Porcine Cytomegalovirus
LEVELS: Rarely occurs; No human illness; Already in the herd; Laboratory-dependent; Minor; Negligible; Little; Available, or not needed
| Register id | porcine_cytomegalovirus |
| Type | virus |
| Scientific name | Suid betaherpesvirus 2 |
| NCBI taxid | 1608255 |
| Evidence | 3 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Porcine cytomegalovirus is a herpesvirus carried by almost every pig — herd prevalence exceeds 90% and more than 98% of individual animals are positive in Europe, North America and Japan — and it very rarely causes disease. Infection is normally acquired in the first weeks of life by contact within the litter or cohort, and most pigs shed it in nasal secretions between three and eight weeks old; it also passes across the placenta. Like all herpesviruses it then persists for life in a latent state. The exception is the very young pig: in a herd without established immunity, congenital or neonatal infection can be fatal, causing fetal and piglet death, runting, rhinitis, pneumonia and occasionally neurological signs, with 100% morbidity in the affected cohort. In pigs over three weeks the infection is subclinical to mild and self- limiting. There is no vaccine and no treatment. Its topical importance is entirely outside conventional pig farming: no naturally acquired human infection has ever been reported, but because the virus replicated in baboons receiving pig heart and kidney xenografts and can infect human cells in the laboratory, it is a recognised concern for xenotransplantation, and eliminating it by early weaning and hand rearing is described as feasible for building a biomedical pig population but not for commercial production.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Rarely occurs: Human infection from pigs is plausible but has only rarely been reported, and specific control points are not commonly implemented to prevent transmission to humans
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c1l2, is a plausible zoonotic agent and important to signal this because is a key concern for emerging xenotransplant industry"
Basis. ch31 31.3.3, a Public Health section of its own: "PCMV is ubiquitous in pig populations and induces latent infections in pigs. ALTHOUGH NO NATURALLY ACQUIRED HUMAN INFECTIONS HAVE BEEN REPORTED and PCMV plays NO ROLE IN THE MORE TRADITIONAL OR ROUTINE AREAS OF CONCERN TO PUBLIC HEALTH, the potential use of live porcine cells, tissues, and organs for XENOTRANSPLANTATION has led to concerns regarding exposure of immunocompromised humans to infectious PCMV." Then the evidence on that route: replication detected in baboons receiving pig heart or thymokidney xenografts, though pig-to-primate islet studies found no transmission; "PCMV could infect human fibroblasts in vitro"; and "the DETECTION OF PCMV IN PERIPHERAL BLOOD MONONUCLEAR CELLS OF THE FIRST HUMAN RECIPIENT OF A HEART TRANSPLANT FROM A GENETICALLY MODIFIED PIG was reported (Griffith et al. 2022), reinvigorating the potential xenotransplantation-associated risk". 31.3.2: PCMV "is genetically closer to human herpesviruses 6 and 7 than to cytomegaloviruses". shic_pcmv: "Infection with PCMV has not been documented in humans; however, concern about transmission through xenotransplantation exists." "Further research is needed on the virus zoonotic potential."
How this level was decided
RE-READ AND HELD AT L2 2026-09-04 AGAINST THE REWORDED LABELS. FLAG. ch31 31.3.3: "NO NATURALLY ACQUIRED HUMAN INFECTIONS HAVE BEEN REPORTED." What keeps it at level 2 is that the one human detection IS attributed to a pig -- PCMV in the peripheral blood mononuclear cells of the first recipient of a genetically modified pig heart. A xenograft is transmission from a pig, but it is not pig or pork EXPOSURE in any sense the pork industry produces, so level 1 is arguable.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: Level 2, and FLAGGED AS A LEVEL 1 OR 2 JUDGMENT because the route that produced the only human detection is a surgical one rather than a farm one. Level 2 is scored because the level 1 label says there is NO evidence that pigs transmit the agent to humans, and there is some: PCMV was found in the blood of the first pig-heart xenograft recipient, it replicates in baboons carrying pig organs, and it infects human fibroblasts in culture. Rarely reported is the honest description. THE CASE FOR LEVEL 1 is that none of this is transmission from a pig to a person in any way the pork industry produces: it requires a pig organ to be surgically placed in an immunosuppressed human, the chapter says outright that no naturally acquired human infection has ever been reported, and it says PCMV plays no role in routine public health. Whichever way this goes, the entry should be read as a xenotransplantation question, not an occupational or foodborne one. Level 2 held. No human infection has ever been documented, which alone reads as level 1 -- but PCMV is one of the specific agents xenotransplantation programmes screen donor pigs for, so a pig-origin route to a person is taken seriously enough to design around. That is "plausible but only rarely reported".
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch31 31.3.3: "no naturally acquired human infections have been reported and PCMV plays no role in the more traditional or routine areas of concern to public health." No human illness caused by PCMV is described anywhere in the chapter -- the xenotransplantation concern is about graft outcome and about exposure of immunocompromised recipients, not about a described human disease. shic_pcmv: "Infection with PCMV has not been documented in humans."
How this level was decided
Level 1. C2 grades the severity of illness acquired from pigs, and no illness has been attributed to this virus in any person, including the xenograft recipient in whom it was detected. THE LABEL MUST NOT BE READ AS "THIS VIRUS IS HARMLESS TO PEOPLE": what it records is that no human illness has been shown, in an area of active research where people are looking hard. If a xenotransplant recipient is ever shown to have suffered PCMV disease, this cell moves with C1. Level 1 confirmed.
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. ch31 31.3.4: "PCMV IS HIGHLY PREVALENT IN PIGS THROUGHOUT THE WORLD WITH HERD PREVALENCE GREATER THAN 90% AND MORE THAN 98% OF ANIMALS POSITIVE IN EUROPE, NORTH AMERICA, AND JAPAN." "Natural infection with PCMV is limited to pigs, including wild boar, i.e. NON-PORCINE RESERVOIRS AND ARTHROPOD VECTORS HAVE NOT BEEN REPORTED." "PCMV is transmitted horizontally via the oronasal route, but CONGENITAL TRANSMISSION IS ALSO WELL DOCUMENTED. Infection most commonly occurs PERINATALLY in commercial pig holdings... The majority of pigs shed PCMV in nasal secretions between 3 and 8 weeks of age. This suggests that infection is usually acquired BY CONTACT WITHIN THE INFECTED COHORT." 31.3.10: the virus can be eliminated "by early weaning and motherless rearing of neonatal pigs... This approach may be feasible to establish a special pig population for biomedical purposes, BUT NOT FOR COMMERCIAL PRODUCTION." The second document in the folder shows the same virus circulating in Croatian wild boar. shic_pcmv: "PCMV is endemic in nearly all swine populations worldwide, including North America, with seroprevalence approaching 100% in many areas." "Latent PCMV infections can develop and become reactivated when pigs are stressed." "Preventing PCMV is challenging since nearly all swine are infected."
How this level was decided
Level 1, on the strongest prevalence numbers in the batch. More than 98% of pigs in North America are positive, the reservoir is the pig itself with no non-porcine host or vector, infection is acquired perinatally from the dam and within the cohort, and the virus persists latently for life. There is no introduction event to prevent. The chapter closes the question from the other side too: elimination has been achieved only by caesarean-style motherless rearing for biomedical herds, and it says in terms that this is not available to commercial production. Level 1 confirmed as strongly as the criterion allows -- endemic in North America at close to 100% seroprevalence, with latency on top.
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. ch31 31.3.8: "PCMV-associated diseases must be differentiated from infection with classical swine fever virus, enterovirus, parvovirus, PRRSV, PCV2, and PRV. VIRUS ISOLATION OR PCR-BASED ASSAYS for detection of viral DNA can be used for positive identification." "THE COMBINATION OF INCLUSION BODIES, CYTOMEGALY, AND KARYOMEGALY IS PATHOGNOMONIC." "PCMV infection in a herd is confirmed by serology using serum samples from grower-finishers. ELISAs have been described and adapted to differentiate IgG and IgM responses." Fischer et al. 2023 combined sensitive PCR with a peptide-based gB ELISA to "effectively distinguish pigs with active infection, pigs with latent infection, and noninfected pigs". Two limits are recorded: 31.3.2, "since CPEs are lacking in cell culture, confirmatory immunostaining is necessary", and 31.3.8, "no PCMV antibodies are induced by in utero infection", so antibody is not expected in colostrum-deprived neonatal sera. shic_pcmv: "Traditionally, PCMV is diagnosed via histological examination of tissue sections... where basophilic intranuclear inclusions are commonly observed, as well as cytomegaly and karyomegaly." "Polymerase chain reaction (PCR) assays have been developed, as well as enzyme-linked immunosorbent assays (ELISAs) for antibody detection."
How this level was decided
Level 2. The clinical presentation does not point here -- sneezing, nasal discharge and poor doing in a young pig sit behind six other agents on the chapter's own differential -- but validated assays exist and run in ordinary diagnostic laboratories: PCR, virus isolation, IgG and IgM ELISAs, and a histopathological picture the chapter calls pathognomonic. That is the level 2 label. NOTE THE ONE INTERPRETIVE TRAP, which matters because it inverts: a congenitally infected piglet does not seroconvert, so a negative serology on the animals most likely to die of this virus means nothing. Level 2 confirmed. Characteristic histopathology plus PCR and ELISA -- routine diagnostic laboratory work.
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, short lived and self-resolving infection of young pigs, present on essentially all farms"
Basis. ch31 31.3.1: "PCMV is ubiquitous and exists in nearly all pig populations, but CLINICAL DISEASE IS RARE with the exception of young piglets, in which a fatal systemic disease develops. IN IMMUNOLOGICALLY SUSCEPTIBLE HERDS, the virus causes fetal and piglet mortality, runting, rhinitis, pneumonia, and sometimes neurological signs." 31.3.6: "The disease is generally SELF-LIMITING. The course of disease is usually subclinical to mild in pigs >3 weeks of age but can lead to death of the fetus or newborn pig without any clinical signs... Although infection is usually subclinical in older pigs if uncomplicated, MORBIDITY AFTER CONGENITAL OR NEONATAL INFECTION IS 100%. THE MORTALITY IN A NAIVE HERD CAN BE 10%, BUT IT MAY INCREASE TO 50% in the presence of secondary bacterial or viral infections." "PCMV has been associated with the porcine respiratory disease complex in pigs of different ages", and a significant correlation with PCV2 has been found. shic_pcmv: "While neonates can develop fatal systemic disease, death is rare in older pigs. However, co-infections may increase morbidity and mortality when present." "PCMV does not cause severe losses in swine." "In older pigs, PCMV has been associated with porcine respiratory disease complex (PRDC)."
How this level was decided
Level 2, and the reason it is not level 4 is the same fact that puts C3 at level 1: with more than 98% of North American pigs positive, immunologically susceptible herds barely exist, so the 10 to 50% mortality figure describes a situation that almost never arises. This is the standing note SCORING/production_cost_impact working as intended -- score against modern US production, not the clinical picture the chapter can describe. What remains in an endemic herd is subclinical to mild disease in pigs over three weeks, some perinatal loss, and a contribution to PRDC. Small and generally short-lived losses. FLAGGED AS A LEVEL 2 OR 3 JUDGMENT on the PRDC association: if PCMV is a routine contributor to respiratory disease in US herds rather than an incidental finding, the losses are chronic rather than short-lived and this is level 3. Level 2 confirmed by direct statement -- PCMV does not cause severe losses in swine.
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 and widespread, no impact on market"
Basis. A virus carried by more than 98% of North American pigs, with no trade measure, movement control or consumer response recorded anywhere in chapter 31.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact, an agent endemic in essentially every US pig and diagnosed for seventy years without a market move on record is level 1. Unchanged. Endemic worldwide at near-universal seroprevalence with no market event; level 1.
C7 Treatment potential
Potential for treatment to improve outcomes
Little: Effective pathogen-directed treatment is available and works, or animals recover acceptably without it
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c7l1, no clinical imperative for vaccine development" He wrote "vaccine" against a treatment cell; the criterion prefix and the level both match C7, C8 was not open on this sheet, and the point he is making -- that there is no clinical imperative to develop anything for this virus -- reads the same way on either criterion. Read as c7l1. C8 was already at level 1 on the same reasoning.
Basis. ch31 31.3.10: "NO VACCINE OR SPECIFIC TREATMENT IS AVAILABLE FOR PCMV." 31.3.6: "The disease is generally SELF-LIMITING. The course of disease is usually subclinical to mild in pigs >3 weeks of age", though it "can lead to death of the fetus or newborn pig without any clinical signs". 31.3.9: piglets acquire maternal antibodies which "provide some protection", and seroconversion coincides with the disappearance of viraemia.
How this level was decided
Level 1 on the second clause -- animals recover acceptably without treatment -- and FLAGGED AS A LEVEL 1 OR 3 JUDGMENT, because Eric's pHEV rule of 2026-09-02 says that where an agent is lethal in neonates and trivial in adults you SCORE THE NEONATE, and on its face this virus is that pattern: fatal systemic disease in young piglets, subclinical over three weeks of age. THE REASON LEVEL 1 IS SCORED ANYWAY is that the neonatal form requires an immunologically naive herd, and at over 98% seroprevalence those are rare -- unlike the enteric coronaviruses he named, which break in immune herds every year. In the herd as it actually exists, pigs meet this virus behind maternal antibody, become viraemic, seroconvert and recover. If he reads the rule as governing regardless of how often the naive herd occurs, this cell is level 3 and moves with C5. Unchanged.
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
Basis. ch31 31.3.10: "NO VACCINE or specific treatment is available for PCMV." The control measures the chapter offers instead are managing the risk from introduced stock, "due to the reactivation of latent infections or primary infections of susceptible herds", and elimination by early weaning and motherless rearing -- explicitly "feasible to establish a special pig population for biomedical purposes, but not for commercial production". shic_pcmv: "There is no vaccine for PCMV." "No vaccines are available. It has been suggested that a vaccine could be used to eliminate PCMV from swine herds." "To minimize the risk of PCMV transmission through xenotransplantation, donor pigs should be delivered via Cesarean section and specified pathogen-free or designated pathogen-free breeding practices should be used."
How this level was decided
Level 1 on the "not needed" clause of the 2026-08-28 rewording, not on availability -- there is no vaccine at all. The test is whether the disease would clinically or economically justify one, judged on the agent's own weight, and a virus that is subclinical in almost every pig that meets it does not. This is consistent with C5 at level 2 and C7 at level 1 on the same evidence. NOTE THE ONE PLACE A PCMV VACCINE WOULD BE WANTED, which the criterion cannot see: xenotransplantation needs PCMV-free donor herds, and that demand is met by caesarean derivation rather than by vaccination, and belongs to human medicine rather than to pig production. Level 1 held, with the counter-argument recorded because the factsheet raises it: it suggests a vaccine could be used to ELIMINATE PCMV from herds. That is an eradication-tool argument rather than a disease-burden one, and the standing note grounds level 3 in a disease that would warrant a vaccine -- while this factsheet also says PCMV does not cause severe losses. The elimination interest comes from xenotransplantation, which is a human-medicine objective, not a swine-production one. Level 1 stands, but this is the clearest instance in the batch of a stated wish for a vaccine that does not amount to a clinical imperative.
Levels and evidence are generated from data/assignments/porcine_cytomegalovirus.yml; the overview is authored in data/overviews/porcine_cytomegalovirus.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.