Porcine Circovirus Type 2d (PCV2d) has emerged as the predominant PCV2 genotype, accounting for 90% of the porcine circovirus-associated disease (PCVAD) infections (confirmation and sequencing) in the United States.¹ In certain circumstances, some pigs within PCV2a-vaccinated herds may present clinical signs of PCVAD. In these cases, PCV2d infection can be thought of as lingering in the “corners of the room.”

 

Study Key Findings

 

• Severe co-infection of porcine circovirus Type 2 (PCV2d) and porcine reproductive and respiratory syndrome virus (PRRSV) resulted in mortality of more than 60% of non-vaccinates, compared to only 8.2% of PCV2d vaccinates.² 

• PCV2d vaccinates demonstrated a significant reduction in lymphoid lesion severity and viral replication under severe PCVAD field conditions compared to non-vaccinates and PCV2a vaccinates.²  

• The number of pigs requiring treatment in the acute phase of PCVAD was significantly fewer among PCV2d vaccinates compared to non-vaccinates and PCV2a vaccinates.²  

 

Study Design 

 

Overview  

This randomized, blinded challenge study measured whether a PCV2d-based vaccine would provide more robust and targeted protection against PCVAD in cases of severe PCV2d co-infections (PRRS, influenza A virus in swine [IAV-S] and endemic bacteria) compared to cross-protection levels of a PCV2a-based vaccine. 

Study Design 

The study consisted of 1,410 conventional production pigs, randomized and blocked based upon weight and gender, into three groups on day 0: 470 non-vaccinated controls, 470 PCV2a vaccinates and 470 PCV2d vaccinates. On day 28, all groups were inoculated with 1 mL IM and 1 mL IN of PCV2d, as well as 2 mL IM of PRRSV 1-7-4. Mortality, percentage of treated pigs and body weights were recorded on days 0, 28, 56 and 140. On day 56, 20 pigs from each group were euthanized to evaluate gross lesions, lymphoid changes, amount of virus in tissue and viremia levels. 

 

Study Results 

 

Results Summary 

Experimental co-infection resulted in high mortality and severe PCVAD among non-vaccinates. Table 1 shows the effect of overall lymphoid lesion score and the detection of the virus. Viremia results are highlighted in Table 2.² 

 

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Average daily gain (ADG) was significantly higher among both vaccinated groups compared to non-vaccinates (Table 3). ADG was 0.03 lb./day higher among PCV2d vaccinates than PCV2a vaccinates.² 

 

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There were no significant differences in mortality between the vaccinated groups (Table 4). The PCV2d vaccinates had 1.5% lower mortality and 7.6% fewer treated pigs than PCV2a vaccinates.  

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Conclusion 

 

Under severe PCVAD conditions, PCV2d vaccinates demonstrated a reduction in lymphoid lesion severity and viral replication (serum and tissue) compared to PCV2a vaccinates. Both vaccinated groups had significantly higher ADG and significantly lower mortality rate and number of treatments than non-vaccinates. 

For swine herds experiencing severe PCVAD associated with PCV2d and co-infections, the homologous PCV2d-based vaccine can help producers protect their entire herd, including the “corners of the room” where heterologous protection can’t reach. 

 

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References 

¹ Franzo G, Cortey M, Segales J, et al. Phylodynamic analysis of porcine circovirus Type 2 reveals global waves of emerging genotypes and the circulation of recombinant forms. Mol Phylogenet Evol 2016;100:269–280. 

² Fano E, et al. Exploring the efficacy of a PCV2d-based vaccine under current severe PCVAD conditions, in Proceedings. AASV 2022. 

 

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