Porcine Parvovirus 1
LEVELS: Highly unlikely; No human illness; Already in the herd; Laboratory-dependent; Minor; Negligible; Little; Available, or not needed
| Register id | porcine_parvovirus_1 |
| Type | virus |
| Scientific name | Porcine parvovirus 1 |
| NCBI taxid | 2039697 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Porcine parvovirus 1 is probably the most important cause of reproductive failure in pigs worldwide. It does nothing to the sow — infected gilts and boars stay clinically well — but if a susceptible female is infected during pregnancy the virus crosses the placenta about two weeks later and kills the developing pigs. What happens then depends on timing: before about day 35 the embryos die and are resorbed, so the sow simply returns to heat or produces a small litter; between then and about day 70 the fetuses die and mummify; after that they mount their own immune response and are usually born alive. The signature finding is a litter containing normal piglets alongside mummified fetuses that died at visibly different stages. The virus is endemic almost everywhere, with antibodies in 70-100% of herds, and it survives for months in buildings and on equipment, so keeping a breeding herd free of it is not realistic — the practical goal is to keep the herd immune. Inactivated vaccines are cheap, effective and routine, and revaccination every four to six months may be needed; losses are low in vaccinated herds but unvaccinated ones, or ones where the vaccine was given incorrectly, can suffer devastating losses. It is not infectious for people.
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. ch34 34.3, a Public Health section of its own and one sentence long: "THERE IS NO EVIDENCE THAT PPVs ARE INFECTIOUS FOR HUMANS OR PLAY ANY ROLE IN PUBLIC HEALTH." Nothing elsewhere in the chapter qualifies it. The one human-adjacent fact is laboratory rather than clinical: 34.8 records that "PPV1 AGGLUTINATES ERYTHROCYTES of a variety of animal species, including rat, monkey, chicken, guinea pig, AND HUMAN (blood group 0)", which is the basis of the haemagglutination-inhibition assay.
How this level was decided
Level 1. The chapter answers the criterion directly and covers the whole genus while doing it. NOTE THE ONE THING THAT COULD BE MISREAD, since it appears in the same chapter: PPV1 agglutinates human red cells in a test tube. That is a property exploited by the diagnostic assay, not evidence of human infection, and it should not be carried into a brief as though it were.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch34 34.3: "There is no evidence that PPVs are infectious for humans or PLAY ANY ROLE IN PUBLIC HEALTH." No human illness with any porcine parvovirus is described anywhere in the chapter.
How this level was decided
Level 1, following C1. Under C2 as rescoped on 2026-09-01, level 1 means pigs are not a source of human illness with this agent, which is what the chapter states.
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. ch34 34.4: "PPV1 IS ENDEMIC TO PIGS IN MOST PARTS OF THE WORLD... serological surveys in various parts of the world showed that PPV1 ANTIBODIES WERE PRESENT IN 70-100% OF THE HERDS." 34.10 states the consequence for exclusion in terms: "PPV1 IS PREVALENT IN THE PIG POPULATION AND HIGHLY STABLE IN THE ENVIRONMENT. THESE FACTORS MAKE IT DIFFICULT TO ESTABLISH AND MAINTAIN BREEDING POPULATIONS FREE OF THE VIRUS. A MORE PRACTICAL GOAL IN COMMERCIAL HERDS IS TO MAINTAIN HERD IMMUNITY AGAINST PPV1." On why it is hard to keep out, 34.4: "PPV1 CAN REMAIN INFECTIOUS FOR MONTHS IN THE ENVIRONMENT AND ON CONTAMINATED FOMITES, thereby serving as a constant source of new infections. PPV1 can be transported between herds via fomites, for example, clothes, boots, and equipment. Likewise, RODENTS FUNCTIONING AS MECHANICAL VECTORS have reportedly introduced the virus into herds", and it resists ethanol, quaternary ammonium and low-concentration hypochlorite.
How this level was decided
Level 1, and the chapter states the label rather than implying it: present in 70-100% of herds, and the profession has given up on exclusion in favour of maintaining herd immunity. There is no introduction event to prevent because the virus is already there. NOTE THAT THE EXCLUSION DIFFICULTIES ARE REAL AND DO NOT CHANGE THE LEVEL: months of environmental survival, resistance to the common disinfectants, fomite and rodent carriage would all argue for a high level IF the question were how hard this is to keep out of a clean herd. C3 asks that question only where there is a clean herd to protect, and the chapter says maintaining one is impractical. Scored level with Streptococcus suis, Glaesserella parasuis and Staphylococcus hyicus for the same reason -- the agent is already in.
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. ch34 34.8: "CONSIDER PPV1 WHEN REPRODUCTIVE CONSEQUENCES COMPATIBLE WITH PPV1 INFECTION ARE OBSERVED, e.g. an increase in the return-to-estrus index or delays in parturition with increased numbers of mummified fetuses and smaller litters, especially in first- or second-parity females. A MIX OF NORMAL PIGS AND MUMMIFIED FETUSES THAT DIED AT DIFFERENT DEVELOPMENT STAGES IN THE SAME LITTER IS A STRONG INDICATION OF PPV1 INFECTION." But the differential is long: "pseudorabies (Aujeszky's disease), brucellosis, leptospirosis, porcine reproductive and respiratory syndrome (PRRS), toxoplasmosis, nonspecific bacterial uterine infection, and others." On confirmation: "DETECTION OF VIRAL ANTIGEN IN FETAL TISSUES BY IMMUNOFLUORESCENCE (IF) IS A RELIABLE PROCEDURE... For routine diagnostics, POLYMERASE CHAIN REACTION (PCR) IS THE MOST EFFECTIVE TECHNIQUE for detecting PPV1 in fetal tissues, semen, and other samples", and "THE ENZYME-LINKED IMMUNOSORBENT ASSAY (ELISA) FORMAT IS A PREFERABLE ALTERNATIVE TO HI because it can be standardized and automated for high-throughput testing. DIFFERENTIAL ELISAs CAN DISTINGUISH VACCINATED ANIMALS FROM ANIMALS INFECTED WITH PPV1." The traps are also named: "diagnostic tests on fetal tissues OFTEN PRODUCE FALSE NEGATIVE RESULTS, possibly due to the autolyzed state of fetal tissues", and serology is confounded by "the normally high prevalence of PPV1 in populations and the time lag between infection and the observation of reproductive losses."
How this level was decided
Level 2, and it is the worked example at this level in criteria_levels.yml. The presentation does not name the agent -- a mummified litter raises half a dozen reproductive pathogens, and the chapter lists them -- so it is not level 1; but the mixed-stage mummy pattern is a strong pointer, and confirmation is IF, PCR or a standardised ELISA at any regional diagnostic laboratory. That is the level 2 label. NOTE THE TWO TRAPS WORTH CARRYING INTO A BRIEF, because both produce wrong answers rather than no answer: autolysed fetal tissue gives false negatives, so a negative test on a rotten mummy means nothing; and serology in a 70-100% seropositive, routinely vaccinated population needs the differential ELISA or paired sera to say anything at all.
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
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Corrected by Eric from L3 Moderate. Reason: "c5l2, I think we downgrade it a bit because losses due to clinical disease when they occur are short lived and one-off due to lifetime immunity. Vaccines are not expensive and well below the cost of the diseaes in an unvaccinated herd. I see the arguement for l3 but i think l2 is a better fit. it would be seen as an aberration to have this at l3 - in modern production, most farm workers have never seen the disease."
Basis. ch34 34.1: "PPV1 IS PROBABLY THE MOST IMPORTANT CAUSE OF REPRODUCTIVE FAILURE IN PIGS WORLDWIDE." What that means in a vaccinating industry, 34.6: "REPRODUCTIVE LOSSES ARE TYPICALLY LOW IN VACCINATED HERDS, BUT PPV1 CAN CAUSE DEVASTATING ABORTION STORMS IN UNVACCINATED HERDS OR IN SITUATIONS IN WHICH THE VACCINE WAS ADMINISTERED INCORRECTLY." The standing cost of holding it there, 34.10: "REGULAR REVACCINATION OF BREEDING SOWS AT 4- TO 6-MONTH INTERVALS MAY BE NECESSARY to maintain protective immunity in sows." And 34.6 on what the loss is: "Maternal reproductive failure is THE MAJOR AND ONLY WELL-ESTABLISHED CLINICAL SIGN of PPV1 infection", with embryonic death and resorption before day 35 and mummification after it. Adults show no clinical signs at all.
How this level was decided
INFERRED, AND FLAGGED, because the standing note SCORING/production_cost_impact and the chapter's own headline point in opposite directions and the pass has chosen between them. LEVEL 3 IS SCORED. The note says score modern US production rather than the chapter, and in modern US production this agent is controlled -- reproductive losses are typically low in vaccinated herds, and essentially every US breeding female is vaccinated. THE COST DOES NOT DISAPPEAR WHEN THE DISEASE DOES: it becomes the programme that suppresses it, and the chapter prices that at revaccination of the entire breeding herd every four to six months, indefinitely, in perpetuity, on 70-100% of herds. That is a measurable, continuous increase in cost of production absorbed within normal farm operations, which is the level 3 label, and it is the same reasoning that put Actinobacillus pleuropneumoniae at level 3 -- vaccination cost counts. THE ARGUMENT FOR LEVEL 2 is that the residual losses in a vaccinated herd are small and short-lived, which is literally what the chapter says. If you score C5 on realised loss alone rather than on loss plus the cost of preventing it, this is level 2. THE ARGUMENT FOR LEVEL 4 is the abortion storm in a herd where the vaccine was given wrongly, and it fails on your Menangle rule: a level is a claim about the general case, and the general case here is a vaccinated herd.
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, old disease, widespread, no market impct"
Basis. PPV1 is endemic worldwide with antibodies in 70-100% of herds (ch34 34.4), it has been diagnosed in US pigs continuously since the 1970s, and no trade measure, movement restriction or consumer response to a PPV1 diagnosis is recorded anywhere in the chapter.
How this level was decided
INFERRED. Level 1 under the standing note SCORING/market_impact: an agent long endemic and routinely diagnosed in US pigs, with no market move ever observed. The absence is an observation rather than an assumption. The disease is invisible outside the farrowing house -- adults show no signs, and the loss is fetuses that never reach a market.
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. No treatment for PPV1 is described anywhere in chapter 34; the whole of 34.10 is vaccination and herd immunity. On why treatment has no window, 34.6: "TRANSPLACENTAL TRANSMISSION AND SUBSEQUENT EMBRYO/FETAL INFECTION OCCUR AROUND 15 DAYS AFTER INOCULATION of susceptible gestating females", the sow herself stays clinically well -- "gilts and boars infected with PPV1 REMAIN CLINICALLY HEALTHY, except for reproductive losses in seronegative gilts or sows" -- and the damage is done in utero: infection before day 35 gives "embryonic death and maternal resorption", after it "fetal death followed by mummification", and after day 70 "fetal infection is subclinical, and the piglet is born with anti-PPV antibodies". 34.6 also notes the detection problem that makes intervention impossible: "evidence of infection MAY APPEAR WEEKS AFTER INFECTION".
How this level was decided
Level 1, and it is the transplacental clause of the standing note SCORING/treatment_potential applied exactly: "level 1 still holds where the harm is transplacental and complete before birth, because THERE IS NO WINDOW IN WHICH ANY TREATMENT COULD ACT -- getah_virus, the pestiviruses and japanese_encephalitis_virus are scored there for that reason, NOT FOR LACK OF A PRODUCT." PPV1 is the cleanest instance of it in the register. The sow is never ill, so nothing presents for treatment; by the time the litter shows the loss, the fetuses died weeks earlier; and the animal that would need the drug is a fetus behind a six-layered epitheliochorial placenta that the chapter says will not pass even an antibody. NOT SCORED LEVEL 1 ON THE GROUND THAT NOBODY TREATS VIRAL DISEASE, which your 2026-09-02 rule forbids -- the ground is that there is no moment at which a treatment could be given.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Available, or not needed: Effective vaccines are widely available in the US or secured for national outbreak response, or the disease does not clinically or economically justify vaccinating
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l1, existing vaccine adequate, no new development required"
Basis. ch34 34.10: "A more preferable and reliable approach is REGULAR VACCINATION OF BREEDING FEMALES AGAINST PPV1... MOST COMMERCIAL PPV1 VACCINES ARE BASED ON CHEMICALLY INACTIVATED tissue culture-derived virus... THESE VACCINES INDUCE ANTIBODY TITERS SUFFICIENT TO PREVENT DISEASE, BUT NOT INFECTION." On the evidence they work: "Limited experimental infections of pregnant sows... revealed that VACCINATIONS RESULTING IN VERY STRONG HUMORAL IMMUNE RESPONSES WERE ABLE TO PREVENT REPRODUCTIVE DISORDERS", and "IN ALL CASES (FOR INACTIVATED OR MLV), TRANSPLACENTAL TRANSMISSION OF PPV1 WAS PREVENTED." Modified-live and subunit vaccines have also been developed. Against that, the chapter closes by asking for better ones: "A REVIEW OF THE CURRENT VACCINATION STRATEGY AGAINST PPV1 INFECTION IS WARRANTED... NEW PPV1 VACCINES THAT INDUCE LONG-LASTING IMMUNITY AND PROTECT AGAINST ALL PREVALENT VIRUS STRAINS circulating in pig populations ARE NEEDED", and 34.4 records that "the virus is able to replicate even in vaccinated pigs... virus circulation within a population CANNOT BE COMPLETELY PREVENTED BY VACCINATION."
How this level was decided
INFERRED, AND FLAGGED, because this is the level 1 / level 2 boundary and the chapter argues both sides of it. LEVEL 1 IS SCORED, on the first half of the label rather than the "not needed" clause: effective vaccines ARE widely available in the US, they are the standard of care in every commercial breeding herd, and the chapter says in terms that they prevent the disease and prevented transplacental transmission in every controlled study. THE ARGUMENT FOR LEVEL 2 is that they do not prevent infection or shedding, that immunity lasts only four to six months so the whole breeding herd must be redone twice a year, and that the chapter explicitly says new vaccines protecting against all circulating strains are NEEDED. THAT IS THE STRONGEST CASE FOR LEVEL 2 IN THE REGISTER THAT I HAVE NOT TAKEN, and the reason I have not is that C8 asks whether a vaccine GAP is worth funding: SMEDI is prevented today by a cheap product every producer already uses. What the chapter wants is a better vaccine, not a vaccine.
Levels and evidence are generated from data/assignments/porcine_parvovirus_1.yml; the overview is authored in data/overviews/porcine_parvovirus_1.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.