Ross River Virus
LEVELS: Highly unlikely; Moderate; Routine biosecurity keeps it out; Reference or research laboratory required; Negligible; NOT ASSIGNED; Little; Available, or not needed
| Register id | ross_river_virus |
| Type | virus |
| Scientific name | Ross River virus |
| NCBI taxid | 11029 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
Ross River virus is a mosquito-borne alphavirus endemic to Australia, Papua New Guinea and Indonesian Papua, and it is an important cause of human illness there — typically joint pain or arthritis affecting the limbs, sometimes with fever and rash, occasionally persisting for a long time. Its natural cycle runs between mosquitoes and macropod marsupials, kangaroos and wallabies, with people drawn in; during epidemics in densely populated areas the virus reaches high enough levels in human blood that a direct human-mosquito-human cycle is thought to operate. Pigs have no part in any of this. The reference chapter states plainly that Ross River virus is not known to cause disease in pigs, and experimental infection of juvenile domestic and feral pigs produced either no detectable virus or only a moderate short-lived viraemia. It has never occurred in the Americas, and its establishment elsewhere is thought unlikely without both abundant macropods and the right mosquitoes. There is no vaccine and no treatment for pigs, and no disease in pigs for either to address.
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. ch41 41.6.2.4: "RRV is regularly transmitted via a human-mosquito-macropod marsupial-mosquito-human cycle. However, in epidemics in densely populated areas, a direct human-mosquito-human route is believed to occur because of the high levels of viremia reached in humans." 41.6.3.4: "RRV is not known to cause disease in pigs. Experimental infection of juvenile domestic and feral pigs resulted in no detectable virus or only moderate viremia at 0-5 DPI."
How this level was decided
Level 1, and the chapter supplies the mechanism rather than leaving it to the standing note. The maintenance cycle runs through macropods and humans, and humans themselves reach the high viraemia that sustains epidemic transmission -- pigs reach no detectable virus or only moderate viraemia experimentally, which is too little to seed a mosquito. Eric's standing note at chikungunya_virus/zoonotic_potential names this virus specifically: "Same dead-end reasoning applies to Ross River, Sagiyama, dengue, Zika, eastern equine encephalitis and Murray Valley." The framework scores pig-to-human only, and a pig that does not seed a mosquito is not a source however much virus is in the neighbourhood. Unchanged. The Getah factsheet is placed in this folder as a thin alphavirus comparison and says nothing about Ross River transmission from pigs.
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. ch41 41.6.1: "Infection with RRV may cause disease in humans, typically showing peripheral polyarthralgia or arthritis, sometimes with fever and rash."
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. Polyarthritis that is debilitating and prolonged but not life-threatening.
PREVIOUS ANSWER, written under the pig-attribution reading: MOVED L3 -> L1 on 2026-09-01 by the C2 rescoping. Same shape as chikungunya and the same reasoning Eric applied to it: the maintenance host is a macropod, pigs are not part of the transmission cycle, and C1 is level 1 on that ground. Ross River virus causes a real and sometimes prolonged polyarthritis in people, and no part of that burden is attributable to pigs. Level 1 records the absence of a pig-to-human route, not the absence of human disease. 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
INFERRED — reasoned, not stated. The evidence implies this level rather than stating it. The reasoning is below.
Corrected by Eric from L4 Extraordinary biosecurity required. Reason: "c3l2, Hendra was set at this level due to the fact the reservoir does not exist in the US and we will rate RRV the same. We do not have an appropriate combination of reservoir and arthropod to rate this any higher." [RENUMBERED level 2 to 3, from_level 3 to 4 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.]
Basis. ch41 41.6.2.4: "RRV is endemic to Australia, Papua New Guinea, and Irian Jaya, Indonesia. Several RRV epidemics occurred in South Pacific islands in 1979-1980, but it did not become permanently established there." "The main vectors are Aedes vigilax, Aedes camptorhynchus, Aedes polynesiensis, and Culex annulirostris." "the threat may be low for RRV to emerge in areas where the macropod population and the density of major vector species are not abundant". shic_getah (placed thin, alphavirus context): "GETV prevention in endemic areas centers on mosquito control (i.e., remove standing water where mosquitoes lay eggs, use insecticides to kill both mosquito larvae and adults, house animals indoors/in screened buildings, etc.)." "Alphaviruses are not stable in the environment."
How this level was decided
MOVED L3 -> L4 on 2026-09-01 by the five-level rework. This is the Hendra reasoning: the maintenance host is a macropod, absent from the US, so there is no reservoir to establish and this is not L5. What remains is a mosquito-borne virus, and no quarantine or C&D programme excludes a mosquito, so the machine reading is L4. NOTE FOR ERIC: you corrected this to the old L2 on the ground that the onward source here would be other pig herds, which renumbers to L3 and still stands as your ruling. The gap between your L3 and this L4 is exactly the question of whether a US incursion would move pig-to-pig or vector-to-pig, and it is worth one look on the C3 sheet. 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. LEVEL 3 ON ERIC'S RULING of 2026-08-31: "c3l2, Hendra was set at this level due to the fact the reservoir does not exist in the US and we will rate RRV the same. We do not have an appropriate combination of reservoir and arthropod to rate this any higher" -- renumbered to 3 when the scale changed, the decision unaltered. CORRECTION TO THIS PASS, 2026-09-06: the re-assessment wrote "level 4 confirmed" and argued from the Getah factsheet's mosquito control measures. That contradicted his ruling and was reached by reading the stored level rather than the resolved one. His point stands and the factsheet does not touch it: the vector-plus-reservoir combination that would make RRV excludable-with-difficulty is not present here. The factsheet is still useful in the folder.
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. ch41 41.6.4: "For RRV, evidence of seroconversion of immunoglobulin G in paired sera by ELISA is indicative of a recent infection. Detection of immunoglobulin M is diagnostically unreliable, particularly in endemic areas. RRV RT-PCR assays have been described for testing equine sera and should be used in conjunction with serology."
How this level was decided
The only assays described are an equine RT-PCR and paired-serum ELISA, with IgM explicitly unreliable, and nothing in a pig would prompt a test since RRV causes no disease in them. Reference or research laboratory work. Level 3. Unchanged.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
Basis. ch41 41.6.3.4: "RRV is not known to cause disease in pigs. Experimental infection of juvenile domestic and feral pigs resulted in no detectable virus or only moderate viremia at 0-5 DPI."
How this level was decided
The chapter states it directly and backs it with experimental infection that produced no disease. No measurable effect on cost of production. Level 1. Unchanged.
C6 Market impact
Duration of material disruption to pork and pig markets
NOT ASSESSED — no evidence in folder. No level was assigned on this criterion. This is a statement about what the evidence folder holds, not a finding about the agent.
Corrected by Eric from L1 Negligible. Reason: CONFIRMED AS NOT ASSESSABLE. "no level assigned, again like Hendra I don't think we can predict how the market would behave. It would be so unusual an event that I don't think it would fly entirely below the radar. I think this puts it into KISS analysis?" The pass had scored level 1 on the ground that a virus causing no disease in pigs has no route to the market. He is overriding that, and the reasoning is the same he gave for hendra_virus C6 -- the event is unprecedented, so there is no basis to predict the response, and level 1 would assert confidently that nothing would happen.
Basis. Section 41.6 records no trade measure, movement control or consumer response for RRV. The virus causes no disease in pigs and is absent from the Americas.
How this level was decided
INFERRED. An agent that does not make pigs ill has no route to pork supply or demand even if it arrived. Level 1. Unchanged. NOTE: this cell is null on Eric's ruling of 2026-09-02, on the ground that no market anywhere has been observed reacting to Ross River in a pig. The Getah factsheet does not supply such a precedent, so the null stands.
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. ch41 41.6.3.4: "RRV is not known to cause disease in pigs." No treatment for pigs is described. shic_getah: "There are no alphavirus-specific antiviral drugs."
How this level was decided
No treatment exists and none is needed -- the second clause of level 1, on an explicit statement that the agent causes no disease in this species. Level 1 held. The absence of any alphavirus antiviral is now sourced rather than assumed, though under the standing note the level rests on there being no established swine disease to treat rather than on the absence of a product.
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. ch41 41.6.5: "No vaccine is available for RRV." 41.6.3.4: "RRV is not known to cause disease in pigs."
How this level was decided
Level 1 on the second clause of the reworded criterion. No vaccine exists for any species, but vaccinating pigs against a virus that does not make them ill is not a justified need. Under the old wording this would have been level 3. Unchanged.
Levels and evidence are generated from data/assignments/ross_river_virus.yml; the overview is authored in data/overviews/ross_river_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.