Many of us tend to speak of swine dysentery in the past tense, since efforts to eliminate the disease from herds were very successful several years ago. However, we continue to find the causative agent, Brachyspira hyodysenteriae, in a small number of cases of finishing pig enteric disease submitted to the University of Minnesota Veterinary Diagnostic Laboratory (MVDL).
Several diagnostic tools have been available for determining whether Brachyspira hyodysenteriae is present, including culture, dark field microscopic examination and immunohistochemistry. Additionally, polymerase chain reaction (PCR) tests can be used for detection and identification of Brachyspira sp. bacteria.
Culturing Brachyspira sp. from colon samples of pigs is a sensitive diagnostic tool. Limitations of culture are that it can take from several days to a couple of weeks to complete, and it is not possible to determine which species of Brachyspira sp. is present by culture alone. Culture tends to be the most sensitive test for detecting Brachyspira sp. in fecal samples, however.
Dark field microscopic examination of a colon sample is very rapid, but only confirms that spirochetes are present, without providing any information as to what genus of bacteria is present.
Immunohistochemistry confirms the presence of Brachyspira sp., but requires time for tissue fixation, sectioning and staining. It cannot be used to identify the specific Brachyspira sp. organism, but is useful for seeing the agent associated with lesions when looking at sections of the colon microscopically.
Testing samples by PCR has the advantage of being able to detect Brachyspira hyodysenteriae specifically with a rapid test. It can also be used to detect Brachyspira pilosicoli, a different spirochete that causes a milder, non-hemorrhagic form of diarrhea.
Additionally, these PCR tests are used to test isolates cultured from samples to identify them as Brachyspira pilosicoli, Brachyspira hyodysenteriae or different Brachyspira species (reported as untypable). The untypable species could be commensal or weakly pathogenic Brachyspira species. Isolates that are untypable but associated with bloody diarrhea require further testing with other methods, such as genetic sequencing or additional PCR tests.
PCR tests for Brachyspira sp. are available at several veterinary diagnostic laboratories. A summary of Brachyspira sp. test results from the MVDL for the fiscal year (July 2008 to June 2009) is shown in Figure 1. The figure shows the number of samples (including isolates, tissue samples and fecal samples) that tested positive for Brachyspira pilosicoli, positive for Brachyspira hyodysenteriae positive for Brachyspira sp. or negative for all Brachyspira sp. by PCR monthly over the sample period.
Click to view graphs.