Epidemiologic and immunologic characteristics of Streptococcus equi infection in foals.

The study investigates the impacts of Streptococcus equi infection on foals that have never encountered or have previously dealt with the infection, and finds that high serum S equi M protein-specific IgG levels at the start of the outbreak offer disease protection.

Study Design

• The researchers designed a 2-phase study to investigate Streptococcus equi infection impact on foals with no previous exposure and those that had already been exposed to this bacteria.
• In the first phase, 22 foals that were part of a naturally occurring epizootic of S. equi were examined along with a comparison group of 11 unexposed foals. This comparison group was carefully chosen to match the age, sex, and breed of the infected foals.
• Six months later, for phase two, an epizootic was artificially instigated amongst foals from the first phase, both exposed and unexposed.

Measurements

• Multiple variables were measured to determine the effects of the infection like the prevalence and duration of clinical signs, the risk of getting the disease relative to the exposure level, results from bacteriologic culture, hematologic responses, and both mucosal and serum immunologic responses.

Results

• The findings revealed that disease protection aligns with high quantities of serum S equi M protein-specific IgG at the initiation of the outbreak. This was statistically significant with P < 0.02 for phase 1 and P < 0.01 for phase II.
• Further, a rapid mucosal S equi M protein-specific IgG response, occurring within two weeks of exposure, was also associated with disease protection. This had statistical significance with P < 0.05 for phase I and P = 0.01 for phase II.

Conclusion

• The study suggests that a rapid mucosal response and high initial levels of specific serum antibodies, specifically IgG, can protect foals against Streptococcus equi infection.