Review of methods for the detection of Lawsonia intracellularis infection in pigs

Abstract

Lawsonia intracellularis is an obligate intracellular bacterium associated with enteric disease in pigs. Clinical signs include weight loss, diarrhea, and, in some cases, sudden death. The hallmark lesion is the thickening of the intestinal mucosa caused by increased epithelial cell replication, known as proliferative enteropathy. The immune response to L. intracellularis is not well defined, and detection of the infection, especially in the early stages, is still a significant challenge. We review here the main approaches used to identify this important but poorly understood pathogen. Detection of L. intracellularis infection as the cause of clinical disease is confounded by the high prevalence of the pathogen in many countries and that several other pathogens can produce similar clinical signs. A single L. intracellularis–specific ELISA and several amplification assays are available commercially to aid detection and surveillance, although histopathology remains the primary way to reach a conclusive diagnosis. There are major gaps in our understanding of L. intracellularis pathogenesis, especially how the host responds to infection and the factors that drive infection toward different clinical outcomes. Knowledge of pathogenesis will increase the predictive value of antemortem tests to guide appropriate interventions, including identification and treatment of subclinically affected pigs in the early stages of disease, given that this important manifestation reduces pig productivity and contributes to the economic burden of L. intracellularis worldwide.

Porcine Lawsonia intracellularis Ileitis in Italy and Its Association with Porcine Circovirus Type 2 (PCV2) Infection

“…Experimental infection studies have shown that at least five days of intracellular replication are necessary to reach detectable levels of L. intracellularis by IHC or in situ hybridization (ISH). The antigen could be detected up to 14 days post-infection [ 5 ]. It is plausible that the examination of more than one pig would have increased the probability of detecting cases with antigen detectable by immunohistochemistry.…”

“…Several types of investigation for diagnosing PE in swine are available, each with its strengths and limitations [ 5 ]. The clinical presentation alone is inadequate for diagnosis as it overlaps with other intestinal pathogens such as Brachyspira hyodysenterie, Brachyspira pilosicoli , Salmonella enterica , Escherichia coli , and PCV2 [ 2 , 5 ]. The gross features of PE are also shared with PCV2 enteritis [ 2 , 10 ].…”

“…Necrotic enteritis (NE) is a less frequent form of the disease and is characterized by mucosal necrosis and fibrin exudation due to complication by other bacteria. Its chronic evolution leads to mural fibrosis, known as regional ileitis or “hosepipe guts” [ 3 , 4 , 5 ]. In addition to the acute (PHE) and chronic (PIA) clinical presentations of PE, subclinical forms of infection must also be considered.…”

“…Therefore, the final diagnosis of PE caused by L. intracellularis requires histologic confirmation of the typical lesion, which is represented by the hyperplasia of intestinal crypts. In addition, its co-localization with the presence of the antigen through the immunohistochemistry or immunofluorescence or in situ hybridization [ 5 , 7 ] is also required for a definitive diagnosis.…”

Neues zur Epidemiologie von Lawsonia-intracellularis-Infektion bei Schweinen

“…Für den direkten Erregernachweis am lebenden Tier eignet sich die Untersuchung von Kot mittels quantitativer Polymerase-Kettenreaktion (qPCR), um eine intrazelluläre Vermehrung des Erregers im Tier und damit eine mögliche Beeinträchtigung des Tieres festzustellen. Serologische Untersuchungen bei heranwachsenden und adulten Schweinen beweisen ausschließlich eine Exposition zum Erreger und eignen sich darum lediglich zum Screening in Herden oder zur Feststellung des Infektionszeitpunktes, jedoch nicht zur Diagnose einer gegenwärtigen Erkrankung der Tiere [4]. Weiter ist dabei zu beachten, dass maternale Antikörper bis etwa zur 5.…”