Chikungunya virus
LEVELS: Highly unlikely; Moderate; Extraordinary biosecurity required; No validated assay; Negligible; Negligible; Little; Available, or not needed
| Register id | chikungunya_virus |
| Type | virus |
| Scientific name | Chikungunya virus |
| NCBI taxid | 37124 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Chikungunya virus is a mosquito-borne alphavirus that causes a debilitating human illness — fever and muscle pain, with joint pain in more than 95% of patients that can persist for years, a rash in about half, and serious disease in infected newborns. It is spread by Aedes aegypti and Aedes albopictus and cycles between primates and mosquitoes in Africa and directly between people and mosquitoes in urban settings. Pigs play no known part in it. Natural infection of swine has never been documented, no lesions in pigs have ever been described, and in two separate experimental studies pigs inoculated with the virus developed no viraemia and no clinical signs, though they did produce neutralising antibody. There are no diagnostic tests validated for pigs and no information at all on how the virus would behave in one. It is on this register because it appears on the published SHIC viral matrix and because competent mosquito vectors exist in the United States, so introduction through travellers is a continuing possibility — but the risk it poses is to people, not to pigs. It is not a WOAH-listed disease and there are no import restrictions from affected countries.
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, and it was his ruling that fixed the criterion. 2026-08-26: "C1 means reaching humans from pigs - fix the L1 label - I think that is correct interpretation. In this case, there is a reverse zoonosis potential from Chikungunya but evidence seems like pigs are not a risk to humans. It is different for different related viruses like JEV." The L1 label was rewritten from "No evidence that the agent infects humans" to "No evidence that pigs transmit the agent to humans", and C1 was re-scored from INFERRED to SUPPORTED against the corrected label. Recorded here rather than only as a note so the ruling is attributable to him, which a note cannot be.
Standing note. CONTEXT, not a ruling -- the ruling is the confirmation above. The pig is a dead-end host: inoculated pigs develop no viremia, so a pig cannot infect the mosquito that would infect a person. The plausible direction is the reverse, a viremic human to a mosquito to a pig, which is how pigs come to carry antibodies at all and explains 35% seroprevalence in 1964 Thai swine without making pigs a source. The framework scores pig-to-human only. Same dead-end reasoning applies to Ross River, Sagiyama, dengue, Zika, eastern equine encephalitis and Murray Valley.
Basis. SHIC 2021: "Natural CHIKV infection has not been documented in swine." "In one experimental study, pigs inoculated with CHIKV subcutaneously did not develop viremia or clinical signs of disease, although an antibody response was detected via the plaque reduction neutralization test." Repeated in a 2016 study of North American species: "no pigs developed detectable viremia or clinical signs of disease". The maintenance cycles do not involve pigs -- "In Africa, CHIKV cycles between non-human primates and Aedes spp.... The urban cycle is seen where large populations of humans and urban Aedes spp. co-exist, maintaining human-mosquito-human transmission."
How this level was decided
Eric ruled on 2026-08-26 that C1 means reaching humans FROM PIGS, and the L1 label was rewritten from "No evidence that the agent infects humans" to "No evidence that pigs transmit the agent to humans" -- the old wording was false for chikungunya and would have misled anyone reading the line alone. Under the corrected label the evidence settles this directly rather than by inference: a pig inoculated with CHIKV develops no viremia, and without viremia it cannot infect the mosquito that would infect a person. The pig is a dead-end host. Level 1. The plausible direction is the reverse -- a viremic human, a mosquito, a pig -- which is how pigs come to carry antibodies at all, and explains 35% seroprevalence in 1964 Thai swine without making pigs a source. The framework scores pig-to-human only. Contrast JEV, where pigs amplify the virus and genuinely raise human risk; Eric: "It is different for different related viruses like JEV."
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. SHIC 2021: "Most people infected with CHIKV develop clinical disease; however, death is infrequent." "In adults, fever and myalgia are very common, followed by polyarthralgia, which occurs in more than 95% of patients. In some instances, arthritic disease can persist for years. A maculopapular pruritic rash... is seen in 40-50% of patients." "Neonates infected with CHIKV can develop serious disease affecting the heart, skin, and brain. Bleeding and disseminated intravascular coagulation have also been observed."
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. Returns to the level it held before 2026-09-01. SHIC 2021 in the folder: "Most people infected with CHIKV develop clinical disease; however, DEATH IS INFREQUENT", with fever, myalgia and polyarthralgia that can persist. Clinically important, rarely fatal -- level 3.
PREVIOUS ANSWER, written under the pig-attribution reading: MOVED L3 -> L1 on 2026-09-01 by the C2 rescoping, and this entry is where the whole question started. Eric fixed C1 on chikungunya on 2026-08-26 -- "C1 means reaching humans from pigs" -- and this entry has sat at C1 level 1 ever since, on the source itself: the maintenance cycles do not involve pigs and experimentally inoculated pigs developed no viraemia. Chikungunya is a serious human disease, and none of it comes from a pig. Under the rescoped criterion that is level 1. THE LABEL MUST NOT BE READ AS A FINDING THAT CHIKUNGUNYA IS MILD -- it records that pigs are not a source.
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 at level 4 on the C3 review sheet. "l4, insect vector, would require air filtration"
Basis. SHIC 2021: "The main vectors for CHIKV are Aedes aegypti and Ae. albopictus." On the US specifically: "There is continual risk of CHIKV introduction to the United States through travelers. Additionally, there is potential for autochthonous transmission since competent mosquito vectors are present." On control: "There are no specific control measures for CHIKV in pigs. Standard biosecurity practices should be in place on swine premises." Prevention "is based on control of mosquito vectors".
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: RENUMBERED L4 -> L5 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 only route to a pig is an infected mosquito, and the source states that competent vectors are already present in the US. An arthropod vector is named in the L4 label as a reservoir outside the pig industry, and no farm biosecurity excludes mosquitoes -- the source says as much, offering only vector control and standard biosecurity. This is a US reservoir, not an imported one, so the rule that stopped Hendra reaching L4 does not apply here. Note this scores the ROUTE, not the consequence: the same source says natural infection has never been documented in swine, which is why C5 is level 1.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "L4, little to no experience with this in the US, much less in US diagnostic labs, is almost certainly a L4 situation"
Basis. SHIC 2021, under Gaps in Preparedness: "Little is known about CHIKV infection in swine. Natural infections have not been reported and clinical signs of disease have not been described." And directly: "There are no diagnostic tests validated for pigs." Under Diagnosis, every method named is a human one -- "Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) is used for diagnosis in humans. Serology (IgM-capture ELISA) can be used to rule out CHIKV... A positive result can be confirmed by the plaque reduction neutralization test (PRNT)."
How this level was decided
INFERRED, AND LEVEL 3 IS ARGUABLE. Nothing would prompt suspicion in the first place: no clinical signs in pigs have ever been described, so there is no presentation to recognise. And the source states outright that no test is validated for pigs. That is level 4. The counter-argument for level 3 is that PRNT, HI and CF assays were in fact run on pig sera in the serosurveys this document summarises, so a reference laboratory could confirm it -- unvalidated is not the same as nonexistent. Level 4 is scored because an assay borrowed from another species and never validated in this one is not something a diagnostician can rely on.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
Basis. SHIC 2021: "Natural CHIKV infection has not been documented in swine." "No lesions caused by CHIKV have been documented in swine." Experimentally, "pigs inoculated with CHIKV subcutaneously did not develop viremia or clinical signs of disease", and in the 2016 North American study "no pigs developed detectable viremia or clinical signs of disease, although neutralizing antibodies were identified 14 days post-infection". "No information was found regarding the pathogenesis of CHIKV in swine."
How this level was decided
No natural infection, no clinical signs under experimental inoculation, and no lesions ever described. There is no mechanism by which an infected farm incurs cost. Level 1, and this is one of the few cells in the pilot where the evidence states the answer about as directly as evidence can.
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
Basis. SHIC 2021, under Disease Reporting: "CHIK is not an OIE-listed disease. There are no restrictions for importation of animals from countries or zones affected by CHIKV. Any suspicious clinical or necropsy findings should always be reported to the USDA and your State Animal Health Official."
How this level was decided
Not notifiable, and the source says explicitly that no import restriction attaches to affected countries or zones. With no disease in pigs to trigger movement controls and no trade instrument to invoke, there is no route to a material effect on the supply of or demand for pork. Level 1. Unusually for this criterion, the level is stated by the evidence rather than inferred -- most entries have nothing on markets at all.
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. "agree c7l1". No antiviral exists, but pigs have no disease to recover from, so the treatment opportunity is negligible rather than substantial.
Basis. SHIC 2021: "There are no alphavirus-specific antiviral drugs. Supportive care includes use of analgesics and anti-inflammatory drugs. Experimentally, a number of antivirals have demonstrated in vitro efficacy against CHIKV; however, most have not been tested in animal models or have been shown to be less effective in vivo." Set against: "Natural CHIKV infection has not been documented in swine" and pigs inoculated experimentally "did not develop viremia or clinical signs of disease".
How this level was decided
C7 scores the size of the opportunity, not whether a product exists. No antiviral exists, which alone would suggest level 3 -- but level 1 is satisfied by its second clause, "animals recover acceptably without it", and pigs have no disease to recover from. A treatment for a condition that does not occur cannot improve outcomes. INFERRED because no document discusses treating pigs; the level is reasoned from the absence of disease. This is the same shape of call as influenza D C7, resolved the same way.
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, experimental infection has been confirmed but natural infection has not, so at this time we have no clinical or economic justification to rate any higher than L1"
Basis. The SHIC review states that no vaccine exists for humans or animals, and that natural infection of swine has never been documented -- inoculated pigs developed no viremia and no clinical signs.
How this level was decided
MOVED L3 -> L1 by the rewording. INFERRED. The pig is a dead-end host with no disease to prevent, so vaccinating pigs is not justified on any clinical or economic ground. Eric ruled the parallel point at C1, that the framework scores pig-to-human only. Human chikungunya vaccines are a human health question and outside this register.
Levels and evidence are generated from data/assignments/chikungunya_virus.yml; the overview is authored in data/overviews/chikungunya_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.