Porcine circovirus (PCV) poses a serious threat to pig farms in my country, with PCV2 and PCV3 being the most harmful, and mixed infections are common. Studies have found that infection patterns vary significantly among pigs of different ages, making precise prevention and control difficult.
A study recently published in the journal Animals detailed the prevalence of four porcine circoviruses (PCV1, PCV2, PCV3, and PCV4) in pigs of different ages on large-scale swine farms in my country, providing valuable frontline data and key findings.
The study, conducted between January and March 2024, covered 30 breeding farms (with sows between 1,000 and 3,000, and gilts vaccinated against PCV2) and 27 finishing farms (with over 4,000, and commercial pigs vaccinated between 14 and 21 days of age) across 14 provinces across China. The researchers collected 415 testicular fluid samples (each pooled from 20 litters) collected at castration from suckling piglets (3 to 5 days of age), as well as 1,583 serum samples from sows, nursery pigs (7 to 10 weeks of age), and finishing pigs (14 to 20 weeks of age).
Introduction
Porcine circoviruses (PCV1, 2, 3, and 4) are prevalent in Chinese pig farms. PCV2 and PCV3 are the most harmful, often leading to slower growth and reduced resistance in pigs. They are also susceptible to other diseases such as blue ear disease and mycoplasma pneumonia, resulting in significant losses. Although PCV4 has also been detected, its infection rate is very low.
Research Results
1. Distribution of PCVs in Pigs at Different Stages
The study identified infection patterns in pigs of different ages:
· PCV-3 was the most common virus in the testicular fluid of suckling pigs (75.4%), followed by PCV-1 (56.9%) and PCV-2 (31.1%). The detection rates of PCV-3 and PCV-1 in testicular fluid were significantly higher than in blood.
· PCV-2 was most frequently detected in nursery pigs (31.4%) and finishing pigs (43.1%). PCV-1 was found more frequently in finishing pigs (28.7%) and sows (26.7%), significantly higher than PCV-3 in finishing pigs (8.5%).
PCV-3 was most commonly detected in sows (46.1%), significantly higher than in nursery pigs (17.8%) and finishing pigs (8.1%).
PCV-4 was the least common, with extremely low detection rates in all pig populations (0.0%-2.2%).
Figure 1. PCV Detection Rates in Pigs of Different Ages
Red boxes indicate mixed samples.
TS: testicular fluid sample; SS: serum sample.
Conclusion: The prevalence of PCV2 and PCV3 in pigs exhibits a distinct "one rises, the other falls" pattern. PCV2 is most prevalent during the fattening stage, while PCV3 primarily affects lactating piglets and sows.
2. Ct Value Distribution in Pigs of Different Ages
The study (Figure 2) showed that viral load (lower Ct values indicate more virus) varied across different viruses and pig groups. PCV3 load was highest in the testicular fluid of suckling pigs (average Ct value 30.2), significantly higher than that of other viruses. Both PCV1 and PCV3 loads in testicular fluid were significantly higher than in serum samples from other pig groups. PCV2 load was highest in fattening pigs (Ct value 30.3), significantly higher than that of nursery pigs and sows. PCV1 load in fattening pigs (Ct value 35.57) was also relatively higher than that of nursery pigs and sows. However, PCV3 load in the serum of pigs of different age groups showed little variation. Furthermore, PCV4 was detected in very few samples, and very few samples had high loads.
Figure 2. Ct values of PCV DNA-positive samples at different age groups
Red boxes indicate mixed samples.
TS: testicular fluid sample; SS: serum sample.
Conclusion: The viral loads of different viruses varied significantly across different pig herds. PCV3 was found to be the highest in the testicular fluid of suckling pigs, while PCV2 and PCV1 were found at higher levels in finishing pigs. PCV4 was rarely detected, and high-load samples were even rarer.
3. Correlation among Individuals at Different Stages
The results showed that the co-detection rates of different PCV types varied significantly across pig herds. In nursery pigs, the co-detection rate of PCV2 and PCV3 was the highest (9.3%), but the correlation between the two was not significant. The co-detection rates of PCV1 and PCV2, and PCV1 and PCV3, were lower and showed no significant correlation. In finishing pigs, the co-detection rate of PCV1 and PCV2 was 11.8%, PCV2 and PCV3 was 4.7%, and PCV1 and PCV3 was 2.8%, with no significant correlation between the two. In sows, the co-infection rate of PCV1 and PCV3 was the highest at 12.6%, followed by PCV2 and PCV3, and PCV1 and PCV2, with similarly weak correlations. Overall, the co-infection rate of various PCV types across different pig herds was low, and the correlations between them were generally weak.
Conclusion: In nursery pigs, fattening pigs and sows, the co-infection rate among different PCV types was generally low, and the correlation between them was weak, especially the correlation between PCV4 and other types was extremely weak.
Conclusion
This study demonstrates that PCV1, PCV2, and PCV3 are highly prevalent in sows and their offspring, with different genotypes exhibiting distinct infection patterns. Although mixed infection with multiple PCV types is common, there is no significant correlation at the individual level. This discrepancy suggests that prevention and control measures must be implemented in stages, targeting key viruses at each stage. This study provides valuable insights for developing preventive strategies.
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