Science Page: Actinobacillus pleuropneumoniae: a case of suspected lateral transmission (Part 2: outbreak investigation)

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we are sharing the second part of a report regarding an Actinobacillus pleuropneumoniae outbreak in the Midwest, across 3 systems and 5 farms.

If you missed part 1, you can find it here.

Key Points:

  • Communication between veterinarians and farm managers can help unravel patterns that might seem unique in one system.
  • Even though the source of APP was not determined outbreak investigation can help to find common links between sources.

A series of Actinobacillus pleuropneumoniae (APP) outbreaks involving five farms belonging to three different production companies were reported. Serotype 8 was confirmed as the source of the clinical signs in all the cases. The outbreak started with the two southernmost located farms (Company A Farm 1 and Company B Farm), followed by Company C (Farm 1) four weeks later. The distance among these growing pig sites ranged from 0.6 to 8.3 miles and the region where they are located can be considered as a high hog density area (Picture 1).

APP farm locations
Map of the farms involved in the APP outbreak

Common links between several sites were revealed after conversations among veterinarians and production managers. The main transmission route for this bacterium is introducing APP carrier pigs. In this case, it can be easily ruled out as these are sites that flow independently.

Other possibilities include indirect transmission through fomites and aerosol. Although these production companies do not share employees or tools they do have a common link in that some did share the same rendering company which could have been servicing other sites that were APP positive. As for manure removal, companies do not use the same manure removal company. One company did have the same individual doing the manure removal procedure at one site while breaking and then proceeded to the next one. Airborne transmission has been suggested as another possibility and after preliminary wind direction analyses during the outbreak dates it was inconclusive.

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