Affiliation:
1. Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa, USA
2. Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
Abstract
ABSTRACT
Streptococcus equi
subspecies
zooepidemicus
(
S. zooepidemicus
) was reported to cause epizootic outbreaks in swine, resulting in significant economic losses in Asia in the 1970s and in North America in 2019. In February 2021, another outbreak due to
S. zooepidemicus
occurred in 2-year-old adult sows in a production system in Indiana. Whole-genome sequencing analysis of three outbreak isolates from Indiana revealed that all were genetically distant from the isolates of a strain that caused high mortality events in Ohio and Tennessee in 2019, as well as from the ATCC 35246 strain that caused outbreaks in China in the 1970s. The Indiana outbreak isolates were also distantly related to outbreak-unrelated swine isolate AZ-45470 from Arizona but closely related to an
S. zooepidemicus
equine isolate from Iowa. Comparative genomic analysis revealed that one genomic island, GI-13, was unique to the genome of a representative Indiana outbreak isolate, IN-6992. The genomic islands GI-1, GI-3, and GI-10 were also present in IN-6992 but absent from the Ohio and Tennessee outbreak isolates. In addition, the ATCC 35246-type
szM
gene and the Fic domain-containing protein gene (
bifA
) were absent from IN-6992, while present in all isolates from the Ohio and Tennessee outbreaks. Our findings have significant implications for understanding, monitoring, and developing control measures against diseases caused by
S. zooepidemicus
.
IMPORTANCE
This study highlights a
Streptococcus equi
subspecies
zooepidemicus
(
S. zooepidemicus
) strain isolated from an outbreak in Indiana, which resulted in mortality events among a swine herd in 2021. The Indiana outbreak strain was found to be genetically and phylogenetically distant to a strain isolated from the 2019 outbreaks in Ohio and Tennessee, which caused high swine mortality. We also discovered multiple unique genetic features in the Indiana outbreak strain, including distinct
S. zooepidemicus
genomic islands, and notable
S. zooepidemicus
virulence genes—many of which could serve as biomarkers for the diagnosis of this strain. These findings provide significant insights into monitoring and potentially preventing severe outbreaks caused by the Indiana outbreak strain in the future.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
1 articles.
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