Molecular epidemiology of Streptococcus zooepidemicus infection in naturally occurring equine respiratory disease.

This research explores the occurrence and diversity of the bacteria Streptococcus zooepidemicus in respiratory infections in Welsh mountain ponies. The study identifies different types of the bacterium and tracks their prevalence over time in infected ponies.

Study Design

• The study was designed to understand the molecular epidemiology, or the distribution and determinants of different strains of S. zooepidemicus over time
• Living conditions of the ponies selected for study were accounted for, they were recently weaned and pastured
• Sampling occurred weekly over a 10-week period in 29 ponies, both from nasopharyngeal swabs (from the nose and throat) and tracheal washes (from the windpipe)

Identification of S. zooepidemicus

• To identify and categorize the different strains of S. zooepidemicus found in the samples, two Polymerase Chain Reaction (PCR) typing methods were used. These methods relied on characterizing differences in the M-protein hypervariable region, a part of the bacteria that often varies between strains, and the 16S-23S rRNA gene intergenic spacer, another diverse area of the bacterial genome.

Findings

• Infection by S. zooepidemicus was prevalent in this population of ponies, being identified in both the tracheal and nasopharyngeal samples of nearly all animals tested
• A total of 39 different types of S. zooepidemicus were identified over the course of the study
• More types were found in the trachea than in the nasopharynx
• The temporal patterns in the detection of different S. zooepidemicus types suggests a pattern of clonal succession, in which one strain becomes dominant over time
• Several new or previously unidentified S. zooepidemicus types were discovered. These included previously untyped HV regions and multiple examples of both HV and intergenic spacer types within a single strain

Implications

• The findings of this study contribute to the understanding of S. zooepidemicus epidemiology in naturally occurring pony respiratory disease
• The discovery of previously unknown types of S. zooepidemicus indicates that there is a lot more to understand about this bacteria
• The high prevalence of the bacteria in the examined ponies suggests that it is a significant concern for this population
• The clonal succession observed over time could have implications for treatment and control of the bacteria in equine populations