Streptococcus suis (S. suis) continues to be a health problem in pig production on a global basis. S. suis serotype 2 is a frequently isolated serotype globally but within regions a number of other serotypes can present a significant pathogen burden in various aged pigs. In the Netherlands , where this study took place, there has been an emergence of S. suis serotype 9 as a more significant problem. It is well known that adult and young pigs can carry S. suis in the nose, tonsils, nasopharynx as well as in the genital tract, mammary glands and gastrointestinal tract piglets can be colonized by more than one serotype. Some colonization will initially occur during the suckling period with exposure to shedding sows, littermates and other contaminated fomites. Colonization continues after weaning.
There is a transition that occurs between protective maternally derived immunity and active immunity associated with growing pig infection. There can be an “immune gap” that occurs when decreasing maternal derived antibodies (MDA) and insufficient levels or functionality of actively produced antibodies in weaned pigs such that there is a period where growing pigs have an increased susceptibility to S. suis infections. The researchers did point out that in addition to MDA there is a role for other parts of the immune system such as the transfer of pathogen-specific T cells by colostrum that could enhance and guide the development of active immunity in the growing pig. This cellular immunity was not measured in this study. In order to better understand these dynamics the researchers from the Netherlands conducted two studies. Study I evaluated the associations between sow antibodies in colostrum and serum, birth parameters (e.g., birth weight, colostrum intake and piglet growth) and the levels of S. suis-specific (serotypes 2 and 9) antibodies in one-day-old piglets from four farms. Study II used one of the farms from study 1 to evaluate S. suis-specific and total antibody kinetics in piglets (10 litters with 6 selected piglets per litter, total n = 60) from birth until 10 weeks of age. Additionally, tonsil swabs from sows and piglets were taken to evaluate the S. suis tonsillar carrier status (serotypes 2 and 9) before and after weaning.
The researchers found the following:
- Across farms colostrum intake, birth weight, weight on day 1 and Ss9Ab level in colostrum had a significant positive association (P < 0.05) with the amount of S. suis-specific antibodies in one-day-old piglets. Study 1 demonstrated that there was a lot of variability in serum and colostrum antibody levels between and within the four farms.
- Piglets born later in the farrowing process acquired fewer S. suis-specific antibodies.
- All piglet tonsils were colonized with S. suis serotype 9 before weaning. Although many piglet tonsils were colonized with S. suis serotype 2 by weaning the colonization gradually progressed during the nursey phase.
- Even sows with high levels of antibodies in colostrum due to natural exposure or autogenous prefarrowing vaccine appeared to infect a percentage of their piglets.
- S. suis-specific Maternally Derived Antibodies (MDA) were at their peak at 24 hours of age in piglets. This makes sense in that “gut closure” to colostral antibodies has occurred by 24 hours of age and therefore there will be no additional colostral antibodies entering the piglets body after 24 hours.
- After 18 to 19 days of age there was an increase in S. suis specific antibodies in the growing pigs and the researchers believed this was due to actively acquired immunity. The antibody test that they used could not differentiate maternal vs actively acquired antibodies but this was still a pretty safe assumption. Colostrum intake, birth weight and 24-h weight gain after birth were important parameters that were positively associated with S. suis antibody levels in piglets after birth but also affected these antibody levels at a later age. Chart 1
- The researchers commented that several other studies showed that piglets started to produce IgM antibodies (Early active response) around 6 to 10 weeks of age and that it wasn’t until 7 weeks of age that weaned pig antibodies were present in optimal quantity and functionality to aid in the killing of S. suis
Take Home Messages:
- Total serum immunoglobulins or antibodies that provide immunity to S. suis declined after birth and reached their lowest level just before weaning (18 to 19 days average).
- There were differences between the timing of colonization between the S. suis serotype 2 and serotype 9 with serotype 9 being much more prone to achieving early and almost complete colonization in this study.
- The researchers recommended that producers should focus on piglets with low birth weights and late-born piglets for colostral management when time is limited given that both of these factors will reduce the S. suis-specific MDA preweaning and the specific antibodies acquired postweaning.
- Transition periods between declining MDA and active antibody production can present an opportunity for disease. We need to optimize both types of antibodies in order to survive “The Changing Of The Guard”
Reference: Sandra Vreman , Rutger Jansen , Mikael Bastian , Patricia Beckers , Miriam van Riet , Helmi Fijten , Jan Fledderus , Astrid de Greeff , Hélène Winkelman , Norbert Stockhofe-Zurwieden , Lluís Fabà , Henk J Wisselink , Manouk Vrieling The kinetics of maternal and self-developed Streptococcus suis-specific antibodies Porcine Health Manag . 2025 Feb 7;11(1):7. doi: 10.1186/s40813-025-00422-z.
