Microscopic view of a pig's tonsil with DNA and virus particles, symbolizing PRRSV infection.

Swine Flu Under Scrutiny: New Insights into PRRS Virus and Pig Health

Lena Kashyap in Health & Wellness December 2025 • 4 min read.

"Unlocking the secrets of Porcine Reproductive and Respiratory Syndrome (PRRS) to enhance pig farming practices and reduce economic losses."

Porcine Reproductive and Respiratory Syndrome (PRRS) is a formidable challenge in the swine industry. Known for its global reach and significant economic impact, this disease affects not only the health and welfare of pigs but also the financial stability of farms. For over two decades, U.S. swine producers have battled PRRS, struggling to contain its spread and mitigate its effects. The persistent nature of PRRS virus (PRRSV) and its ability to adapt make it a particularly difficult adversary.

The primary phase of PRRS is characterized by serum viremia, during which the virus circulates in the bloodstream. This phase typically lasts between 21 and 42 days post-infection (dpi). However, the virus can persist in the tonsils for much longer periods, often exceeding 150 dpi. The ability of PRRSV to establish a long-term presence in the tonsils contributes to the ongoing cycle of infection and transmission.

Recent research has focused on understanding the dynamics of PRRSV in the tonsils, particularly at later stages of infection (6-7 weeks post-infection). This research seeks to determine if measuring virus levels in the tonsils can provide insights into the persistence of the virus and its potential to influence the duration of infection. Scientists are working to identify factors that affect tonsil virus levels, including interactions with serum viremia, to develop more effective strategies for managing PRRS.

What Factors Influence Virus Levels in Pig Tonsils?

Microscopic view of a pig's tonsil with DNA and virus particles, symbolizing PRRSV infection.

A detailed study was conducted involving pigs experimentally infected with either the NVSL-97-7895 (NVSL) or KS-2006-72109 (KS06) PRRSV type 2 isolates. The study spanned five trials, encompassing a total of 852 pigs. The primary goals of this research were to:

The research team meticulously analyzed various factors to understand their impact on tonsil virus levels. These included:

Estimating the heritability of tonsil virus levels at 35 or 42 dpi.
Identifying factors affecting tonsil virus levels, including serum viremia.
Locating genomic regions associated with tonsil virus levels.
Comparing results between the two PRRSV isolates.

The heritability estimates for tonsil virus levels were found to be low for both isolates, indicating that genetic factors alone do not fully determine the extent of viral presence in the tonsils. This suggests that environmental factors and interactions between the virus and the host immune system play significant roles in shaping the course of infection.

Key Findings and Implications for Pig Farming

This research provides valuable insights into the complexities of PRRS virus infection in pigs. By identifying factors that influence virus levels in the tonsils, scientists and producers can develop more targeted strategies for managing this costly disease. Understanding the interplay between serum viremia, genetics, and environmental factors is crucial for reducing the impact of PRRS on pig health and the swine industry.

About this Article -

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Everything You Need To Know

What is Porcine Reproductive and Respiratory Syndrome, and why is it a concern for pig farmers?

Porcine Reproductive and Respiratory Syndrome (PRRS) is a disease that affects pigs, causing reproductive issues in sows and respiratory problems in young pigs. It is important because it leads to significant economic losses for swine producers due to decreased productivity, increased mortality, and the costs associated with managing the disease. The persistent nature of the PRRS virus (PRRSV) makes it difficult to control, requiring ongoing research and management strategies.

What is serum viremia in the context of Porcine Reproductive and Respiratory Syndrome, and how long does it typically last?

The primary phase of PRRS involves serum viremia, where the PRRS virus circulates in the bloodstream. Serum viremia typically lasts for 21 to 42 days after infection. It's important because the level of virus in the blood during this phase can influence the severity and duration of the infection. Furthermore, the virus can persist in the tonsils for much longer periods, exceeding 150 days, contributing to ongoing transmission.

Do genetics alone determine how much virus is present in a pig's tonsils during a Porcine Reproductive and Respiratory Syndrome infection?

Research indicates that genetic factors alone do not fully determine the extent of viral presence in the tonsils. This means that while some pigs may have a genetic predisposition to higher or lower virus levels, environmental factors and the pig's immune response also play significant roles. Understanding these non-genetic factors is crucial for developing comprehensive management strategies.

What were the NVSL-97-7895 and KS-2006-72109 isolates, and what role did they play?

The study involved infecting pigs with two different PRRSV type 2 isolates: NVSL-97-7895 (NVSL) and KS-2006-72109 (KS06). Comparing the effects of these different isolates helps researchers understand the variability in PRRSV behavior and how different strains may affect infection dynamics. It enables the creation of more robust and adaptable management techniques.

What are some strategies for managing Porcine Reproductive and Respiratory Syndrome in pig farming?

Managing PRRS involves understanding the interplay between serum viremia, genetics, and environmental factors. Strategies may include improving biosecurity measures to prevent the introduction and spread of the virus, optimizing pig management practices to reduce stress and enhance immune function, and potentially utilizing vaccines or other interventions to control virus levels. Given the low heritability of tonsil virus levels, management should focus on environmental and immunological factors to complement any genetic considerations.