Strep suis immunity based on some Dutch research, By Clint Lichti from South West Ontario Veterinary Service

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.