Outbreak of upper respiratory disease in horses caused by Streptococcus equi subsp. zooepidemicus ST-24.

This study explores an outbreak of upper respiratory disease in horses, believed to be caused by a particular strain of the bacterium Streptococcus equi subsp. zooepidemicus. Common among horses, the specific ST-24 strain was isolated in all affected horses, suggesting that certain strains may be more virulent than others.

Objective of the Study

• The primary goal of the research was to determine if specific strains of the bacterium Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) could cause upper respiratory diseases in horses.
• The study also aimed to investigate whether there are certain genogroups of S. zooepidemicus that are more harmful than others.

Methodology

• The researchers analyzed upper respiratory samples from horses suffering from the disease. The samples were cultured and tested using real-time PCR for the presence of S. zooepidemicus and S. equi.
• Genetic differentiation was carried out using sequence analysis of the SzP protein gene and multi-locus sequence typing (MLST).
• Serum samples were also tested for antibodies against S. equi and common viral respiratory pathogens.

Findings

• The findings revealed that the ST-24 strain of S. zooepidemicus was isolated from all horses with clinical signs of disease, while other strains of S. zooepidemicus were found in healthy horses.
• Bacteriological, molecular, and serological analysis suggested that the ST-24 strain was responsible for the disease outbreak.
• The results imply that some strains of this bacterium, generally considered harmless in horses, might be more virulent or harmful than others.

Significance of the Research

• The study provides important evidence that specific strains of S. zooepidemicus can directly cause disease in horses, challenging the existing view of this bacterium as a mere opportunist or commensal organism.
• The finding has significant implications for the management of equine respiratory health and may lead to improved treatment and prevention strategies against disease caused by S. zooepidemicus.