Porcine Circovirus 4
LEVELS: Highly unlikely; No human illness; NOT ASSIGNED; No validated assay; NOT ASSIGNED; Negligible; NOT ASSIGNED; NOT ASSIGNED
| Register id | pcv4 |
| Type | virus |
| Scientific name | Porcine circovirus 4 |
| NCBI taxid | 2686039 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Porcine circovirus 4 was discovered in 2019 in both diseased and healthy pigs in China, has since been reported from other Asian countries, Spain and — as of 2024 — the United States, and beyond that almost nothing is known about it. The reference chapter says so repeatedly and plainly: its pathogenic potential and epidemiology are largely unknown, almost no information is available on its pathogenesis, there are no peer-reviewed data on how it is shed or transmitted, and it has never been isolated in cell culture. The limited number of sequences available constrains even the genetic work. It is on this register because a newly recognised circovirus in US pigs is something SHIC would want positioned rather than ignored, not because there is a body of knowledge to weigh. What can be said is that circoviruses are not zoonotic, that no vaccine exists, and that PCV2 vaccination would not be expected to protect against it.
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
Basis. ch27 27.3, the whole Public Health section for the chapter, and it is written about the genus: "PCVS ARE NOT ZOONOTIC. PCV DNA has been detected in vaccines produced for use in humans and swine. These findings reflect quality control issues in vaccine production. PCV2 and PCV3 have been detected in other species besides suids, but not in humans." ch27 27.1: "Porcine circovirus 4 (PCV4) WAS RECENTLY DISCOVERED (2019) in both diseased and healthy domestic pigs in China, other Asian countries, and, more recently, in Spain and IN THE UNITED STATES (Kroeger et al. 2024). THE PATHOGENIC POTENTIAL AND EPIDEMIOLOGY OF PCV4 ARE LARGELY UNKNOWN AT PRESENT." 27.5: "ALMOST NO INFORMATION IS AVAILABLE REGARDING PCV4 PATHOGENESIS." 27.4: "To date, LITTLE DATA ON PCV4 EXCRETION ROUTES IS AVAILABLE... To date, NO PEER-REVIEWED DATA IS AVAILABLE ON THE SHEDDING AND TRANSMISSION PATTERNS OF PCV4." 27.2.4: "There are NO REPORTS TO DATE OF PCV4 ISOLATION IN CELL CULTURE." 27.2.1: "The LIMITED NUMBER OF SEQUENCES available for PCV4 makes classification premature at present." shic_2026_pcv3: "Porcine circoviruses (PCVs), including PCV3, are not considered to be zoonotic."
How this level was decided
Level 1, and it is supported rather than inferred because the chapter's public health statement is about PCVs as a group -- "PCVs are not zoonotic" -- rather than about PCV2 and PCV3 individually. The sentence that follows names those two because they are the ones anyone has looked for in other species. NOTE HONESTLY WHAT IS AND IS NOT ESTABLISHED: nobody has surveyed humans for PCV4, and this virus was unknown before 2019. What carries level 1 is a genus-level statement plus the absence of any human report in the six years since, not a study. Level 1 confirmed for the genus.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch27 27.3: "PCVs are not zoonotic." No human illness with any porcine circovirus is described anywhere in the chapter. shic_2026_pcv3: "Porcine circoviruses (PCVs) ... are not considered to be zoonotic."
How this level was decided
Level 1, following C1. Under C2 as rescoped, level 1 means pigs are not a source of human illness with this agent. C1L1 implies C2L1 and validate_criteria.py checks it. Level 1 confirmed.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
NOT ASSESSED — no evidence in folder. No level was assigned on this criterion. This is a statement about what the evidence folder holds, not a finding about the agent.
Corrected by Eric from L1 Already in the herd. Reason: CONFIRMED NOT ASSESSABLE, re-ruled 2026-09-06. Against this cell he wrote only "kiss", confirming his 2026-09-03 ruling. It was put back to him because the SHIC PCV3 factsheet was deliberately placed in the PCV4 folder despite being thin, to test whether it could release the cell. It cannot: it establishes that PCV4 exists and was found in diseased pigs in 2019, with no prevalence figure, no geography and nothing about whether it is present in US herds. The reason the cell was nulled is unchanged.
Basis. ch27 27.1: "Porcine circovirus 4 (PCV4) WAS RECENTLY DISCOVERED (2019) in both diseased and healthy domestic pigs in China, other Asian countries, and, more recently, in Spain and IN THE UNITED STATES (Kroeger et al. 2024). THE PATHOGENIC POTENTIAL AND EPIDEMIOLOGY OF PCV4 ARE LARGELY UNKNOWN AT PRESENT." 27.5: "ALMOST NO INFORMATION IS AVAILABLE REGARDING PCV4 PATHOGENESIS." 27.4: "To date, LITTLE DATA ON PCV4 EXCRETION ROUTES IS AVAILABLE... To date, NO PEER-REVIEWED DATA IS AVAILABLE ON THE SHEDDING AND TRANSMISSION PATTERNS OF PCV4." 27.2.4: "There are NO REPORTS TO DATE OF PCV4 ISOLATION IN CELL CULTURE." 27.2.1: "The LIMITED NUMBER OF SEQUENCES available for PCV4 makes classification premature at present." What is known about the genus, from 27.4: PCVs "circulated undetected in swine for decades or even centuries", oronasal exposure is the primary route, and for this virus specifically "THE SYSTEMIC NATURE OF PCV4 INFECTION SUGGESTS VIRAL EXCRETION LIKELY MIMICS OTHER PCVS", while "the wide tissue tropism of this virus has prompted speculation that HORIZONTAL AND VERTICAL TRANSMISSION ALSO OCCURS". PCV4 has been found in both diseased and healthy pigs wherever it has been looked for -- China, other Asian countries, Spain, and the United States. shic_2026_pcv3: "Currently, there are four recognized circoviruses of swine, designated PCV1-4. A novel PCV, tentatively named PCV5, has recently been detected in China." "PCV4 and PCV5 were identified in samples from pigs with respiratory, enteric, and reproductive disease in 2019 and 2025, respectively." "Evidence suggests that PCVs have been circulating in swine long before they were first detected."
How this level was decided
INFERRED, and inferred from the genus rather than from the entry, which is why the support flag says so. What is known is that PCV4 is in US pigs, is found as readily in healthy pigs as in sick ones, and is a circovirus -- a group whose members are ubiquitous, shed by every route, transmitted vertically as well as horizontally, and environmentally tough. Level 1 follows: there is no introduction event to prevent for an agent that is already here and behaves like its relatives. FLAGGED because the chapter says in terms that no peer-reviewed data exist on PCV4 shedding or transmission, so this rests on family resemblance and on presence in the United States, not on measurement. NULL HELD, on Eric's ruling of 2026-09-03. The new source was placed here deliberately despite being thin, to see whether it could release the cell, and it cannot: it establishes that PCV4 exists and was found in diseased pigs, but gives no prevalence figure, no geography and nothing about whether it is present in US herds. The reason the cell was nulled is unchanged.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
No validated assay: No pathogen-specific test of known reliability exists anywhere, and identification depends on sequencing or on primers that have not been critically evaluated
Basis. ch27 27.1: "Porcine circovirus 4 (PCV4) WAS RECENTLY DISCOVERED (2019) in both diseased and healthy domestic pigs in China, other Asian countries, and, more recently, in Spain and IN THE UNITED STATES (Kroeger et al. 2024). THE PATHOGENIC POTENTIAL AND EPIDEMIOLOGY OF PCV4 ARE LARGELY UNKNOWN AT PRESENT." 27.5: "ALMOST NO INFORMATION IS AVAILABLE REGARDING PCV4 PATHOGENESIS." 27.4: "To date, LITTLE DATA ON PCV4 EXCRETION ROUTES IS AVAILABLE... To date, NO PEER-REVIEWED DATA IS AVAILABLE ON THE SHEDDING AND TRANSMISSION PATTERNS OF PCV4." 27.2.4: "There are NO REPORTS TO DATE OF PCV4 ISOLATION IN CELL CULTURE." 27.2.1: "The LIMITED NUMBER OF SEQUENCES available for PCV4 makes classification premature at present." The only detections reported anywhere are by PCR and sequencing, and 27.5.4.1 shows the assay in use: a retrospective investigation of porcine dermatitis and nephropathy syndrome cases "found 100% of PCV2 infected pigs while only 30% harbored PCV3 DNA and NONE PCV4". No serological assay, in situ hybridisation probe or immunohistochemistry reagent for PCV4 is described. shic_2026_pcv3: "New diagnostic tools are needed for surveillance and detection of new PCV strains."
How this level was decided
Level 4, on the axis C4 was reworded onto in 2026-08-29: whether a VALIDATED assay exists, not whether a test can be run. PCV4 PCR plainly can be run -- it was, on a case series -- but nothing about its reliability has been established, the virus has never been isolated in cell culture so there is no material to validate against, and there are too few sequences even to settle how many genotypes exist. That is the level 4 label: no pathogen-specific test of known reliability exists anywhere, and identification depends on sequencing or on primers that have not been critically evaluated. This is the same position as porcine norovirus and porcine sapovirus, the framework's worked examples at that level, and PCV4 is behind both of them -- they at least have published sensitivity concerns rather than no evaluation at all. Level 4 held, and lightly corroborated.
C5 Production cost
Financial impact on the infected farm's cost of production
CONFIRMED NOT ASSESSABLE. No level was assigned on this criterion, and Eric has reviewed that and ruled it correct — the folder holds nothing bearing on it. This is a statement about what the evidence supports, not a finding about the agent.
Confirmed by Eric. RULED NOT ASSESSABLE AND ROUTED TO KISS ANALYSIS. Against this cell on the C27 gaps sheet he wrote only "KISS analysis for this", and on C8 he added the reason that covers all four: "don't really understand the disease causing potential of this agent yet." THIS IS THE PORCINE TOTTORIVIRUS PATTERN, and the fourth time he has used it: where the folder cannot support a claim about what the agent does, the cell stays empty and the entry becomes unexportable rather than being filled with a level that would be indistinguishable from a real one. The pass had already left this null, so he is confirming an empty cell rather than emptying a full one. The chapter says the pathogenic potential of PCV4 is largely unknown and reports it "in both diseased and healthy domestic pigs" without separating them.
Basis. ch27 27.1: "Porcine circovirus 4 (PCV4) WAS RECENTLY DISCOVERED (2019) in both diseased and healthy domestic pigs in China, other Asian countries, and, more recently, in Spain and IN THE UNITED STATES (Kroeger et al. 2024). THE PATHOGENIC POTENTIAL AND EPIDEMIOLOGY OF PCV4 ARE LARGELY UNKNOWN AT PRESENT." 27.5: "ALMOST NO INFORMATION IS AVAILABLE REGARDING PCV4 PATHOGENESIS." 27.4: "To date, LITTLE DATA ON PCV4 EXCRETION ROUTES IS AVAILABLE... To date, NO PEER-REVIEWED DATA IS AVAILABLE ON THE SHEDDING AND TRANSMISSION PATTERNS OF PCV4." 27.2.4: "There are NO REPORTS TO DATE OF PCV4 ISOLATION IN CELL CULTURE." 27.2.1: "The LIMITED NUMBER OF SEQUENCES available for PCV4 makes classification premature at present." shic_2026_pcv3: "PCV4 and PCV5 were identified in samples from pigs with respiratory, enteric, and reproductive disease in 2019 and 2025."
How this level was decided
NOT ASSESSED, and deliberately so. The chapter says in terms that the pathogenic potential of PCV4 is largely unknown and that almost no information is available on its pathogenesis, and the virus is reported "in both diseased and healthy domestic pigs" without any attempt to separate the two. That is an ABSENCE OF EVIDENCE rather than an examined negative, and the difference decides the cell: porcine norovirus is scored level 1 on C5 because every field detection was in a pig with NO clinical signs, which is a finding; here nobody has looked. NULLS STAY NULL -- an imputed level would be indistinguishable from a real one, and 1000minds accepts no empty cells, so this entry is correctly unexportable until the question is answered. The pattern follows porcine_tottorivirus and saint_valerien_like_virus. NULL held. Detection in diseased pigs is not attribution of the disease to the agent, and the factsheet makes that distinction explicitly for PCV3, whose primary-pathogen status it still calls unclear after a decade of work.
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, already awareness of PCVAD from long pcv2 history, a few years of pcv3, and now people are not particularly surprised that a pcv4 has been identifed"
Basis. PCV4 has been detected in the United States (Kroeger et al. 2024) as well as China, other Asian countries and Spain, in both diseased and healthy pigs. No trade measure, movement control or consumer response is recorded anywhere in chapter 27, for this virus or for any circovirus.
How this level was decided
INFERRED. The standing note SCORING/market_impact draws the line at whether anything has ever been observed: where an agent is already present in US pigs and no market move has followed, that absence is evidence and the level is 1; where nothing has ever been observed anywhere and the event would be conspicuous, the cell is left unassessed. PCV4 is on the scoreable side -- it has been found in US pigs and reported in the literature with no market consequence. THIS IS ALSO WHY C6 IS SCORED WHILE C5 AND C7 ARE NOT: silence about the market is informative for an agent that is already here, and silence about the clinical role is not. Unchanged.
C7 Treatment potential
Potential for treatment to improve outcomes
CONFIRMED NOT ASSESSABLE. No level was assigned on this criterion, and Eric has reviewed that and ruled it correct — the folder holds nothing bearing on it. This is a statement about what the evidence supports, not a finding about the agent.
Confirmed by Eric. RULED NOT ASSESSABLE AND ROUTED TO KISS ANALYSIS. Against this cell on the C27 gaps sheet he wrote only "KISS analysis for this", and on C8 he added the reason that covers all four: "don't really understand the disease causing potential of this agent yet." THIS IS THE PORCINE TOTTORIVIRUS PATTERN, and the fourth time he has used it: where the folder cannot support a claim about what the agent does, the cell stays empty and the entry becomes unexportable rather than being filled with a level that would be indistinguishable from a real one. Also already null, and confirmed. C7 asks whether outcomes would improve if a treatment existed, and there is no outcome on record either to improve or to rule out.
Basis. ch27 27.1: "Porcine circovirus 4 (PCV4) WAS RECENTLY DISCOVERED (2019) in both diseased and healthy domestic pigs in China, other Asian countries, and, more recently, in Spain and IN THE UNITED STATES (Kroeger et al. 2024). THE PATHOGENIC POTENTIAL AND EPIDEMIOLOGY OF PCV4 ARE LARGELY UNKNOWN AT PRESENT." 27.5: "ALMOST NO INFORMATION IS AVAILABLE REGARDING PCV4 PATHOGENESIS." 27.4: "To date, LITTLE DATA ON PCV4 EXCRETION ROUTES IS AVAILABLE... To date, NO PEER-REVIEWED DATA IS AVAILABLE ON THE SHEDDING AND TRANSMISSION PATTERNS OF PCV4." 27.2.4: "There are NO REPORTS TO DATE OF PCV4 ISOLATION IN CELL CULTURE." 27.2.1: "The LIMITED NUMBER OF SEQUENCES available for PCV4 makes classification premature at present."
How this level was decided
NOT ASSESSED. C7 asks whether outcomes would meaningfully improve if a treatment existed, and that cannot be answered for an agent whose role in disease is unknown -- there is no outcome on record either to improve or to rule out. Scoring level 1 would assert that pigs recover acceptably without treatment, which nobody has established, and Eric's rule of 2026-09-02 forbids the other easy answer: that nobody treats viral disease is the prevailing opinion the criterion measures against, not evidence about the answer. This cell moves when C5 does. NULL held. Nothing in the new source bears on it.
C8 Vaccine availability
Availability of effective vaccines or bacterins
NOT ASSESSED — no evidence in folder. No level was assigned on this criterion. This is a statement about what the evidence folder holds, not a finding about the agent.
Corrected by Eric from L1 Available, or not needed. Reason: RULED NOT ASSESSABLE AND ROUTED TO KISS ANALYSIS. Against this cell on the C27 gaps sheet he wrote only "KISS analysis for this", and on C8 he added the reason that covers all four: "don't really understand the disease causing potential of this agent yet." THIS IS THE PORCINE TOTTORIVIRUS PATTERN, and the fourth time he has used it: where the folder cannot support a claim about what the agent does, the cell stays empty and the entry becomes unexportable rather than being filled with a level that would be indistinguishable from a real one. THE PASS HAD SCORED THIS LEVEL 1 ON THE "NOT NEEDED" CLAUSE AND HE IS OVERRIDING IT. The argument had been that level 3 is reserved for a genuine gap, so an agent not shown to cause disease cannot reach it, leaving level 1 as a true statement about the state of knowledge. He rejects that: asserting a vaccine is NOT NEEDED is still a claim about the disease, and it is the same override he made on pasivirus_a C8 on 2026-08-30. NOTE THE CONSEQUENCE FOR THE OTHER ENTRIES SCORED THAT WAY -- saint_valerien_like_virus C8 sits at level 1 on this reasoning, and he ruled it there himself on 2026-09-02 after supplying the field evidence the chapter lacked. The difference is that he had evidence there and has none here.
Basis. ch27 27.7: cofactor management is "the only approach to control PCV3-induced (AND POTENTIALLY PCV4-INDUCED) DISEASE AS NO VACCINES ARE AVAILABLE FOR THESE TWO VIRUSES." 27.2.2: "based on sequencing data, no or very limited cross-protection is expected between PCV2 and PCV3 or PCV4", so the PCV2 vaccine every pig receives does nothing here. ch27 27.1: "Porcine circovirus 4 (PCV4) WAS RECENTLY DISCOVERED (2019) in both diseased and healthy domestic pigs in China, other Asian countries, and, more recently, in Spain and IN THE UNITED STATES (Kroeger et al. 2024). THE PATHOGENIC POTENTIAL AND EPIDEMIOLOGY OF PCV4 ARE LARGELY UNKNOWN AT PRESENT." 27.5: "ALMOST NO INFORMATION IS AVAILABLE REGARDING PCV4 PATHOGENESIS." 27.4: "To date, LITTLE DATA ON PCV4 EXCRETION ROUTES IS AVAILABLE... To date, NO PEER-REVIEWED DATA IS AVAILABLE ON THE SHEDDING AND TRANSMISSION PATTERNS OF PCV4." 27.2.4: "There are NO REPORTS TO DATE OF PCV4 ISOLATION IN CELL CULTURE." 27.2.1: "The LIMITED NUMBER OF SEQUENCES available for PCV4 makes classification premature at present."
How this level was decided
INFERRED at level 1 on the "not needed" clause, and this is the one cell of the three unknowns that can still be scored -- the reason is the shape of the C8 test after the 2026-08-28 rewording. Level 3 is reserved for a GENUINE GAP, meaning no vaccine AND a disease that would warrant one, so an agent not shown to cause disease cannot reach level 3 however absent the vaccine is. Level 1 records that nothing currently justifies a vaccine, which is a statement about the state of knowledge and is true. NOTE THE ASYMMETRY WITH C5 AND C7, which are left null: those criteria would have to assert something about the disease to be scored at all, and this one does not. NOTE ALSO THE CONTRAST WITH PCV3, scored level 3 on the same absence of a vaccine -- the difference is that PCV3 is called pathogenic and has agreed case definitions, and PCV4 has neither. NULL held, on Eric's ruling. This is the cell the standing C8 note cites pcv4 for -- asserting a vaccine is not needed is a claim about the disease, and nobody can make it about a disease nobody has characterised. The new source does not characterise it.
Levels and evidence are generated from data/assignments/pcv4.yml; the overview is authored in data/overviews/pcv4.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.