Porcine Astrovirus
LEVELS: Highly unlikely; No human illness; Already in the herd; No validated assay; Minor; Negligible; Little; Available, or not needed
| Register id | porcine_astrovirus |
| Type | virus |
| Scientific name | Mamastrovirus 3 |
| NCBI taxid | 1239567 |
| Evidence | 3 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Porcine astroviruses are small RNA viruses found in pig populations worldwide, including throughout the United States. Several genetically distinct lineages circulate at the same time, and infection is extremely common, especially in nursery and grow-finish pigs — they are a routine component of the normal gut virome of healthy animals. Most infections cause nothing, or mild self-limiting diarrhoea usually alongside other pathogens, so finding the virus in a scouring pig proves very little on its own. The exception is worth knowing: one lineage, the neurotropic PAstV-3, has been clearly linked to severe neurological disease in piglets, including inflammation of the brain and spinal cord and paralysis. Even so, astroviruses are not regarded as significant drivers of production loss across a population, and no formal control or eradication effort is directed at them.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. REVIEWED ON C1_C2_RECLASSIFICATION.md, 2026-09-04, after the C1/C2 rewording that separated exposure from consequence. Eric marked up every moved cell and reversed his own earlier setting on twenty of the twenty-one: "In almost every case, I agreed with new opinion and reversed my old setting." HIS MARKUP HERE WAS "l1". Reverses his 2026-09-03 level 2. The basis was that recombination "may have occurred in the past" -- evolutionary history, not a route operating now -- and no human case attributed to a pig appears in the folder.
Basis. ch25 25.3, the whole Public Health section in two sentences: "THE ZOONOTIC POTENTIAL OF AstVs IS UNCLEAR. THE POSSIBILITY OF ZOONOTIC TRANSMISSION IS SUSPECTED, BUT ADDITIONAL DATA IS NEEDED." 25.4 puts the suspicion in evolutionary rather than clinical terms: "Discoveries of novel AstVs, in combination with genetic and evolutionary studies, support the hypothesis that CROSS-SPECIES TRANSMISSION AND NATURAL RECOMBINATION AMONG AstVs OF HUMANS, PIGS, AND OTHER ANIMAL SPECIES, POSSIBLY THROUGH UNKNOWN INTERMEDIATE HOSTS, MAY HAVE OCCURRED IN THE PAST." Against that, 25.1: "AstVs FROM DIFFERENT ANIMAL SPECIES ARE ANTIGENICALLY DISTINCT", and 25.2 records that human and animal astroviruses fall in phylogenetically distinct clusters. No human case attributed to a pig appears anywhere. shic_2026_pastv: "Clinical illness due to PAstVs has not been documented in people." "Genetic evidence suggests that recombination between human and porcine strains occurs."
How this level was decided
MOVED L2 -> L1, re-read 2026-09-04 AGAINST THE REWORDED LABELS. ch25 25.3: "THE ZOONOTIC POTENTIAL OF AstVs IS UNCLEAR", the evidence is that recombination "MAY HAVE OCCURRED IN THE PAST", and astroviruses of different species are antigenically distinct. No human case attributed to a pig appears anywhere in the folder.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: INFERRED. Level 2 -- plausible but never reported, with no control point implemented, which is the label. The evidence is entirely phylogenetic: recombination between human and pig astroviruses MAY HAVE OCCURRED IN THE PAST, which is a statement about evolutionary history rather than about a route operating now. THE ARGUMENT FOR LEVEL 1 is your porcine rotavirus ruling from earlier this evening, made on the same shape of evidence: species specificity plus an absence of attributed cases. This is one step weaker than rotavirus, where porcine-like virus was actually found in children. If you took rotavirus C1 to level 2 and its C2 to level 1, this entry should probably sit at or below that. Level 1 confirmed. The recombination note is a hypothesis about future potential, which the general rule forbids scoring.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c2l1, no evidence of human infection to date"
Basis. No human illness attributed to a porcine astrovirus is described anywhere in ch25. On human astroviruses generally, 25.5: "In humans, AstVs were found to be THE THIRD TO FOURTH MOST COMMON CAUSE OF VIRAL DIARRHEA IN YOUNG CHILDREN worldwide" -- caused by the human lineages, which 25.1 says are antigenically distinct from the porcine ones. shic_2026_pastv: "Clinical illness due to PAstVs has not been documented in people."
How this level was decided
INFERRED. Level 1, and it FOLLOWS YOUR ROTAVIRUS RULING OF THIS EVENING RATHER THAN THE PASS'S FIRST INSTINCT: "even though it is a plausible zoonosis, rotaviruses are VERY SPECIES SPECIFIC so until some evidence comes to light, I ASSUME THEY ARE MORE LIKELY TO BE INCIDENTAL INFECTIONS RATHER THAN CAUSING DISEASE." The same two facts hold here and the chapter states the first of them -- astroviruses of different species are antigenically distinct, and no human illness has been attributed to a porcine one. NOTE THAT THIS IS THE SECOND ENTRY TONIGHT WHERE C1 SITS AT 2 AND C2 AT 1, which is the combination the C2 level 1 label does not describe and which you have approved rewriting at the end. 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. ch25 25.4: "PAstVs have been identified in pig feces in [six countries] and recently in 16 MORE COUNTRIES ON 5 CONTINENTS, indicating a worldwide distribution. THE PREVALENCE OF PAstVs CAN BE HIGH IN BOTH DIARRHEIC AND CLINICALLY HEALTHY SWINE. For example, PAstVs... WERE DETECTED IN 64% (326/509) OF US PORCINE FECAL SAMPLES... One or more PAstVs were identified in 31.6% of the suckling pigs sampled, 75.1% OF THE NURSERY PIGS, 72.3% of the grow-finish pigs." 25.7 states the consequence: "ELIMINATION OF AstVs FROM INFECTED FARMS WOULD BE DIFFICULT BECAUSE THEY ARE APPARENTLY WIDELY DISTRIBUTED IN SWINE POPULATIONS AND STABLE IN THE ENVIRONMENT." The second document agrees from a different angle: degroof_2025 found porcine astroviruses 3, 4 and 5 in CLINICALLY HEALTHY pigs on seven Dutch farms selected for having under 5% of pens with diarrhoea. shic_2026_pastv: "The global pooled prevalence of PAstV is approximately 28%... North America has the highest rate (63%)." "There are five distinct PAstV lineages (PAstV-1 to PAstV-5), each of which has been known to circulate in herds in the United States." "Persistent shedding can continue long after infection."
How this level was decided
Level 1. Sixty-four percent of US faecal samples and three quarters of nursery pigs, on five continents, in healthy animals as well as sick ones -- there is no introduction event to prevent, and the chapter says elimination would be difficult for exactly that reason. Level 1 confirmed as strongly as the criterion allows -- all five lineages circulate in US herds and North American prevalence is the highest in the world at 63%.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
No validated assay: No pathogen-specific test of known reliability exists anywhere, and identification depends on sequencing or on primers that have not been critically evaluated
Basis. ch25 25.6: "VIRUS ISOLATION FOR PAstVs HAS PROVEN DIFFICULT. PAstV1 has been isolated in porcine kidney cells with the addition of trypsin... THERE HAVE BEEN NO REPORTS OF SUCCESSFUL ISOLATION OF PAstV2-PAstV4. Virus neutralization and immunofluorescent antibody assays can be used to demonstrate PAstV1 seroconversion, BUT THE DIAGNOSTIC PERFORMANCE OF THESE METHODS HAS NOT BEEN ESTABLISHED." What exists instead is molecular: RT-PCR, a multiplex RT-PCR differentiating PAstV1 to PAstV5, a multiplex real-time assay for neurotropic viruses, and "NEXT-GENERATION SEQUENCING METHODS USING RANDOM PRIMERS-BASED AMPLIFICATION". 25.4 adds why cross-species work is hard: "NO COMMON MOLECULAR PROBES, ANTIBODIES, OR OLIGONUCLEOTIDE PRIMERS ARE AVAILABLE to identify AstV strains across different species." shic_2026_pastv: "PAstVs are difficult to propagate. Reverse transcription polymerase chain reaction (RT-PCR) assays are used to detect viral RNA. Newer multiplex tests detect all five PAstV lineages simultaneously." "Enzyme-linked immunosorbent assay (ELISA) and serum neutralization have been used to detect antibodies for AstV in pigs."
How this level was decided
Level 4, and it is the worked example at this level alongside porcine norovirus, porcine sapovirus and Bungowannah virus. The chapter states the level 4 test almost in the criterion's own words: the serological methods exist but THEIR DIAGNOSTIC PERFORMANCE HAS NOT BEEN ESTABLISHED, three of the five lineages have never been isolated at all, and identification rests on PCR primers and next-generation sequencing. Under the C4 rewording of 2026-08-29 the axis is whether a VALIDATED assay exists, and a published primer set is not one. Nothing in the clinical picture would prompt a test either -- the enteric form is a mild diarrhoea indistinguishable from several others. LEVEL 4 HELD, AND FLAGGED. The January 2026 update adds multiplex tests covering all five lineages simultaneously, which is a considerable advance on what the folder held and is hard to square with "no validated assay -- no reliable test exists anywhere". Held because the factsheet still says the virus is difficult to propagate and does not say the multiplex is validated or diagnostically offered, and because the deeper problem it describes is attribution rather than detection. A candidate for 3.
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, 10-15 years ago there was some intertest in this being a more consequential disease but substantial evidence never appeared to show the agent was emergin in a meaningful way"
Basis. ch25 25.5: PAstVs "have been associated with SEVERE DIARRHEA IN NATURAL INFECTIONS, BUT ONLY IN THE PRESENCE OF OTHER KNOWN ENTERIC PATHOGENS." Experimentally: "MILD DIARRHEA developed in 4-day-old pigs... continued for 5-6 days"; a Chinese isolate "caused MILD DIARRHEA, GROWTH RETARDATION, and damage of the villi... WITH RECOVERY IN 7-10 DAYS." Against that, the newer finding: "In 2017, NEUROINVASIVE PAstV3-ASSOCIATED NEUROLOGICAL DISEASE (MENINGOENCEPHALOMYELITIS, WEAKNESS, AND FLACCID PARALYSIS) WAS REPORTED ON SWINE FARMS IN HUNGARY AND THE UNITED STATES... confirmed by in vivo inoculation study in swine... These results suggested that PAstV infections have a MORE COMPLEX PATHOGENESIS AND MORE SERIOUS DISEASE OUTCOME, E.G. FATALITY, THAN PREVIOUSLY THOUGHT." 25.7 gives the chapter's economic verdict: "EFFORTS TO ELIMINATE AstVs WOULD ALSO BE DIFFICULT TO JUSTIFY ON THE BASIS OF THEIR CLINICAL EFFECTS." shic_2026_pastv: "The role of porcine astrovirus (PAstV) as a primary pathogen remains unclear... it is also found in healthy animals, and co-infections are common." "PAstVs have been isolated at higher rates in asymptomatic pigs compared to diarrheic pigs."
How this level was decided
INFERRED. Level 2 -- small and generally short-lived losses. The chapter supplies its own judgment in 25.7, and the enteric disease is a mild diarrhoea that resolves in seven to ten days with weight recovered, in a population where two thirds of pigs carry the virus without being ill. THE NEUROLOGICAL FORM IS THE REASON THIS IS NOT LEVEL 1: PAstV3 meningoencephalomyelitis with flaccid paralysis was reported on US farms in 2017 and reproduced experimentally, so it is a real disease and not a coincidence. UNDER YOUR MENANGLE RULE IT DOES NOT MAKE THE LEVEL EITHER -- a level is a claim about the general case, and the general case for an agent found in 64% of US faecal samples is subclinical carriage. Level 2 confirmed, and the detail is telling: PAstV is found MORE often in asymptomatic pigs than in diarrhoeic ones, which is the opposite of what a primary pathogen looks like.
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, no evidence of impact during its early appearance so no reason to think it will have an impact now"
Basis. Porcine astroviruses are present in 64% of US porcine faecal samples (ch25 25.4) and have been for as long as anyone has looked, and no trade measure, movement restriction or consumer response is recorded anywhere in the folder.
How this level was decided
INFERRED. Level 1 under the standing note SCORING/market_impact: an agent already ubiquitous and repeatedly reported in US pigs with no market move ever observed. Unchanged. Endemic in US herds at 63% with no market event.
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 or market imperative to develop a treatment"
Basis. ch25 25.7: "Assuming that lesions caused by infection with AstVs are confined to the intestinal tract, ORAL REHYDRATION WOULD BE EXPECTED TO BE EFFECTIVE IN AFFECTED PIGS. THERE ARE NO COMMERCIALLY AVAILABLE ANTIVIRAL DRUGS OR VACCINES." On outcome without pathogen-directed treatment, 25.5: mild diarrhoea "with RECOVERY IN 7-10 DAYS post inoculation". shic_2026_pastv: "There is no treatment for PAstV infection."
How this level was decided
INFERRED. Level 1, on the same structure as porcine rotaviruses, which is the worked example at this level: the treatable part of the enteric disease is the dehydration, oral rehydration is expected to handle it, and the pigs recover in a week or so anyway. NOT SCORED LEVEL 1 BECAUSE NO ANTIVIRAL EXISTS, which your 2026-09-02 rule forbids. THE NEUROLOGICAL FORM IS THE HONEST QUALIFICATION and the reason this is inferred rather than supported: a piglet with flaccid paralysis is not helped by rehydration, and nothing in the folder says what would help it. That form is rare enough not to set the level. 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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l1, no clinical or market imperative to develop a vaccine"
Basis. ch25 25.7: "THERE ARE NO COMMERCIALLY AVAILABLE ANTIVIRAL DRUGS OR VACCINES", and, in the same paragraph, "EFFORTS TO ELIMINATE AstVs WOULD ALSO BE DIFFICULT TO JUSTIFY ON THE BASIS OF THEIR CLINICAL EFFECTS." shic_2026_pastv: "There are no commercially available PAstV vaccines."
How this level was decided
INFERRED. Level 1 on the "not needed" clause, by the FIRST route in the standing note SCORING/vaccine_availability -- low clinical significance -- and THE CHAPTER MAKES THE CLAIM RATHER THAN THE PASS, which is what your PCV4 rule requires. Its own words are that control efforts are difficult to justify on the clinical effects. That is not an absence of information about the disease: two thirds of US pigs carry these viruses, the enteric form is a mild self-limiting diarrhoea, and the case for a vaccine has been considered and found wanting. Level 1 held -- primary-pathogen status unclear, so no clinical imperative.
Levels and evidence are generated from data/assignments/porcine_astrovirus.yml; the overview is authored in data/overviews/porcine_astrovirus.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.