Streptococcus suis Infection in Pigs: Meningitis, Sepsis, and Joint Disease
- See your vet immediately if a pig has fever, sudden weakness, paddling, tremors, head tilt, inability to stand, or severe lameness after weaning.
- Streptococcus suis is a major bacterial disease of post-weaned piglets and can cause septicemia, meningitis, arthritis, and sometimes sudden death.
- Early treatment matters. Many cases are treated with vet-directed beta-lactam antibiotics such as penicillin or amoxicillin, plus supportive care and isolation of affected pigs.
- Diagnosis usually needs a farm history, exam, and lab confirmation with bacterial culture. PCR may help confirm the organism, especially when samples come from the tonsils or upper airway.
- There is no universal commercial vaccine that works for all strains. Prevention focuses on reducing stress, improving ventilation and hygiene, managing mixing and weaning carefully, and controlling coinfections.
What Is Streptococcus suis Infection in Pigs?
Streptococcus suis is a bacterial infection of pigs that can lead to meningitis, septicemia, arthritis, and sometimes endocarditis. It is considered one of the most important bacterial pathogens in pigs, especially in post-weaned piglets. Many pigs carry lower-virulence strains in the upper respiratory tract without looking sick, but some strains can invade the bloodstream and spread to the brain, joints, and other tissues.
The disease often shows up 2 to 5 weeks after weaning, when pigs are dealing with stress from diet change, mixing, transport, crowding, or other infections. In some pigs, the first sign may be sudden death from overwhelming sepsis. In others, the most noticeable problem is neurologic disease, with paddling, tremors, incoordination, or inability to rise.
This infection also matters for people working with pigs because S. suis is zoonotic. Human infection is uncommon in the United States, but it can happen through close exposure to pigs or raw pork, especially when skin is broken. Good hygiene and protective equipment are important when handling sick pigs or tissues.
Symptoms of Streptococcus suis Infection in Pigs
- Fever
- Sudden death
- Ataxia or incoordination
- Paddling, tremors, or seizures
- Head tilt or abnormal posture
- Depression and reluctance to move
- Lameness or swollen joints
- Recumbency or inability to rise
- Occasional respiratory signs
See your vet immediately if a pig has neurologic signs, sudden collapse, high fever, or severe lameness, especially in the weeks after weaning. These signs can overlap with other serious swine diseases, including Glasser-like disease, erysipelas, salmonellosis, and viral infections. Fast evaluation helps your vet decide which pigs need treatment, which need isolation, and which samples should go to the lab.
What Causes Streptococcus suis Infection in Pigs?
Streptococcus suis is caused by infection with the bacterium S. suis, which commonly lives in the upper respiratory tract of pigs. Not every strain causes disease. Some are low-virulence colonizers, while others are more invasive and can enter the bloodstream, then spread to the brain, joints, heart, or body cavities.
Outbreaks are often linked to weaning stress, mixing litters, crowding, poor ventilation, temperature swings, transport, and other disease pressure. Coinfections can make problems worse. Merck Veterinary Manual notes that outbreaks are frequently reported alongside porcine reproductive and respiratory syndrome virus (PRRSV) and less often with swine influenza virus.
The bacteria are usually spread through close pig-to-pig contact and secretions from the nose and mouth. Small injuries to the mouth, skin, or mucous membranes may help bacteria invade deeper tissues. Farm-level risk rises when pigs are stressed, groups are unstable, sanitation slips, or there is ongoing circulation of virulent strains in the herd.
How Is Streptococcus suis Infection in Pigs Diagnosed?
Your vet will usually start with the age group affected, timing after weaning, clinical signs, and how many pigs are involved. Meningitis in recently weaned pigs raises concern for S. suis, but the signs are not unique to this disease. That means a presumptive diagnosis on signs alone is not enough for herd planning.
Confirmation usually requires bacterial culture from appropriate samples, such as tissues from affected pigs collected early in the disease course or at necropsy. Merck Veterinary Manual notes that diagnosis is suspected from history and signs and then confirmed by culture. Because other streptococci can live in the upper airway, PCR may be needed to confirm that isolates from the tonsils are truly S. suis.
Depending on the case, your vet may also recommend necropsy, joint fluid or tissue sampling, cerebrospinal or meningeal tissue testing, and antimicrobial susceptibility testing. These steps help separate S. suis from other causes of sepsis, meningitis, and lameness, and they guide a treatment plan that fits the pigs on your farm.
Treatment Options for Streptococcus suis Infection in Pigs
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Prompt exam by your vet or farm-call triage
- Isolation of affected pigs
- Empiric vet-directed injectable antibiotic therapy, often a beta-lactam when appropriate for the farm history
- Anti-inflammatory medication if your vet feels it is appropriate
- Fluids, warmth, easy access to water, and reduced competition
- Basic necropsy and limited sample submission from one representative pig when feasible
Recommended Standard Treatment
- Full veterinary exam and herd history review
- Targeted treatment of sick pigs plus pen or room-level management changes
- Culture and confirmation testing, with PCR support when needed
- Antimicrobial susceptibility testing when isolates are available
- Supportive care plan for neurologic and lame pigs
- Review of weaning flow, stocking density, ventilation, sanitation, and mixing practices
- Plan to address coinfections such as PRRSV or influenza if suspected
Advanced / Critical Care
- Comprehensive herd outbreak investigation with multiple sample submissions
- Necropsy of several representative pigs
- Expanded lab work including culture, PCR confirmation, serotyping support, and isolate comparison when available
- Detailed antimicrobial stewardship review and treatment protocol revision
- Consultation on autogenous vaccine use where legally and practically appropriate
- Facility, airflow, and production-flow review to reduce stress and transmission
- Intensive nursing or hospital-style care for high-value pigs when feasible
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Streptococcus suis Infection in Pigs
Bring these questions to your vet appointment to get the most out of your visit.
- Do my pigs' signs fit Streptococcus suis, or are other diseases equally likely?
- Which pigs should be treated right away, and which should be isolated or monitored?
- What samples should we collect for culture or PCR before treatment changes the results?
- Is the current antibiotic choice appropriate for our farm history, and do we need susceptibility testing?
- Could PRRS, influenza, or another coinfection be making this outbreak worse?
- What changes to weaning, mixing, ventilation, or stocking density would lower risk on our farm?
- Would an autogenous vaccine be reasonable in this herd, and what are its limits?
- What biosecurity steps should people use since this infection can also affect humans?
How to Prevent Streptococcus suis Infection in Pigs
Prevention is mostly about reducing stress and lowering bacterial spread. Focus on careful weaning, stable groups, good ventilation, clean water, dry bedding or flooring, and avoiding overcrowding. Because disease often appears after weaning, that period deserves extra attention. Small improvements in flow, temperature control, and mixing practices can make a meaningful difference.
Your vet may also look for coinfections, especially PRRSV and sometimes swine influenza, because these can increase the chance of outbreaks. Good herd health programs, quarantine of incoming pigs, and prompt attention to coughing, fever, or poor growth can help reduce the background disease pressure that lets S. suis become invasive.
There is no universal commercial vaccine that reliably protects against all S. suis strains. In some herds, your vet may discuss autogenous vaccines, but results vary and they are not a stand-alone solution. Prevention usually works best as a package: biosecurity, stress reduction, sanitation, thoughtful antimicrobial stewardship, and lab-guided herd planning.
Because S. suis can infect people, anyone handling sick pigs, carcasses, or raw tissues should use gloves, cover broken skin, wash hands well, and follow your vet's and farm's safety protocols.