV2, porcine circovirus type 2; MHP, Mycoplasma hyopneumoniae; IgG, immunoglobulin G; PCV2d, porcine circovirus type 2d; G1, Myco-X PCV2d challenge (Myco-X-vaccinated); G2, Myco-XD PCV2d challenge (Myco-XD-vaccinated); 2dC, PCV2d challenge control (unvaccinated challenged); NC, negative control (unvaccinated unchallenged). ^a,bDifferent letters indicate a significant difference (p < 0.05) between groups.

Fig. 4. Mean values of the PCV2d-specific IFN-γ in the different groups.

PCV2d, porcine circovirus type 2d; IFN-γ, interferon-γ; G1, Myco-X PCV2d challenge (Myco-X-vaccinated); G2, Myco-XD PCV2d challenge (Myco-XD-vaccinated); 2dC, PCV2d challenge control (unvaccinated challenged); NC, negative control (unvaccinated unchallenged). ^a,b,cDifferent letters indicate a significant difference (p < 0.05) between groups.

Fig. 5. Gross lung lesions in lungs in different groups. (A) G1, (B) G2, (C) 2dC, and (D) NC groups.

PCV2d, porcine circovirus type 2d; G1, Myco-X PCV2d challenge (Myco-X-vaccinated); G2, Myco-XD PCV2d challenge (Myco-XD-vaccinated); 2dC, PCV2d challenge control (unvaccinated challenged); NC, negative control (unvaccinated unchallenged).

Fig. 6. Histopathological findings in the lungs, tonsils, and lymph nodes in different groups (H&E ×100). (A) G1, (B) G2, (C) 2dC, and (D) NC groups.

PCV2d, porcine circovirus type 2d; G1, Myco-X PCV2d challenge (Myco-X-vaccinated); G2, Myco-XD PCV2d challenge (Myco-XD-vaccinated); 2dC, PCV2d challenge control (unvaccinated challenged); NC, negative control (unvaccinated unchallenged).

Fig. 7. Immunohistochemistry of PCV2 antigen in the lungs, tonsils, and lymph nodes in different groups (×200). (A) G1, (B) G2, (C) 2dC, and (D) NC groups.

PCV2, porcine circovirus type 2; PCV2d, porcine circovirus type 2d; G1, Myco-X PCV2d challenge (Myco-X-vaccinated); G2, Myco-XD PCV2d challenge (Myco-XD-vaccinated); 2dC, PCV2d challenge control (unvaccinated challenged); NC, negative control (unvaccinated unchallenged).