Sendai Virus
LEVELS: Highly unlikely; No human illness; Routine biosecurity keeps it out; Reference or research laboratory required; Minor; Negligible; Little; Available, or not needed
| Register id | sendai_virus |
| Type | virus |
| Scientific name | Murine respirovirus |
| NCBI taxid | 3052731 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Sendai virus is a respiratory virus of laboratory mice and rats that once, seventy years ago, swept through the pigs of Japan and then vanished. It belongs to the same group as the human parainfluenza viruses and goes by several names — murine parainfluenza virus type 1, or haemagglutinating virus of Japan. The swine episode is worth knowing because it is the only one: outbreaks began in Japan in 1953, serum testing at a Tokyo slaughterhouse in 1955 found 44% of pigs positive across 15 districts, and pigs under a month old died while two-to-four-month-olds developed brain inflammation and sows produced stillborn litters. Then it simply faded — seropositivity fell to 2% by 1958, testing was completely negative from 1961, and by 1970 the Japanese pig industry considered it irrelevant. Nothing has confirmed it in a pig anywhere since, and the one American suspicion turned out on testing to be a different agent, bovine parainfluenza virus 3. It does not infect people: the belief in the 1950s that it did has since been reassigned to human parainfluenza virus 1, and the antibodies found in people are cross-reaction from that human virus rather than evidence of infection from animals. It is worth keeping distinct from porcine parainfluenza virus 1, which is a genuinely separate virus with its own SHIC factsheet — the older literature runs the two together, and modern taxonomy separates them as Respirovirus muris and Respirovirus suis. There is no vaccine for any species and none is needed; where the virus does persist, in rodent colonies, the answer is to depopulate. For a US herd the practical questions are rodent control and normal quarantine of incoming pigs.
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. shic_sendai: "SeV does not affect humans." "In the 1950s, SeV was believed to affect humans, but now those reports have been attributed to human parainfluenza virus type 1 (hPIV1). SeV is not thought to cause disease in humans; however, neutralizing antibodies for SeV can be found in people due to prior infection with hPIV1."
How this level was decided
Level 1. The agent does not infect people at all, so no route from pigs can exist. Worth noting how the factsheet gets there, because it is the same artefact Eric identified on chikungunya and Getah: human seropositivity for SeV is real but is CROSS-REACTIVITY from prior human parainfluenza virus 1 infection, and the 1950s belief that SeV infected people has since been reassigned to hPIV1. Antibody without infection is not evidence of transmission.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. shic_sendai: "SeV does not affect humans." "SeV is not thought to cause disease in humans." The 1950s human reports "have been attributed to human parainfluenza virus type 1 (hPIV1)."
How this level was decided
Level 1, no human illness. Under the C1/C2 separation of 2026-09-04, C2 asks whether the AGENT causes illness in people irrespective of source, and this one does not -- the historical claim that it did was a misattribution to a different virus. This is the level 1 that the reworded label was written for: not "pigs are not a source" but "the agent does not make people ill".
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
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Basis. shic_sendai: "SeV can naturally infect laboratory mice, rats, and hamsters." "Transmission in mice is via direct contact or aerosols." "Both vertical and lateral transmission were seen in the 1950s outbreak in swine in Japan." "SeV is labile and does not survive well outside of a host." "SeV can be transmitted rapidly throughout a rodent colony. Affected colonies are usually culled to eliminate the virus."
How this level was decided
Level 3. Two routes to a herd, and both are on the routine biosecurity list. The reservoir is rodents, and rodent control is routine; the pig-to-pig route demonstrated in Japan was vertical and lateral, which is quarantine of incoming stock and the usual transport and fomite control. Not level 2, because the route is rodents and other pigs rather than the ground the pig stands on, and housing alone does not exclude a mouse. Not level 4: the virus is labile outside a host and susceptible to ordinary disinfectants, so there is nothing here requiring filtration, treated feed or carrier testing.
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. shic_sendai: "Primers and probes have been described for quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR), and numerous commercial SeV PCR kits are available for use in rodents." "There are numerous commercial enzyme linked immunosorbent assay (ELISA) kits for various laboratory rodent species, but none available for swine." "Because SeV is an established pathogen of rodents, available diagnostic tests may be adaptable for use in swine." "Virus isolation is possible with identification via trypsin overlays, immunofluorescence, or hemadsorption." "Histopathology is not very sensitive or specific for diagnosis."
How this level was decided
LEVEL 3, AND FLAGGED, because this is exactly the boundary the 2026-08-29 C4 rework moved. Validated assays plainly exist and are commercial rather than merely published -- numerous SeV PCR and ELISA kits are sold -- but they are validated in RODENTS, and the factsheet says none is available for swine and that existing tests "may be adaptable", which is not a statement that they have been adapted. I have scored 3 rather than 4 because a validated assay does exist and a reference or research laboratory can run it, and because a viral PCR target does not change with the host species the sample came from. THE ARGUMENT FOR 4: the rework moved three entries L3 -> L4 precisely because the pass was reading an unvalidated-in-swine assay as a validated one, and "may be adaptable" is that phrase. Eric decides.
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
Basis. shic_sendai: "High mortality rates have been observed in one-month-old pigs infected with SeV experimentally." "Fatality rates are highest in pigs less than one-month-old, with two-month-old pigs being much less susceptible to disease. One-month-old pigs can also exhibit stunted growth." "Infected females can produce stillborn pigs." "In the 1950s outbreak in Japan, encephalitis was observed in 2 to 4 month-old pigs." But: seroprevalence fell from "44% SeV prevalence" in 1955 to "only 2%" by 1957-58, "From 1961-1966, serological testing was completely negative in Japan, and SeV was thought to be irrelevant by the Japanese swine industry by 1970."
How this level was decided
Level 2, small and generally short-lived losses -- and the word to lean on is short-lived, which the standing note makes the level 2 / level 3 test. The only swine epizootic on record is a natural experiment in exactly what this criterion asks: SeV disseminated nationwide through Japanese pigs, reached 44% seroprevalence, produced neonatal mortality, stillbirths and encephalitis -- and then extinguished itself, to 2% in three years and to nothing by 1961, with no intervention described. That is a real but self-limiting insult, not a persistent cost of production. The general rule requires scoring what would happen if the agent were here rather than treating its absence as the answer, which is why this is not level 1.
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
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Basis. shic_sendai: the Japanese epizootic reached "44% SeV prevalence in the country, with 15 different districts having high incidence, indicating nationwide dissemination", and the factsheet records no trade, market or regulatory consequence of any kind across the whole 1953-1970 episode. "SeV does not affect humans." "In the United States, SeV has been suspected in pigs; however, diagnostic testing identified bovine parainfluenza virus type 3 instead."
How this level was decided
Level 1. The standing note requires a precedent before this cell is scored at all, and unusually for an exotic agent there is a good one: a nationwide swine epizootic in a major pork-producing country, documented over seventeen years, with no market event recorded. That is the Zika shape Eric confirmed at level 1 -- something has actually been observed -- rather than the dengue shape he nulled, where nothing has. A non-zoonotic, non-reportable respiratory virus that burned out on its own is not a market mover. Inferred because the factsheet documents the epidemiology and is silent on markets, so the absence of a reported reaction is the evidence rather than a positive statement.
C7 Treatment potential
Potential for treatment to improve outcomes
Little: Effective pathogen-directed treatment is available and works, or animals recover acceptably without it
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Basis. shic_sendai: no treatment is described anywhere in the factsheet. Control in the reservoir is depopulation -- "Affected colonies are usually culled to eliminate the virus." The swine episode resolved without intervention: "there were no reported positive cases after 1961 and SeV was not considered a problem in Japan by 1970."
How this level was decided
LEVEL 1, AND I WANT ERIC ON THIS ONE, because two clauses of the standing note point opposite ways. FOR LEVEL 3: the note says where an agent is lethal in neonates and trivial in adults, score the neonate -- and SeV is exactly that shape, highest fatality under one month and much less susceptible by two months, which is the TGEV/PEDV/pHEV pattern he ruled to level 3. FOR LEVEL 1, which I have taken: the note also puts level 1 where the disease is "excludable, absent or subclinical so nothing needs treating", the Trichinella clause, and SeV in pigs is absent -- not merely untreated but not confirmed anywhere in the world since 1961, with the one US suspicion turning out to be bovine parainfluenza 3. The neonate rule was written for diseases that are clinically significant now. I do not think a treatment for a swine disease that has not occurred in sixty-five years is a research gap, but that is a judgment about what the criterion is for.
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. shic_sendai: "There are no commercial SeV vaccines available for any species, including swine." "Cross-protection is observed between SeV and human parainfluenza virus type 1." "Xenotropic parainfluenza vaccines, using live viruses, have been shown to experimentally protect aberrant hosts from infection. Inoculation with human parainfluenza virus type 1 can protect mice from SeV challenge." Seroprevalence in Japanese pigs went from 44% to negative within a decade with no vaccine.
How this level was decided
Level 1, on the first route in the standing note -- low prevalence and low clinical significance, so there is no clinical or market imperative to develop a vaccine. SeV has not been confirmed in a pig anywhere since 1961 and the Japanese industry considered it irrelevant by 1970. THIS IS NOT THE UNSAFE USE OF LEVEL 1 the note warns against: the disease IS characterised -- flu-like signs, neonatal mortality, stillbirths, encephalitis in 2-4 month olds -- so saying a vaccine is not warranted is a supported claim about a known disease with no prevalence, not an inference from silence about an agent nobody has studied. Contrast parechovirus_a, where the disease itself is unknown and C8 is null.
Levels and evidence are generated from data/assignments/sendai_virus.yml; the overview is authored in data/overviews/sendai_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.