Emerging Trends in Veterinary Diagnostic Submissions in Canada and Understanding New Technology
Jackie Gallant B.Sc. (Agr), President: Gallant Custom Laboratories Inc.
Gallant Custom Laboratories operations include a veterinary diagnostic division that receives swine samples from across Canada. The primary function of the diagnostic laboratory is to use adapted technology to evaluate bacterial and viral pathogenic organisms implicated in a given clinical case. Classical bacteriology has now been paired with Polymerase Chain Reaction (PCR) to identify, genotype and virotype micro organisms, providing invaluable information on the virulence potential of strains found in the lab. Diagnostic samples submitted for respiratory cases typically include an entire pluck, but if septicemia is suspected, the submission may also include a brain or meningeal swab, spleen, liver, joint (also for arthritis) or kidney; enteric cases submissions may include intact tied‐off gut loops or rectal swabs, depending on the suspected organism. Laboratory findings in submitted clinical cases may include swine pathogens such as Pasteurella multocida, Staphylococcus hyicus and Escherichia coli, which are typically associated with atrophic rhinitis, greasy pig and diarrhea disease, respectively. However, a review of our diagnostic results reveals that these organisms are emerging as a causative agent in other clinical signs, as well, such as septicemia, polyserositis and arthritis, and they are more frequently presenting themselves as a primary pathogen. Their presence in the brain, heart, joint and kidney in our clinical cases reveal correlations to reduced performance and increased mortality, resulting in expensive treatments or economic losses. Gallant has routinely isolated these organisms from these atypical sites and proposes that they should be considered when developing treatment and prevention programmes. Knowing the significance of the lab finding will enable an informed and more targeted approach to disease treatment and prevention.
Pasteurella multocida is a gram negative bacterium that is associated with disease in many species such as poultry, swine, cattle, rabbits and humans. Along with Mycoplasma hyopneumoniae, it is the cause of enzootic pneumonia which is considered the most important respiratory disease of swine worldwide7. It is easy to isolate in the lab, on artificial media, from organs and nasal swabs and can now be readily identified by PCR testing. At Gallant, Pasteurella multocida we isolated in approximately 21% of our respiratory cases in 2011 and as high as 26% in 2009 (Table 1). P. multocida isolation as high as 77% (114/148) in cranioventrally located bronchopneumonia cases, has been reported and of these, 85% were in pure culture4. In the same study, they indicated success at isolating P. multocida in the pericardial sac and kidney. Gallant did not receive kidney tissue with our submissions so are unable to comment
on isolation success from this organ. An Ontario5 study reported that P. multocida was isolated in 27% (108/395) of tonsils from swine sampled at a federally inspected Ontario abattoir from June to Dec 2008, indicating that P. multocida is part of the commensal flora in the pig tonsil. Further studies could reveal if this commensal strain of Pasteurella multocida is capable of initiating disease such as bronchopneumonia. Since most of our cases were respiratory it is not unexpected that the most common organ for isolation was the lung at 91%, however, we also found it in the heart, spleen, and brain (see Table 2). The presence of Pasteurella multocida is not new to swine medicine and was recognized as a contributor to fatal swine pneumonia at least 120 years ago.1 Our lab often isolates it with other respiratory organisms such as Haemophilus parasuis, Bordetella bronchiseptica, Actinobacillus suis, and Streptococcus suis and this is typical of other reports1. P. multocida is thought to be a secondary infection that is very common in the final stage of enzootic pneumonia1,2,3,4 with colonization developing after the aggravation of the lung tissue due to the primary invaders. Systemic infections are not often reported but studies3,4 show that systemic spreading of P. multocida does occur and this would concur with Gallant’s findings of P. multocida isolation in the heart, spleen and brain.
There are 4 capsular types of Pasteurella multocida although A and D are most commonly associated with swine disease. Although Type A is most often associated with pneumonia and Type D with atrophic rhinitis, through PCR molecular analysis3,4, strain and virulence factor differences have also been found between the strains that cause atrophic rhinitis and pneumonia. The virulent capabilities of Pasteurella multocida is something to consider when interpreting diagnostic reports and designing treatment options.
Generally, P. multocida is sensitive to cephalosporins, quinolines, penicillins, aminoglycosides, tetracyclines and erythromycin and resistant to tylosin, vancomycin, metronidazole, dapsone and tiamulin 1. Commercially available combination P. multocida and B. bronchiseptica bacterins have been successfully used in prevention of atrophic rhinitis but the differences in the strains capable of causing pneumonia may create a different challenge for bacterin success against P. multocida pneumonia.
P. multocida is an important swine pathogen that is implicated in atrophic rhinitis, enzootic pneumonia and systemic infection. It is routinely cultured during laboratory analysis from multiple sample sites and should be considered a significant finding. Damage to turbinates from atrophic rhinitis and lung tissue from bronchopneumonia would result in poor performance or death7. Understanding its role in the clinical signs is essential to controlling the damage and the losses.