Porcine Parainfluenza Virus 1
LEVELS: Highly unlikely; No human illness; Already in the herd; Laboratory-dependent; Negligible; Negligible; Little; Available, or not needed
| Register id | porcine_parainfluenza_virus_1 |
| Type | virus |
| Scientific name | Respirovirus suis |
| NCBI taxid | 3052733 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Porcine parainfluenza virus 1 was identified in Hong Kong in 2013 and has since turned up almost everywhere anyone has looked — the United States, Chile, Hungary, Germany, the Netherlands, South Korea, Poland and China. In the US it is common: PCR testing of 1,589 diagnostic submissions from 27 states found 34% positive, most often in nursery pigs. Whether it causes disease is another matter, and the honest answer is that nobody has been able to show that it does. Four separate studies looked. Naturally infected weaned pigs shed virus for up to ten days with no clinical signs. Experimental inoculation produced nothing beyond occasional mild coughing, with lung lesion scores no different from controls, and the pigs seroconverted by three weeks. The reference chapter's conclusion is that its role as a pathogen of swine is uncertain for lack of evidence of disease after experimental infection. It is assumed to spread by aerosol. There is no vaccine and no specific control measures have been developed. It has never been reported in people, but because it is genetically similar to human parainfluenza virus 1, the possibility of human infection is treated as an open question rather than a closed one.
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 33.5.3, the entire Public Health section: "THERE ARE NO REPORTS OF PPIV1 INFECTION IN HUMANS. HOWEVER, PPIV1 IS GENETICALLY SIMILAR TO HUMAN PARAINFLUENZA VIRUS 1 AND THE POSSIBILITY OF HUMAN INFECTION SHOULD BE A CONSIDERATION UNTIL HUMAN SUSCEPTIBILITY OR RESISTANCE TO PPIV1 IS CLEARLY ESTABLISHED." 33.5.1: PPIV1 was identified in Hong Kong in 2013 "with sequences most closely related to HUMAN PARAINFLUENZA VIRUS 1 and Sendai virus", and has since been found in the United States, Chile, Hungary, Germany, the Netherlands, South Korea, Poland and China. 33.5.4 gives the US exposure: PPIV1 was positive in 542 of 1589 diagnostic submissions (34.1%) from 27 states in 2016, so a very large number of US pigs and the people who work with them have met this virus. shic_ppiv1: "There is no evidence that PPIV1 can infect humans." "To date, PPIV1 has been found only in domestic pigs."
How this level was decided
MOVED L2 -> L1, re-read 2026-09-04 AGAINST THE REWORDED LABELS. ch33 33.5.3: "THERE ARE NO REPORTS OF PPIV1 INFECTION IN HUMANS." Never reported, so level 1 on the first clause. PPIV1 has been in a third of US diagnostic submissions since 2016 and on four continents with no human case anywhere.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: Level 2, and the chapter states the level 2 position in its own words: no report of human infection, and an open question that the authors decline to close. The label asks whether human infection from pigs is plausible but never or rarely reported, with no control point implemented against it, and all three clauses hold. THE PLAUSIBILITY IS GENETIC, NOT EPIDEMIOLOGICAL, and that is worth saying plainly because it is the whole basis: the virus sits next to human parainfluenza virus 1 in sequence, and nothing else. Against it, PPIV1 has been in a third of US diagnostic submissions since 2016 and in pigs on four continents, with no human case reported anywhere -- so if it were a ready human pathogen there has been ample opportunity to notice. Level 1 confirmed.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch33 33.5.3: "There are no reports of PPIV1 infection in humans." No human illness is described anywhere in section 33.5. shic_ppiv1: "There is no evidence that PPIV1 can infect humans."
How this level was decided
Level 1. C2 grades the severity of illness ACQUIRED FROM PIGS, and no human illness has been attributed to this virus at all. THE LABEL MUST NOT BE READ AS "THIS VIRUS IS HARMLESS TO PEOPLE" -- its nearest human relative causes croup in children and is a common cause of childhood respiratory illness. What level 1 records is that pigs have not been shown to be a source of any human illness, which is the question C2 asks after the 2026-09-01 rescoping. This is the same pairing already used for influenza_d_virus, mycoplasma_hyorhinis and sads_cov: C1 level 2 for a plausible route, C2 level 1 because no illness exists to grade. 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. ch33 33.5.4: "Gauger et al. (2016) reported that PPIV1 PCR TESTING OF 1589 DIAGNOSTIC SUBMISSION SAMPLES COLLECTED IN 2016 FROM 27 US STATES PRODUCED 542 (34.1%) POSITIVE SAMPLES. PPIV1 WAS DETECTED MOST OFTEN IN NURSERY PIGS, followed by grow-finish pigs, and was uncommon in suckling and adult pigs." "Cumulatively, THE DATA SUGGEST THAT PPIV1 IS WIDESPREAD", with reports from Chile, Hungary, Germany, the Netherlands, South Korea, Poland and China "indicating a wide geographic distribution". On transmission: "PPIV1 IS ASSUMED TO BE TRANSMITTED MAINLY VIA AEROSOLS. Under experimental conditions, NAIVE PIGS PLACED 0.9 M (3 FT) FROM PPIV1-INOCULATED PIGS BECAME INFECTED." 33.5.5: in an unselected group of eleven weaned pigs taken off a naturally infected farm, six were already positive at day 0 and three more seroconverted within a fortnight. shic_ppiv1: "The virus has been identified in China and parts of the U.S. including Iowa, Illinois, Minnesota, North Carolina, Texas, Oklahoma, and Nebraska." "Limited studies suggest that PPIV1 is widespread is some swine herds in the U.S. Serological testing of swine from eight states identified anti-PPIV1 antibodies in approximately 53% and 66% of samples."
How this level was decided
Level 1. A third of US diagnostic submissions across 27 states are positive, the virus is in every pig-producing region that has looked for it, and it moves through a nursery on aerosol at a metre. That is present in most herds, so there is no introduction event to prevent. NOTE THE AGE PATTERN, which is the signature of an agent that is simply part of the nursery rather than something that arrives: uncommon in sucklings, commonest in nursery pigs, falling away in adults, which is a virus circulating in each new cohort as maternal protection fades. Nothing in the chapter proposes excluding it, and 33.5.7 says outright that no prevention or control measures have been developed. Level 1 confirmed with specific US figures -- seven named states and 53-66% seropositivity across eight.
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. ch33 33.5.6: "PPIV1 INFECTION MUST BE DIFFERENTIATED FROM AGENTS THAT PRODUCE RESPIRATORY SIGNS, SUCH AS INFLUENZA VIRUS, PRRSV, PCV2, AND OTHERS. A PPIV1-SPECIFIC REAL-TIME RT-PCR HAS BEEN DEVELOPED and nucleotide sequencing and comparative analyses can be used for further characterization. PPIV1 can be isolated on LLC-MK2 cells. Appropriate specimens for PPIV1 PCR and virus isolation include lung, nasal swab, and oral fluid samples. EXPERIMENTAL ISH, IHC, AND SEROLOGICAL ASSAYS HAVE BEEN DEVELOPED FOR PPIV1, HOWEVER, THE DIAGNOSTIC PERFORMANCE OF THESE ASSAYS IS NOT WELL-ESTABLISHED." The PCR is plainly in routine service: 33.5.4 reports it run on 1589 diagnostic submissions from 27 states in a single year. shic_ppiv1: "PPIV1 has not been cultured in cells. In situ hybridization can be used to visualize antigen in respiratory tissues." "Reverse transcriptase polymerase chain reaction (RT-PCR) and quantitative RT-PCR (qRT-PCR) assays have been developed experimentally to identify PPIV1." "Anti-PPIV1 antibody can be detected using an immunoprecipitation coupled to PCR detection assay (ICPD) and an indirect ELISA using a recombinant fusion (F) protein peptide."
How this level was decided
Level 2, and the deciding fact is that the assay is already doing diagnostic work at scale. Under C4 as reworded on 2026-08-29 the axis is whether a validated assay exists and where it can be run, and a real-time RT-PCR that a US veterinary diagnostic laboratory ran on 1589 field submissions in one year is validated in the only sense that matters -- it is producing answers people act on. That rules out levels 3 and 4. It is not level 1 because nothing about the presentation points here: mild cough, sneezing and serous nasal discharge sit behind influenza A, PRRSV and PCV2, and PPIV1 is frequently found alongside them. NOTE THE LIMIT THE CHAPTER RECORDS, which applies to the ancillary assays rather than the PCR: the diagnostic performance of the ISH, IHC and serological tests is not well established. LEVEL 2 HELD, AND FLAGGED IN THE OTHER DIRECTION from the rest of this batch -- the new evidence suggests this cell may be too LOW rather than too high. The virus has never been cultured, and the factsheet says the RT-PCR assays were developed EXPERIMENTALLY, which is the exact phrase the 2026-08-29 rework treats as short of a validated assay. Level 2 says a local laboratory can confirm it once suspected, and nothing here supports that. A 3, and arguably a 4. Held because moving a signed-off level is Eric's call, and because the serosurveys covering eight states imply somebody is running these assays at scale.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
Basis. ch33 33.5.1: "Field and experimental studies have demonstrated PPIV1 replication and shedding in pigs, but CLINICAL SIGNS AND PATHOLOGICAL CHANGES PRODUCED BY PPIV1 INFECTION APPEAR TO BE MINIMAL. Thus, THE ROLE OF PPIV1 AS A PATHOGEN OF SWINE IS UNCERTAIN due to the lack of evidence of disease after experimental inoculations." 33.5.5 gives four separate attempts to find disease and their results. Eleven naturally infected weaned pigs followed for a fortnight: "VIRUS WAS DETECTED IN NASAL SECRETIONS FOR 2-10 DAYS BY PCR, BUT NO CLINICAL SIGNS WERE OBSERVED." Thirty conventional pigs and ten caesarian-derived colostrum-deprived pigs inoculated intranasally and intratracheally: all shed virus, and "NO CLINICAL SIGNS WERE OBSERVED IN EITHER CONVENTIONAL OR CDCD PIGS, WITH THE EXCEPTION OF SPORADIC MILD COUGHING AFTER 9 DPI". A coinfection study: "FURTHER STUDIES INVOLVING COINFECTION WITH PPIV1 AND INFLUENZA A VIRUS FAILED TO DEMONSTRATE ANY SIGNIFICANT DISEASE." And on lesions: "MACROSCOPIC LUNG LESIONS WERE MINIMAL in PPIV1-inoculated pigs and HISTOPATHOLOGY LUNG LESION SCORES WERE NOT SIGNIFICANTLY DIFFERENT BETWEEN THE PPIV1-INOCULATED PIGS AND CONTROL PIGS." Where the virus was first found alongside cough and nasal discharge, "the contribution of PPIV1 to the observed clinical signs is uncertain because other viruses... were detected concomitantly". shic_ppiv1: "Pigs infected with PPIV1 may suffer from mild to moderate respiratory disease or may be asymptomatic. Clinical disease is seen most often in pigs less than 21 days-of-age." "PPIV1 causes no pathognomonic lesions, and the frequent presence of viral co-infections makes the interpretation of any observed changes difficult."
How this level was decided
Level 1, and this is one of the best-supported level 1 cells in the register because it is an EXAMINED NEGATIVE several times over, not a silence. Investigators inoculated conventional pigs, inoculated colostrum-deprived pigs, followed naturally infected pigs, and coinfected pigs with influenza A -- and measured lung lesion scores against controls. The virus replicated and shed every time and produced nothing. The distinction that matters here is the one drawn on porcine tottorivirus: an absence of evidence would leave this cell unassessed, but people looked hard and found no effect, which is evidence. No measurable effect on cost of production. Level 1 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, unlike to have a market impact given we already know the virus is circulating widely in the US"
Basis. A respiratory virus found in a third of US diagnostic submissions across 27 states, and on four continents, with no clinical disease attributable to it. No trade measure, movement control or consumer response is recorded anywhere in section 33.5.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact, an agent already endemic in US pigs and diagnosed routinely without a market move on record is level 1. There is a precedent to reason from rather than a void: PPIV1 has been detected in US herds since 2016, has been reported in the veterinary literature and in diagnostic laboratory summaries, and nothing has followed. Unchanged.
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 PPIV1 is described anywhere in chapter 33. 33.5.7, the whole Prevention and Control section: "THE CLINICAL SIGNIFICANCE OF PPIV1 INFECTION IS NOT FULLY UNDERSTOOD AND NO SPECIFIC PREVENTION AND CONTROL MEASURES HAVE BEEN DEVELOPED FOR PPIV1." 33.5.5: experimental infection produced no clinical signs beyond sporadic mild coughing, lung lesion scores did not differ from controls, and pigs seroconverted by 21 days post inoculation. shic_ppiv1: "There is no treatment for PPIV1."
How this level was decided
Level 1 on the second clause -- animals recover acceptably without treatment, because on the evidence they do not become ill. Eric's rule of 2026-09-02 forbids the lazy route to this answer, that nobody treats viral disease, and it is not the route taken: C7 asks whether outcomes would meaningfully improve if a treatment existed, and repeated experiments have failed to produce an outcome to improve. His second limb, that shortening how long a pig sheds counts as a benefit in its own right, does not rescue a level 3 here either -- the virus is already in a third of US submissions, so shortening one pig's ten days of shedding changes nothing at herd level. This cell moves with C5 if PPIV1 is ever shown to cause disease. Level 1 held.
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. No vaccine for PPIV1 is mentioned anywhere in chapter 33. 33.5.7: "The clinical significance of PPIV1 infection is not fully understood and NO SPECIFIC PREVENTION AND CONTROL MEASURES HAVE BEEN DEVELOPED for PPIV1." shic_ppiv1: "There is currently no vaccines against PPIV1." "Cross-reaction between PPIV1, HPIV1, and SeV may occur."
How this level was decided
Level 1 on the "not needed" clause of the 2026-08-28 rewording. There is no vaccine, so the question is whether the disease would justify one on the agent's own clinical and economic weight, and an agent that four separate experiments could not make sick a pig does not. This is consistent with C5 at level 1 and C7 at level 1 on the same evidence. Level 3 is reserved for a genuine gap where the disease would warrant a product, and this is the opposite case: a widespread virus with no demonstrated disease. Level 1 held -- mild to moderate or asymptomatic disease, no imperative.
Levels and evidence are generated from data/assignments/porcine_parainfluenza_virus_1.yml; the overview is authored in data/overviews/porcine_parainfluenza_virus_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.