Strangles organism, active case organism vs the inapparent carrier bacteria

Though the title is somewhat technical, the message for everyday horse owners is important. In this study they looked at the difference between the Strangles organism in active cases and those isolated from inapparent carriers, a known problem in horses. There was none. In other words, it seems likely that the difference is in the host (horse) that allowed for the inapparent carrier state. This is important because it means that inapparent carriers are immediately dangerous to a population of horses they are introduced to. The old injectable vaccine for Strangles had a questionable cost-benefit analysis. However, the intranasal vaccine has a more favorable profile when given carefully. See the article for more.
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Differences in the genome, methylome, and transcriptome do not differentiate isolates of Streptococcus equi subsp. equi from horses with acute clinical signs from isolates of inapparent carriers
PLoS One. 2021 Jun 14;16(6):e0252804.

Authors
Ellen Ruth A Morris 1 , Ashley G Boyle 2 , Miia Riihimäki 3 , Anna Aspán 3 , Eman Anis 4 , Andrew E Hillhouse 5 6 , Ivan Ivanov 7 , Angela I Bordin 1 , John Pringle 3 , Noah D Cohen 1
Affiliations

1 Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
2 Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, Kennett Square, Pennsylvania, United States of America.
3 Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
4 Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, Kennett Square, Pennsylvania, United States of America.
5 Department of Veterinary Pathobiology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
6 Texas A&M Institute for Genome Sciences and Society, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
7 Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.

Abstract

Streptococcus equi subsp. equi (SEE) is a host-restricted bacterium that causes the common infectious upper respiratory disease known as strangles in horses. Perpetuation of SEE infection appears attributable to inapparent carrier horses because it neither persists long-term in the environment nor infects other host mammals or vectors, and infection results in short-lived immunity. Whether pathogen factors enable SEE to remain in horses without causing clinical signs remains poorly understood. Thus, our objective was to use next-generation sequencing technologies to characterize the genome, methylome, and transcriptome of isolates of SEE from horses with acute clinical strangles and inapparent carrier horses-including isolates recovered from individual horses sampled repeatedly-to assess pathogen-associated changes that might reflect specific adaptions of SEE to the host that contribute to inapparent carriage. The accessory genome elements and methylome of SEE isolates from Sweden and Pennsylvania revealed no significant or consistent differences between acute clinical and inapparent carrier isolates of SEE. RNA sequencing of SEE isolates from Pennsylvania demonstrated no genes that were differentially expressed between acute clinical and inapparent carrier isolates of SEE. The absence of specific, consistent changes in the accessory genomes, methylomes, and transcriptomes of acute clinical and inapparent carrier isolates of SEE indicates that adaptations of SEE to the host are unlikely to explain the carrier state of SEE. Efforts to understand the carrier state of SEE should instead focus on host factors.