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Streptococcus equi subsp. zooepidemicus infection in pigs: vaccine evaluation and environmental survival studies



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Streptococcus equi subsp. zooepidemicus (Strep. zoo) in swine has been a concern in North America after its initial detection in 2019, where it was associated with increased mortality and high abortion rates. Historically, the ST-194 strain was associated with the death of more than 300,000 pigs during the 1970s in China. There is no approved vaccine for this disease and limited information about the disease in swine operations. Overall, our objective was to assess the efficacy of a novel live attenuated vaccine in preventing this disease and determine the viability of the bacteria in different farm-like conditions. First, a live attenuated vaccine was evaluated. Thirty-nine, 5-week-old pigs were allocated to three groups: live vaccinated (20), killed vaccinated (10) and placebo (n = 9). Four pigs were euthanized a week after vaccination to assess the safety of the vaccine. The other pigs were given two doses of the vaccine 23 days apart. Pigs were challenged with a virulent strain 42 days after the initial dose. No mortalities were observed in H1 vaccinated while 100% mortality and 66% mortality occurred in pigs receiving the killed vaccine and placebo, respectively. A second experiment evaluated the survival time of Strep. zoo under farm conditions. Strep. zoo was spread on the surface of rubber, plastic, wood, and concrete. Samples were incubated under ideal culture conditions (37°C, 5% CO2) or farm-like conditions (20°C, air), in the presence of absence of feces. In a farm setting, the bacterium can survive up to 17 days under ideal conditions without feces, and up to 3 days under farm conditions with feces. This work described a novel live attenuated vaccine which can be used to prevent clinical sign and deaths in pigs. The oral or nasal route of vaccination ensures that mass vaccination can be easily achieved. Similarly, the results on viability time of Strep. zoo under different conditions iv and the different surfaces provided valuable information to develop elimination plans from operations affected with Strep. zoo pathogen during the outbreak.



zooepidemicus, swine, vaccine, sudden death, bacterial survival



Master of Science (M.Sc.)


Western College of Veterinary Medicine


Large Animal Clinical Sciences


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