Subclinical PCV2: the silent enemy

Subclinical infection with porcine circovirus type 2 (PCV2) is probably the most common form in which this pathogen manifests in modern intensive production farms. Unlike evident clinical outbreaks, this presentation goes unnoticed, without clear signs that alert producers. However, its productive and economic impact can be enormous, accumulating silently throughout the entire production cycle.

In subclinical infection, the virus replicates persistently, generating constant stimulation of the immune system. This forces the animal to divert energy and resources that, under optimal conditions, would be allocated to growth and feed conversion efficiency. Recent studies in Europe estimate economic losses associated with subclinical PCV2 reaching an average of €9.1 per pig (90% CI: €2.5–16.9), considering the combined impact on weight gain, feed conversion ratio, and additional days to reach market weight. Although individual losses may seem quite small, such as a reduction of 30 or 40 grams per day in weight gain, the cumulative effect on an entire batch of animals is extremely significant.

Several studies have shown that subclinical infection rarely acts alone. Therefore, coinfections with viruses such as PRRSV or bacteria such as Mycoplasma hyopneumoniae must be considered, as they worsen the situation by weakening the immune response and enhancing the negative effects of PCV2. Even in the absence of marked clinical signs, these associations can drastically reduce batch uniformity and increase variability in slaughter weight, affecting the final profitability of farms.

In recent monitoring carried out on commercial farms, it has been observed that PCV2 prevalence increases as the production cycle progresses. On farms where detection at weaning was low (below 5%), viral circulation close to 40% has been recorded in the final phase of nursery or the beginning of finishing. This phenomenon suggests that, even under standardized vaccination programs, the virus can find conditions to remain circulating and be transmitted among animals.

One of the main challenges in controlling subclinical infection is its difficult diagnosis. Production losses may be mistakenly attributed to other factors such as genetics, nutrition, or environmental conditions. Therefore, the use of laboratory-based diagnostic tools such as PCR or serology, combined with close monitoring of production parameters, is essential to identify and quantify the problem at an early stage.

The impact of subclinical infection is not limited to an isolated batch. Its persistence over time and its ability to interact with other pathogens favor the constant circulation of the virus on the farm, making its eradication difficult. In addition, stress due to environmental changes, transport, or dietary transitions can act as triggers that exacerbate viral replication and its consequences.

Even in the absence of evident mortality, subclinical PCV2 infection represents a major sanitary and economic challenge. The only way to minimize its impact is to address it as an integrated management issue, in which biosecurity, control of coinfections, and regular health monitoring work together to keep this silent enemy under control.

Summary

• Subclinical infection as the most common presentation of PCV2, with economic losses of up to €9.1 per pig due to lower weight gain, poorer feed conversion, and more days to market.
• High frequency of coinfections with PRRSV and Mycoplasma hyopneumoniae that worsen the productive impact and reduce batch uniformity.
• Complex diagnosis requiring laboratory tools and integrated management to keep viral circulation on the farm under control.

References

• Segalés J. (2015). Best practice and future challenges for vaccination against porcine circovirus type 2. Vet. Microbiol.
• Saade G., et al. (2020). Coinfections and their impact on pig health. Porc. Health Manag.
• Opriessnig T., et al. (2011). Porcine circovirus type 2: current status of knowledge. Vet. Microbiol.
• D’Annunzio R., et al. (2023). PCV2d in Latin American swine populations. Transbound. Emerg. Dis.
• Eddicks M., et al. (2025). Update on the prevalence of PCV2 major genotypes in German fattening farms in 2024. Vet. Sci.
• Wang D., et al. (2025). Amino acid mutations in PCV2 capsid increase immune evasion. Virulence.
• Boeters M., et al. (2023). Economic impact of endemic respiratory disease in pigs. Porcine Health Manag.