5.1.5 Detection of Lawsonia intracellularis antigen or DNA

Lawsonia intracellularis cannot be easily isolated and grown in cell cultures. Thus, diagnostics are restricted to the detection of Lawsonia intracellularis by silver staining of the bacteria, or more specifically, by the use of FITC- or peroxidase- labelled polyclonal or monoclonal antibodies against Lawsonia intracellularis. However, these methods are only used in post mortem samples. The detection of genomic DNA from Lawsonia intracellularis by a one or two step polymerase chain reaction (PCR or nPCR) has been shown to be highly sensitive and highly specific. This method can be used in post mortem tissue sam­ples as well as in faeces. Lawsonia intracellularis is not consistently excreted in faeces. It can usually be detected early after infection and prior to seroconversion. Later on excretion becomes more infrequent and intermittent. Faecal samples (1–2g or 1 to 2 faecal swabs) may be taken from individual animals directly. Pooling samples for PCR minimizes costs but increases the difficulty of interpretation of the results of the test.