Clinical and epidemiological investigation of chronic upper respiratory diseases caused by beta-haemolytic Streptococci in horses.

A study investigated an outbreak of disease resembling strangles in horses in central Italy, using several diagnostic methods. It found that beta-haemolytic streptococci other than Streptococcus equi may be responsible for the disease.

Methodology and Investigation Details

• The research was motivated by an outbreak of a disease that was similar to strangles, in which horses suffered from upper respiratory conditions. This outbreak involved 26 horses in central Italy.
• Several diagnostic techniques were used to investigate the disease. These included clinic examinations, endoscopy, cytology, bacteriology, and polymerase chain reaction (PCR).
• Sample collection included three nasal swabs and one guttural pouches lavage fluid (GPLF) from each involved horse at weekly intervals.

Findings and Analysis

• None of the horses were found to be carriers of Streptococcus equi subsp. equi, the bacterium typically associated with strangles. There were signs of disease, however, such as pharyngeal lymphoid hyperplasia (enlarged pharyngeal lymph nodes) and changes in the endoscopic appearance of the guttural pouches.
• Different types of bacteria were isolated from the horses. Streptococcus dysgalactiae subsp. equisimilis was found in 14 horses, and S. equi subsp. zooepidemicus was found in six horses.
• PCR helped confirm the identification of these bacteria, which was first done via biochemical and serological tests. Additionally, PCR was able to detect these bacteria in 10 cases where bacteriological tests were negative.
• The findings suggest that other beta-haemolytic streptococci Aside from S. equi, specifically S. dysgalactiae subsp. equisimilis and S. equi subsp. zooepidemicus, could be causing the strangle-like disease.

Significance

• This research may inform the development of more effective diagnostic, prevention, and treatment strategies for dealing with chronic upper respiratory diseases in horses.
• As the study suggests that non-S. equi Streptococci bacteria may be the causative agents, future research into respiratory diseases in horses may need to extend beyond the traditional focus on S. equi.