Other Actinobacillus Species
LEVELS: Highly unlikely; No human illness; Already in the herd; Reference or research laboratory required; Minor; Negligible; Some; Available but inconsistent
| Register id | other_actinobacillus_species |
| Type | bacteria |
| Scientific name | Actinobacillus |
| NCBI taxid | 713 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
This entry groups six Actinobacillus organisms of pigs that are neither A. pleuropneumoniae nor A. suis, both scored separately: A. equuli, A. minor, A. porcinus, A. rossii, A. porcitonsillarum and the unnamed Bisgaard Taxon 10. Eric grouped them because they present the same risk picture — "all similar". Most are simply normal inhabitants of the tonsils of healthy pigs, and the reference chapter states plainly that the virulence potential of these other actinobacilli has not been demonstrated. The exception is A. equuli, primarily a pathogen of horses, which has recently been confirmed as a cause of swine infection in several countries, in some cases with high morbidity and mortality severe enough that farms resorted to autogenous vaccines; where it comes from in most affected herds is unknown. The dominant practical theme for the group is misidentification rather than disease: A. equuli is easily confused with A. suis, and A. porcitonsillarum with A. pleuropneumoniae, so laboratories can report the wrong organism and, in the second case, wrongly suggest a herd has APP.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Highly unlikely: Human infection with the agent has never been reported, or has been reported but is not attributed to pig or pork exposure
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c1l1, little evidence for these agents or others in the genus to move from pigs to humans"
Basis. THE ENTRY IS A GROUP OF SIX -- A. equuli, A. minor, A. porcinus, A. rossii, A. porcitonsillarum and Bisgaard Taxon 10 -- and ch43 43.3 is ONE PARAGRAPH, the whole of what the folder holds on them. The only human sentence in the chapter is here: "A CASE OF HUMAN INFECTION BY A. SUIS OR A. EQUULI HAS BEEN REPORTED RECENTLY IN ITALY (Montagnani et al. 2015)." Nothing says where that person acquired it, whether they had pig contact, or which of the two organisms it was. A. equuli is introduced in the same paragraph as "A PRIMARY INFECTIOUS AGENT OF HORSES". No Public Health section is given to any member of the group.
How this level was decided
Level 1, FLAGGED, and it is the same cell as actinobacillus_suis C1 because it is the same sentence -- the one reported human case is attributed to either A. suis or A. equuli and the chapter does not resolve it. THE PIG ATTRIBUTION IS WEAKER HERE THAN IT IS THERE, not stronger: A. equuli is primarily a horse organism, so a human isolate has an obvious non-pig source available. Scored level 1 on your Clostridium perfringens type C reasoning -- human disease with the organism is on record, a link attributing pigs as the source is not. RULE THE TWO ENTRIES TOGETHER; whichever way this one goes, actinobacillus_suis C1 should match it or the register will say the same case means two different things.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c2l1, not likely to cause disease in people"
Basis. THE ENTRY IS A GROUP OF SIX -- A. equuli, A. minor, A. porcinus, A. rossii, A. porcitonsillarum and Bisgaard Taxon 10 -- and ch43 43.3 is ONE PARAGRAPH, the whole of what the folder holds on them. No human illness with any member of the group is described. The single Italian case is reported as an isolation, with no clinical description and no outcome.
How this level was decided
RE-SCORED 2026-09-04. C2 now grades the severity of the illness the agent causes in a person, independent of how the person was exposed -- the 2026-09-01 pig-attribution reading is reversed, and C1 alone carries the source question. FLAG, on the same reasoning as actinobacillus_suis -- the folder says nothing about the severity of human infection with these organisms.
PREVIOUS ANSWER, written under the pig-attribution reading: Level 1, FOLLOWING C1 AND FLAGGED WITH IT. As with actinobacillus_suis, note that if C1 moves off level 1 this cell does not simply become level 2 -- the folder says nothing about the severity of the Italian case, so it would become a null.
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. THE ENTRY IS A GROUP OF SIX -- A. equuli, A. minor, A. porcinus, A. rossii, A. porcitonsillarum and Bisgaard Taxon 10 -- and ch43 43.3 is ONE PARAGRAPH, the whole of what the folder holds on them. ch43 43.3: "MANY SPECIES OF ACTINOBACILLUS OTHER THAN APP CAN BE FOUND IN SWINE TONSILS, SUCH AS A. MINOR, A. PORCINUS, A. ROSSII, BISGAARD TAXON 10, AND A. PORCITONSILLARUM (Lowe et al. 2010)." 43.1.2 says the same from the other direction, that APP "has to be differentiated from OTHER NAD-DEPENDENT PASTEURELLACEAE PRESENT IN THE UPPER RESPIRATORY TRACT OF SWINE, such as A. minor, A. porcinus, A. porcitonsillarum." On the one member that is not simply commensal: swine infection by confirmed A. equuli "has been recently reported in several countries... with, in some cases, high morbidity and mortality that required the use of autogenous vaccines. THE SOURCE OF THE INFECTION IN MOST HERDS REMAINS UNKNOWN."
How this level was decided
Level 1. Five of the six are normal tonsillar flora of pigs -- carried by the pigs themselves, present in most herds, no introduction event to prevent -- which is the level 1 label. NOTE THE ONE GAP AND WHY IT DOES NOT CHANGE THE LEVEL: for A. equuli the chapter says outright that the source of infection in most herds is unknown, so nobody can say what would exclude it. An unknown route is not evidence of a hard route, and it applies to one member of a group whose other five are already resident.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Reference or research laboratory required: A validated assay exists, but only at a national reference or research laboratory rather than at local or regional level
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Corrected by Eric from L4 No validated assay. Reason: "c4l3, conceivable that many labs could isolate and type to genus level but may likely require assistance from a reference laboratory to confirm the species"
Basis. THE ENTRY IS A GROUP OF SIX -- A. equuli, A. minor, A. porcinus, A. rossii, A. porcitonsillarum and Bisgaard Taxon 10 -- and ch43 43.3 is ONE PARAGRAPH, the whole of what the folder holds on them. The whole paragraph is an account of misidentification. On A. equuli: it "has been suggested as being involved in several swine infections in Europe many years ago... HOWEVER, MOST OF THESE INFECTIONS WERE PROBABLY CAUSED BY A. SUIS, SINCE BOTH PATHOGENS ARE PHENOTYPICALLY AND GENETICALLY VERY SIMILAR. A revised definition of the Actinobacillus spp. recovered from animals (FROM A DIAGNOSTIC POINT OF VIEW) has been published (Christensen and Bisgaard 2004)... DIAGNOSTIC LABORATORIES MUST BE AWARE OF THE POTENTIAL OF A. EQUULI IN PIGS AND CLEARLY DIFFERENTIATE FROM A. SUIS INFECTIONS." On A. porcitonsillarum: it "MAY BE EASILY MISIDENTIFIED AS APP", and "INTERESTINGLY, A. PORCITONSILLARUM WAS CONFIRMED AS A NEW SPECIES WHEN THE COMPLETE GENOME WAS PUBLISHED (Dona and Perreten 2018)." One member, Bisgaard Taxon 10, has no formal species name at all. No assay specific to any member of the group is named anywhere in the chapter; the species-specific molecular tests it does cite (Li 2019, Schaller 2001, Scherrer 2022, Tobias 2012) are tests FOR APP, used to rule these organisms out.
How this level was decided
Level 4, INFERRED AND FLAGGED -- this is the cell in the batch I am least sure of and it turns on something the folder does not contain. WHAT THE FOLDER SUPPORTS: no validated species-specific assay is described for any of the six, an entire literature of swine A. equuli infection is now believed to have been A. suis, the newest member was resolved only by whole-genome sequencing, and one member is an unnamed taxon for which a species-specific test cannot exist. That is the level 4 label -- no pathogen-specific test of known reliability, identification depending on sequencing. WHAT I CANNOT SEE FROM THE FOLDER, AND WHERE YOU CAN: MALDI-TOF is described in this same chapter as suitable for routine identification of isolates, it is now standard equipment in US veterinary diagnostic laboratories, and if it identifies A. equuli and A. minor to species reliably then this cell is level 2, not level 4. THE QUESTION FOR YOU IS ONE LINE: do US diagnostic laboratories reliably speciate the non-APP Actinobacillus isolates in routine practice? If yes, level 2. If they report them as "Actinobacillus sp.", level 4 stands.
C5 Production cost
Financial impact on the infected farm's cost of production
Minor: Small and generally short-lived losses with little effect on overall 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. "c5l2, agents not routinely associated with consequential clinical signs or occur in entire cohorts of pigs"
Basis. THE ENTRY IS A GROUP OF SIX -- A. equuli, A. minor, A. porcinus, A. rossii, A. porcitonsillarum and Bisgaard Taxon 10 -- and ch43 43.3 is ONE PARAGRAPH, the whole of what the folder holds on them. ch43 43.3 ends: "Although usually considered as avirulent, A. PORCITONSILLARUM HAS BEEN ISOLATED FROM DISEASED ANIMALS PRESENTING A VARIETY OF PATHOLOGIES (Martinez and Maldonado 2006; Ohba et al. 2007), and it seems to present a HIGHER ANTIBIOTIC RESISTANCE THAN APP... THE VIRULENCE POTENTIAL OF OTHER ACTINOBACILLI HAS NOT BEEN DEMONSTRATED (Mayor et al. 2006)." Against that, the one member with a disease record: confirmed A. equuli swine infection "has been recently reported in several countries (Ramos-Vara et al. 2008; Maul et al. 2020) WITH, IN SOME CASES, HIGH MORBIDITY AND MORTALITY THAT REQUIRED THE USE OF AUTOGENOUS VACCINES."
How this level was decided
Level 2, INFERRED AND FLAGGED, because a group entry with one member that causes high morbidity and mortality and five that are commensals is genuinely awkward to score as one number. WHAT LEVEL 2 SAYS: across the group and across US production these are small, sporadic, generally short-lived losses -- five of the six are tonsillar flora whose virulence potential has not been demonstrated, and the sixth causes occasional herd events in a handful of reported countries. THE ARGUMENT FOR LEVEL 3 is that "high morbidity and mortality... required the use of autogenous vaccines" is not a small loss on the farm it happens to, and if you score a group on its worst member this is level 3. THE ARGUMENT FOR LEVEL 1 is that the chapter's closing sentence is an examined negative for five of the six. I have taken the middle because the group as a whole is what the register scores; tell me if you score groups on the worst member instead, because that rule would apply to several entries still to come.
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 evidence to suggest there is a market impact"
Basis. THE ENTRY IS A GROUP OF SIX -- A. equuli, A. minor, A. porcinus, A. rossii, A. porcitonsillarum and Bisgaard Taxon 10 -- and ch43 43.3 is ONE PARAGRAPH, the whole of what the folder holds on them. These organisms are normal tonsillar flora of US pigs, and no trade measure, movement restriction or market response to any of them is recorded anywhere in chapter 43.
How this level was decided
INFERRED. Level 1 under the standing note SCORING/market_impact: agents already resident in US pigs, diagnosed from time to time, with no market move ever observed.
C7 Treatment potential
Potential for treatment to improve outcomes
Some: Treatment exists but is inconsistent, requires extralabel use, or works only in some circumstances
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c7l2, extralabel treatment available and likely to work when necessary"
Basis. THE ENTRY IS A GROUP OF SIX -- A. equuli, A. minor, A. porcinus, A. rossii, A. porcitonsillarum and Bisgaard Taxon 10 -- and ch43 43.3 is ONE PARAGRAPH, the whole of what the folder holds on them. ch43 43.3 says nothing at all about treating any member of the group. The only pharmacological remark is that A. porcitonsillarum "SEEMS TO PRESENT A HIGHER ANTIBIOTIC RESISTANCE THAN APP (Matter et al. 2007)", and the only intervention named for A. equuli outbreaks is prophylactic rather than therapeutic -- outbreaks "REQUIRED THE USE OF AUTOGENOUS VACCINES". THE FOLDER CONTAINS NO US LABEL INFORMATION FOR ANY PRODUCT.
How this level was decided
FLAGGED, and it is the same question as actinobacillus_suis C7 -- your 2026-09-02 note named the Actinobacillus chapter as where this would land. No US swine label names A. equuli, A. minor, A. porcinus, A. rossii or A. porcitonsillarum on my reading, and Bisgaard Taxon 10 has no name to put on a label, which would make any treatment of these organisms extralabel and the level 2. LEVEL 2 IS SCORED PROVISIONALLY on that reading. Note that it does not rest on the label alone: the one member with real outbreaks was controlled with autogenous vaccine rather than with antimicrobials, and A. porcitonsillarum is reported more resistant than APP, so treatment here looks like something that exists but works only in some circumstances either way. Confirm the label reading and this cell is settled.
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. THE ENTRY IS A GROUP OF SIX -- A. equuli, A. minor, A. porcinus, A. rossii, A. porcitonsillarum and Bisgaard Taxon 10 -- and ch43 43.3 is ONE PARAGRAPH, the whole of what the folder holds on them. ch43 43.3, on confirmed A. equuli infection in pigs: reported in several countries "WITH, IN SOME CASES, HIGH MORBIDITY AND MORTALITY THAT REQUIRED THE USE OF AUTOGENOUS VACCINES." No commercial vaccine for any member of the group is described, and no vaccine of any kind is mentioned for the other five.
How this level was decided
Level 2. Autogenous vaccines have been made and used against a member of this group in response to real outbreaks, which is the "available" half of the level 2 label, and the chapter reports no efficacy figure, which leaves protection undemonstrated rather than established -- inconsistent in the sense the level means. NOT LEVEL 3, because level 3 is reserved for a genuine gap where no vaccine is available, and here one was made and given. NOT LEVEL 1 ON THE "NOT NEEDED" CLAUSE, and this is deliberate under your PCV4 rule of 2026-09-03: five of the six almost certainly do not justify vaccinating, but asserting that is a claim about the disease, and A. equuli plainly did justify it in the herds that made an autogenous product.
Levels and evidence are generated from data/assignments/other_actinobacillus_species.yml; the overview is authored in data/overviews/other_actinobacillus_species.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.