Equis ISSN 2398-2977

Lawsonia intracellularis

Synonym(s): L. intracellularis, Ileal symbiont intracellularis, IS intracellularis

Contributor(s): Sarah Binns, Uneeda K Bryant, Richard Walker, Catriona Mackenzie




  • Family: Desulfovibrionaceae.
  • Delta subdivision of Class: Proteobacteria.
  • Genus: Lawsonia.
  • Species: intracellularis.


  • Lawson - G H K Lawson, the discoverer of the bacterium.
  • L: intra- within.
  • L: cella - storeroom, chamber.

Active Forms

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Clinical Effects



  • Obligate intracellular bacterium.
  • Found in many animal species, including wild deer and rabbits.


  • Reproduces in the cytoplasm of infected cells.


  • Likely to be feco-oral.

Pathological effects

  •  Species specificity of L. intracellularis strains is thought to play a role in the development of immune responses and clinical disease.
  • Most growing pigs clinically infected with L. intracellularis show a humoral immune response, with high levels of IgM.
  • Many older pigs may seroconvert without showing signs of disease.
  • An IgA response has been observed in the intestinal tract.
  • Cell-mediated immune responses appear to be an important feature in protecting animals from reinfection.
  • Most studies have been carried out in pigs and hamsters; however over recent years there has been increasing research into the disease in horses.
  • It is assumed that the bacterium is motile, and attaches to enterocytes in the crypts of the intestine, particularly the lower ileum.
  • Bacteria initially enter cells in vacuoles, but then live and divide freely in the cytoplasm.
  • Infected cells are stimulated to proliferate and produce hyperplastic intestinal glands; the cell population may increase to up to three times that of normal mucosa.
  • In affected horses, lesions are most commonly seen in the ileum, near the ileal-cecal junction.

Other Host Effects

  • Endemic infection occurs in pig herds; variable numbers of animals show clinical disease.
  • Similar findings are reported in groups of foals. It is also common for some foals within the group to be infected without developing overt clinical disease.


Control via animal

  • Supportive therapy has been used in affected horses, due to definitive diagnosis being obtained post mortem.

Control via chemotherapies

  • The preferred antibiotics are erythromycin Erythromycin with or without rifampin or enrofloxacin.
  • Tetracycline class drugs such as oxytetracyline Oxytetracycline or doxycycline are commonly used for treatment in horses.

Control via environment

  • Avoid contamination of environment with feces from clinical cases and free-ranging domestic and wildlife animal that can serve as reservoirs of the bacteria.


  • An avirulent live L. intracellularis vaccine is commonly used for the prevention of disease in pigs.
  • The same vaccine has been used in foals with encouraging results.

Other countermeasures

  • Supportive care with fluid therapy.


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Page A E, Slovis N M & Horohov D W (2014) Lawsonia intracellularis and equine proliferative enteropathy.Vet Clin North Am Equine Pract 30 (3), 641-658 PubMed.
  • Vannuci F A & Gebhart C J (2014) Recent advances in understanding the pathogenesis of Lawsonia intracellularis infections. Vet Pathol 51 (2), 465-477 PubMed.
  • Arroyo L G, Ter Woorf F, Baird J D et al (2013) Lawsonia intracellularis-associated ulcerative and necro-hemorrhagic enteritis in 5 weanling foals. Can Vet J 54 (9), 853-858 PubMed.
  • Pusterla N & Gebhart C J (2013) Equine proliferative enteropathy-a review of recent developments. Equine Vet J 45 (4), 403-409 PubMed.
  • Page A E & Fallon L H et al (2012) Acute deterioration and death with necrotizing enteritis associated with Lawsonia intracellularis in 4 weanling horses. J Vet Intern Med 26 (6), 1476-1480 PubMed.
  • Allen K J, Pearson G R, Fews D, McOrist S & Brazil T J (2009) Lawsonia intracellularis proliferative enteropathy in a weanling foal, with a tentative histological diagnosis of lymphocytic plasmacytic enteritis. Equine Vet Educ 21 (8), 411-414 VetMedResource.
  • Guimaraes-Ladeira C Vet al (2009) Faecal shedding and serological cross-sectional study ofLawsonia intracellularisin horses in the state of Minas Gerais, Brazil. Equine Vet J 41 (6), 593-596 PubMed.
  • Merlo J Let al (2009) Outbreak of Lawsonia intracellularis on a Standardbred breeding farm in North Carolina. Equine Vet Educ 21 (4), 179-182 VetMedResource.
  • Pusterla N, Higgins J C, Smith P, Mapes S & Gebhart C (2008) Epidemiological survey on farms with documented occurrence of equine proliferative enteropathy due to Lawsonia intracellularis. Vet Rec 163 (5), 156-158 PubMed.
  • Deprez Pet al (2005) Lawsonia intracellularis infection in a 12-month-old colt in Belgium. Vet Rec 157 (24), 774-776 PubMed.
  • Smith D G E & Lawson G H K (2001) Lawsonia intracellularis - getting inside the pathogenesis of proliferative enteropathy. Vet Microbiol 82, 311-345 PubMed.
  • Lawson G H K & Gebhart C J (2000) Proliferative enteropathy. J Comp Pathol 122, 77-100 PubMed.
  • Brees D J, Sondhoff A H, Kluge J P, Andreasen C B & Brown C M (1999) Lawsonia intracellularis-like organism infection in a miniature foal. JAVMA 215 (4), 511-514 PubMed.
  • Frank N, Fishman C E, Gebhart C J & Levy M (1998) Lawsonia intracellularis proliferative enteropathy in a weanling foal. Equine Vet J 30 (6), 549-552 PubMed.

Other sources of information

  • Brenner D J, Krieg N R & Staley J R (2005) Bergeys Manual of Systematic Bacteriology. 2nd edn. Vol 2. pp 940-943.