A great challenge! Developing an effective vaccine against Streptococcus suis

Managing this disease is frustrating for farmers, as the pork industry is increasing its effort to reduce antibiotic use and there are no available vaccines that effectively fight infections caused by this encapsulated bacterium. In fact, the only vaccines available and used on farms are made with whole cell inactivated bacteria (bacterin) and most are autogenous vaccines. These are low cost solutions, but the protective effects are controversial and, when observed, the protection is generally limited to similar bacterial strains.

Looking for a universal vaccine

A serotype is associated with a number (e.g. serotype 2) to classify bacteria according to the reaction of specific antibodies against an antigen produced by the bacteria. In the case of S. suis, the polysaccharide capsule (CPS) is the antigen used for serotype classification. However, a factor that complicates vaccine development is that there are lots of differences between strains sharing the same serotype. This highlights the need to focus our research efforts on developing a universal vaccine, or at least one that is effective against the serotype(s) most associated with infection.

A research team at CRIPA composed of an immunology professor, Mariela Segura (Faculty of veterinary medicine, Université de Montréal) and a chemistry professor, René Roy (Canadian Research Chair in Therapeutic Chemistry, UQAM), applied a technique that is typically used in human vaccinology to develop the first glycoconjugate vaccine in swine medicine that targets the polysaccharide capsule of S. suis serotype 2. This serotype is the most virulent and common cause of infection worldwide for this dreaded zoonotic pathogen. To build the glycoconjugate vaccine, the technique requires the addition of the S. suis polysaccharide capsule to the tetanus toxoid, a protein that is used safely in animals and humans to induce an immune response. In mice and pigs, this vaccine was demonstrated to be effective and, therefore, was protective against S. suis.

Reaching the next level

The vaccine formulation must be improved and a simple, low-cost chemical method must be developed for this vaccine to become widely used in porcine medicine. This vaccine prototype also opens the door for the future development of a human vaccine, especially in regions where people are at high risk of contracting S. suis infections such as in Asia where this zoonotic pathogen is common.