Pseudorabies Virus
LEVELS: Rarely occurs; Severe; Extraordinary biosecurity required; Laboratory-dependent; Substantial; Negligible; Little; Available, or not needed
| Register id | pseudorabies_virus |
| Type | virus |
| Scientific name | Suid alphaherpesvirus 1 |
| NCBI taxid | 10345 |
| Evidence | 4 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Pseudorabies, also called Aujeszky's disease, is caused by a herpesvirus for which pigs are the natural host. In young piglets it causes severe neurological disease and very high mortality; in growers it causes respiratory disease; and in the breeding herd it causes abortion and stillbirths. Older pigs often survive, and that is the heart of the problem — like all herpesviruses it establishes a lifelong latent infection in the nerve ganglia, so a recovered pig remains a carrier that can shed again under stress. In other species, including cattle, sheep, dogs and cats, infection is invariably fatal and accompanied by intense itching, which gave the disease its old name of mad itch. The United States eradicated pseudorabies from commercial herds in 2004, a genuine achievement built on marker vaccines that allowed vaccinated pigs to be told apart from infected ones. It persists in feral swine across much of the country, so the risk of re-introduction is permanent. It is not classically regarded as a zoonosis, though a small number of severe human infections have been reported, mainly in China among people with occupational exposure, and this has prompted renewed review of that position.
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, i think l2 is correct as evidence is no pretty conclusive from china that human infections do occur but rarely, see paper in the inbox about this"
Basis. ch31 31.2.4: "The susceptibility of humans to PRV is controversial... recent anecdotal case reports describe natural infections of humans with PRV characterized by encephalitis and endophthalmitis... MOST AFFECTED INDIVIDUALS WERE WORKING ON PIG FARMS and had injuries to their fingers." cfsph_2024 doubts the whole literature: "None of the cases were confirmed by detecting the virus, its antigens or nucleic acids", and additional studies are needed "for definitive confirmation of pseudorabies as a human pathogen". favoreel_2026_prv_human_infection_review.md settles it, and it is the document Eric pointed at: "based on the available evidence, IT IS REASONABLE TO ASSUME THAT, IN VERY RARE CASES, PRV MAY INFECT HUMANS." The count: 17 suspected cases between 1914 and 2011, mild and mostly severe itching, plus a 1970 self-inoculation experiment that produced "neither symptoms nor seroconversion"; then 34 suspected cases since 2011, ALL IN CHINA, all detected by next-generation sequencing of cerebrospinal fluid, coinciding with the surge in genotype II variants there. "ALL REPORTED PATIENTS HAD OCCUPATIONAL OR OTHER FREQUENT CONTACT WITH RAW (and possibly PRV-infected) PIG MATERIAL", and 11 of 34 "had skin damage on the hands and/or fingers around the time of supposed contact". "HUMAN-TO-HUMAN SPREAD OF PRV HAS NEVER BEEN REPORTED", and "the risk for human PRV infection REMAINS VERY LOW". shic_2026_prv: "Humans have long been considered resistant to PRV. Variant PRV has recently been associated with encephalitis and ophthalmic disease in people who have extensive contact with pigs or pork in China."
How this level was decided
RE-READ AND HELD AT L2 2026-09-04 AGAINST THE REWORDED LABELS. favoreel_2026: 34 suspected cases since 2011, all in China, and "MOST AFFECTED INDIVIDUALS WERE WORKING ON PIG FARMS and had injuries to their fingers". Occupational attribution to pigs is explicit and the cases are rare. This is the cleanest level 2 in the register and Eric's own worked example at the level.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: Level 2, confirmed by Eric on 2026-09-03 with this paper in front of him: "i think l2 is correct as evidence is now pretty conclusive from china that human infections do occur but rarely." That is the level 2 label in his own words -- human infection from pigs is plausible and has rarely been reported. THE REVIEW RESOLVES THE DISAGREEMENT BETWEEN THE OTHER TWO DOCUMENTS in this folder: Diseases of Swine treats the CSF isolate as direct evidence, CFSPH treats the whole literature as unconfirmed, and Favoreel concludes that human infection is real but very rare. WHY IT IS NOT LEVEL 3: level 3 needs a known occupational or foodborne risk that materialises when a control point fails, and 34 cases worldwide in fifteen years, all in one country during a variant surge, is not that. NOTE THE SEROLOGY WARNING the review supplies, because it is the reason the case count cannot simply be trusted upward: PRV gB is 54-56% identical to its herpes simplex 1, herpes simplex 2 and varicella-zoster orthologs, the ELISAs used were developed and validated for PIG serum, and 3.86% of a HEALTHY Chinese cohort tested anti-PRV gB positive. Level 2 confirmed, and this is a substantial strengthening. The folder previously supported level 2 on plausibility; the 2024/2026 factsheet reports human encephalitis and ophthalmic disease in people with extensive PIG OR PORK contact. That is pig-attributed human infection, rarely reported -- the level 2 label.
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. ch31 31.2.4 describes the recent human cases as "characterized by encephalitis and endophthalmitis" and says "all patients survived and clinical symptoms resolved". favoreel_2026_prv_human_infection_review.md CORRECTS THE CHAPTER ON THAT POINT and gives the outcomes in full for all 34 cases since 2011: "all of these were associated with SEVERE ENCEPHALITIS AND/OR VISION LOSS... All cases except one were diagnosed with encephalitis, typically with very severe and long-term neurological sequelae, ranging from MODERATE TO SEVERE MENTAL AND PHYSICAL DISABILITY (most cases) to PERMANENT COMA OR UNRESPONSIVENESS (n = 4), and sometimes DEATH (n = 6). ONLY ONE CASE DESCRIBED COMPLETE RECOVERY OF THE PATIENT." "Several cases were associated with severe eye damage, including endophthalmitis and/or acute retinal necrosis, leading to SEVERELY AND MOSTLY PERMANENTLY IMPAIRED VISION OR BLINDNESS. THIS WAS REPORTED FOR 17 OUT OF 34 PATIENTS", and may be an underestimate because those who died or stayed comatose were not assessed. Antiviral treatment was "largely disappointing". The clinical course: flu-like symptoms, then loss of responsiveness and seizures, then respiratory failure requiring mechanical ventilation. shic_2026_prv: "Variant PRV has recently been associated with encephalitis and ophthalmic disease in people."
How this level was decided
Level 4, and the paper moves this cell from an inference off two words in the chapter to one of the best-evidenced C2 cells in the register. The label asks for a substantial risk of life-threatening illness, death or permanent disability EVEN IF HUMAN INFECTIONS ARE UNCOMMON, and the case series is six deaths, four permanent comas, blindness or severe visual impairment in half the patients, and a single full recovery out of 34. THE CHAPTER IS WRONG ON THIS POINT and the correction is worth carrying: Diseases of Swine says all patients survived and their symptoms resolved. They did not. NOTE HOW C1 AND C2 DIVIDE THE WORK HERE, because the pair looks odd otherwise: C1 is level 2 because it almost never happens, C2 is level 4 because when it does happen the person usually does not recover. Both are true and the criteria are meant to carry them separately. Level 4 confirmed. Encephalitis and ophthalmic disease carry substantial risk of life-threatening illness or permanent disability.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Extraordinary biosecurity required: Exclusion needs measures beyond the routine, such as air filtration, thermally treated feed and bedding, or repeated costly testing to find carriers, and may still fail
Basis. ch31 31.2.5: "Despite successful elimination of PRV from domestic pigs, THE DISEASE IS WIDESPREAD IN POPULATIONS OF NONDOMESTIC SWINE, including feral pigs, wild boar, and hybrids, around the world. Although PRV in wild boar generally has not impacted the AD-free status of domestic pigs, INFECTED WILD BOARS REPRESENT A CONSTANT DANGER FOR REINTRODUCTION OF PRV INTO FREE HERDS AND REGIONS." "PRV IS ALSO ENDEMIC IN FERAL SWINE POPULATIONS IN THE UNITED STATES AT PREVALENCES RANGING FROM 0.5% TO 61%." Canada, New Zealand and the United States are free of AD in domestic pigs. 31.2.5.4 on persistence: infectious at 25, 15 and 4 degrees C for about 6, 9 and 20 weeks respectively, in slurry for 1-2 months, in soil for 5-6 weeks, on hay and straw for 15 and 40 days. shic_2026_prv: "The domestic pig population in the United States is free from PRV, but infection has been documented in feral swine." "Pigs with latent infection, showing no clinical signs, can introduce PRV into susceptible herds." "Direct oronasal contact is the main route of transmission in domestic swine. The virus is also spread by air, water, and contaminated fomites." "Swine feedback tissues have been implicated in PRV transmission in China."
How this level was decided
RENUMBERED L5 -> L4 on 2026-09-03, when C3 was reduced from five levels to four and level 4 absorbed level 5. THE JUDGMENT IS UNCHANGED and this one really is a renumber: the merged level 4 label carries what level 5 said, ending "and may still fail". IT WAS STILL CHECKED rather than assumed, because the last renumber on 2026-09-01 was mechanical and moved twenty-one entries past a level they should have been judged against. The check is the exclusion test -- does housing close the route? For this entry it does not.
EARLIER REASONING, kept because it is the evidence read: Level 5, and this entry is the framework's worked example at that level. The label asks for an epidemiologically important reservoir outside the farm and the industry that is a persistent threat nobody can remove, and US feral swine at up to 61% prevalence are precisely that -- the chapter calls them a constant danger for reintroduction in its own words. THIS SCORE IS LOAD-BEARING BEYOND THIS ENTRY and should not be moved without deciding what replaces it. Pseudorabies and African swine fever both sit at level 5 and therefore score identically on C3, which is correct and deliberate: the industry's far greater fear of ASF is real but is not a BIOSECURITY difference, and C5, C6 and C8 already separate the two. PAPRIKA adds the criteria, so letting that fear into C3 as well would give it extra weight invisibly. NOTE THE ONE QUALIFICATION the chapter makes, which does not change the level: "PRV-infected nondomestic swine pose a limited risk to domestic animals, unless they come into direct contact." Level 5 is about the permanence of the reservoir, not the ease of the route. Level 4 confirmed. Latent, clinically silent carriers introducing the virus is the repeated-costly-testing case verbatim, and airborne spread is on top of it. This is the entry the standing rule uses as its worked example: feral swine do not enter a barn, but PRV arrives in a truck.
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 31.2.9.2: "Clinical observations are ONLY SUFFICIENT TO LEAD TO A SUSPICION of AD because the infection produces NO PATHOGNOMONIC clinical signs or gross postmortem lesions in swine. Therefore, laboratory confirmation is required." 31.2.9.1 lists the differential: rabies, teschovirus and sapelovirus polioencephalomyelitis, porcine astrovirus 3, classical and African swine fever, Nipah, Japanese encephalitis, haemagglutinating encephalomyelitis, EMC, PCV2, highly virulent PRRSV, Streptococcus suis meningoencephalitis, swine influenza, salt poisoning, hypoglycaemia, arsenic or mercury poisoning, congenital tremors. On the assays: "Detection of PRV DNA in secretions or organ samples using PCR is commonly used", with nested and real-time quantitative assays "with the capacity to differentiate between wild-type and gene-deleted vaccine viruses", though "there is NO ESTABLISHED INTERNATIONAL STANDARD". "The virus neutralization test... has been WIDELY REPLACED BY ELISAs", and the gE ELISAs that distinguish infection from vaccination "BECAME A KEY PART OF PRV ERADICATION PROGRAMS". Serology also works on meat juice. shic_2026_prv: "Many different polymerase chain reaction (PCR) assays have been described in the literature, including some that can differentiate infected from vaccinated animals (DIVA) and some that can detect many swine pathogens at once." "The enzyme-linked immunosorbent assay (ELISA) has largely replaced virus neutralization as the preferred serological testing method."
How this level was decided
Level 2, on both halves of the label. Nothing about the presentation points here -- the differential is one of the longest in the register, running from rabies to salt poisoning -- so it is not level 1. But validated assays plainly exist and plainly run outside reference laboratories: the gE differential ELISA was the instrument of national eradication programmes, which means it was run at scale on ordinary surveillance samples, and PCR is routine. That is level 2, not level 3. NOTE the absence of an international PCR standard, which is a comparability problem between laboratories rather than a validity problem within one. Level 2 confirmed. DIVA-capable PCR and routine ELISA -- this is well-served diagnostically, as an eradicated disease under surveillance has to be.
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
Basis. ch31 31.2.2: "PRV can cause DEVASTATING LOSSES by fatal infection of piglets and abortions in pregnant animals." 31.2.7 gives the numbers: "In neonatal pigs less than 7 days of age, the disease may be characterized by SUDDEN DEATH with few, if any, clinical signs. In 2- to 3-week-old piglets, severe signs of CNS involvement... are seen WITH MORTALITY UP TO 100%. Older animals (3-6 weeks of age) may show neurological signs, but usually develop age-dependent resistance. MORTALITY MAY DECREASE TO 50% BY THE FOURTH WEEK of age, to less than 5% in 5-month-old pigs." "In finishing and fattening pigs, because of the population density, clinical signs can amplify, and ANIMALS OFTEN DIE FROM SECONDARY BACTERIAL PNEUMONIA." In sows: "embryonic death, resorption of fetuses, mummified fetuses, abortion, or stillbirth". With PRRSV, PCV2 or influenza coinfection, "a severe and often fatal proliferative and necrotizing pneumonia may develop". shic_2026_prv: "In domestic pigs, neurological signs are most common in suckling pigs but sudden death can also occur. In older, growing pigs, respiratory signs include cough, dyspnea, and rhinitis. Reproductive failure is common in breeding herds." "If variant PRV were to enter the United States, it could cause significant losses to the swine industry."
How this level was decided
Level 4, and the standing note SCORING/production_cost_impact points that way rather than against it for once. That note says to score against modern US production rather than the chapter's clinical picture, because chapters describe severity that US confinement has engineered out. Here the two coincide: THE UNITED STATES IS FREE OF PRV IN DOMESTIC PIGS, so every US herd is fully naive, and the naive-herd picture IS the US picture. Up to 100% mortality in two- to three-week-old piglets, 50% in the fourth week, whole-litter reproductive loss in sows and secondary fatal pneumonia in finishers is a major and potentially unsustainable increase in cost of production. This is scored level with classical swine fever and foot-and-mouth disease, which is the right company. Level 4 confirmed.
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, there was a small outbreak in Iowa commercial herds as recent as 2026 and there was no market impact. In a multi-site or multi-state outbreak, I suppose you could conceive of some supply effects based on movement controls but at this time, this appears to be a hypothetical case only." HE SUPPLIED A US PRECEDENT THE CHAPTER DOES NOT HAVE, and it is the reason this cell is settled rather than argued: a small pseudorabies outbreak occurred in Iowa commercial herds in 2026 with no market impact. That is the observation SCORING/market_impact asks for -- something actually happened in US pigs and nothing followed -- and it answers the objection the pass raised, which was that the free status makes the historical endemic period a poor guide. It also means the criteria file needs its C6 level 2 example moved, since it names pseudorabies virus and validate_criteria.py reports the disagreement.
Basis. ch31 31.2.5: AD "became one of the most important infectious diseases of domestic pigs" and was endemic in US domestic herds for decades before national eradication; the United States is now free of AD in domestic pigs. 31.2.5.2: "the World Organization for Animal Health (WOAH) set international standards and recommendations for movement of pigs between areas with differing disease status (free, provisionally free, endemic)." No trade suspension, consumer response or supply disruption is recorded anywhere in section 31.2, and none is recorded for the decades in which the virus was endemic in US herds. shic_2026_prv: "PRV is a World Organization for Animal Health (WOAH)-listed disease and must be reported internationally according to the Terrestrial Animal Health Code." "Classical pseudorabies virus (PRV) was first isolated in the early 1900s and eradicated from U.S. commercial swine in 2004." "Components of PRV eradication programs have included culling PRV-infected animals, vaccination with marker vaccines, restriction of swine imports, and isolation of domestic pigs from feral swine."
How this level was decided
INFERRED, AND FLAGGED AS THE JUDGMENT IN THIS ENTRY MOST LIKELY TO MOVE. It is scored level 1 by applying the standing note SCORING/market_impact literally: that note says the absence of any historical market move is evidence the market does not respond, for agents already endemic or already diagnosed in US pigs, and pseudorabies was endemic in US pigs for decades while the industry traded normally. That is a precedent, and the note asks for precedent. THE ARGUMENT AGAINST IT IS THAT THE SITUATION HAS CHANGED. The US now holds a free status it did not hold then, WOAH standards govern movement between areas of differing status, and losing that status is a different event from never having had it. If the view is that a reintroduction would suspend export negotiations or trigger state movement standstills for weeks or months, this is level 2 or level 3. NOTE WHAT IT SHOULD NOT BE: foot-and-mouth disease and classical swine fever sit at level 4, and pseudorabies is not in that class -- it is not a disease that closes borders. AND THE CRITERIA FILE DISAGREES, which validate_criteria.py reports: pseudorabies virus is a worked example at C6 LEVEL 2. That is a second, independent reason to put this cell in front of Eric, and it means the choice is not really between level 1 and level 3 but between the standing note read literally and the framework's own calibration. If he rules level 2, the example stands and nothing else needs touching; if he rules level 1, the example moves, as Cystoisospora suis and Mycoplasma hyopneumoniae have already done. *** LEVEL 1 HELD BUT FLAGGED, AND THIS IS THE FLAG I AM LEAST COMFORTABLE LEAVING. *** Unlike PRRSV above, the endemic-and-already-diagnosed argument does not apply here: the US eradicated PRV from commercial swine in 2004 and is officially free, the disease is WOAH-listed with mandatory international reporting, and eradication programmes have historically included RESTRICTION OF SWINE IMPORTS. A re-introduction would cost that free status. On the standing note's own logic -- use the foreign or historical precedent where one exists -- the US eradication campaign is exactly such a precedent, and it points well above level 1. I have not moved it because it is a signed-off cell and a move of three levels, but of everything in this round this is the cell I would most want Eric to look at.
C7 Treatment potential
Potential for treatment to improve outcomes
Little: Effective pathogen-directed treatment is available and works, or animals recover acceptably without it
Corrected by Eric from L3 Substantial. Reason: "c7l1, this disease is not a clean fit in the levels but I will override because a) I don't think outcomes would be meaningfully improved as in L3, and b)the vaccine is so good that there is little imperative to develop a treatment."
Basis. No treatment for pseudorabies is described anywhere in chapter 31 or in cfsph_2024; both discuss control entirely in terms of vaccination, eradication and biosecurity. cfsph_2024 on the herd remedy: "Pseudorabies can be eradicated from a herd by DEPOPULATION, followed by cleaning, disinfection, and restocking with virus-free animals." ch31 31.2.7: mortality up to 100% in 2- to 3-week-old piglets, with sudden death and few clinical signs in neonates. 31.2.10.2: immunity after infection "is durable, very stable, and protective against viremia and clinical disease... However, STERILIZING IMMUNITY IS NOT ACHIEVED", and 31.2.6.2 records lifelong latency with reactivation under transport stress. shic_2026_prv: "There is no available treatment for PRV infection in swine." "Components of PRV eradication programs have included culling PRV-infected animals."
How this level was decided
Level 3, and FLAGGED AS A LEVEL 1 OR 3 JUDGMENT because Eric has set rules that pull in both directions and this entry sits between them. LEVEL 3 IS SCORED on his 2026-09-02 pHEV rule: C7 measures the value of a treatment that does not exist, not the industry's willingness to use one, and WHERE AN AGENT IS LETHAL IN NEONATES AND TRIVIAL IN ADULTS, SCORE THE NEONATE. Pseudorabies is that pattern in its purest form -- 100% mortality at two to three weeks, under 5% at five months -- and a treatment that saved those piglets, or that cleared latency from a carrier, would plainly improve outcomes. THE ARGUMENT FOR LEVEL 1 IS HIS TRICHINELLA BOUNDARY: where an agent can be kept off a farm by management there is no imperative to develop a treatment for pigs, and pseudorabies is not merely excludable but has actually been eradicated from US domestic herds and is preventable by a highly effective vaccine. That is a stronger excludability case than Trichinella's. Level 3 is scored because the exclusion is national rather than farm-level and the reservoir is permanent, so the naive herd that meets this virus meets it with nothing to offer the piglets at all. Level 1 held, on Eric's correction, and the new source supports his reasoning: the response to PRV is culling and eradication, so an infected pig is removed rather than treated. Same shape as his swine vesicular disease ruling.
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 31.2.11: "solid immunity against PRV infection can be induced by vaccination"; modified live vaccines "have proven HIGHLY EFFECTIVE in decreasing clinical signs of AD"; and the marker vaccines that carry a gE deletion, paired with a differential ELISA, "made it possible to discriminate between vaccinated, PRV-uninfected animals and wild-type PRV-infected animals". "AD has been the PRIME EXAMPLE of using companion diagnostic ELISA tests to differentiate infected from vaccinated animals (DIVA)... the combination of highly efficacious DIVA vaccines and accurate differential ELISAs HAS MADE ERADICATION OF AD FROM LARGE AREAS OF THE WORLD PRACTICAL AND FEASIBLE." Against that, 31.2.5: "IN PRV-FREE COUNTRIES, VACCINATION IS PROHIBITED", and the United States is a PRV-free country. cfsph_2024 adds the limitation: vaccines "do not provide sterile immunity or prevent latent infections". shic_2026_prv: "Components of PRV eradication programs have included culling PRV-infected animals, vaccination with marker vaccines."
How this level was decided
Level 1, and it needs both halves of the level 1 label to get there, which is worth setting out because the first half alone fails. Effective vaccines are NOT widely available in the US -- they are banned, because the US is free and vaccination would compromise the surveillance that proves it. What carries the level is the rest of the clause: the disease does not currently justify vaccinating, and highly efficacious DIVA vaccines demonstrably exist, are the tool that eradicated the disease across most of the developed world, and could be deployed for outbreak response. This is the same reading already applied to classical swine fever and foot-and-mouth disease, both scored level 1, and for the same reason -- a product that exists and works but is deliberately not used in a free country is not a vaccine GAP. Level 3 is reserved for a genuine gap, and this is the opposite of one. Level 1 confirmed. Marker (DIVA) vaccines exist and were a named component of the eradication that succeeded -- a product that exists and works.
Levels and evidence are generated from data/assignments/pseudorabies_virus.yml; the overview is authored in data/overviews/pseudorabies_virus.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.