Streptococcus equi subspecies zooepidemicus (commonly abbreviated Streptococcus zooepidemicus or simply Strep zoo) is a bacterium which has become a growing concern in the swine industry worldwide. In China, repeated outbreaks of Strep zoo over the past decade have revealed genetic changes of the strains associated with a more severe disease. Starting in 2019, North American swine producers began noting die-offs associated with Strep zoo detection. In November 2019, the USDA issued an Emerging Risk Notice as multiple states throughout the US exhibited disease connected with Strep zoo infection, with genetic characterization matching that of the Chinese virulent strains. In the past two months, Strep zoo was isolated by the Animal Diagnostic Laboratory in association with swine morbidity and mortality in Pennsylvania. In summary, Strep zoo has historically been an economically important bacterial pathogen in swine in China, and a virulent Strep zoo strain has recently emerged in US swine.
There is an opportunity during this early phase of emergence in the US to limit Strep zoo before the more virulent strain becomes persistent. If diagnosed early, Strep zoo spread can be controlled through antibiotic therapy and/or culling followed by rigorous disinfection. However, if not detected in a timely manner, mortality can quickly reach 30 to 50 percent. The traditional method for detecting Strep zoo is via bacterial isolation in culture followed by biochemical tests and protein spectral analysis by MALDI-TOF spectrometry. This process requires 24 to 72 hours. Significantly, some recent isolates identified genetically as Strep zoo have demonstrated atypical MALDI-TOF and/or biochemical assay results. This
includes isolates identified at the Animal Diagnostic Laboratory at Penn State University. These discrepancies indicate a change in Strep zoo’s biology which could correspond with the more virulent and invasive strains noted in the latest Chinese and now Canadian and US swine mortality events. Relying on these traditional tests alone for Strep zoo diagnostics not only loses valuable time when Strep zoo is suspected but can also create false-negative
diagnostic results.
An alternative diagnostic procedure which is highly sensitive, rapid, and specific is the use of polymerase chain reaction. PCR can identify presence of a pathogen within hours instead of days. In this proposal we aim to optimize a PCR procedure for identification of Strep zoo in swine, including determining appropriate samples for reliable detection of Strep zoo. Due to the strong possibility of genetic mutation driving higher virulence of Strep zoo, we also propose to characterize the Strep zoo strains in PA by whole genome sequencing. Rapid and specific identification tools and in-depth analysis of the genetic sequences of emerging Strep zoo from swine can help to limit Strep zoo mortality and spread in PA swine. The aim of this project aligns with the board’s priority of “Advance Animal Agriculture in Pennsylvania
and the Eastern Region” and has significant economic benefits for PA soybean and swine producers.