Nipah Virus
LEVELS: Likely to occur; Severe; Routine biosecurity keeps it out; Reference or research laboratory required; Substantial; Prolonged disruption; Little; Needed but not available
| Register id | nipah_virus |
| Type | virus |
| Scientific name | Henipavirus nipahense |
| NCBI taxid | 3052225 |
| Evidence | 3 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Nipah virus is the most dangerous zoonosis a pig can carry. Fruit bats of the genus Pteropus are its reservoir, and the 1998-99 Malaysian outbreak is believed to have begun when bats contaminated fruit that pigs then ate. In pigs the disease is not particularly dramatic — often subclinical, with a characteristic barking cough, respiratory or neurological signs, and mortality under 5% in growers — but once it was in pigs, the movement of infected animals carried it between farms, between states and internationally to Singapore. In people it killed 105 of 265 cases in Malaysia and one of 11 abattoir workers in Singapore. Almost all human cases were pig farmers and others in close contact with infected pigs: feeding, handling, assisting at farrowing, treating or removing sick and dead animals were the risky activities, while simply living on an infected farm was not. Every subsequent outbreak, in India, Bangladesh and the Philippines, has occurred without pigs, and those have averaged around 75% case fatality. The response to a confirmed case is not treatment — the reference chapter states plainly that treating affected animals should not be considered — but rapid eradication, which in Malaysia meant culling more than a million pigs. Several pig vaccine candidates are in development, none yet available.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Likely to occur: Transmission from pigs can occur even when control points are intact, or is prevented only by extraordinary control measures such as respiratory protection or vector control
Basis. ch33 33.4.3, a Public Health section that opens "Nipah virus presents a serious threat to public health": in the 1998-99 Malaysian outbreak "MOST HUMAN CASES WERE PIG FARMERS AND OTHER PEOPLE WHO HAD CLOSE CONTACT WITH INFECTED PIGS. Abattoir workers in Singapore who had contact with infected pigs from Malaysia were also affected." 33.4.4 on which contacts mattered: "FEEDING OR HANDLING PIGS, ASSISTING WITH FARROWING, TREATMENT, AND/OR REMOVAL OF SICK OR DEAD PIGS were most likely to result in infection. LIVING ON AN INFECTED PIG FARM WAS NOT A SIGNIFICANT RISK FACTOR. The pattern of human infection suggested spread via SPUTUM OR LARGE DROPLETS, rather than by fine aerosol. Coughing, a frequent clinical sign in infected pigs, or loud squealing would facilitate such a mode of transmission." 33.4.8 on what handling infected pigs requires: "Nipah virus is a high-risk (BSL-4) zoonotic agent and extreme care must be taken during sample collection... Antemortem and postmortem sampling has to be conducted WHILE WEARING PERSONAL PROTECTIVE EQUIPMENT, INCLUDING RESPIRATORY PROTECTION, in a manner that will exclude human contact with body fluids from affected animals." cfsph_2025 records the scale: the outbreak was controlled "by culling more than one million pigs", and "no cases occurred after seropositive animals had been culled". shic_2021_nipah: "In an outbreak in Malaysia (1998-99), NiV was associated with swine contact." "Pigs can become sick and act as amplifying hosts." "The health of swine workers and responders must be protected since NiV is zoonotic."
How this level was decided
Level 4, and the label names the control measure this virus actually requires: transmission from pigs can occur even when control points are intact, or is prevented only by extraordinary measures SUCH AS RESPIRATORY PROTECTION. That is exactly what the chapter prescribes, and the epidemiology explains why -- the route is droplets from a coughing pig at close quarters, so the exposures that infected people were the ordinary tasks of pig farming: feeding, farrowing, treating, moving dead animals. It is not level 3, because level 3 needs a control point to fail and here the failure mode is doing the job. NOTE THE ONE FACT THAT ARGUES THE OTHER WAY and is the reason the level is not higher still: living on an infected farm was not a significant risk factor, so this is close contact rather than area spread. THIS IS THE HIGHEST C1 IN THE REGISTER SO FAR and it should be: 265 human cases came out of one pig outbreak. Level 4 confirmed. Pig-to-human transmission is not merely plausible here, it is the documented mechanism of the largest outbreak on record.
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
Basis. ch33 33.4.3: "Although the first recognized outbreak of Nipah virus was confined to three states in Peninsular Malaysia, THE CFR WAS 40% (105 DEATHS, 265 CASES). Most human cases were pig farmers... Abattoir workers in Singapore who had contact with infected pigs from Malaysia were also affected (ONE DEATH, 11 CASES; CFR 9%). All subsequent outbreaks have occurred without the involvement of pigs. Human cases have occurred in India and Bangladesh on an almost annual basis since 2001 WITH AN AVERAGE CFR OF 75% (211 deaths, 280 cases). In the Philippines, in 2014, where horses were identified as the source of human infections, THE CFR WAS 53%." 33.4.6: "When Nipah virus infects people, it can cause a severe respiratory illness and/or encephalitis. HUMAN ILLNESS AND MORTALITY CAN BE THE EARLIEST INDICATION OF AN OUTBREAK." shic_2021_nipah: "NiV causes febrile encephalitis and respiratory disease in humans, with high case-fatality rates." "Once NiV enters the human population, it can spread person-to-person. NiV has the potential to become a pandemic agent."
How this level was decided
Level 4, and it is not a close call. The label asks for a substantial risk of life-threatening illness, death or permanent disability, and the pig-attributable arm of this virus killed 105 of 265 people who caught it. C2 GRADES ILLNESS ACQUIRED FROM PIGS, and the Malaysian and Singaporean numbers are precisely that arm -- 40% and 9% case fatality in pig farmers and abattoir workers respectively. The later outbreaks at 75% CFR came from date palm sap and from horses rather than from pigs, so they do not bear on this cell, but they establish that the lower Malaysian figure is not the ceiling for what this virus does to people. Level 4 confirmed.
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. Same pteropid bat reservoir as Hendra, same reasoning: no flying foxes in the US, so do not score L4 on a reservoir that cannot follow the virus here. Not yet assessed; this note exists so the pass does not repeat the Hendra error.
Basis. ch33 33.4.4: "There is strong evidence that FRUIT BATS MAINLY FROM THE GENUS PTEROPUS ARE A RESERVOIR of Nipah virus. The disease outbreak observed in Malaysia is assumed to be the result of the virus spreading from fruit bats into farmed domestic pigs, possibly via contaminated fruit which had been partially eaten by the fruit bats." Once in pigs: "IN MALAYSIA, THE MOVEMENT OF INFECTED PIGS WAS THE PRIMARY MEANS BY WHICH NIPAH VIRUS SPREAD BETWEEN FARMS, BETWEEN STATES, AND INTERNATIONALLY TO SINGAPORE." 33.4.10: "In countries where pteropid bats may be a reservoir of Nipah virus, pig farms should be managed to maximize biosecurity. Farms should be devoid of fruit trees and other vegetation that might attract bats to animal housing. STRICT BIOSECURITY SHOULD BE IN PLACE TO PRECLUDE THE IMPORTATION OF INFECTED ANIMALS. HERD REPLACEMENTS SHOULD BE ISOLATED AND QUARANTINED PRIOR TO INTRODUCTION." The chapter states for the sibling virus at 33.3.9 that "MEGACHIROPTERA ARE NOT FOUND IN NORTH AMERICA." shic_2021_nipah: "Pteropid bats must be kept out of swine farms. Fruit trees should not be planted near farms, and swine barns should be screened if possible. Roof run-off should be diverted away from pig areas, and potentially contaminated fruit should not be fed to pigs." "Pigs acquire NiV from bats through ingestion of contaminated fruit (urine or saliva), water, aborted bat fetuses, or birth products."
How this level was decided
Level 3, under the bat rule this register already applies to hendra_virus, which sits at the same level. AN AGENT ARRIVING HERE BRINGS ITSELF, NOT ITS ECOSYSTEM: pteropid bats are not on this continent and cannot follow, so the reservoir that seeded Malaysia is not a route into a US herd. What remains is the route the chapter says actually moved the virus between farms, between states and across a border -- infected pigs -- and the measure it prescribes against that is quarantine and isolation of herd replacements, which is the level 3 list verbatim. NOTE HOW THE FOUR-LEVEL C3 HANDLES THIS BETTER THAN THE OLD FIVE: under the reservoir framing this looked like a permanent-wildlife-reservoir case, and the answer depended on which continent you were standing on. Under the exclusion framing the question is what a US herd must do, and the answer is quarantine incoming stock. Level 3 held, and worth setting out because the factsheet mentions screening. The route is bat excreta on fruit and in run-off reaching pigs -- that is the ground the pig stands on and what it eats, which housing and feed hygiene close. Screening is offered as "if possible" alongside not planting fruit trees and diverting roof run-off, which are ordinary siting and husbandry measures rather than the extraordinary list. Contrast Getah, where the vector flies in and screening is the primary control rather than an optional extra.
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 33.4.6: "THERE ARE NO PATHOGNOMONIC CLINICAL SIGNS of Nipah virus infection in pigs, although a barking cough was considered characteristic in the Malaysian outbreak", and infection "may be subclinical or result in acute febrile disease with respiratory and/or CNS signs". 33.4.8 lists a differential spanning sudden death in adults, abortion, severe coughing at any age and neurological disease, and notes that "animals coinfected with other pathogens, such as classical swine fever virus and opportunistic bacteria, are likely to display clinical signs most compatible with the co-infectants. THIS MAY PARTIALLY EXPLAIN HOW IT WAS POSSIBLE FOR NIPAH VIRUS TO BE PRESENT, BUT UNIDENTIFIED, IN PIGS IN MALAYSIA SINCE 1996." On the assays: "Real-time RT-PCR assays specific for Hendra virus or Nipah virus have been described and allow the reliable detection of viral RNA in a wide range of tissues and serum", ELISA is preferred for antibody, "any ELISA reactors should be confirmed by VN... IN A BSL-4 LABORATORY", and "when virus isolates are required... procedures should be conducted in A BSL-4 LABORATORY". Specimen and assay guidance is on the WOAH website. shic_2021_nipah: "NiV is a BSL-4 agent." "most U.S. laboratories are not equipped to detect NiV." "Positive test results must be confirmed by virus neutralization in a BSL-4 facility." "Use of recombinant proteins makes testing safe for BSL-2 facilities."
How this level was decided
Level 3, level with foot-and-mouth disease, classical swine fever and African swine fever, which are the worked examples there. Validated assays plainly exist -- WOAH-referenced real-time RT-PCR, recombinant-antigen ELISA, immunohistochemistry on formalin-fixed tissue -- so this is not level 4. What puts it at level 3 rather than level 2 is where they can be run: confirmation by virus neutralisation and any isolation attempt require a BSL-4 laboratory, of which there are very few, and the presentation points nowhere in particular. The Malaysian experience is the strongest possible statement of the second half: the virus was in pigs from 1996 and was not identified until people started dying in 1998. Level 3 confirmed in the factsheet's own words -- most US laboratories are not equipped, and confirmation requires BSL-4.
C5 Production cost
Financial impact on the infected farm's cost of production
Substantial: Severe losses cause a major and potentially unsustainable increase in cost of production
Basis. ch33 33.4.6, on the disease in pigs alone: infection "may be subclinical", mortality in weaners and growers is "low (<5%)", sudden death in sows and boars is "considered an unusual outcome", and mortality was high in suckling pigs. BUT THE DISEASE IS NOT WHAT COSTS THE FARM. 33.4.10: "Nipah virus is a dangerous zoonotic agent... Control measures in cases of confirmed Nipah virus infection will reflect its EXTREME HAZARD as a zoonotic agent... RAPID ERADICATION IS THE RECOMMENDED RESPONSE. This was achieved in Malaysia by quarantine of infected premises and THE CULLING OF ALL SUSCEPTIBLE ANIMALS ON THOSE PREMISES." cfsph_2025: the outbreak was controlled "by CULLING MORE THAN ONE MILLION PIGS". shic_2021_nipah: "Suckling piglets develop neurological disease with high mortality." "Acute death is sometimes seen in adult pigs, with bloody nasal discharge postmortem. Neurological signs and abortion have been reported." "Stop movement and stamping out may be instituted in an NiV outbreak."
How this level was decided
Level 4, and the reasoning has to be stated carefully because the clinical disease alone would not reach it. Under 5% mortality in growers is a level 2 picture. What makes this level 4 is that a confirmed infection ends the farm: the recommended response is rapid eradication by culling every susceptible animal on the premises, and that is what happened to more than a million pigs in Malaysia. C5 measures the financial impact on the INFECTED FARM, and total depopulation is the largest impact there is -- severe losses causing a major and unsustainable increase in cost of production. This is scored level with foot-and-mouth disease, classical swine fever and pseudorabies, which is the right company. NOTE THAT THE REGULATORY RESPONSE IS COUNTED HERE ONCE, as the infected farm's loss, and again in C6 as the market's loss -- those are different quantities, not the same one twice. Level 4 confirmed. Stamping out is the response, which is unsustainable loss by definition for the affected herd.
C6 Market impact
Duration of material disruption to pork and pig markets
Prolonged disruption: Material negative effect on supply or demand lasting more than 6 months when disease occurs on one or more farms
Basis. ch33 33.4.3: the Malaysian outbreak reached "three states in Peninsular Malaysia" and spread "internationally to Singapore, where abattoir workers processing Malaysian pigs became infected". 33.4.4: "the movement of infected pigs was the primary means by which Nipah virus spread between farms, between states, and internationally." 33.4.10: rapid eradication is the response, achieved "by quarantine of infected premises and the culling of all susceptible animals". cfsph_2025: controlled "by culling more than one million pigs", and human cases stopped only "after seropositive animals had been culled". The outbreak ran from 1998 into 1999. shic_2021_nipah: "NiV is an OIE-listed disease and must be reported internationally according to the Terrestrial Animal Health Code." "Entry of NiV into the United States is a public health concern and could lead to swine industry losses." "Widespread NiV outbreaks occurred in people and pigs in Malaysia and Singapore from 1998-99."
How this level was decided
Level 4, and this entry is the precedent the standing note SCORING/market_impact cites by name. The note asks for something actually observed, and this is the largest observation in the register: an outbreak that destroyed more than a million pigs, closed a cross-border trade in live pigs into Singapore, and ran for more than a year. Material disruption lasting more than six months is the level 4 label, and the Malaysian pig industry did not recover on that timescale -- it was restructured. It sits with foot-and-mouth disease and African swine fever, which is where a disease that empties barns for public health reasons belongs. Level 4 confirmed, and this is the entry the standing note cites as scoreable on a foreign precedent -- the 1998 Malaysian cull of 1.1 million pigs. OIE-listed with mandatory international reporting.
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 33.4.10, first sentence: "NIPAH VIRUS IS A DANGEROUS ZOONOTIC AGENT AND TREATMENT OF CLINICALLY AFFECTED ANIMALS SHOULD NOT BE CONSIDERED." The prescribed response is rapid eradication by culling. 33.4.9: neutralising antibodies appear 7-10 days post infection and full protection requires both antibody and a cell-mediated response; there is no evidence of persistent infection. shic_2021_nipah: "There is no specific treatment for NiV infection." "Stop movement and stamping out may be instituted in an NiV outbreak. The health of swine workers and responders must be protected since NiV is zoonotic."
How this level was decided
Level 1, and it needs the careful version of the argument because Eric's rule of 2026-09-02 forbids the lazy one. C7 scores the value of a treatment that does not exist, not the industry's current willingness to use one, so "nobody treats it" is not the answer. The answer is that a treatment would not change the outcome that matters: an infected pig is culled regardless of whether it could be cured, because the reason for the cull is the 40% case fatality rate in the people who handle it. THE PUBLIC HEALTH IMPERATIVE OVERRIDES ANY CLINICAL BENEFIT, which is a different route to level 1 than the usual "animals recover acceptably". Foot-and-mouth disease, classical swine fever and swine vesicular disease are all scored level 1 on the same structure -- the problem these viruses present is not one that treating the pig solves. Level 1 held, and the new source strengthens the specific argument the cell already made: the response to NiV is stamping out, driven by the risk to the people handling the pigs, so an infected pig is culled whether or not it could be cured. The public health imperative overrides any clinical benefit a treatment could deliver.
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
Basis. ch33 33.4.10: "A NUMBER OF VACCINE CANDIDATES FOR PIGS ARE IN DEVELOPMENT AND COULD BE USED IN THE FACE OF FUTURE OUTBREAKS. One group has demonstrated that a bovine herpes virus-4 vector expressing Nipah virus glycoproteins induced potential protective immune responses in pigs. Another group is working on a recombinant subunit vaccine that uses the Nipah virus soluble G glycoprotein. THE HIGHLY EFFECTIVE HENDRA VIRUS VACCINE USED IN HORSES IN AUSTRALIA IS ALSO BASED ON THE SOLUBLE G GLYCOPROTEIN." cfsph_2025: "No vaccines are currently" available for the species at risk. shic_2021_nipah: "Multiple vaccines are in development, but none are commercially available for people or pigs." "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." "There are no licensed vaccines in the United States."
How this level was decided
Level 3, a genuine gap on both halves of the test. There is no licensed vaccine for pigs anywhere -- only candidates in development. And the disease would plainly justify one: it kills 40% of the people who catch it from pigs, its control measure is destroying every pig on the premises, and the proof that the immunology works is already in commercial use, because the Hendra vaccine given to Australian horses is built on the same soluble G glycoprotein against the sister virus. A protein platform that has been licensed for one henipavirus in one species and not built for the other is the definition of a gap that funding could close. NOTE THE CONTRAST WITH FOOT-AND-MOUTH DISEASE AND CLASSICAL SWINE FEVER, both at level 1: for those, effective vaccines exist and are banked for outbreak response, so there is nothing to fund. Level 3 confirmed, and the tractability evidence is now explicit: a henipavirus subunit vaccine is licensed and in commercial use in another species, and cross-protects against NiV experimentally. A genuine gap rather than an unbuildable product.
Levels and evidence are generated from data/assignments/nipah_virus.yml; the overview is authored in data/overviews/nipah_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.