Streptococcus suis
LEVELS: Sometimes occurs; Severe; Already in the herd; Laboratory-dependent; Moderate; Negligible; Little; Available but inconsistent
| Register id | streptococcus_suis |
| Type | bacteria |
| Scientific name | Streptococcus suis |
| NCBI taxid | 1307 |
| Evidence | 6 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Streptococcus suis is the most important streptococcal pathogen of pigs worldwide. It lives in the tonsils, nose, genital tract and saliva of healthy carriers and passes from sow to piglet and then pig to pig, so essentially every herd has it. Disease appears mainly in five- to ten- week-old pigs as septicaemia, meningitis — the classic paddling, convulsing nursery pig — joint and serosal inflammation, and heart valve infection. Whether a carrier pig becomes a sick pig depends on the virulence of the strain, immunity, management, and co-infection, PRRSV especially. Twenty-nine serotypes are recognised; serotype 2 dominates in Europe and Asia while North America carries more variety, which makes vaccination difficult and pushes farms towards autogenous bacterins. It is a serious zoonosis. In people it causes meningitis that frequently leaves permanent hearing loss, and in parts of Southeast Asia it is among the commonest causes of adult bacterial meningitis, acquired mainly by eating raw or undercooked pork; two Chinese outbreaks, in 1998 and 2005, each killed more than fifty people with a toxic-shock-like syndrome.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Sometimes occurs: Known risk of transmission to humans (foodborne or occupational), but requires failure of one or more control points for transmission to humans
Basis. Farias 2026: "Human infection occurs primarily through skin wounds or consumption of contaminated pork". Bakpatina-Batako 2025, reviewing all 47 documented South American cases: "Infections were primarily linked to pig or pork exposure, although some occurred after consuming undercooked meat", with exposure recorded as "contact while handling pigs for consumption, consuming undercooked pork, hunting wild boars, or a combination of those factors". Farias 2026 also describes S. suis as "considered an occupational disease agent in humans". Yao 2026 frames the whole review as farm to fork, calling S. suis "An Emerging Foodborne Threat".
How this level was decided
UNCHANGED at level 3, but on far better evidence than the single chapter sentence it previously rested on. Every route these papers describe is a control-point failure: a skin wound during handling or butchery, or pork eaten undercooked. Gloves, hand hygiene and cooking are exactly the control points C1 names, and where they hold, transmission does not occur. Eric made the same argument from the other direction on 2026-08-26: the US "has not had the abattori-related outbreaks in humans that have been reoprted in Asia, I suspect due to different abattoir condistions/worker safety rahter than anything different about the organism itself." That is control points working, which is level 3 and not level 4.
C2 Zoonotic impact
Severity of human illness caused by the agent
Severe: Infection carries a substantial risk of life-threatening illness, death, or permanent disability, even if human infections are uncommon
Basis. CFSPH 2020: S. suis "has emerged as a significant agent of streptoccoccal meningitis, septicemia, toxic shock-like syndrome and other human illnesses, especially in parts of Asia."
How this level was decided
Level 4 unchanged, and this is the third document to carry it. Eric corrected this cell to level 4 on 2026-08-26 on the human burden; meningitis, septicaemia and streptococcal toxic shock syndrome are a substantial risk of death or permanent disability, including deafness in survivors.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Already in the herd: Present in most herds, or carried by pigs themselves, so there is no introduction event to prevent
Basis. "Transmission of virulent strains between herds usually occurs by the introduction of carrier pigs." The chapter treats S. suis as a normal inhabitant of the upper respiratory tract, present in essentially all herds. (ch57 §57.2.3.2)
How this level was decided
This is the level 1 case the criterion was rewritten for. S. suis is carried by healthy pigs as normal flora, so there is no introduction event to prevent -- the herd already has it. What varies between herds is which strains are present, which is a different question from exclusion.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Laboratory-dependent: The presentation does not point to this disease specifically, but local or regional laboratories can confirm it with a validated assay once it is suspected
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "l2, straightforward to diagnose"
Basis. "until very recently, isolates belonging to serotypes 2 and 1/2, as well as those of serotypes 1 and 14, could not be differentiated by polymerase chain reaction... some of these isolates remain untypable even by PCR." (ch57 §57.2)
How this level was decided
Culture and identification are routine work for a regional laboratory. Serotyping is harder and sometimes fails, but the criterion asks about recognising and confirming infection, not about strain characterisation.
C5 Production cost
Financial impact on the infected farm's cost of production
Moderate: Losses measurably increase cost of production but remain manageable within normal farm operations, whether acute, chronic, or associated with endemic disease
Basis. "Streptococcus suis-associated diseases are some of the most important bacterial infections affecting nursery piglets and significantly affect swine production worldwide." "the average cost of S. suis per pig was recently established between 0.60 and 1.30 euros... in the absence of antimicrobials, mortality rates can reach 20%." (ch57 §57.2.1)
How this level was decided
A costed figure per pig, and 20% nursery mortality without antimicrobials. Measurable and material, but managed within normal operations rather than threatening farm viability.
C6 Market impact
Duration of material disruption to pork and pig markets
Negligible: Little or no material disruption to supply or demand when disease occurs on one or more farms
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "should be C6L1. S.suis is ubiquitous and US has not had the abattori-related outbreaks in humans that have been reoprted in Asia, I suspect due to different abattoir condistions/worker safety rahter than anything different about the organism itself."
Basis. CFSPH 2020 describes S. suis as "mainly a pathogen of suids... maintained in both domestic pigs and wild boar", ubiquitous in pig populations, with human cases concentrated in parts of Asia. It records no trade measure, movement control or consumer response following a swine diagnosis.
How this level was decided
Level 1 unchanged but now SUPPORTED rather than inferred. The standing note SCORING/market_impact applies cleanly: S. suis is endemic in US herds and routinely diagnosed, and no diagnosis has ever moved the market. The Asian human outbreaks did not disrupt US pork.
C7 Treatment potential
Potential for treatment to improve outcomes
Little: Effective pathogen-directed treatment is available and works, or animals recover acceptably without it
Basis. "in the absence of antimicrobials, mortality rates can reach 20%", implying they are effective when used; §57.2.8 Treatment discusses the choice of antibacterial agent. (ch57 §57.2.8)
How this level was decided
Effective pathogen-directed treatment exists and works -- the chapter's framing is which antimicrobial to choose, not whether one helps. Resistance is a real and growing concern but the criterion asks whether treatment improves outcomes today.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Available but inconsistent: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Basis. Chapter 57: "The most common S. suis vaccines tested in the literature are bacterins (killed whole bacteria), either experimental or autogenous. Very few commercial bacterins are available. Autogenous vaccines (also bacterins) are by far the most common product used as an alternative to the use of antimicrobials to control S. suis diseases." On their reliability: "difficult to control without the use of antimicrobials and through vaccination only, without taking into consideration predisposing factors", and strains for autogenous vaccines "should be isolated from systemic sites such as meninges, spleen, liver, and joints, and not from lungs, nasal cavities, or tonsils".
How this level was decided
MOVED FROM LEVEL 3, AND NOT BECAUSE OF THE NEW PAPERS -- this was a misreading of the chapter that was already in the folder. Level 3 means "effective vaccines not currently available in the US (or have not been developed)". The chapter says the opposite: a few commercial bacterins exist and autogenous bacterins are by far the most common control product in use. That is level 2, "commercial or autogenous vaccines exist in the US but protection may be inconsistent" -- and inconsistent is precisely what the chapter describes, with efficacy depending on serotype match and on which body site the strain came from. Flagged for Eric because this is the point raised on 2026-08-26 as a worked example and then withdrawn for being attributed to him; it was right on its merits and is now scored from the evidence rather than put in his mouth.
Levels and evidence are generated from data/assignments/streptococcus_suis.yml; the overview is authored in data/overviews/streptococcus_suis.md. Do not hand-edit this page — corrections go in data/assignments/CORRECTIONS.yml.
Quoted material marked Basis is from Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, Zhang J, eds. Diseases of Swine, 12th edition. Hoboken: Wiley Blackwell, 2025 — except where another source is named in the quotation itself.