New vaccine against Streptococcus suis in the making

Streptococcus suis infections can make young pigs very sick with meningitis, arthritis or blood poisoning, often even killing them. Farmers all over the world use antibiotics to combat the disease, but S. suis strains are becoming increasingly resistant to commonly used antibiotics. A new vaccine may be the solution.

Sows carry several strains of Streptococcus suis on their tonsils and in the nose without becoming ill themselves. They transmit the virus to the sensitive young piglets via the nose, vagina or orally. “The disease can progress very rapidly and intensively,” says infection biologist Jerry Wells. “Piglets lose their coordination, suffer spasms due to sepsis (the growth of bacteria in the blood) and can die from the infection. People who work with pigs can also become infected and develop meningitis, which is occasionally even fatal.The disease also causes economic damage to farmers, for example in the form of stock losses and the costs of treating the animals. There is currently no vaccine available that effectively protects against all S. suis infections.”

Bacteria from all

Researchers of the Host-Microbe Interactomics chair group want to increase the knowledge of Streptococcus suis and are developing a vaccine that protects against multiple strains. To do this, they collect hundreds of Streptococcus suis strains from pigs all over the world – from Vietnam to Germany and Canada – in cooperation with various partners (see box). “We examine the DNA from a genome (the complete genetic makeup of the bacteria) and select proteins that occur in all pathogenic Streptococcus suis strains that have a high likelihood of inducing an effective cross-protective immune response. The proteins on the outer surface of bacteria are often ideal for this purpose. Such proteins also often play a key role in the development of the disease. The vaccine antigens are produced in laboratory strains of harmless E. coli bacteria and then purified. The body produces antibodies against the vaccine after it has been injected and these bind to the bacteria. The antibodies stimulate the phagocytic cells to absorb the pathogen. These phagocytic cells are specialised in killing bacteria and preventing piglets from falling ill.

Trial in 2021

The researchers currently have 20 protein candidates which they will test further in the laboratory. The best ones will be tested in a trial with young pigs in the summer of 2021. The research teams are also trying to identify a number of markers that can be used in a test to predict whether pigs are at risk of falling ill. “We hope that farmers will be able to identify which pigs are carrying large numbers of pathogenic Streptococcus suis by means of a nose swab. This can help identify animals for vaccination.”

Wells: “A vaccine against Streptococcus suis will help to reduce the use of antibiotics and the spread of resistance to antibiotics that are also used in humans,” says Wells. “The new vaccine will also improve animal welfare and reduce the risk of Streptococcus suis infections in humans.”