Lawsonia intracellularis - Molecular diagnosis (PCR)
Lawsonia intracellularis is an obligate intracellular bacterium highly pathogenic, 1.25 to 1.75 microns x 0.25 to 0.43 microns, without frimbias or spores of the genus Lawsonia, family Desulfovibrionaceae, causing intestinal enteritis processes as proliferative haemorrhagic (SPS), porciana proliferative enteropathy (PPE) or intestinal adenomatous hyperplasia and porcine intestinal adenomatosis (AI). These processes may be similar to those caused by Serpulina hyodysenteriae, causing swine dysentery, or manifestations caused by Salmonella spp. Lawsonia intracellularis is an animal pathogen that affects mainly pigs, although other mammals can affect as horses, dogs, rats, guinea pigs, rabbits, ferrets, hamsters and, among others. This bacterium is widely distributed in pig producing countries. In pig breeding, a problem caused by mortality, reduce feed efficiency, the cost of medication and care required additional animals.
The life cycle of this bacterium involves a host where it multiplies. Animals can be infected with the bacteria through ingestion of faeces , which can survive at least 14 days at room temperature and contaminated fomites. Once inside the host, Lawsonia intracellularis invade intestinal epithelial cells via an entry vacuole. Inside cells the vacuole is broken and the bacteria multiply in the cytoplasm. Infected epithelial cells continue to perform mitosis, and transmit the bacteria to daughter cells; it ends up being released to outside through cytoplasmic extrusions epithelial cells and is deposited on the microvilli or between the crypts. The infection spreads throughout the ileum, distal jejunum, cecum and colon, causing hyperplasia infected cells and leading to the process of pathogenesis of the disease. Removal of Lawsonia intracellularis with feces of infected animals generally begins at 7 days post infection and may persist for at least 10 weeks.
The incubation period of Lawsonia intracellularis is 7 to 14 days with the first appearance of lesions. The peak of the disease occurs about 21 days postinfection. Lawsonia intracellularis infection has two forms of presentation: acute or chronic. The acute hemorrhagic proliferative enteropathy cause (EPH), as evidenced by pallor, due to an acute haemorrhagic anemia, diarrhea and massive intestinal bleeding can be fatal. In pregnant animals, the acute form may cause abortion. The chronic form affects young animals with diarrhea without the presence of blood , causes swine intestinal adenomatosis (AI), intestinal adenomatous hyperplasia or porcine proliferative enteritis (PPE). Signs and symptoms associated with chronic form include anorexia, decreased growth and diarrhea. Porcine proliferative enteritis (PPE), variables can manifest clinical signs such as diarrhea, constant weight loss, or not even show signs. Animals with mild disease may recover without treatment. At necropsy there are not pathognomonic lesions as dilated bowel, hemorrhages present or absent intestinal mucosa hypertrophied with deep transverse grooves, in the histopathology seen with elongated crypts mucous, enlarged, hypertrophic coated epithelial cells. Epithelial cell proliferation generates a thickening of the mucosa of the ileum, jejunum and large intestine, enterocytes with hyperplasia of the crypts with numerous mitoses and absent or decreased mucus producing cells. In the apical cytoplasm of enterocytes hypertrophic, with appropriate stains intracellular bacteria can be seen as small, curved bacilli.
Recommended tests for diagnosis:
Lawsonia intracellularis is an obligate intracellular bacterium that requires use cell cultures for growth in vitro, making diagnosis difficult. Microscopic observation requires fixing intestinal biopsies, and the use of special stains such as silver staining Warthin-Starry, including viewing curved bacteria inside the apical cytoplasm of enterocytes. However, this observation does not confirm the existence of Lawsonia intracellularis, and allows differentiation of Campylobacter, or other curved bacteria. For these reasons, the diagnosis is based on detection of antibodies, which encounters the difficulty of preparing antigen due to the special characteristics of this bacteria culture, and molecular diagnostic methods (PCR).
Tests in IVAMI:
- Molecular diagnosis (PCR), to detect DNA of Lawsonia intracellularis.
- Recent stool.
- Scraping or biopsy intestinal mucosa.
Preservation and shipment of sample:
- Refrigerated (preferred) for less than 2 days.
- Frozen: over 2 days (for molecular diagnostic tests only).
- Microscopic examination: 24 hours.
- Molecular diagnosis (PCR): 24 to 48 hours.
Cost of the test: