APP15 Outbreak Insights - Iowa's Swine Health Revelation

By Andi Anderson

This research project, funded by the Swine Health Information Center (SHIC) and conducted by Marcelo Almeida and Alyona Michael from Iowa State University, aimed to understand and mitigate a severe outbreak of Actinobacillus pleuropneumoniae (APP) serotype 15 in Iowa finishers in 2021. The study focused on three main objectives:

APP Serological Status of Sows:

• Cross-sectional sampling was conducted to determine the serological status of sow farms supplying pigs to affected finisher sites.
• 15 out of 19 farms were serologically negative for APP serogroup 3-6-8-15, indicating that the majority of sow farms providing pigs were free of APP15.
• It was suggested that sites experiencing outbreaks may have been laterally infected with APP15 during the post-weaning period.

APP Persistence in Finishers:

• A prospective longitudinal study was conducted at one Iowa site following a confirmed recent APP15 outbreak.
• Tonsil scrapings had a higher detection rate than nasal swabs or oral fluid, suggesting tonsil scrapings as the most sensitive means of screening for individual carriers long-term.
• Oral fluids showed a more temporally robust utility for post-outbreak population surveillance than previously reported.
• Environmental sampling for APP15 genetic material was primarily detected in areas of human traffic and deadstock collection sites.

Comparative Stability of APP15 Strains:

• The longitudinal viability of APP15, for outbreak and historical strains, was compared to APP1 at different temperatures, surfaces, and organic matrices under laboratory conditions.
• Concrete surfaces exhibited the longest stability for both APP15 and APP1, with viability up to seven days post-inoculation at -20ºC and up to 48 hours at 4ºC.
• Rubber and stainless-steel surfaces exhibited viability at 4ºC and 25°C but not at 37°C.

Key Findings:

• The outbreak strain of APP15 did not exhibit enhanced persistence compared to other serotypes.
• Contributing factors to the spread and geographic persistence could include PCR detection at rendering piles, increased survival on concrete and rubber surfaces under laboratory conditions, and cold ambient temperatures during the winter 2021 outbreak.
• The study generates important knowledge related to APP ecology and epidemiology.
• The findings can impact disease diagnosis, monitoring, and surveillance, as well as inform biosecurity practices for improved APP control on swine farms.

Photo Credit: istock-srdjan-stepic