Diagnosing Porcine Proliferative Enteropathy: A Practical Guide for Field Veterinarians

Porcine proliferative enteropathy (PE), caused by Lawsonia intracellularis, remains one of the most important enteric diseases affecting commercial swine production. For field veterinarians, diagnosis can be challenging because the disease presents in multiple forms, ranging from subclinical infection with poor growth performance to acute haemorrhagic disease associated with mortality. The presence of asymptomatic carriers and intermittent bacterial shedding further complicates herd-level diagnosis¹. Successful disease control depends on recognising clinical patterns, selecting appropriate diagnostic tests, and interpreting laboratory findings alongside herd history and management practices. 

Recognising When to Suspect PE 

Clinical presentation varies according to the stage and severity of infection. Acute cases may present with haemorrhhagic diarrhoea, sudden death, weakness, and pallor, whereas chronic cases are more commonly associated with persistent diarrhoea, reduced weight gain, and poor feed efficiency. In many herds, however, subclinical infection predominates, resulting in reduced growth performance and poor flock uniformity without obvious clinical signs¹. 

Because these clinical findings overlap with several other enteric diseases, clinical examination alone is rarely sufficient for a definitive diagnosis. A complete assessment should include: 

• Clinical signs within affected groups 

• Age of affected pigs 

• Herd history and production records 

• Vaccination status 

• Previous antimicrobial use 

• Laboratory confirmation¹ 

Choosing the Right Diagnostic Test 

No single diagnostic method is suitable for every clinical situation. Test selection should be guided by the purpose of investigation, sample availability, and herd circumstances. 

• Quantitative PCR (qPCR): Considered the current gold standard for diagnosing porcine proliferative enteropathy because of its high sensitivity, rapid turnaround, and ability to quantify Lawsonia intracellularis DNA^2,3. 

• Conventional PCR: Useful for detecting L. intracellularis DNA and can support diagnosis when molecular confirmation is required^3,4. 

• Immunohistochemistry (IHC): Confirms the presence of L. intracellularis within characteristic intestinal lesions, making it particularly valuable for post-mortem diagnosis^3,4,5. 

• ELISA: Supports herd-level surveillance by identifying previous exposure to L. intracellularis but should not be used as the sole method to confirm active infection^3,5. 

• Histopathology and Fluorescence In Situ Hybridisation (FISH): Provide additional diagnostic support, particularly when intestinal tissue samples are available, and can help correlate pathological changes with the presence of the organism^3,5. 

Understanding Diagnostic Limitations 

Even highly sensitive laboratory tests require careful interpretation. L. intracellularis is shed intermittently, so sample timing directly affects molecular test sensitivity. Poor sample quality, delayed transport, or tissue degradation can also reduce the accuracy of both molecular and histopathological testing⁴. 

In addition, recently vaccinated pigs receiving live attenuated vaccines may transiently shed vaccine organisms, which can complicate the interpretation of PCR results because current diagnostic assays do not differentiate vaccine strains from naturally occurring strains⁴. Co-infections with pathogens such as Salmonella spp. or PCV2 may further mask or intensify clinical signs, making differential diagnosis essential^1,4. 

Integrating Laboratory Results with Herd Assessment 

Laboratory confirmation should never be interpreted in isolation. Reliable diagnosis requires integrating laboratory findings with clinical observations, production records, herd epidemiology, biosecurity practices, and vaccination history¹. Serology can support herd surveillance by identifying previous exposure, whereas histopathology remains valuable for confirming characteristic intestinal lesions, including enterocyte proliferation and goblet cell reduction^1,4,6. 

Emerging technologies, including metagenomic sequencing and rapid on-farm diagnostic tests, may further improve disease detection in the future, particularly by identifying co-infections and supporting timely herd-level decision-making^1,7. 

Clinical Pearl 

Accurate diagnosis of porcine proliferative enteropathy depends on combining clinical assessment with appropriate laboratory testing rather than relying on a single diagnostic method. While qPCR remains the current gold standard for detecting active Lawsonia intracellularis infection, the greatest diagnostic confidence is achieved by interpreting test results alongside clinical findings, herd history, vaccination status, and pathological changes. A herd-level approach enables earlier intervention and supports more informed disease-control decisions.

References 

1. Campillo M, Smith SH, Gally DL, Opriessnig T. Review of methods for the detection of Lawsonia intracellularis infection in pigs. Journal of Veterinary Diagnostic Investigation. 2021 Jul;33(4):621-31. https://journals.sagepub.com/doi/pdf/10.1177/10406387211003551 

2. Pedersen KS, Stege H, Jensen TK, Guedes R, Ståhl M, Nielsen JP, Hjulsager C, Larsen LE, Angen Ø. Diagnostic performance of fecal quantitative real-time polymerase chain reaction for detection of Lawsonia intracellularis–associated proliferative enteropathy in nursery pigs. Journal of Veterinary Diagnostic Investigation. 2013 May;25(3):336-40. https://journals.sagepub.com/doi/pdf/10.1177/1040638713480499 

3. Luppi A, D’Annunzio G, Torreggiani C, Martelli P. Diagnostic approach to enteric disorders in pigs. Animals. 2023 Jan 18;13(3):338. https://www.mdpi.com/2076-2615/13/3/338 

4. Gómez-Osorio LM, Penagos-Tabares F, Bosnjak-Neumuller J, Guedes RM, Vasiljevic M, Steiner T, McOrist S. Porcine proliferative enteropathy: overview of disease dynamics and non-antibiotic alternatives for prevention and control strategies. Frontiers in Veterinary Science. 2025 Nov 7;12:1596316. https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2025.1596316/pdf 

5. Vannucci FA, Gebhart CJ, McOrist S. Proliferative enteropathy. Diseases of swine. 2019 Jun 3:898-911. https://www.academia.edu/download/60674736/Diseases_of_Swine__11th_Edition_VetBooks.ir20190922-31639-a6z8g5.pdf#page=922 

6. Baldasso DZ, Guizzo JA, Dazzi CC, Paraboni Frandoloso GC, Feronato C, von Berg S, Carvalho Guedes RM, Wilson HL, Kreutz LC, Frandoloso R. Development and validation of a flow cytometry antibody test for Lawsonia intracellularis. Frontiers in immunology. 2023 Mar 21;14:1145072. https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2023.1145072/pdf 

7. Arnold M, Crienen A, Swam H, Berg SV, Jolie R, Nathues H. Correlation of Lawsonia intracellularis positivity in quantitative PCR and herd factors in European pig herds. Porcine health management. 2021 Jan 22;7(1):13. https://link.springer.com/content/pdf/10.1186/s40813-021-00192-4.pdf