Menangle Virus
LEVELS: Sometimes occurs; Moderate; Routine biosecurity keeps it out; Reference or research laboratory required; Moderate; Temporary disruption; Little; Available, or not needed
| Register id | menangle_virus |
| Type | virus |
| Scientific name | Menangle virus |
| NCBI taxid | 152219 |
| Evidence | 3 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Menangle virus has caused exactly one recorded outbreak in pigs, on a 3,000-sow farrow-to-finish farm near Sydney in 1997, and it was eradicated from the affected farms afterwards. It has never been reported in pigs anywhere else. The outbreak was a reproductive disaster: over five months the farrowing rate fell from 82% to as low as 38%, sows returned to service late or stayed falsely pregnant beyond 60 days, and up to 45% of litters contained mummified and stillborn piglets, many with skeletal and brain malformations. The pigs themselves showed nothing — infection lasts ten to fourteen days and produces no clinical signs; the damage is done by the virus replicating in rapidly developing fetal tissue. Fruit bats are the source, which is the key fact for the United States: the megabats that carry it do not occur in North America, and the recommended precautions — covering outdoor walkways, not planting fruiting trees near pig buildings — apply only where they do. Elimination is achievable without a vaccine, by moving the actively infected age group off site and restocking cleaned buildings. Two of more than thirty exposed farm workers were infected and both had a severe febrile illness with rash and a prolonged convalescence, but both recovered fully and no one else, including veterinarians and abattoir workers, was affected.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Sometimes occurs: Known risk of transmission to humans (foodborne or occupational), but requires failure of one or more control points for 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. "c1l3, appropriate based on our criteria description. Not particularly transmissible between people but seems to be a known occupational exposure in the limited cases of the disease in AU" THIS SETTLES A DISAGREEMENT WITH THE CRITERIA FILE, which names Menangle virus as a worked example at C1 LEVEL 4 beside influenza A virus and Japanese encephalitis virus. His ruling confirms level 3, so the example moves to level 3 -- the third example relocated on his ruling after Cystoisospora suis and Mycoplasma hyopneumoniae.
Basis. ch33 33.3.3, a Public Health section of its own: "In contrast to Nipah virus, MENANGLE VIRUS DOES NOT APPEAR TO BE HIGHLY INFECTIOUS FOR HUMANS. However, care should be taken when working with potentially infected pigs or suspect reproductive specimens. WHILE ONLY 2 OUT OF MORE THAN 30 HUMANS DIRECTLY EXPOSED TO INFECTED PIGS WERE INFECTED with the virus, both experienced a severe febrile illness associated with a macular rash, followed by prolonged debility. There was NO EVIDENCE OF INFECTION IN A LARGE NUMBER OF OTHER PEOPLE, including veterinarians, abattoir workers, and laboratory workers, who had LESS DIRECT AND LESS PROTRACTED CONTACT with potentially infective material. TRANSMISSION TO HUMANS MAY REQUIRE THE CONTAMINATION OF CUTS AND ABRASIONS WITH INFECTIOUS BODY FLUIDS OR TISSUES OR POSSIBLY SPLASHING OF MATERIAL ONTO THE CONJUNCTIVAE." cfsph_2017 adds that human infections "have not been reported except during the" 1997 outbreak. shic_2021_menangle: "Following the 1997 swine outbreak in New South Wales, Australia, two people working at the affected farm developed flu-like symptoms and a non-pruritic rash. Both fully recovered. Thirteen percent of exposed people developed neutralizing antibodies to Menangle virus." "Menangle virus is also a concern for people working in close contact with pigs, since zoonotic transmission occurs."
How this level was decided
Level 3, and the chapter identifies the control point that has to fail. The label asks for a known occupational or foodborne risk that requires the failure of one or more control points, and Menangle is that in the most literal sense available: two piggery workers were infected out of more than thirty directly exposed, and the proposed route is infectious material entering a cut or splashing into an eye. Gloves, eye protection and intact skin are the control points, and they are ordinary ones. IT IS NOT LEVEL 4, and the contrast with Nipah on the facing page is the reason: there, ordinary handling infected people and respiratory protection was required; here, everyone with less direct contact -- vets, abattoir workers, laboratory staff -- stayed negative. IT IS NOT LEVEL 2 either, because this is not a plausible-but-unreported risk: two people were infected and both were ill. FLAGGED: THIS SCORE DISAGREES WITH THE CRITERIA FILE, and validate_criteria.py reports it. criteria_levels.yml names Menangle virus as a worked example at C1 LEVEL 4, beside influenza A virus and Japanese encephalitis virus. THE COMPANY IS THE PROBLEM: influenza A moves from pigs to people readily and repeatedly, and JEV is delivered by a mosquito that no farm practice stops -- both are the level 4 label, transmission occurring even when control points are intact. Menangle infected two of more than thirty directly exposed people and spared every veterinarian, abattoir worker and laboratory worker with less protracted contact, and the chapter says transmission "MAY REQUIRE the contamination of cuts and abrasions... or possibly splashing of material onto the conjunctivae". That is a control point failing, which is level 3. THE CASE FOR THE FRAMEWORK'S LEVEL 4 is that both infected men were doing ordinary work and both became seriously ill, and that two out of thirty is a high attack rate for an agent nobody was protecting against. Eric to settle; if he agrees with level 3 the example moves, as Cystoisospora suis and Mycoplasma hyopneumoniae have already done. Level 3 confirmed and well supported: documented occupational transmission from pigs to two farm workers, with 13% of exposed people seroconverting. Transmission after contact with infected pigs, which is the level 3 shape.
C2 Zoonotic impact
Severity of human illness caused by the agent
Moderate: Clinically important illness is common and may require medical treatment or hospitalization, but death or permanent disability is uncommon
Basis. ch33 33.3.3: the two infected workers "both experienced A SEVERE FEBRILE ILLNESS ASSOCIATED WITH A MACULAR RASH, FOLLOWED BY PROLONGED DEBILITY". 33.3.6: "During subsequent medical investigations, it was found that both had experienced a severe febrile illness with headache. Extensive testing failed to identify any other possible cause of the illness... BOTH WORKERS RECOVERED FULLY AFTER A PROLONGED PERIOD OF CONVALESCENCE." cfsph_2017: "Both recovered after 10 to 14 days" and "both patients recovered spontaneously, without specific" treatment. shic_2021_menangle: "two people ... developed flu-like symptoms and a non-pruritic rash. Both fully recovered."
How this level was decided
Level 3. The label asks for clinically important illness that is common among those infected and may require medical treatment or hospitalisation, without death or permanent disability being common, and that is what two out of two cases show: severe febrile illness with rash and headache, ten to fourteen days of it, prolonged convalescence, and full recovery without specific treatment. It is not level 2, because "usually mild and self-limiting" does not describe an illness the chapter twice calls severe and follows with prolonged debility. It is not level 4, because neither patient died or was left disabled, and there are no other cases to widen the picture. Level 3 held, with the counter-argument recorded: the only two human cases on record were flu-like with a rash and both fully recovered, which reads as level 2 mild and self-limiting. Held because two cases is too small a series to grade the agent's severity, and because the henipavirus-adjacent paramyxoviruses warrant the upward hedge Eric applied to porcine reovirus.
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
Standing note. Pteropid fruit bat reservoir, absent from the US. See the Hendra note. Not yet assessed.
Basis. ch33 33.3.9: "FRUIT BATS (MEGACHIROPTERA) ARE THE PRIMARY SOURCE OF INFECTION FOR PIG POPULATIONS. MEGACHIROPTERA ARE NOT FOUND IN NORTH AMERICA, but are present in Africa, the Middle East, Southern Asia, Australia, and many Pacific Islands." The advice that follows is for countries where they do occur: cover outside walkways, and do not grow flowering or fruiting trees near pig buildings. 33.3.4 on how it moved once in pigs: the virus reached two grow-out farms "separated from the main farm and each other by several hundred kilometers... WHEN YOUNG GROWING PIGS WERE MOVED", and "it appeared that CLOSE CONTACT BETWEEN PIGS WAS REQUIRED for spread of infection and that THE VIRUS DID NOT SURVIVE IN THE ENVIRONMENT FOR LONG. Susceptible sentinel pigs moved into an uncleaned area occupied 3 days previously by infected pigs did not become infected." Testing of 1114 sera from other Australian farms showed infection was confined to the affected farm and its two grow-outs. shic_2021_menangle: "Bats must be excluded from swine barns to prevent contamination with feces, urine, or tissues. Swine barns should not be located near potential bat roosting areas and feeding areas, and flowering or fruit-bearing trees should not be grown near swine buildings." "Pigs are infected with Menangle virus through ingestion of bat feces, urine, or tissues."
How this level was decided
Level 3, and the bat rule decides it exactly as it did for hendra_virus and nipah_virus, which sit at the same level. The chapter states the geography itself: Megachiroptera are not found in North America. AN AGENT ARRIVING HERE BRINGS ITSELF, NOT ITS ECOSYSTEM -- the flying foxes cannot follow, so the route that seeded the New South Wales piggery does not exist for a US herd. What is left is the route that actually moved the virus between farms in the outbreak, which was moving young pigs, and quarantine of incoming stock is the level 3 measure against it. THE VIRUS ALSO MAKES ITSELF EASY TO EXCLUDE: it does not survive in the environment, and sentinel pigs put into a pen infected animals had left three days earlier did not pick it up. Level 3 confirmed, on the same reasoning as Nipah and Hendra: the route is bat excreta reaching what the pig eats and stands on, and the controls are siting and husbandry measures -- barn placement, tree planting, bat exclusion.
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 33.3.8: "MENANGLE VIRUS HAS ONLY BEEN DETECTED IN THE 1997 OUTBREAK." The presentation is reproductive: "A marked reduction in normal live piglets at farrowing and a number of stillborn piglets with teratogenic defects is suggestive." The differential is long -- porcine parvovirus first, then EMCV, the pestiviruses including classical swine fever and Bungowannah, pseudorabies, Japanese encephalitis, PRRSV and LPMV -- and "A FEATURE THAT DISTINGUISHES MENANGLE VIRUS INFECTION FROM ALL BUT JAPANESE ENCEPHALITIS VIRUS INFECTION IS THE PRESENCE OF CONGENITAL MALFORMATIONS IN PIGLETS. However, it should be noted that THESE ARE ONLY EVIDENT IN APPROXIMATELY ONE-THIRD OF AFFECTED LITTERS." On the assays: virus isolation in BHK-21 cells where "three to five passages may be necessary before suggestive cytopathic effects are observed"; "as the virus does not hemagglutinate, identification will depend on electron microscopy, neutralization of an isolate with specific antiserum, or testing by A MENANGLE VIRUS-SPECIFIC qRT-PCR ASSAY", which is also used for direct detection in tissues and swabs. shic_2021_menangle: "Electron microscopy or virus neutralization (using specific anti-serum) are required to identify viral isolates, since Menangle virus is non-hemagglutinating and non-hemadsorbing." "A quantitative real-time polymerase chain reaction (qRT-PCR) assay detecting the nucleocapsid gene has been described." "Virus neutralization using serum or body cavity fluids from stillborns is most useful for routine testing."
How this level was decided
Level 3. A validated assay exists -- a virus-specific qRT-PCR, plus neutralisation and electron microscopy -- so this is not level 4. What holds it at level 3 is that those reagents live in one place: this virus has been seen once, in one country, in 1997, and the assay was published by the laboratory that investigated that outbreak. No US diagnostic laboratory holds Menangle antiserum or runs the PCR. The clinical route in is no better, since the one distinguishing feature, congenital malformation, appears in only a third of affected litters and otherwise the picture is parvovirus. Level 3 confirmed. The routine shortcuts do not work -- the virus neither haemagglutinates nor haemadsorbs -- so identification needs electron microscopy or virus neutralisation with specific antiserum, which is reference-laboratory work.
C5 Production cost
Financial impact on the infected farm's cost of production
Moderate: Losses measurably increase cost of production but remain manageable within normal farm operations, whether acute, chronic, or associated with endemic disease
Corrected by Eric from L4 Substantial. Reason: "c5l3, i will downgrade to l3 because we only know the clinical effect based on one outbreak. It clearly can cause severe disease, but the frequency and/or variation among affected farms is uncertain" THE DOWNGRADE IS ABOUT CONFIDENCE, NOT SEVERITY, and he says so: the disease "clearly can cause severe disease" and the farrowing rate did fall from 82% to 38%. What he will not do is score level 4 off a single farm. A level is a claim about the general case, and one outbreak cannot support the general case however bad that outbreak was.
Basis. ch33 33.3.6, the only outbreak on record: in a "3000-SOW, INTENSIVE FARROW-TO-FINISH PIG FARM near Sydney", over five months, "THERE WERE SOME WEEKS WHEN THE FARROWING RATE DECREASED FROM AN EXPECTED 82% TO AS LOW AS 38%. Many sows showed delayed returns to estrus at approximately 28 days after mating, while others remained in a state of PSEUDOPREGNANCY UNTIL MORE THAN 60 DAYS post mating. The disease occurred sequentially in all four breeding units at the pig farm, affecting the progeny of sows of all parities. In the weeks of low farrowing rates, UP TO 45% OF SOWS FARROWED LITTERS WITH REDUCED NUMBERS OF LIVE PIGLETS." Against that: "THERE WERE NO CLINICAL SIGNS EVIDENT IN GROWING PIGS OF ANY AGE and the only clinical signs in sows on the main farm were those associated with reproductive failure", and 33.3.5 records that infection is short, ten to fourteen days, and "results in strong immunity". shic_2021_menangle: "Menangle virus causes reproductive failure (stillbirth, mummification) and congenital defects of the musculoskeletal system and central nervous system in affected piglets. Delayed return to estrus and pseudopregnancy can also occur. Piglets born alive are unaffected, and no clinical signs are seen in grower pigs." "profound production losses"
How this level was decided
Level 4, and FLAGGED AS A LEVEL 3 OR 4 JUDGMENT because it turns on whether five months counts as manageable. Level 4 is scored on the size of the hole: a farrowing rate falling from 82% to 38% in a 3000-sow unit, across all four breeding units, with 45% of the sows that did farrow producing reduced litters, is most of a breeding herd's output for most of a year -- severe losses causing a major and potentially unsustainable increase in cost of production. THE ARGUMENT FOR LEVEL 3 is that it is self-limiting and self-solving: growing pigs showed nothing, the sows became immune, and the herd came back without intervention, which is closer to "manageable within normal farm operations" than a disease that keeps taking. Eric will know better than the chapter whether a sow farm survives that. Level 3 confirmed, on Eric's correction down from 4. The new source supports the correction rather than the original: the loss is entirely reproductive, and piglets born alive are unaffected with no signs in growers.
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, i think if this was diagnosed in the Us (unlikely of course) it would have a temporary affect on markets. It is zoonotic, unusual, and causes severe disease in both people and pigs. We know from other SE Asia examples, bat borne diseases attract public attention and i think we would anticipate regulatory action, even if in a single herd." NOTE WHAT HE IS SCORING, because it is not what the Australian precedent shows. The 1997 outbreak was contained on three farms with no recorded market consequence, which is why the pass scored level 1 on the standing note. He is scoring the US event instead, and the reason he gives is about attention rather than epidemiology: "bat borne diseases attract public attention and i think we would anticipate regulatory action, even if in a single herd." THE RULE THAT FOLLOWS: where an agent is zoonotic, unusual and bat-associated, a first US detection is a public event and the foreign precedent understates it.
Basis. ch33 33.3.1: Menangle virus "was first identified during THE ONLY KNOWN OUTBREAK IN PIGS in New South Wales, Australia in 1997 and was SUBSEQUENTLY ERADICATED FROM THE AFFECTED FARMS." 33.3.4: testing of 1114 sera from pig farms across Australia showed "infection was confined to the affected pig farm and the two associated grow-out facilities". No trade measure, movement restriction, export suspension or consumer response is recorded anywhere in section 33.3 or in cfsph_2017, and the virus has never been reported in pigs in any other country.
How this level was decided
INFERRED, and level 1 is scored on the precedent rather than on silence, which is what the standing note SCORING/market_impact asks for. Something was observed here: an outbreak occurred, two people fell ill, it was investigated publicly, the virus was eradicated from three farms, and no market consequence of any kind is recorded. That is the scoreable side of the line the note draws -- unlike Hendra or dengue, where nothing has ever happened in pigs anywhere and the cell is left null. FLAGGED AS A LEVEL 1 OR 2 JUDGMENT for one reason: this is a zoonosis, two piggery workers were hospitalised, and the Australian outbreak was contained on three farms rather than tested against a national market. A US incursion with human cases attached might not pass as quietly. Unchanged. Level 2 on Eric's correction.
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. ch33 33.3.9: "There is no specific treatment for Menangle virus. BY THE TIME CLINICAL SIGNS ARE OBSERVED, THE VIRUS IS LIKELY TO BE WIDELY DISSEMINATED IN THE AFFECTED POPULATION, NEGATING MEASURES TO LIMIT SPREAD." 33.3.5: "THE PRINCIPAL CAUSE OF REPRODUCTIVE LOSS ASSOCIATED WITH MENANGLE VIRUS APPEARS TO BE IN UTERO INFECTION, OFTEN RESULTING IN FETAL DEATH... The teratogenic defects observed are THE DIRECT RESULT OF VIRUS REPLICATION AND CELL DESTRUCTION IN RAPIDLY DEVELOPING FETAL TISSUES." Infection in the pig itself is short, ten to fourteen days, produces no clinical signs in growers, and gives strong immunity. shic_2021_menangle: "There is no specific treatment for Menangle virus infection." "Piglets born alive are unaffected, and no clinical signs are seen in grower pigs."
How this level was decided
Level 1, on the boundary Eric drew for the transplacental agents. His rule of 2026-09-02 says C7 scores the value of a treatment that does not exist rather than the industry's willingness to use one -- but it carries an explicit exception, that LEVEL 1 STILL HOLDS WHERE THE HARM IS TRANSPLACENTAL AND COMPLETE BEFORE BIRTH, because no treatment could act in any window. Getah virus, the pestiviruses and Japanese encephalitis virus are all scored level 1 for that reason. Menangle is the same case: the damage is done in the uterus to fetuses already dead or deformed by the time anything is visible, the sow herself is not ill, and the chapter says the virus has already swept the population before the first affected litter is farrowed. Level 1 confirmed, and this entry is now the cleanest example in the register of the clause the Getah correction clarified: the harm is transplacental and COMPLETE BEFORE BIRTH -- the factsheet says piglets born alive are unaffected -- so there is no living animal for any treatment to act on. Contrast Getah, where piglets are born healthy and then die.
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 Menangle virus is mentioned anywhere in chapter 33 or in cfsph_2017. 33.3.9 gives the control approach instead, and it works: "THE ERADICATION OF MENANGLE VIRUS FROM AN ENDEMICALLY INFECTED PIG POPULATION CAN BE ACHIEVED BY MOVING ALL THE AGE GROUPS IN WHICH INFECTION IS ACTIVE (e.g. pigs between 10 and 16 weeks of age) to another site. If affected facilities are cleaned, vacated for a few weeks, and then restocked with unexposed pigs or pigs known to be immune to the virus, THE CYCLE OF ENDEMIC INFECTION IN THE HERD SHOULD BE BROKEN AND THE VIRUS ELIMINATED NATURALLY." In small herds it dies out unaided: "there would be insufficient numbers of susceptible animals available to maintain a cycle of infection, as THERE IS NO CARRIER STATE and, unlike parvovirus, environmental survival of this virus is poor."
How this level was decided
Level 1 on the "not needed" clause of the 2026-08-28 rewording. There is no vaccine, so the whole question is whether the disease would justify one, and it would not: one outbreak has ever occurred, the virus was eradicated from the farms it reached by moving pigs and cleaning, it cannot persist without a continuous supply of susceptible animals, and natural infection gives strong immunity that ends the reproductive losses. A disease that goes away when you move the ten- to sixteen-week-old pigs to another shed does not need a product built for it. NOTE THE CONTRAST WITH NIPAH on the facing page, scored level 3: same family, same bat reservoir, and the difference is entirely in what the disease does. Unchanged. A single outbreak in 1997 that has never recurred -- no clinical or market imperative.
Levels and evidence are generated from data/assignments/menangle_virus.yml; the overview is authored in data/overviews/menangle_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.