Streptococcus suis is one of the more frequent causes of bacterial-related nursery mortality in U.S. swine herds. All herds tend to maintain one or more resident strains of Strep with the impact that those strains have on herd health depending on several factors. Piglets are exposed and colonized by Strep bacteria during birth and throughout the lactation period.
Multiple Strep serotypes exist; some of which are considered part of the pig's normal microflora and do not induce clinical disease, while others are highly pathogenic and have the potential to cause severe clinical disease. Pathogenic strains of Strep maintain the ability to cross into the blood stream, allowing bacteria to travel systemically to several locations including the brain, joints, heart and multiple other critical organ systems. Infection of the brain induces the classic clinical signs we associate with Strep, including a lack of coordination, nystagmus and convulsions.
Joint infections can cause short-term swelling and stiffness as well as long-term damage to the joint space resulting in moderate to severe arthritis later in life. Alternatively, Strep infection can lead to sudden mortality without the presence of visual signs of infection. At Swine Vet Center we take a multifaceted approach including natural exposure, autogenous vaccine and antibiotic therapy to help control this frustrating bacterial disease.
Because Strep is a bacterial pathogen, antibiotics can be used to treat clinical disease when present in pigs. In some cases, those antibiotic treatment programs add a lot of cost and can be unsuccessful in controlling Strep disease in groups of pigs. When we describe the management of Strep with producers, ultimately the discussion revolves around two goals, reducing the level of disease pressures within the herd along with building the herd and individual pig immunity to Strep bacteria circulating within the herd. Once the herd has sufficient immunity to the pathogen the individuals within the herd will be able to protect themselves from the bacteria which helps prevent clinical disease and reduce antibiotic use.
The lessening of disease pressures isn't only the reduction of Strep alone. Strep doesn't seem to discriminate between excellent, moderate or poor health status herds. We know through several of our own experiences in the herds we work with that the greatest success in controlling Strep requires the management of some the biggest swine industry pathogens, including porcine reproductive and respiratory syndrome, Mycoplasma hyopneumoniae, circovirus and influenza. The immunosuppressive nature of these pathogens opens the door for more generalized bacterial infection which makes control increasingly difficult. Management of these primary pathogens through closures, vaccination and herd stabilization programs should be main part of any successful Strep control program.
Stabilizing the previously described pathogens is only one part of a complete Strep control program in herds. The other major component is the attempt to build immunity toward the specific Strep bacteria present within the herd. The generation of immunity against Strep infection within a herd is complicated. Autogenous vaccines built from the herd's strains of Strep do assist us in eliciting specific herd immunity for each system. Within a sow herd we utilize both autogenous vaccination and natural exposure to the adult population to generate immunity that helps to reduce shedding of these bacteria from sow to piglet and is passed to offspring in the form of colostrum.
For the piglet, the passive immunity gained through colostrum intake wanes over time as the piglet ages and at some point those young pigs will need to generate active immunity to defend against Strep infection. Pigs are being naturally exposed to several different strains of Strep prior to weaning, which helps in starting to stimulate active immunity in those pigs.
Keep in mind during this time, maternal immunity is defending against natural infection and in the case of farrowing, there may be antibiotic programs in place that lessen the amount of natural exposure that occurs in a young pig. Autogenous vaccine has had a lot of value in aiding natural exposure ability to build immunity during this time. Like many killed antigen vaccines, we feel that multiple doses to piglets give us the greatest success in creating piglet immunity to the specific Strep that will challenge those pigs.
Vaccine use in combination with the management strategies described above has yielded an improvement in Strep-related morbidity and mortality in the herds we consult with. When creating an autogenous vaccine it is important to obtain a flow-specific, pathogenic isolate from an animal exhibiting clinical signs. Sequencing of the Strep isolated gives us an idea about the pathogenicity of a particular isolate as well as help us determine relatedness to other Strep bacteria isolated within the herd.
To date, there is no single management strategy that can be implemented to completely eliminate Strep challenges from a flow. To make headway with this disease, it requires the combination of doing many little things right. This includes boosting immunity through autogenous vaccination, antibiotic use in a manner which allows piglet immune response generation from natural exposure both in the farrowing house and nursery, environmental management and supportive therapy in animals exhibiting clinical signs.
Antibiotics should always have a place in any Strep management program. Our goal is to reduce incidence of disease by utilizing all of the tools at our disposal and in the process reduce the need to use antibiotics.