La Piedad Michoacán Paramyxovirus
LEVELS: Highly unlikely; No human illness; Routine biosecurity keeps it out; Reference or research laboratory required; Substantial; Temporary disruption; Substantial; Available but inconsistent
| Register id | la_piedad_michoacan_paramyxovirus |
| Type | virus |
| Scientific name | La Piedad Michoacan Mexico virus |
| NCBI taxid | 2898537 |
| Evidence | 3 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
La Piedad Michoacán paramyxovirus causes blue eye disease, so called for the corneal opacity that is its most recognisable sign. It has never been reported outside Mexico, where it has been endemic in the centre of the country since 1980 at a seroprevalence of 9-23%. In a naive herd it is severe: about 20% of litters are affected, 20-50% of the piglets in those litters fall ill, and around 90% of affected piglets die, usually with central nervous signs; outbreaks with 20% mortality have also been seen in 15-45 kg pigs. In the breeding herd it causes two to eleven months of reproductive failure — returns to service, smaller litters, stillbirths — and in boars inflammation of the testes and epididymis. The combination of corneal opacity with orchitis in boars is unique to this virus and is what distinguishes it from pseudorabies and PRRS, though those infections often coexist on the same farm. It spreads nose to nose from subclinically infected pigs, in nasal secretions and urine, and can persist in the boar's reproductive tract for months, so semen is a route. There is no treatment; pigs with corneal opacity usually recover on their own while those with severe nervous signs generally die. Two inactivated vaccines are available in Mexico, though a single-strain product may not protect against all antigenic subtypes. 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. ch33 33.2.3, the entire Public Health section, one sentence: "LPMV DOES NOT HAVE ANY PUBLIC HEALTH SIGNIFICANCE AND IS NOT INFECTIOUS FOR HUMANS." 33.2.4 lists the species that have been tested: "Pigs are the only species known to be clinically affected by LPMV following natural exposure. Experimentally, LPMV affects mice, rats, and chick embryos. Rabbits, dogs, cats, and peccaries do not show clinical signs; rabbits, cats, and peccaries produce antibodies." People appear nowhere on that list. The virus has been endemic in central Mexico since 1980 at a seroprevalence of 9-23%, so the human question has had forty-five years of exposure to answer it. shic_2021_porv: "PoRV does not cause illness in humans. However, PoRV antibodies have been detected in serum from Mexican swine veterinarians."
How this level was decided
Level 1, and this is a stated negative rather than a silence. The chapter gives the agent a Public Health heading and uses it to say the virus is not infectious for humans, in a chapter whose other two subjects -- Menangle and Nipah -- are both proven zoonoses with their own case counts. The authors were plainly attentive to the question. NOTE THE ONE ODDITY that does not change the level: LPMV agglutinates human erythrocytes and is closely related to Mapuera virus from fruit bats, so it is a rubulavirus with a bat lineage like its neighbours in this chapter. Forty-five years of endemic circulation in a country with a large pig industry and no human case is the answer to that. LEVEL 1 HELD, AND FLAGGED. Antibodies in swine VETERINARIANS is occupational exposure to pigs producing human seroconversion, which is infection reaching people from pigs -- and C1 measures infection, not illness. That reads as level 2, "plausible but only rarely reported". Held because the same sentence says the virus does not cause illness in humans, and because Eric has twice ruled that antibody without illness can be alphavirus cross-reactivity rather than infection -- on chikungunya and on Getah. But this is a paramyxovirus in the veterinarians of the only country where the virus occurs, which is a narrower and more pointed finding than either of those.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch33 33.2.3: "LPMV does not have any public health significance and is not infectious for humans." No human illness is described anywhere in section 33.2 or in cfsph_2017. shic_2021_porv: "PoRV does not cause illness in humans."
How this level was decided
Level 1. Under C2 as rescoped, level 1 means pigs are not a source of human illness with this agent, and the chapter says the agent does not infect people at all. C1L1 implies C2L1 and validate_criteria.py checks it; this pair is the straightforward case. Level 1 confirmed by direct statement.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Routine biosecurity keeps it out: Quarantine of incoming stock, transport and fomite control, cleaning and disinfection, and the usual monitoring reliably exclude it
Basis. ch33 33.2.1: "LPMV HAS NEVER BEEN REPORTED OUTSIDE OF MEXICO", where it is endemic in the centre of the country at 9-23% seroprevalence. 33.2.4: "SUBCLINICALLY INFECTED PIGS FROM AFFECTED FARMS ARE THE PRIMARY SOURCE OF LPMV. The virus is apparently transmitted by NOSE-TO-NOSE CONTACT between infected and susceptible pigs... The virus is mainly disseminated in nasal secretions and urine. TRANSMISSION THROUGH SEMEN IS POSSIBLE and virus can be recovered from semen (5-45 DPI)" and from the male reproductive tract "for up to 142 DPI". "The virus may also be disseminated by FOMITES (e.g. people and vehicles), and possibly by fruit bats, birds, and wind." 33.2.9 states the control programme: "HERD HEALTH PROGRAMS ARE THE MOST RELIABLE METHOD OF PREVENTING THE INTRODUCTION OF LPMV INTO A FARM. REPLACEMENTS SHOULD BE SELECTED FROM A HEALTHY HERD, QUARANTINED, AND TESTED PRIOR TO INTRODUCTION. STANDARD BIOSECURITY MEASURES provide insurance against infection, (e.g. perimeter fencing, separate load-out areas, changing rooms and showers, wildlife control (birds, rats, and mice), prompt waste removal and disposal of dead pigs, control of the movement of personnel, visitors, and vehicles). Serological screening and testing of replacement animals by PCR are recommended." shic_2021_porv: "As of 2021, PoRV has occurred only in Mexico. However, transboundary spread remains a concern for the U.S. pork industry." "Replacement animals should be selected from PoRV-free sources and quarantined before they are introduced to the herd. Serological screening can be used to detect PoRV infection in replacements." "The major route of transmission is direct contact (nose-to-nose). Subclinically infected pigs spread the disease to susceptible pigs. Transmission via semen and fomites may also be possible."
How this level was decided
Level 3, and the chapter writes the level 3 list almost word for word: quarantine and testing of incoming stock, fomite and vehicle control, personnel control, waste removal. That is a routine biosecurity programme, and the chapter says it reliably prevents introduction. The primary source is another pig -- a subclinically infected one -- which housing does nothing about, so this is not level 2. It is not level 4 either: nothing here needs air filtration or thermally treated feed, and elimination from an infected herd has been achieved by herd closure, cleaning and all-in/all-out. NOTE THE SEMEN ROUTE, which is why testing rather than quarantine alone is specified: virus is recoverable from the reproductive tract for up to 142 days, so an apparently recovered boar is still a risk. Level 3 confirmed, and the factsheet lists the routine tier item by item: sourcing replacements from free herds, quarantine, serological screening of incoming stock. The route is pigs and semen, so housing does nothing -- not level 2 -- but nothing here needs filtration or treated feed.
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
Basis. ch33 33.2.8: "Clinical signs such as encephalitis, corneal opacity, and reproductive failure in the sow and orchitis and epididymitis in the boar are consistent with a diagnosis of BED... ONLY LPMV PRODUCES CORNEAL OPACITY ALONG WITH ORCHITIS AND EPIDIDYMITIS IN BOARS." Against that, "other causes of encephalitis and reproductive disease must also be considered, e.g. pseudorabies virus and PRRSV", and "it is common to have BED associated with PRRSV and/or influenza A virus on the same farm". On the assays: paired sera fifteen days apart tested by haemagglutination inhibition, virus neutralisation, immunofluorescence or ELISA, with HI the most frequently used but needing properly treated chicken erythrocytes "to avoid false positive results"; virus isolation in PK-15 or primary pig kidney cells; and "QUANTITATIVE REAL-TIME REVERSE TRANSCRIPTASE POLYMERASE CHAIN REACTION (qRT-PCR) ASSAYS ARE MORE SENSITIVE and target either the phosphoprotein gene or the nucleoprotein gene ACROSS ALL STRAINS OF LPMV". shic_2021_porv: "Virus can be cultured in pig kidney cell lines... There are also quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) assays that detect either the P (phosphoprotein) gene or the NP (nucleoprotein) gene across all strains of PoRV." "Antibodies can be detected via hemagglutination inhibition, virus neutralization, and enzyme-linked immunosorbent assay (ELISA)."
How this level was decided
Level 3, and it is a where-not-whether judgment. Validated assays plainly exist and are used routinely -- in Mexico. A strain-inclusive qRT-PCR, four serological formats and a cultivable virus is more than most entries have, so this is nowhere near level 4. What puts it at level 3 is that the disease has never been reported outside one country, so no US diagnostic laboratory holds LPMV antigen, antiserum or primers, and a suspicion here would go to a national reference laboratory. That is the same position as classical swine fever, foot-and-mouth disease and African swine fever, all scored level 3. NOTE THE ONE STRONG CLINICAL POINTER, which is unusual and worth carrying into a brief: corneal opacity together with orchitis and epididymitis in boars occurs with nothing else. Level 3 held. Assays are good -- qRT-PCR covering all strains -- so nowhere near level 4. Held at 3 rather than 2 because the agent has never occurred outside Mexico, so no US diagnostic laboratory offers or holds reagents for it.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l4, this agent is part of an important class of emerging viruses. Surprisingly, it has yet to be seen outside Mexico which suggests it is not a major transboundary threat, but to my knowledge it is still unclear where the virus came from so is naive to think the US can ignore it. Clinical affect has been variable, but at its worst, especially in new outbreaks, the impact can be substantial" HIS REASON IS A WARNING ABOUT THE WHOLE ENTRY, not just this cell: "it is still unclear where the virus came from so is naive to think the US can ignore it." Forty-five years confined to one country is not evidence that it stays there.
Basis. ch33 33.2.6, on the initial outbreak in a naive herd: "During an outbreak, ABOUT 20% OF THE LITTERS FARROWED ARE AFFECTED. In these litters, PIGLET MORBIDITY IS 20-50% AND MORTALITY IN AFFECTED PIGLETS IS ABOUT 90%... During an initial outbreak, deaths occur for 2-9 weeks." In older pigs: "Outbreaks with 20% MORTALITY and severe CNS manifestations have been observed in 15-45 kg pigs." In the breeding herd: "In pregnant sows, REPRODUCTIVE FAILURE LASTING 2-11 MONTHS (usually 4 months) is observed... an increase in the number of animals returning to estrus, a reduction in farrowing rate, and an increase in the wean-to-service interval and nonproductive sow days. The rates of stillbirths and mummified fetuses also increase." And in boars: "SEMEN EVALUATION DEMONSTRATED THAT ABOUT 30% OF BOARS IN HERDS INFECTED WITH LPMV SHOWED TEMPORARY OR PERMANENT INFERTILITY... In some boars there is azoospermia", with testicular atrophy following. cfsph_2017 records that "most acute outbreaks in naive herds appear to be self-limiting". shic_2021_porv: "causes CNS signs and high mortality in piglets, respiratory disease in pigs over 30 days-of-age, reproductive disease in sows and boars, and corneal opacity (blue eye) in pigs of all ages." "Boars infected with PoRV develop ... orchitis and epididymitis followed by testicular atrophy."
How this level was decided
Level 4, and FLAGGED AS A LEVEL 3 OR 4 JUDGMENT alongside the Menangle cell, because both turn on whether a severe but self-limiting reproductive failure is manageable. Level 4 is scored because three parts of the herd are hit at once and one of the injuries is permanent: piglets dying at 90% in a fifth of litters, up to 20% mortality in growers, four months of reproductive failure as the usual case, and thirty percent of boars temporarily or permanently infertile with some going azoospermic. Losing a third of the boar stud is not a loss the herd recovers from by acquiring immunity. THE ARGUMENT FOR LEVEL 3 is the chapter's own phrase that outbreaks in naive herds are self-limiting, and that in Mexico this is an endemic disease that farms live with rather than a disease that closes them. Level 4 confirmed. High piglet mortality plus reproductive failure in both sexes, with permanent testicular atrophy in boars.
C6 Market impact
Duration of material disruption to pork and pig markets
Temporary disruption: Material negative effect on supply or demand lasting less than a month when disease occurs on one or more farms
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Corrected by Eric from L1 Negligible. Reason: "c6l2, it is an exotic disease that causes significant disease. If it showed up in the US, I think it is plausible there would be local or regional movement restrictions" Same reading as his Menangle ruling made in the same sheet, and the pair should be read together: the forty- five-year Mexican precedent says the disease does not move a market where it is endemic, and he is scoring what a first US detection of an exotic paramyxovirus would do instead. Both entries move from level 1 to level 2.
Basis. ch33 33.2.1: LPMV "HAS NEVER BEEN REPORTED OUTSIDE OF MEXICO", and inside Mexico it has been endemic since 1980 with a seroprevalence of 9-23%, rising to 20-40% in some areas per cfsph_2017. Neither document records any trade measure, movement restriction, export suspension or consumer response, in Mexico or anywhere else, in forty-five years.
How this level was decided
INFERRED, and level 1 rests on a foreign precedent rather than on silence, which is what the standing note SCORING/market_impact asks for. Mexico has had this disease in a large commercial pig industry for four and a half decades, at up to 40% seroprevalence in places, and no market consequence is recorded. The note says that where a foreign precedent exists it should be used, and this is an unusually long one. FLAGGED AS A LEVEL 1 OR 2 JUDGMENT for the reason the precedent cannot settle: a first US detection of a paramyxovirus that has never left Mexico would be an exotic disease event here, whatever it is in Michoacán, and exotic disease events stop pig movements while they are investigated. The Mexican precedent says the disease does not move a market; it does not say a first detection would not. Unchanged. Level 2 on Eric's correction.
C7 Treatment potential
Potential for treatment to improve outcomes
Substantial: No effective treatment (antimicrobial, antiviral, antiparasitic, herbal or other) is available, but outcomes would meaningfully improve if one existed
Basis. ch33 33.2.9: "As with most viral diseases of swine, THERE IS NO SPECIFIC TREATMENT FOR BED. Pigs with corneal opacity frequently recover spontaneously, whereas PIGS WITH SEVERE CENTRAL NERVOUS SIGNS GENERALLY DIE. Antimicrobial therapy is commonly used to treat and prevent secondary infections." 33.2.6: mortality in affected piglets is about 90%, and in the first cases "piglets usually die within 48 hours of the appearance of clinical signs, but in later cases, death occurs after 4-6 days". 33.2.4: persistence is long -- viral RNA in brain for 53 days, in boar reproductive tracts for 277 days, and mRNA detectable in brain, lung, tonsil, salivary gland and pancreas for up to 270 days in convalescent pigs. shic_2021_porv: "There is no treatment for PoRV infection." "Suckling piglets develop progressive neurological signs often culminating in death."
How this level was decided
Level 3, on Eric's rule of 2026-09-02 that C7 scores the value of a treatment that does not exist rather than the industry's willingness to use one, and that WHERE AN AGENT IS LETHAL IN NEONATES AND TRIVIAL IN ADULTS YOU SCORE THE NEONATE. This is that pattern: 90% mortality in affected piglets against transient anorexia and a cloudy eye in adults. There is a window to act in, unlike the transplacental agents he put at level 1 -- piglets take four to six days to die in later cases -- and a treatment that saved them, or that cleared the 277-day carriage from a boar, would plainly improve outcomes. That is the same reading that put TGEV, PEDV, PDCoV, SADS-CoV and pHEV at level 3. Level 3 confirmed on the standing note's neonate rule -- progressive disease in live suckling piglets is a window a treatment could act in, unlike the purely transplacental agents at level 1.
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
Corrected by Eric from L1 Available, or not needed. Reason: "c8l2, severity of the diseaese in mexico has meant a push for vaccine candidates there. While not commercially available, autogenous seem to provide some benefit but the scope of the problem has meant we don't actually know how well these vaccines work." THIS IS THE THIRD READING OF AN AUTOGENOUS PRODUCT IN THE REGISTER and it lands where Mycoplasma hyorhinis did rather than where Brachyspira pilosicoli did. Pilosicoli is level 3 because its autogenous bacterin was field-tested and failed. M. hyorhinis is level 2 because its autogenous products are in use and have never been evaluated. He puts blue eye disease with the second: products exist, they appear to help, and nobody knows how well.
Basis. ch33 33.2.9: "At present, THERE ARE TWO COMMERCIAL INACTIVATED VIRUS VACCINES used in pregnant sows, gilts, boars, and piglets. HOWEVER, SOME DATA INDICATE THAT A MONOVALENT VACCINE WILL NOT COMPLETELY PROTECT AGAINST THE DIFFERENT ANTIGENIC SUBTYPES." An experimental recombinant HN vaccine produced in E. coli "induced an effective humoral response in pregnant sows and the maternally-derived immunity protected suckling piglets against LPMV lethal challenge". cfsph_2017: "AT LEAST ONE COMMERCIAL INACTIVATED VACCINE IS AVAILABLE IN MEXICO. THERE ARE NO PUBLICATIONS DESCRIBING ITS EFFICACY." 33.2.1: the disease "has never been reported outside of Mexico". shic_2021_porv: "There are licensed vaccines for PoRV in Mexico."
How this level was decided
Level 1 on the "not needed" clause rather than on availability, and this is the pattern Eric ruled on E. coli edema disease on 2026-09-02: "I am not aware of the vaccine at all, and am sure is not currently available in US. but if there is evidence it is available and works, L1 is correct (AND IN MOST FARMS IT IS NOT NEEDED ANYWAY)." The same two facts hold here. The vaccines exist but are licensed in Mexico, so they are not available in the US; and the disease has never occurred in the US, so nothing here justifies vaccinating. FLAGGED AS A LEVEL 1 OR 2 JUDGMENT because the products are real and their protection is explicitly inconsistent -- a monovalent vaccine does not cover the antigenic subtypes, and CFSPH notes no published efficacy data at all -- so if the criterion is read as describing the vaccine rather than the US need, this is level 2. Level 2 confirmed, on Eric's correction, and the new source states the ground for it outright: licensed vaccines exist -- in Mexico. A product that exists but is not available here is the level 2 shape rather than the level 3 gap.
Levels and evidence are generated from data/assignments/la_piedad_michoacan_paramyxovirus.yml; the overview is authored in data/overviews/la_piedad_michoacan_paramyxovirus.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.