Zika virus
LEVELS: Highly unlikely; Severe; Extraordinary biosecurity required; Reference or research laboratory required; Negligible; Negligible; Little; Available, or not needed
| Register id | zika_virus |
| Type | virus |
| Scientific name | Zika virus |
| NCBI taxid | 64320 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Zika virus was first described in Uganda and has since spread to more than 80 countries across Africa, Asia, the Pacific and the Americas, where it became notorious for causing birth defects in infants of infected mothers. Its relationship with pigs is ambiguous and probably unimportant. Serological studies indicate pigs are susceptible to natural infection, but other work failed to infect them experimentally, which suggests the virus strain matters. When three- month-old pigs were inoculated to test whether they could amplify the virus, none showed clinical signs, no virus was detectable in blood or tissues, and yet all of them seroconverted within a week — so pigs seem unlikely to play a part in the natural cycle, though they might be useful as sentinels for detecting where the virus is active. The one echo of the human disease is that pig fetuses infected in the uterus developed brain damage ranging from mild to severe, including small brains in the worst cases, although whether the virus can cross the pig placenta at all is disputed. There is no treatment and no vaccine for 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. ch30 30.3.3: "Serologic studies have demonstrated that pigs are susceptible to natural infection with ZIKV, but other studies were unable to show susceptibility after experimental inoculation, suggesting the strain of virus may be important." "The potential for pigs to serve as amplifying or maintenance hosts for ZIKV was also investigated using experimentally inoculated 3-month-old pigs. No clinical signs were observed, viremia was not detected, and no infectious virus was detected in tissues collected at necropsy. However, all pigs seroconverted by day 7 post inoculation. Therefore, although it would appear unlikely that pigs could play a role in the natural amplification cycle of ZIKV, they might prove useful as sentinel animals."
How this level was decided
Level 1, and unlike dengue this one rests on a study that looked for the answer. Pigs do get naturally infected -- serology proves it -- but when the amplification question was put directly, inoculated pigs produced NO detectable viraemia and no infectious virus in any tissue while still seroconverting. A pig that seroconverts without becoming viraemic cannot infect a mosquito, so it is a dead-end host and cannot be a source of human infection. That is an examined negative rather than a silence.
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. ch30 30.3.3: "ZIKV has more recently emerged as an important cause of neurological disease following outbreaks in the Pacific and Latin America." Pigs are shown not to develop viraemia capable of infecting a vector.
How this level was decided
RE-SCORED 2026-09-04. C2 now grades the severity of the illness the agent causes in a person, independent of how the person was exposed -- the 2026-09-01 pig-attribution reading is reversed, and C1 alone carries the source question. Congenital Zika syndrome is permanent disability and is a recognised and meaningful part of the outcome distribution rather than a rare tail, which is the test the C2 description sets. The adult illness alone would be level 2.
PREVIOUS ANSWER, written under the pig-attribution reading: Level 1 under the criterion as rescoped on 2026-09-01: C2 grades illness acquired FROM PIGS, and pigs are a dead end. THE LABEL MUST NOT BE READ AS A FINDING THAT ZIKA IS MILD -- congenital Zika syndrome is exactly the kind of severe permanent outcome C2 level 4 exists for. It records that a pig is not where a person gets it.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Extraordinary biosecurity required: Exclusion needs measures beyond the routine, such as air filtration, thermally treated feed and bedding, or repeated costly testing to find carriers, and may still fail
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c3l5, vector is present and with an expanding range, and a persistent threat remains" RESCALED 2026-09-03, when C3 went from five levels to four and level 4 absorbed level 5. A ruling of his is never overturned by a scale change, so what is recorded here is the same judgment expressed on the new scale. AND THE ENTRY ALSO MOVED, on the pass Eric approved the same day: the whole old level 5 block was re-read against the exclusion test rather than the reservoir test, because twenty-one of those entries had been renumbered past the housing level on 2026-09-01 without being judged against it. See the entry justification for the reason this one moved. Recorded on the old scale as level 5, from_level 5.
Basis. ch30 30.3.3: "ZIKV was first described in Uganda and has since spread to over 80 countries within Africa, Asia, the Pacific, and the Americas." "Serologic studies have demonstrated that pigs are susceptible to natural infection with ZIKV." The vector is Aedes, and 30.1 notes the propensity of orthoflaviviruses to emerge into new regions.
How this level was decided
RENUMBERED L5 -> L4 on 2026-09-03, when C3 was reduced from five levels to four and level 4 absorbed level 5. THE JUDGMENT IS UNCHANGED and this one really is a renumber: the merged level 4 label carries what level 5 said, ending "and may still fail". IT WAS STILL CHECKED rather than assumed, because the last renumber on 2026-09-01 was mechanical and moved twenty-one entries past a level they should have been judged against. The check is the exclusion test -- does housing close the route? For this entry it does not.
EARLIER REASONING, kept because it is the evidence read: INFERRED. Natural infection of pigs is documented, so unlike dengue there is a real introduction event to score. The route is an Aedes mosquito and the reservoir is the human population, neither of which any farm or industry action removes -- level 5. FLAGGED with dengue: the exposure is real but the consequence is nil, and everything else on this entry is level 1.
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. "c4l3, a lot of work has been done globally and published. Assays are available and validated across labs."
Basis. Chapter 30 describes no veterinary diagnostic approach for Zika in pigs. Detection in the studies cited was by viraemia testing, tissue culture and serology, and 30.3.1 records that orthoflavivirus serology requires virus neutralisation to resolve cross-reactions.
How this level was decided
INFERRED, on the same reasoning as dengue in this batch. Validated Zika assays exist and are good, because Zika is a human public health priority -- so not level 4. But they sit in public health laboratories rather than veterinary ones, and nothing clinical in a pig would prompt a request. Level 3.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on 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. "c5l1, the virus circulates in areas of the world where commercial pig production is common and there is little evidence it has or will have any effect on cost of production if it were to occur in the US"
Basis. ch30 30.3.3: "No clinical signs were observed" in experimentally inoculated 3-month-old pigs. Against that: "Pig fetuses infected with ZIKV in utero were found to have mild to severe neuropathology, including microencephaly in severe cases. However, there is some doubt as to whether the virus can cross the placenta." Neonatal pigs inoculated intracerebrally showed leg weakness, ataxia and tremor in 2 of 11.
How this level was decided
INFERRED, and FLAGGED because the fetal finding is the one thing in this entry that could matter. Transplacental orthoflavivirus infection is precisely what makes JEV expensive, and Zika fetuses inoculated in utero developed microencephaly. What holds this at level 1 is that the infection was delivered by direct in utero inoculation rather than across a placenta, the chapter says there is doubt whether the virus can cross the placenta at all, and no natural reproductive loss in pigs has ever been reported. No measurable effect on cost of production on the evidence held. NOTE ON WHAT THIS ENTRY IS. Chapter 30 discusses this virus almost entirely as an ANIMAL MODEL -- "Pigs have been used to develop animal models of human infections caused by DENV and ZIKV... make pigs an attractive alternative to nonhuman primates for studying human infectious diseases". A pig deliberately inoculated in a laboratory is not a pig disease, and this assessment scores only what the folder says about natural infection.
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, again relying on experience from other countries it is unlikely there will be a market effect based on diagnosis in pigs"
Basis. Section 30.3.3 records no trade measure, movement control or consumer response, and Zika is not among the orthoflaviviruses ch30 30.1 identifies as WOAH-listed.
How this level was decided
INFERRED. Pigs are naturally infected without becoming ill or infectious, and the virus is not WOAH-listed. No route to pork supply or demand. Level 1. NOTE, recorded rather than scored: Zika carries unusual public alarm because of congenital disease, so a headline linking pigs to it would not behave like this level -- but that would be a new fact, and C6 records what has happened.
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, little clinical or market imperative to develop a treatment"
Basis. Chapter 30 describes no treatment for Zika in pigs. "No clinical signs were observed" in experimentally inoculated pigs.
How this level was decided
INFERRED. Under the standing note SCORING/treatment_potential there is no imperative to treat, because pigs do not become ill. Level 1 on the second clause.
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, little clinical or market imperative to develop a vaccine"
Basis. No swine Zika vaccine is described in ch30 30.3.3. The chapter's interest in pigs is as a model in which to "test human vaccines and antivirals" rather than as a species needing one.
How this level was decided
INFERRED. No vaccine exists for pigs and none is warranted, since pigs are infected without disease and cannot amplify the virus. Level 1 on the second clause. Note the direction of travel in the chapter: pigs are proposed as a platform for testing HUMAN vaccines, which is the opposite of a swine vaccine gap.
Levels and evidence are generated from data/assignments/zika_virus.yml; the overview is authored in data/overviews/zika_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.