Lawsonia Intracellularis INFECTIONS
Herbert Weissenb ock
Pathology and Forensic Veterinary Medicine, Department of Pathobiology, University of Veterinary Medicine, Vienna, Austria
Lawsonia intracellularis is an obligate intracellular bacterium that does not grow in cell-free media and can only be propagated in tissue cultures.
It occurs worldwide and is the causative agent of porcine proliferative enteropathy. It is able to infect a large variety of animals. Free-ranging wild animal species only exceptionally develop disease, but PCR data indicate the carrier status of the house mouse (Mus musculus), striped field mouse (Apodemus agrarius), yellow-necked mouse (A. flavivcollis), common vole (Microtus arvalis), fox (Vulpes vulpes), wolf (Canis lupus), red deer (Cervus elaphus) and fallow deer (Dama dama). Wild animals kept in game enclosures, wildlife parks or fur farms have more frequently been reported to show clinical disease (blue fox (Alopex lagopus), rabbit ( Oryctola- gus cuniculus), wild boar (S us scrofa), ostrich (S truthio camelus), emu (D romaius novaehollandiae) and Rhesus macaque (Macaca mulatta)~). The disease is also known in hamsters (Mesocricetus spp.) and is increasingly recognized in young horses, but has also been sporadically reported in dogs, rats (Rattus norvegicus) and ferrets (Mustela puto- rius furo).The bacterium colonizes enterocytes and replicates within their cytoplasm. As a reaction the affected portions of the intestine show proliferation of undifferentiated, hypertrophic enterocytes with formation of branching crypts. The changes are generally transient and may completely recede after elimination of the agent.
Clinical signs are usually associated with poor growth, diarrhoea and hypoproteinaemic oedema. Lesions include irregular thickening of the intestine, sometimes with focal necrosis. Histologically, there is a proliferation of undifferentiated enterocytes with lack of goblet cells. Abundant intracellular bacteria are present adjacent to the luminal cell surface and can be visualized by silver impregnation or specific detection assays, such as IHC or in situ hybridization.
Post mortem, the agent is best demonstrated by IHC. For diagnosis in the live animal, a number of PCR assays on faeces are available. Serology is not recommended for diagnosis in individual animals, because it does not indicate the actual presence of the bacteria.
Wild animals do not play a role as reservoirs of the agent for domestic pigs kept in facilities with high biosecurity levels. For free-ranging pigs, infected wild animals may be a potential source ofinfection. The agent is non- pathogenic for humans.