Vaccination of yearling horses against poly-N-acetyl glucosamine fails to protect against infection with Streptococcus equi subspecies equi.

The research paper discusses an unsuccessful attempt to protect yearling horses from a bacterium reported to cause strangles, a common horse disease, through vaccination targeting a specific antigen expressed by the bacterium.

Introduction and Background

• The paper centers on a condition known as strangles, which is a prevalent and widely distributed disease affecting horses globally. This disease is caused by Streptococcus equi subspecies equi (SEE), a particular bacterium.
• Despite the existence of vaccines created to combat strangles, the effectiveness and safety of these vaccines have posed significant concerns. The research aims to address these limitations through the potential use of another type of vaccine targeting the microbial surface antigen β 1→6 poly-N-acetylglucosamine (PNAG), which is produced by SEE.

Methodology and Experimental Outcome

• The researchers administered intramuscular (IM) injections alone or combined IM and intranasal (IN) immunizations to generate antibodies to PNAG in horses. These antibodies functioned to deposit complement (a component of the immune system) while also facilitating the process of opsonophagocytic killing of SEE ex vivo (outside a living organism).
• Unfortunately, the immunization strategies targeting PNAG failed to protect yearling horses from infection when contact was made with infected horses, demonstrating that this approach does not work under experimental conditions.

Implications and Speculations

• The study’s findings imply that the immunity generation mechanism via PNAG targeted immunization is ineffective against the strangles causing bacterium in a real-world setting, despite being theoretically valid.
• The researchers speculate that a protective vaccine against strangles will need supplementary elements. For instance, components targeting SEE enzymes that degrade or neutralize horse IgG (a type of antibody) might be required to create a potent and protective response against the disease-causing bacteria.