Hendra Virus
LEVELS: Highly unlikely; Severe; Routine biosecurity keeps it out; Reference or research laboratory required; Moderate; NOT ASSIGNED; Substantial; Needed but not available
| Register id | hendra_virus |
| Type | virus |
| Scientific name | Henipavirus hendraense |
| NCBI taxid | 3052223 |
| Evidence | 3 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Hendra virus is a henipavirus — a close relative of Nipah virus — that occurs only in Australia, where it is maintained silently in flying foxes. Shedding from the bats rises at unpredictable intervals and occasionally spills over into horses, which then sometimes infect the people caring for them. That is the entire natural history of the disease: all seven recorded human cases arose from contact with sick horses or from performing necropsies on them, and four of those people died, one from an encephalitis that recurred fatally a year after apparent recovery. Pigs have never been found naturally infected — a survey of 100 Queensland herds was entirely seronegative — but they are not immune to it. Experimentally infected pigs given high doses became seriously ill, one to the point of being moribund, while others in the same study showed only fever, depression, respiratory signs or brief neurological signs, and pigs do shed the virus in respiratory and oral secretions and faeces. Treatment in people has been largely supportive, with monoclonal antibodies developed more recently. An equine vaccine exists in Australia, along with a test that distinguishes vaccinated from infected horses; neither has been evaluated in pigs, and nothing is available for pigs anywhere.
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 2026-08-27 level 2. All seven human cases arose from horses, no human case has ever been linked to a pig, and 100 Queensland swine herds tested all seronegative.
Basis. CFSPH 2025: all seven human cases arose from horses -- "Seven clinical cases occurred in people who cared for sick horses or performed necropsies during the early outbreaks". No human case has ever been linked to a pig. But pigs do shed: one study "detected it in respiratory and oral secretions and feces, but not urine, in pigs". And natural infection in pigs has never been found even where the virus circulates -- "a survey reported that 100 swine herds tested in Queensland, Australia were all seronegative".
How this level was decided
MOVED L2 -> L1, re-read 2026-09-04 AGAINST THE REWORDED LABELS. cfsph_2025: all seven human cases arose from horses, and no human case has ever been linked to a pig. 100 Queensland swine herds all seronegative, so natural pig infection does not occur even in the endemic area.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: Level 2 holds and is now supported rather than inferred. C1 scores transmission FROM PIGS. Experimentally infected pigs shed virus in respiratory and oral secretions, so a pig-to-human route is plausible; it has simply never been reported, and 100 seronegative Queensland herds say natural pig infection does not happen even in the endemic area. That is exactly level 2 -- plausible but never or rarely reported. Not level 1, because the shedding data mean the route is not ruled out. Unchanged. The Nipah factsheet is placed thin here as henipavirus context and reports nothing on Hendra transmission from pigs.
C2 Zoonotic impact
Severity of human illness caused by the agent
Severe: Infection carries a substantial risk of life-threatening illness, death, or permanent disability, even if human infections are uncommon
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "agree c2l4". Four of the seven known human cases were fatal, and one person developed fatal relapsing encephalitis a year after apparent recovery.
Basis. CFSPH 2025: "Seven clinical cases occurred in people who cared for sick horses or performed necropsies during the early outbreaks, and four were fatal." And a late recurrence -- "One person developed recurrent, fatal encephalitis a year after apparent recovery from the initial illness."
How this level was decided
Four deaths in seven cases, plus fatal relapsing encephalitis a year after apparent recovery. Level 4 asks for a substantial risk of life-threatening illness, death or permanent disability even where human infections are uncommon, which describes this exactly. Now supported by case data rather than inferred from the Nipah comparison the chapter drew. Unchanged.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED 2026-08-27 -- "agree c3l2". This began as a correction on 2026-08-26, when the pass scored L4 on the pteropid bat reservoir and Eric pointed out there are no pteropid bats in the US: an agent arriving here brings itself, not its ecosystem, so a reservoir existing only in the agent's native range creates no introduction risk to a US herd. The CFSPH factsheet placed on 08-27 then made the dependence explicit -- the virus "occurs only in Australia, where it is maintained in asymptomatic flying foxes" and "equids do not act as maintenance hosts" -- and the pass now reaches L2 unaided. Recorded as a confirmation rather than a correction because the pass and his ruling now agree; from_level is 2 so this does not flag as decided against a different answer. [RENUMBERED level 2 to 3, from_level 2 to 3 on 2026-09-01 when C3 went from four levels to five. The words above are exactly as recorded and the decision is unchanged -- only the number beside it moved, because the scale did. C3 now runs on the EFFORT REQUIRED TO EXCLUDE: L1 already in the herd, L2 housing alone keeps it out, L3 routine biosecurity keeps it out, L4 extraordinary biosecurity required, L5 exclusion may not be achievable.]
Standing note. Reservoir is pteropid bats (flying foxes), which do not occur in the US. Score C3 on what an incursion's onward source would actually be here -- other pig herds -- not on the Australian reservoir. Corrected to L2 on 2026-08-26.
Basis. CFSPH 2025: Hendra "occurs only in Australia, where it is maintained in asymptomatic flying foxes (pteropid fruit bats). Virus shedding from these bats increases at unpredictable intervals, sometimes resulting in spillover to a few horses." Horses are not maintenance hosts -- "While equids do not act as maintenance hosts, they occasionally infect horses or other mammals during close contact." shic_2021_nipah (placed thin, henipavirus context): "Pteropid bats must be kept out of swine farms. Fruit trees should not be planted near farms... Roof run-off should be diverted away from pig areas, and potentially contaminated fruit should not be fed to pigs."
How this level was decided
RENUMBERED L2 -> L3 on 2026-09-01, when C3 went from four levels to five. The argument below is unchanged and so is the judgment. What changed is the scale it sits on. C3 now runs on the EFFORT REQUIRED TO EXCLUDE: L1 already in the herd, L2 housing alone keeps it out, L3 routine biosecurity keeps it out, L4 extraordinary biosecurity required, L5 exclusion may not be achievable. The pass now reaches level 2 on its own, where before it reached level 4 and Eric had to correct it. The standing note on this entry is why: an agent arriving in the US brings itself, not its ecosystem, and there are no pteropid bats here. This factsheet makes the dependence explicit -- the reservoir is flying foxes, and even horses do not maintain the virus. With no maintenance host on this continent, the onward source after an incursion is other pig herds, which routine biosecurity closes. Level 3 confirmed. The exclusion measures for a pteropid-bat henipavirus are set out here in detail and are siting and husbandry measures, which is the routine tier.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "l3, may have indicative diagnosis at L2 lab but confirmation almost certainly would involve l3 lab" Transcribed by the assistant and confirmed by Eric on 2026-08-31 -- "i confirm the six". The harvester refused it because the comment names two levels, but the second is a noun phrase for a level-N-capable laboratory rather than a second assignment.
Basis. CFSPH 2025: "Clinical cases are often diagnosed by PCR. The most commonly used tests target the viral matrix protein gene and have been updated to identify genotype 2 as well as genotype 1 viruses." Serology: "ELISAs and serum neutralization assays are the usual diagnostic tests... A test that can determine whether antibodies are the result of infection or vaccination (DIVA test) is available at government laboratories in Australia."
How this level was decided
Validated assays exist, so this is not level 4. But they sit in national and government laboratories -- the DIVA test explicitly so -- and a BSL-4 henipavirus is not something a US regional laboratory confirms. Level 3. Nothing in the clinical picture would prompt the suspicion in the first place either: no natural swine infection has ever been described, so there is no recognisable presentation to react to. Unchanged.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED, and he supplied the reasoning before the pass reached it: "make this c5l3 based on small number of experimentally infected pigs - most had minor clinical signs though some were more severe. See the hendra.pdf paper in inbox and reassess Hendra to make sure we haven't misclassified any criteria." The factsheet he asked for was placed, the pass read the same passage, and it moved this cell from NOT ASSESSED to L3.
Basis. CFSPH 2025, on the only experimental swine infection: "Two experimentally infected pigs given high viral doses were also reported to be seriously ill, with one animal becoming moribund before both were euthanized, but other pigs in this study were only mildly affected. Some pigs had nonspecific signs (e.g., fever, depression) and/or respiratory signs, and transient mild neurological signs were observed on a single day in a pig that recovered."
How this level was decided
INFERRED, and it replaces a NOT ASSESSED. Eric read the same passage and reached the same place: "make this c5l3 based on small number of experimentally infected pigs - most had minor clinical signs though some were more severe." A spread from moribund to mildly affected, arising on a farm, is a measurable increase in cost of production that remains manageable within normal operations. Inferred rather than supported because the evidence is experimental inoculation at high dose, not field disease -- no natural swine infection has ever been recorded. Unchanged.
C6 Market impact
Duration of material disruption to pork and pig markets
CONFIRMED NOT ASSESSABLE. No level was assigned on this criterion, and Eric has reviewed that and ruled it correct — the folder holds nothing bearing on it. This is a statement about what the evidence supports, not a finding about the agent.
Confirmed by Eric. CONFIRMED AS NOT ASSESSABLE -- "hendra c6 ... no level". Eric: "I don't think we have enough info to assess. This is a case where we have enough evidence for some criteria, but not for others. In cases like this, we need a way to keep track of the agent so we can put them into the alternate ranking process we still need to develop. How?" The CFSPH factsheet is about a horse disease and says nothing about pork or pig markets. This is deliberately different from an unreviewed blank: he has looked and ruled that no level should be assigned, which is what a null correction records. The alternate ranking track for entries that cannot carry a complete score vector is an open design question -- see TODO.md.
Basis. The factsheet addresses horses, flying foxes and human cases. It says nothing about pork or pig markets, trade restrictions, movement controls or consumer demand, and Hendra is not discussed as a swine trade disease anywhere in the folder.
How this level was decided
NOT ASSESSED. No level assigned. Eric reached the same conclusion independently: "I do not think we have enough info to assess." The new factsheet does not change it -- it is a veterinary factsheet about a horse disease, and market consequences for pigs are not its subject. Unchanged. NULL held on Eric's ruling -- no pig market anywhere has been observed responding to Hendra, and the Nipah factsheet supplies a Nipah precedent, not a Hendra one. Substituting the Malaysian cull here would be exactly the assumption the standing rule forbids.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. RE-RULED. His markup said "I don't think we have enough info to assess", but he wrote that before the CFSPH factsheet he had asked for was placed. Shown the factsheet, he ruled "hendra c7l3". It states that treatment "has mainly been supportive", that whether antiviral drugs benefited any patient is uncertain, and that the monoclonal antibodies are human and experimental. No effective pathogen-directed treatment exists and the disease in pigs can leave an animal moribund, so the opportunity is substantial.
Basis. CFSPH 2025: "Treatment of Hendra virus infections, to date, has mainly been supportive. Antiviral drugs were administered to some patients, but whether they had any benefit is uncertain. Monoclonal antibodies have also been developed. Preliminary analyses suggest that at least some of these antibodies are expected to be effective against genotype 2 as well as genotype 1."
How this level was decided
THIS SUPERSEDES A NOT ASSESSED, AND ERIC SHOULD RE-RULE IT. He wrote "I do not think we have enough info to assess" -- but he wrote that before this factsheet was placed, and it is the paper he asked to have assessed. It settles the question: treatment is supportive only, antiviral benefit is uncertain, and the monoclonals are human and experimental. No effective pathogen-directed treatment exists, while the disease in pigs can be severe enough to leave an animal moribund. That is level 3 -- the opportunity is substantial. Unchanged.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Needed but not available: No effective vaccine is available in the US or has been developed, and the disease would justify vaccinating if one existed
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED, again reached independently: "make this c8l3. We have no autogenous or commercial vaccine available for pigs in US stockpiles or even overseas." The one Hendra vaccine is equine, Australian, and has not been evaluated in pigs.
Basis. Eric, 2026-08-26: "make this c8l3. We have no autogenous or commercial vaccine available for pigs in US stockpiles or even overseas." The one Hendra vaccine is equine, Australian, and has not been evaluated in pigs. shic_2021_nipah: "A sub-unit vaccine based on G glycoprotein from Hendra virus is licensed for use in horses in Australia and provided good cross-protection against NiV in an experimental ferret model."
How this level was decided
STAYS L3, on his ruling, unchanged in meaning by the rewording. He framed it as an absence rather than as an absence of need, and a BSL-4 agent with a case fatality of four in seven human cases is not one where a vaccine would be unwarranted. NOTE FOR HIM: a case could be made for level 1 on the ground that pigs are not naturally infected -- 100 Queensland herds seronegative in the endemic area -- which would make a swine vaccine pointless. Left at 3 because that is his stated ruling and it is not obviously wrong. Level 3 confirmed, and now on direct evidence rather than inference: a Hendra vaccine exists, is licensed, and works well enough to cross-protect against a related henipavirus. It is licensed for horses, not pigs, and not in the United States -- which is a demonstrated gap in exactly the shape level 3 is reserved for.
Levels and evidence are generated from data/assignments/hendra_virus.yml; the overview is authored in data/overviews/hendra_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.