Streptococcus zooepidemicus
LEVELS: Sometimes occurs; Severe; Routine biosecurity keeps it out; Laboratory-dependent; Substantial; Negligible; Some; Needed but not available
| Register id | streptococcus_zooepidemicus |
| Type | bacteria |
| Scientific name | Streptococcus equi subsp. zooepidemicus |
| NCBI taxid | 40041 |
| Evidence | 4 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Streptococcus equi subsp. zooepidemicus is a group C streptococcus best known in horses, which has emerged as a cause of explosive septicaemic outbreaks in pigs. It was first described in swine in a 1975 outbreak in western China, and in 2019 sequence type 194 appeared in North America — genetically close to that 1970s Chinese strain — causing outbreaks with 50–90% mortality in sows and feeder pigs. Any pig after weaning is susceptible. Signs come on fast: fever above 40 °C within eight hours of infection, lethargy, huddling, reluctance to stand and loss of appetite, with sows aborting at any stage. Post-mortem findings are those of a bacterial septicaemia — pinpoint haemorrhages in many organs, a haemorrhagic gallbladder, congested spleen and enlarged lymph nodes. It is probably underreported in Southeast Asia. There is no effective vaccine: killed bacterins and prior exposure to related strains do not prevent it, and control rests on prolonged antimicrobial treatment, with depopulation used when that fails.
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. cfsph_2020_streptococcosis names the pig route among the food routes: "some organisms have been acquired in UNDERCOOKED PORK PRODUCTS (E.G., S. SUIS, S. EQUI SUBSP. ZOOEPIDEMICUS), HORSEMEAT (S. equi subsp. zooepidemicus)... or unpasteurized dairy products (S. equi subsp. zooepidemicus and other organisms)." On the animal-contact route: "Clinical cases have occurred AFTER EXPOSURE TO HEALTHY COLONIZED ANIMALS AS WELL AS THOSE THAT WERE SICK, such as horses or dogs with respiratory disease. There were also a few outbreaks linked to the consumption of unpasteurized dairy products, and some cases with no obvious zoonotic or foodborne source." On carriage: "S. equi subsp. zooepidemicus is a common commensal and opportunistic pathogen in horses. GUINEA PIGS, PIGS AND MONKEYS ALSO SEEM TO BE CARRIERS." The control points are named in the Prevention section: "Avoidance of unpasteurized milk products, UNDERCOOKED PORK PRODUCTS or raw fish helps prevent foodborne illnesses caused by S. equi subsp. zooepidemicus, S. suis or S. agalactiae ST283... Particular care should be taken when cleaning fish or BUTCHERING PIGS. Protective clothing and gloves should be used when treating sick animals." ma_2024 adds the emphasis from the other side: "The human infections with SEZ are PRIMARILY ACQUIRED THROUGH DIRECT OR INDIRECT CONTACT WITH HORSES or infected animals, or by exposure to bacteria through animal-derived food products that have not been adequately sterilized... SEZ is more prevalent in areas where HORSES are bred in large quantities and where raw meat or unpasteurized dairy products are consumed." shic_2021_szoo: "Zoonotic disease due to S. zooepidemicus is relatively uncommon. Illness is mostly associated with consumption of unpasteurized dairy products or animal contact." "In the 1980s, an outbreak of septicemia in Hong Kong was linked to pork consumption."
How this level was decided
Level 3, and it is scored the same as streptococcus_suis in the same chapter, which is the right company for it. Both halves of the level 3 label are met: a known risk of transmission, both foodborne and occupational, that requires a control point to fail -- and the folder names the control points explicitly, cooking pork and gloves when handling sick animals. NOTE WHAT COULD HAVE PULLED THIS TO LEVEL 1 OR 2 AND WHY IT DOES NOT. Both documents put HORSES at the centre of the human epidemiology, and Ma is explicit that human cases follow horse contact and unpasteurized dairy; on the pig-attribution reasoning you have used three times now -- Clostridium perfringens type C, chikungunya, Actinobacillus suis -- an agent whose human cases all trace elsewhere sits at level 1. IT DOES NOT APPLY HERE, because CFSPH names undercooked PORK products as a documented acquisition route and tells people to take particular care butchering pigs. The pig link is stated, not inferred from the genus. Level 3 confirmed. A human septicaemia outbreak linked to pork consumption is transmission from pigs after a control point failed.
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_streptococcosis: "S. EQUI SUBSP. ZOOEPIDEMICUS, IN PARTICULAR, HAS BEEN ISOLATED FROM A WIDE RANGE OF MILD TO SEVERE ILLNESSES, FROM SKIN INFECTIONS TO TOXIC SHOCK SYNDROME AND POSTSTREPTOCOCCAL GLOMERULONEPHRITIS. FOODBORNE OUTBREAKS caused by this organism or S. agalactiae ST283 CAN RESULT IN SERIOUS ILLNESSES SUCH AS PNEUMONIA, MENINGITIS, ENDOCARDITIS, SEPTIC ARTHRITIS AND ACUTE NEPHRITIS." On outcome: "S. equi subsp. zooepidemicus is most often reported in immunocompromised individuals with comorbidities, BUT HEALTHY PEOPLE CAN BE AFFECTED... The mortality rate varies with the syndrome. STREPTOCOCCAL TOXIC SHOCK-LIKE SYNDROME IS PARTICULARLY SERIOUS DUE ITS RAPID ONSET AND CLINICAL COURSE, AND MANY CASES ARE FATAL EVEN WITH TREATMENT. ONE REPORT SUGGESTED A CASE FATALITY RATE OF 63%." ma_2024 is a review devoted to the point: "S. suis and SEZ are TWO EMERGING AGENTS OF ZOONOTIC INFECTIONS WITH SEVERE MENINGITIS IN HUMANS", and the prevalent lineage ST194 is "a major causative agent of swine and human streptococcosis, leading to symptoms like SEPSIS AND MENINGITIS." shic_2021_szoo: "Humans may develop pharyngitis, glomerulonephritis, skin/soft tissue infection, toxic shock syndrome, infectious arthritis, and invasive disease."
How this level was decided
Level 4, and the folder states it rather than implying it. The label asks for a substantial risk of life-threatening illness, death or permanent disability EVEN IF HUMAN INFECTIONS ARE UNCOMMON, and a 63% case fatality rate in toxic shock-like syndrome, with meningitis, endocarditis and acute nephritis in foodborne outbreaks, is squarely that. Scored level with Streptococcus suis, Brucella suis, Taenia solium and Nipah virus. NOTE THE LINEAGE POINT, because it is what makes this a pig question rather than a horse one: ST194 is the lineage behind both the 2019 North American swine outbreaks and human streptococcosis, so the strain killing pigs in Minnesota and Kansas is from the branch that causes severe human disease. Level 4 confirmed -- toxic shock syndrome and invasive disease.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Routine biosecurity keeps it out: Quarantine of incoming stock, transport and fomite control, cleaning and disinfection, and the usual monitoring reliably exclude it
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c3l3, can't be higher than l3 because most herds have not been infected, suggesting normal biosecurity is adequate for exclusion. however, the epidemiology around the clinical disease has not been satisfactorily described and it remains an important emerging pathogen"
Basis. ch57 57.3.3: "In 2019, S. ZOOEPIDEMICUS SEQUENCE TYPE (ST) 194 EMERGED IN NORTH AMERICA, associated with high mortality outbreaks affecting sows and feeder pigs... ALL NORTH AMERICAN ISOLATES linked to high-mortality outbreaks are, so far, GENETICALLY SIMILAR TO THE ISOLATE OBTAINED FROM THE 1970S OUTBREAK IN CHINA." On environmental survival: "under ideal conditions WITHOUT FECES, the bacterium survived for up to 17 days on plastic and rubber surfaces, 4 days on wood, and LESS THAN 1 DAY ON CONCRETE. Samples with feces and FARM-LIKE SETTINGS without feces WERE NEGATIVE BY DAY 1 POST INOCULATION, regardless of the surface material used." On what is not known: "GIVEN ITS UNKNOWN EPIDEMIOLOGY IN SWINE OPERATIONS, this strategy [depopulation] HAS FAILED IN APPROXIMATELY 25% OF THE ATTEMPTS." cfsph_2020 on the introduction mechanism in the species where it has been studied: outbreaks in guinea pigs "usually occur when SICK ANIMALS ARE ADDED TO A HEALTHY COLONY OR NAIVE ANIMALS ARE MIXED WITH ASYMPTOMATIC CARRIERS", and pigs are named among the carrier species. shic_2021_szoo: "Mode(s) of transmission are not known for recent swine outbreaks." "Transmission in other species can be due to direct contact with infected animals; indirect contact with contaminated equipment, housing, bedding, or clothing; and ingestion." "Prevention is aimed at eliminating stress and practicing good biosecurity." "S. zooepidemicus is a commensal found in the upper respiratory tract of horses, pigs, and other animals."
How this level was decided
INFERRED, AND FLAGGED, because the chapter says in terms that the on-farm epidemiology is unknown and the pass is reasoning past that. LEVEL 3 IS SCORED on what the folder does establish: the agent is not resident in US herds -- it emerged in 2019 and causes discrete outbreaks -- the route into a herd is animals rather than the ground, and it dies within a day on farm surfaces under realistic conditions, so quarantine of incoming stock plus transport and fomite control is the programme that addresses it. That is the level 3 list. THE ARGUMENT FOR LEVEL 4 IS THE 25% FIGURE: depopulation, the most extreme measure available, fails a quarter of the time because nobody knows where the organism is hiding, which reads like the "and may still fail" clause. IT IS NOT TAKEN because that statistic is about ELIMINATING the agent from an infected herd, not about keeping it out of a clean one, and C3 asks only the second question. If you read the unknown epidemiology as meaning we cannot say what excludes it, the honest alternative is not level 4 but a null. Level 3 held, and the factsheet is candid that the transmission route in the recent swine outbreaks is unknown, which limits how well any exclusion level can be supported. The commensal status is worth noting as an argument for level 1 -- if it already lives in the upper respiratory tract of pigs there is nothing to exclude -- but the outbreak strains behave as introduced pathogens rather than as resident flora.
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
Basis. ch57 57.3.3: "CLINICAL AND POSTMORTEM FINDINGS ARE SIMILAR TO THOSE OF BACTERIAL SEPTICEMIA. Animals present with fever, lethargy, huddling, reluctance to rise, and inappetence." On laboratory capacity, and the sentence cuts both ways: "S. zooepidemicus is likely a very significant but UNDERREPORTED cause of disease in southeastern Asian pig herds, AS DIAGNOSTIC LABORATORIES LACK THE CAPACITY OF PROPERLY IDENTIFYING THIS BACTERIUM." cfsph_2020: "Streptococci are usually identified by Lancefield group and a few phenotypic tests, but SOME STREPTOCOCCAL SPECIES CAN BE DIFFICULT TO RECOGNIZE OR MAY BE CONFUSED WITH OTHER ORGANISMS... PCR TESTS HAVE BEEN DEVELOPED FOR SOME ORGANISMS INCLUDING S. EQUI SUBSP. ZOOEPIDEMICUS... BUT HOW OFTEN THESE TESTS ARE USED IN CLINICAL LABORATORIES IS UNCLEAR." shic_2021_szoo: "Culture and biochemical testing remain common methods of identification. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has also been used." "A qPCR assay based on a conserved region of the szM gene has been recently developed, and it is highly sensitive and specific to virulent swine isolates."
How this level was decided
Level 2. The presentation does not point at this organism -- the chapter says the clinical and postmortem picture is indistinguishable from bacterial septicaemia generally -- so it is not level 1. Confirmation is culture, Lancefield grouping and a species PCR, all within reach of a regional diagnostic laboratory, which is the level 2 label. THE UNDERREPORTING SENTENCE DOES NOT LIFT THIS TO LEVEL 3 OR 4, and the distinction matters: it says southeastern Asian laboratories LACK CAPACITY, which is a statement about resources in a region, not about whether a validated assay exists. The North American test of that came in 2019, when US and Canadian laboratories identified the outbreak isolates and sequenced them to 99% homology with a 1970s Chinese strain within the same year. Level 2 confirmed and now well supported: routine culture and MALDI-TOF, plus a recent qPCR that is specific to the VIRULENT swine isolates, which is what separates the outbreak organism from the commensal.
C5 Production cost
Financial impact on the infected farm's cost of production
Substantial: Severe losses cause a major and potentially unsustainable increase in cost of production
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l4, though relatively few herds have been involved in the localized outbreaks, the severity on those outbreaks is notable. These were adult, healthy sows that had severe disease including death."
Basis. ch57 57.3.3, on the US and Canadian outbreaks: "In 2019, S. zooepidemicus sequence type (ST) 194 emerged in North America, ASSOCIATED WITH HIGH MORTALITY OUTBREAKS AFFECTING SOWS AND FEEDER PIGS... Sows at any gestational stage MAY ABORT OR SUFFER RESORPTION, SIGNIFICANTLY AFFECTING REPRODUCTIVE PERFORMANCE. MORTALITY RATES RANGE FROM 50 TO 90%, DEPENDING ON HERD HEALTH STATUS, LEADING TO A CATASTROPHIC ECONOMIC IMPACT (Costa et al. 2022; Hau et al. 2022b; Sitthicharoenchai et al. 2020)." On the scale it reached where it started: "an outbreak of S. zooepidemicus in swine occurred in western China, resulting in SUBSTANTIAL ECONOMIC LOSSES", and ma_2024 puts numbers on that outbreak -- "AFFECTING OVER A MILLION PIGS AND RESULTING IN THE DEATHS OF OVER 300,000." On what is left when treatment fails: "As resistance emerges rapidly during outbreaks, DEPOPULATION HAS BEEN USED to eliminate S. zooepidemicus from affected herds." shic_2021_szoo: "Weakness, lethargy, fever, and rapidly escalating mortality are associated with S. zooepidemicus in pigs. Abortion has also been reported." "In sows and feeder pigs experimentally infected... clinical signs begin within 24 hours post-infection, with severe depression and lethargy noted by 36 hpi."
How this level was decided
Level 4, and FLAGGED -- not because the evidence is weak, which it is not, but because of what the level means. THE EVIDENCE IS AS DIRECT AS THIS CRITERION EVER GETS: fifty to ninety percent mortality, sow abortion at any stage, the chapter's own word "catastrophic", three citations behind it, and depopulation as the end point when antimicrobials fail. That is a major and potentially unsustainable increase in cost of production on the affected farm, which is the level 4 label. WHAT YOU SHOULD RATIFY IS THE COMPANY IT KEEPS: African swine fever is currently the only entry in the register at C5 level 4 and is the worked example there. This puts a second agent alongside it -- one already present in US herds since 2019 rather than exotic. I believe that is right on the evidence, and the criterion asks about THE INFECTED FARM rather than about national prevalence, but it is a call worth your signature rather than mine. Level 4 confirmed -- rapidly escalating mortality, with experimental disease inside 24 to 36 hours.
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. "c6l1, no market impact despite widespread reporting in the industry about the outbreaks. This could change in the future but l1 reflects the status today"
Basis. ST194 emerged in North America in 2019 with high-mortality outbreaks in Manitoba, Minnesota and Kansas (ch57 57.3.3; ma_2024), and no trade measure, movement restriction or consumer response is recorded anywhere in the folder as having followed. Neither document mentions a market consequence of any kind, in either the North American outbreaks or the far larger Chinese one. shic_2021_szoo: "S. zooepidemicus is not an OIE-listed disease. Individual states may have different disease reporting requirements. In early 2020, Pennsylvania designated S. zooepidemicus as a Dangerous Transmissible Disease."
How this level was decided
INFERRED. Level 1, and this is a scoreable case under the standing note SCORING/market_impact rather than a void: the agent is now present and repeatedly diagnosed in US pigs, so the absence of any market move since 2019 is an observation. NOTE THE ARGUMENT AGAINST, since it is not frivolous: this is a zoonosis acquired from undercooked pork with a 63% case fatality in its worst syndrome, and a consumer-facing story could in principle move demand. Nothing of the sort has happened in the seven years since it arrived, and the note is explicit that where an agent is already diagnosed here, the absence of a historical move is the evidence. Level 1 held, and the new fact is recorded rather than acted on: a US state has designated this a Dangerous Transmissible Disease, which is a regulatory response but a state-level one, and the factsheet reports no market or trade consequence from the North American outbreaks.
C7 Treatment potential
Potential for treatment to improve outcomes
Some: Treatment exists but is inconsistent, requires extralabel use, or works only in some circumstances
Basis. ch57 57.3.3, the whole of what the chapter says about treating it: "OUTBREAK CONTROL RELIES SOLELY ON PROLONGED ANTIMICROBIAL THERAPY. AS RESISTANCE EMERGES RAPIDLY DURING OUTBREAKS, DEPOPULATION HAS BEEN USED TO ELIMINATE S. ZOOEPIDEMICUS FROM AFFECTED HERDS. Given its unknown epidemiology in swine operations, this strategy has failed in approximately 25% of the attempts." On the general susceptibility of the group, 57.3.2: "BETA-HEMOLYTIC STREPTOCOCCI ARE SENSITIVE TO BETA-LACTAM ANTIBIOTICS." shic_2021_szoo: "S. zooepidemicus isolates from North American swine have been susceptible to many commonly used antibiotics including ceftiofur, enrofloxacin, penicillin, tiamulin, and tilmicosin." "Pigs that are sick should receive treatment and supportive care."
How this level was decided
Level 2. Treatment exists and is not merely available but is the ONLY thing standing between a herd and depopulation -- and it works only in some circumstances, which is the level 2 clause: the therapy must be prolonged, and resistance emerges rapidly during the outbreak itself, so the drug that works in week one may not in week three. THE LABEL QUESTION IS NOT ASKED HERE, and it is worth saying why rather than flagging it out of habit: no US label information is in the folder, but the level 2 clause about inconsistent efficacy is satisfied independently of any label, so a ruling on label wording could not change the answer. It would matter only if the pass were arguing level 1, and it is not. Level 2 held. Susceptibility to five commonly used antibiotics is real and useful, but the C7 label test asks whether a US label names the agent, not whether the drug works -- and none of these products is labelled for S. zooepidemicus in swine, which is extralabel use and therefore level 2. This is exactly the case Eric said to bring to him rather than guess at, so it is flagged.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Needed but not available: No effective vaccine is available in the US or has been developed, and the disease would justify vaccinating if one existed
Basis. ch57 57.3.3: "AN INACTIVATED BACTERIN DELIVERED INTRAMUSCULARLY OR PREVIOUS EXPOSURE TO HETEROLOGOUS S. ZOOEPIDEMICUS LIVE STRAINS DOES NOT PREVENT INFECTION OR DISEASE NOR DOES IT LEAD TO TRANSFER OF PASSIVE IMMUNITY (Hau et al. 2022a,b). A LIVE ATTENUATED VACCINE HAS BEEN SHOWN TO PREVENT MORTALITY UNDER EXPERIMENTAL CONDITIONS (Costa et al. unpublished). Outbreak control relies solely on prolonged antimicrobial therapy." cfsph_2020 records the only product it knows of, and not for pigs: "autogenous vaccines for S. equi subsp. zooepidemicus were made at one time FOR GUINEA PIGS (the availability of the latter vaccines is currently unclear)."
How this level was decided
Level 3, and it is one of the best-evidenced level 3 cells in the register, because the gap is DEMONSTRATED rather than merely unreported. Both halves of the label hold. No effective vaccine is available in the US: the bacterin was tested and shown not to prevent infection or disease or to confer passive immunity, and the one product that works is unpublished and experimental. And the disease plainly justifies vaccinating, judged on its own clinical and economic weight as the 2026-08-28 rewording requires -- fifty to ninety percent mortality with the alternative being depopulation. THIS IS THE OPPOSITE OF THE "NOT NEEDED" SITUATION the level 1 clause covers: here somebody built a vaccine, tried it, and it failed. Unchanged. Level 3 remains the best-evidenced instance in the register: a bacterin was built, tested, and failed to prevent infection or disease, against 50-90% mortality.
Levels and evidence are generated from data/assignments/streptococcus_zooepidemicus.yml; the overview is authored in data/overviews/streptococcus_zooepidemicus.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.