Recent US experiences and a series of severe Streptococcus equi subspecies zooepidemicus outbreaks in Canada and globally since 2019 led to a Swine Health Information Center/American Association of Swine Veterinarians webinar on November 29, 2023. Presentations from Canadian and US experts provided 173 live participants from seven countries and 26 US states field experiences, background, and what you need to know to take action during a Strep. zoo outbreak. Access to the webinar, conducted by the Iowa State University Swine Medicine Education Center, is available for viewing here.
Prior to 2019, Strep. zoo had only been sporadically reported as causing disease in pigs in Asia. The first US cases with significant mortalities were reported in Ohio and Tennessee in 2019 with subsequent identification in Pennsylvania and Indiana. Outbreaks were also reported in Canada in 2019, 2021, and 2022.
Dr. Frank Marshall of Marshall Swine and Poultry of Camrose, Alberta, shared a recent client experience with Strep. zoo in their 5600-sow, three-site system during the webinar. He detailed the clinical picture from the farm, postmortem and necropsy findings, and the diagnostic process. Because clinical signs of Strep. zoo can mimic African swine fever and other hemorrhagic diseases, the differential diagnosis process requires diligence, including being aware of zoonotic potential.
Treatment and control options were detailed by Dr. Marshall with vaccination protocols, feed medication, and management aspects discussed. In all, over 750 sows from the affected sites died or were euthanized with a total cost exceeding $1 million. He also shared there are more questions to be answered and continued scrutiny will be necessary for appropriate preparedness and response efforts.
Dr. Marshall worked closely with Dr. Matheus Costa from the University of Saskatchewan on diagnostic workups. Dr. Costa outlined his work on Strep. zoo noting it is capable of infecting and colonizing a wide range of hosts. Dr. Costa called Strep. zoo a very adaptive bacterium and shared research showing it is a part of the normal microbiome of some, but not all, pigs.
Dr. Costa related findings showing a barn staff member who was extensively exposed to infected animals and secretions in the 2019 outbreak then worked in three different sites over three subsequent years, and those sites all broke with Strep. zoo, implying the survival of the infectious material on the workers’ attire caused spread of the pathogen. Consequently, Dr. Costa highly recommends a travel record of visitors to farm sites be maintained. His presentation touched on other biosecurity measures, concerns, and potential reservoirs of Strep. zoo. Importantly, he shared data showing the global emergence of Strep. zoo, with outbreaks identified in all continents, and the potential use of a vaccine to prevent disease in pigs.
Dr. Ganwu Li of Iowa State University shared information on the genetic analyses of strains causing the US Strep. zoo outbreaks in 2019 (Ohio and Tennessee) and 2021 (Indiana). In his presentation, Dr. Li noted the 2019 outbreak isolates from Ohio and Tennessee (caused 10-50% mortality rates) were closely related based on genetics. Further, these outbreak isolates were closely related to historical isolates from Asia but distant from an Arizona isolate from a pig, which lacked the virulence genes and was unassociated with any swine mortality events. In contrast, the 2021 outbreak isolate from Indiana, which caused a mortality of 2.75% in adult sows, was found to be distant from both Ohio and Tennessee outbreak isolates and the historical isolate from Asia. It was also distant from the Arizona isolate.
The final presentation during the webinar came from Dr. Gus Brihn, USDA Animal and Plant Health Inspection Service, who addressed zoonotic potential of Strep. zoo and stated there is still much to learn about the bacterium. From an infection prevention and control point of view, he recommended use of personal protective equipment when working with sick animals, hand hygiene, and husbandry, such as reducing activities stressful to swine, as keys to prevention. Dr. Brihn also shared USDA APHIS’s One Health interdisciplinary approach to help understand animal and human components of Strep. zoo.
The Swine Health Information Center, launched in 2015 with Pork Checkoff funding, protects and enhances the health of the US swine herd by minimizing the impact of emerging disease threats through preparedness, coordinated communications, global disease monitoring, analysis of swine health data, and targeted research investments. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Paul Sundberg at [email protected] or Dr. Megan Niederwerder at [email protected].