What do you need to know about Streptococcus equi subspecies zooepidemicus? Prior to 2019, Strep. zoo had only been sporadically reported as causing disease in pigs in Asia. The first U.S. 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.
Frank Marshall, DVM, of Marshall Swine and Poultry in Camrose, Alberta, shared a recent client experience with Strep. zoo in their 5,600-sow, three-site system during a Swine Health Information Center (SHIC) and American Association of Swine Veterinarians webinar on Nov. 29. 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 and awareness of zoonotic potential.
Marshall shared treatment and control options, along with vaccination protocols, feed medication and management recommendations. 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, SHIC reports in its December newsletter.
Marshall worked closely with Matheus Costa, assistant professor from the University of Saskatchewan, on diagnostic workups. Costa explained that Strep. zoo is capable of infecting and colonizing a wide range of hosts. Strep. zoo is a very adaptive bacterium, he added, and shared research showing it is a part of the normal microbiome of some, but not all, pigs.
For example, he said 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, Costa highly recommends a travel record of visitors to farm sites be maintained, SHIC reports. His presentation touched on other biosecurity measures, concerns and potential reservoirs of Strep. zoo.
Ganwu Li, professor at Iowa State University, described the genetic analyses of strains causing the U.S. Strep. zoo outbreaks in 2019 in Ohio and Tennessee and 2021 in Indiana. In his presentation, Li noted the 2019 outbreak isolates from Ohio and Tennessee (caused 10-50% mortality rates) were closely related based on genetics, SHIC reports. These outbreak isolates were also 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.
Gus Brihn, USDA Animal and Plant Health Inspection Service, said there is still much to learn about Strep. zoo. 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.
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