North American PRRSV-2

LEVELS: Highly unlikely; No human illness; Extraordinary biosecurity required; Laboratory-dependent; Moderate; Negligible; Substantial; Available but inconsistent


Register id	`prrsv_2`
Type	virus
Scientific name	Betaarterivirus americense
NCBI taxid	2499685
Evidence	2 document(s)
Assigned	2026-09-06, against criteria version `093366e352a2`

Overview

Porcine reproductive and respiratory syndrome is the most economically damaging disease of pigs in North America, and PRRSV-2 is the type that circulates there. The virus does two things: it causes abortion, stillbirths, mummified fetuses and weak piglets in the breeding herd, and pneumonia and poor growth in nursery and finishing pigs. It also suppresses the immune system, so almost every other respiratory pathogen a farm carries becomes worse when PRRSV is active. It spreads readily between farms — in pigs, semen, on vehicles and equipment, and through the air over distances that can reach several kilometres — which is why air filtration is one of the few measures that reliably keeps it out of a breeding herd. What makes it so hard to control is its variability: the virus mutates and recombines continually, immunity to one strain gives incomplete protection against another, and vaccines reduce disease without preventing infection or transmission. New virulent lineages appear periodically and sweep through the population. Herd-level elimination is achievable through closure and controlled exposure, but re-infection is a constant risk. The register scores PRRSV-1 and PRRSV-2 separately because reviewers expect the two genotypes assessed on their own terms, even though their scores come out similar.

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

How this level was decided

Level 1, and it is the worked example at this level. The chapter forecloses the question at the cell-culture level as well as the clinical one -- the virus does not infect human cells, so this is not a case of exposure without disease but of no susceptibility at all. Level 1 confirmed by direct statement.

C2 Zoonotic impact

Severity of human illness caused by the agent

No human illness: Agent does not cause illness in people

How this level was decided

Level 1, the worked example at this level, following C1. Under C2 as rescoped, pigs are not a source of human illness with this agent. Level 1 confirmed.

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

Basis. ch37 TREATS THE TWO SPECIES TOGETHER and says why, 37.1: "In this chapter, PRRSV REFERS TO BOTH SPECIES, UNLESS OTHERWISE NOTED, BECAUSE PRRSV-1 AND PRRSV-2 ACT SIMILARLY IN THE HOST." Where the chapter separates them it is noted in the cell. ch37 37.10.1: "The objective of PRRSV prevention is to STOP THE ENTRY OF PRRSV INTO NEGATIVE HERDS and stop the introduction of new variants into PRRSV-infected herds... FOR BREEDING HERDS IN SOME SWINE-DENSE REGIONS, PREVENTION MAY INCLUDE THE USE OF AIR FILTRATION OR AIR TREATMENT SYSTEMS, SUCH AS UV LIGHT. FILTRATION EFFECTIVELY REDUCES THE RISK of introducing PRRSV and other airborne agents under laboratory and field conditions... Alonso et al. (2013) estimated that AIR FILTRATION LED TO ABOUT 80% REDUCTION IN RISK of novel PRRSV introduction." On how often routine measures fail: "BIOSECURITY HAZARDS IN THE WEAN-TO-MARKET PHASE OF PRODUCTION ARE ABUNDANT AND BIOSECURITY CONTROL MEASURES ABLE TO ADDRESS ALL HAZARDS ARE GENERALLY LACKING. In the United States, it has been estimated that 55% OF GROUPS OF GROWING PIGS THAT ARE NEGATIVE FOR PRRSV AT PLACEMENT BECOME POSITIVE PRIOR TO MARKETING... By 2020, it was estimated that 41% of PRRSV-negative growing pigs became positive post placement." 37.4.5.3: "In swine dense areas, PREVENTING PRRSV INTRODUCTION AND MAINTAINING NEGATIVE HERDS REQUIRES VIGILANCE... IDENTIFYING THE EXACT ROUTE BY WHICH A HERD BECAME INFECTED CAN BE CHALLENGING IN PRACTICE." shic_2021_hp_prrsv: "Methods to prevent the entry of PRRSV into a naive swine herd include quarantine and testing of new breeding animals; sanitation and drying of transport/supply vehicles; shower-in, shower-out or use of Danish entry systems; and implementation of insect control programs (e.g., screening, habitat management, and insecticide use). Air filtration systems can also reduce the risk of PRRSV transmission." "the virus can survive for years at temperatures of -70C to -20C."

How this level was decided

Level 4, and it is the worked example at this level -- the entry the level was written around. Every element of the label is present in the chapter and named: air filtration, deployed on real US breeding herds specifically for this agent; measures beyond the routine that still fail, with four in ten negative growing-pig groups becoming positive before market despite them; and a route of entry that often cannot be identified even after the fact. The "and may still fail" clause is the 80% risk reduction: filtration works and is not sufficient. NOTE WHAT THE FRAMEWORK GIVES UP HERE, recorded on 2026-09-03 and accepted knowingly: African swine fever and PRRSV now score the same on C3. Level 4 confirmed, and the factsheet names the level 4 measure itself -- AIR FILTRATION -- alongside insect screening. This is the entry the level exists to describe.

C4 Detection difficulty

Difficulty of recognizing and confirming infection

Laboratory-dependent: The presentation does not point to this disease specifically, but local or regional laboratories can confirm it with a validated assay once it is suspected

How this level was decided

Level 2, the worked example at this level. The presentation does not name the agent -- PRDC is a syndrome with several causes and reproductive failure has many -- so it is not level 1; and confirmation is commercial real-time RT-PCR and ELISA on serum or oral fluids at any regional diagnostic laboratory, which is the level 2 label. NOTE THE POINT THE C4 REWORDING OF 2026-08-29 TOOK FROM THIS VERY AGENT: validation is the test rather than commercial availability, and PRRSV is the example that proves it, because several laboratories deliberately run in-house primers they validated themselves in preference to commercial kits. The chapter's own caution -- "variation in diagnostic performance has been reported" -- is about which assay, not about whether a validated one exists. Unchanged. The factsheet adds nothing on PRRSV diagnostics beyond what the folder holds; testing is routine and widely available.

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

Basis. ch37 TREATS THE TWO SPECIES TOGETHER and says why, 37.1: "In this chapter, PRRSV REFERS TO BOTH SPECIES, UNLESS OTHERWISE NOTED, BECAUSE PRRSV-1 AND PRRSV-2 ACT SIMILARLY IN THE HOST." Where the chapter separates them it is noted in the cell. ch37 37.10.1 gives US per-pig figures, which this criterion rarely gets: "In the United States, it has been estimated that 55% of groups of growing pigs that are negative for PRRSV at placement become positive prior to marketing, CAUSING ECONOMIC LOSSES OF APPROXIMATELY $2.29 (USD) PER PIG PLACED DUE TO INCREASED MORTALITY AND SLOWER GROWTH (Holtkamp et al. 2013). BY 2020, it was estimated that 41% of PRRSV-negative growing pigs became positive post placement AND THE LOSSES HAD RISEN TO $5.70 USD PER PIG." On the herd course, 37.6.5: acute illness across all ages for two or more weeks, then reproductive failure "for 1-4 months... and HIGH PREWEANING MORTALITY in their live-born progeny", and "WITH EFFECTIVE HERD INTERVENTIONS, HERD PRODUCTIVITY SHOULD RETURN TO PRE-OUTBREAK LEVELS IN 4-5 MONTHS." 37.1 calls the economic impact "POTENTIALLY CATASTROPHIC" and notes the virus "is IMMUNOSUPPRESSIVE by nature, rendering infected pigs susceptible to secondary infections." shic_2021_hp_prrsv: "PRRS has become an economically devastating disease of pigs found in many, but not all, swine-producing areas of the world." "HP-PRRSV causes clinical disease and death in all ages, including adult pigs and pregnant sows." "Chinese strains have not been detected in the United States to date."

How this level was decided

Level 3, the worked example at this level. The label covers losses that measurably increase cost of production but remain manageable within normal farm operations, "whether acute, chronic, or associated with endemic disease", and PRRSV is all three at once: a four-to-five-month outbreak that productivity recovers from, plus a permanent endemic drag priced by the industry at $5.70 per pig placed. NOT LEVEL 4, and the chapter supplies the reason rather than the pass: herd productivity returns to pre-outbreak levels. Level 4 is a major and potentially unsustainable increase in cost of production, and the US industry has carried this agent for thirty-five years while expanding. The word "catastrophic" in 37.1 is qualified by "potentially" and describes the worst herd, not the general case -- which is your Menangle rule. Level 3 held, with the pull upward recorded. "Economically devastating" would support level 4, and HP-PRRSV killing pigs of all ages including adults is worse than the classical picture. Held because the registered entry is PRRSV-2 as it exists in the US, where the disease is endemic and managed continuously rather than unsustainable, and the factsheet says the Chinese highly pathogenic strains have not been detected here.

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, widespread, no market imnpact"

Basis. ch37 TREATS THE TWO SPECIES TOGETHER and says why, 37.1: "In this chapter, PRRSV REFERS TO BOTH SPECIES, UNLESS OTHERWISE NOTED, BECAUSE PRRSV-1 AND PRRSV-2 ACT SIMILARLY IN THE HOST." Where the chapter separates them it is noted in the cell. PRRSV-2 has been endemic in US herds since 1991, is detected in a large proportion of growing pigs every year (41-55% of negative groups converting before market, ch37 37.10.1), and no trade measure, movement restriction or consumer response to a PRRSV diagnosis is recorded anywhere in the chapter. The chapter discusses PRRSV economics entirely as on-farm production loss. shic_2021_hp_prrsv: "PRRS is an OIE-listed disease and must be reported internationally according to the Terrestrial Animal Health Code."

How this level was decided

INFERRED. Level 1 under the standing note SCORING/market_impact, and this is the strongest instance of that note in the register rather than a marginal one: PRRSV is diagnosed in US pigs continuously and at enormous scale, has been for three decades, and the market has never responded. The absence is about as well observed as an absence can be. This is the only one of the eight criteria on which PRRSV is not already a worked example, and level 1 is why -- it is the cell where the most economically damaging endemic disease in US swine production scores at the bottom, because C6 asks about disruption to pork and pig MARKETS and not about cost to producers. LEVEL 1 HELD, AND THE NEW FACT IS WORTH STATING BECAUSE IT LOOKS LIKE IT SHOULD MOVE THE CELL AND DOES NOT. PRRS is OIE-listed with mandatory international reporting, which on most entries lifts C6. It does not here, because the standing note makes the test observed behaviour rather than listing status: PRRSV is endemic in US herds and has been diagnosed continuously for over thirty years with no market response to a diagnosis. That is the endemic-and-already-diagnosed case at level 1, and it is the clearest illustration in the register that listing status and market impact are different questions.

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

How this level was decided

Level 3, the worked example at this level, alongside PEDV. Both halves hold: no effective treatment of any kind exists, and outcomes would meaningfully improve if one did. THE STANDING NOTE SCORING/treatment_potential MAKES THIS EXPLICIT and PRRSV is the agent it was partly written about -- C7 scores the value of a treatment that does not exist, not the industry's current willingness to use one, and "we don't treat viral diseases because no antiviral available" is the prevailing opinion the criterion measures against rather than evidence about it. The note also names the specific gain that would count here: your own words on the coronaviruses, "IT WOULD BE GOOD TO HAVE A TREATMENT AVAILABLE, PARTICULARLY TO DEAL WITH CHRONIC INFECTIONS THAT CAUSE PERSISTENT DISEASE IN BREEDING HERDS, OR TO TREAT AFFECTED JUVENILES AND REDUCE HOW LONG THEY ACT AS A SOURCE OF INFECTION FOR OTHER SITES." That describes PRRSV exactly. Level 3 confirmed. No pathogen-directed treatment for a disease of unquestioned clinical significance, which is the genuine gap level 3 is for.

C8 Vaccine availability

Availability of effective vaccines or bacterins

Available but inconsistent: Commercial or autogenous vaccines exist in the US but protection may be inconsistent

How this level was decided

Level 2, the worked example at this level, and the chapter states the label almost verbatim -- available but protection may be inconsistent. Commercial PRRSV-2 MLV vaccines are available globally and are standard practice in US breeding herds, so this is not level 3; and the failures are catalogued -- variable field efficacy, inadequate cross-protection against the variants actually circulating, non-responders even after repeated dosing, and reversion to virulence. The AASV herd classification system has a whole category for it, Positive Stable WITH VACCINATION (II-vx), which is what an industry builds when a vaccine controls a disease without clearing it. Unchanged. Level 2: modified live and killed PRRSV vaccines are widely used and their protection is notoriously variable against heterologous strains, which is available-but-inconsistent exactly.

Levels and evidence are generated from data/assignments/prrsv_2.yml; the overview is authored in data/overviews/prrsv_2.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.

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