Streptococcus equi subsp. zooepidemicus infection in pigs: vaccine evaluation and environmental survival studies
Date
2023-09-15
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-8788-8166
Type
Thesis
Degree Level
Masters
Abstract
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.
Description
Keywords
zooepidemicus, swine, vaccine, sudden death, bacterial survival
Citation
Degree
Master of Science (M.Sc.)
Department
Western College of Veterinary Medicine
Program
Large Animal Clinical Sciences