Illustration of a pig with glowing tonsils, representing genetic and immunological factors in viral persistence.

Unlocking Pig Health: How Understanding Tonsil Virus Levels Can Improve Swine Well-being

Nico Varela in Health & Wellness December 2025 • 4 min read.

"New research sheds light on the factors influencing virus levels in pigs' tonsils, offering potential strategies for managing Porcine Reproductive and Respiratory Syndrome (PRRS) and enhancing overall swine health."

Porcine Reproductive and Respiratory Syndrome (PRRS) remains a significant challenge for the swine industry, impacting both animal welfare and economic stability. This global disease, characterized by reproductive failure in sows and respiratory distress in young pigs, has proven difficult to contain despite decades of effort.

While the acute phase of PRRS, marked by the presence of the virus in the bloodstream (serum viremia), typically resolves within a few weeks, the virus can persist in the tonsils for much longer periods. This persistence makes the tonsils a critical site for understanding long-term infection dynamics and developing effective control strategies.

Recent research has focused on identifying the factors that influence virus levels in the tonsils of pigs, aiming to uncover potential targets for intervention. By understanding these factors, researchers hope to develop methods to reduce viral persistence, improve the health of swine herds, and minimize the economic impact of PRRS.

Decoding Tonsil Virus Levels: What the Research Reveals?

Illustration of a pig with glowing tonsils, representing genetic and immunological factors in viral persistence.

A comprehensive study investigated the factors associated with virus levels in the tonsils of pigs experimentally infected with PRRSV. The research, conducted across five trials, involved analyzing tonsil samples from pigs infected with two different PRRSV isolates: NVSL-97-7895 (NVSL) and KS-2006-72109 (KS06).

The study's objectives were multifaceted, including estimating the heritability of tonsil virus levels, identifying factors affecting these levels (such as serum viremia), exploring genomic regions associated with virus levels, and comparing results between the two PRRSV isolates. Here’s a breakdown of the key findings:

Heritability: Tonsil virus levels showed low heritability, suggesting that environmental factors and complex genetic interactions play a more significant role than simple inheritance.
Serum Viremia Connection: Pigs with lower tonsil virus levels exhibited faster viral clearance from the serum, indicating a link between the body's ability to clear the virus from the bloodstream and its persistence in the tonsils.
Genomic Regions: While no single gene had a major effect, several genomic regions showed associations with tonsil virus levels. These regions contained genes involved in various processes related to viral infection and immune response.
Key Genes Identified: Genes such as CCL1, CCL2, CCL8, HS3ST3B1, GALNT10, TCF7, C1QA/B/C, HPSE, GOS2, and CD34 were identified in the associated genomic regions. These genes are known to be involved in viral infiltration, replication, immune cell migration, and viral clearance from tissues.

The consistency of results between the two PRRSV isolates suggests that the identified factors and genomic regions may be broadly relevant for understanding PRRSV persistence in swine.

Implications for Swine Health Management

This research provides valuable insights into the complex interplay of factors influencing PRRSV persistence in pigs. The identification of genomic regions and specific genes associated with tonsil virus levels opens avenues for future research aimed at developing targeted interventions. While the heritability of tonsil virus levels is low, the connection with serum viremia suggests that selection for improved viral clearance traits in serum could indirectly reduce viral persistence in the tonsils. Further studies are needed to validate these findings and explore the potential for genetic selection and other management strategies to improve swine health and reduce the impact of PRRS.

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Everything You Need To Know

What is Porcine Reproductive and Respiratory Syndrome (PRRS) and why is it a major concern for swine health?

Porcine Reproductive and Respiratory Syndrome (PRRS) is a global disease affecting pigs, causing reproductive failure in sows and respiratory distress in young pigs. It is a significant concern because it severely impacts both animal welfare and economic stability within the swine industry. Despite extensive efforts, containing and eradicating PRRS has proven difficult, making research into its mechanisms crucial for developing effective control strategies.

Why are scientists focusing on the tonsils in the context of PRRS?

Scientists are focusing on the tonsils because, while the acute phase of PRRS (serum viremia) typically resolves within weeks, the virus can persist in the tonsils for much longer periods. This makes the tonsils a critical site for understanding the long-term infection dynamics of the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and for developing effective control strategies. The persistence of the virus in the tonsils indicates a potential reservoir for the virus and a site where it can evade the immune system.

What were the key findings regarding heritability and its impact on virus levels in the tonsils?

The research revealed that tonsil virus levels showed low heritability. This means that environmental factors and complex genetic interactions have a more significant influence than simple inheritance on the amount of the virus present in the tonsils. This suggests that while genetics play a role, other factors like the pigs' environment, immune response and the specific PRRSV isolate are crucial determinants of how long the virus persists in the tonsils.

How is serum viremia related to the persistence of the PRRSV in the tonsils, and what does this connection imply for swine health?

Pigs with lower tonsil virus levels demonstrated faster viral clearance from the serum. This indicates a link between how quickly the body can clear the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) from the bloodstream and the virus's persistence in the tonsils. This connection suggests that improving the ability of pigs to clear the virus from their serum could indirectly reduce the virus's persistence in the tonsils. This implies that selection for improved viral clearance traits in serum could be a promising strategy to reduce viral persistence and improve overall swine health.

Which genes were identified as potentially associated with tonsil virus levels, and what are their roles in viral infection and immune response?

Several genomic regions were associated with tonsil virus levels. Within these regions, key genes such as CCL1, CCL2, CCL8, HS3ST3B1, GALNT10, TCF7, C1QA/B/C, HPSE, GOS2, and CD34 were identified. These genes play different roles. For example, some, like CCL1, CCL2, and CCL8, are involved in immune cell migration. Others, such as C1QA/B/C, participate in immune responses, and others, like HPSE, could be linked to viral infiltration or clearance. Understanding the roles of these genes provides potential targets for future research aimed at developing targeted interventions to reduce viral persistence and improve swine health.