Ovine Gammaherpesvirus 2 - Porcine Malignant Catarrhal Fever
LEVELS: Highly unlikely; No human illness; Housing alone keeps it out; Reference or research laboratory required; Negligible; Negligible; Little; Available, or not needed
| Register id | ovine_gammaherpesvirus_2_porcine_malignant_catarrhal_fever |
| Type | virus |
| Scientific name | Ovine gammaherpesvirus 2 |
| NCBI taxid | 10398 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Ovine gammaherpesvirus 2 is a harmless passenger in sheep and goats and a lethal infection in the other species it reaches, causing malignant catarrhal fever in cattle, bison, deer and — rarely — pigs. Transmission is mainly through nasal secretions, by contact or aerosol, chiefly from lambs under a year old, and the susceptible species are thought to be dead-end hosts that do not pass the virus on. Porcine malignant catarrhal fever is very rare and poorly documented. For decades overt disease in pigs seemed confined to Norway; individual cases have since been reported from Finland, Sweden and North America. In an affected pig the disease is severe — high persistent fever and death within two to four days — but the reference chapter's judgment is that, even allowing for underdiagnosis, it does not pose a significant threat to the pig population. Two things keep case numbers low: pigs and sheep usually do not share close quarters, and the clinical signs are subtle and non-specific while the diagnostic assays are not widely available, so an unknown number of milder cases recover unrecognised. The differential includes Aujeszky's disease and both swine fevers. There is no treatment and no vaccine; the only advice is to keep pigs and sheep apart. Human infection has never been reported.
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. ch31 31.5.3, a Public Health section of its own, consisting of one sentence: "OVGHV2 INFECTION IN HUMANS HAS NOT BEEN REPORTED." The chapter gives public health sections to pseudorabies, porcine cytomegalovirus and the lymphotropic herpesviruses as well, so the brevity here is an answer rather than an omission. 31.5.4 records the host range it does recognise: "OvGHV2 affects a broader range of natural hosts including sheep, goats, cattle, bison, swine, mule deer, and, at least experimentally, rabbits and hamsters."
How this level was decided
Level 1, and this is the cleanest C1 in the batch. The chapter states the answer directly rather than leaving it to be inferred, and it lists the host range in a separate section without people in it. Level 1 is "no evidence that pigs transmit the agent to humans", which is what a dedicated section saying human infection has not been reported establishes.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch31 31.5.3: "OvGHV2 infection in humans has not been reported."
How this level was decided
Level 1. No human illness exists to grade, and under C2 as rescoped level 1 records that pigs are not a source of human illness with this agent.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Housing alone keeps it out: Raising pigs indoors and off soil breaks the cycle, so no ongoing biosecurity program is needed and only outdoor herds stay exposed
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. "c3l2, by default putting pigs indoors will exclude agent from farm" 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. Recorded on the old scale as level 2, from_level 5.
Basis. ch31 31.5.4: OvGHV2 is the sheep-associated agent, and "SHEEP AND GOATS REMAIN HEALTHY UPON INFECTION, whereas the other susceptible hosts develop MCF". "The exact mode of transmission of OvGHV2 is uncertain, but there is convincing evidence that the predominant mode is VIA NASAL SECRETIONS by contact or aerosol, MAINLY FROM LAMBS UNDER 1 YEAR OLD." "MCF-SUSCEPTIBLE SPECIES ARE THOUGHT TO BE DEAD-END HOSTS THAT DO NOT TRANSMIT VIRUS, thus limiting the spread of disease during outbreaks." "PIGS AND SHEEP USUALLY DO NOT SHARE CLOSE ENVIRONMENTS, WHICH MIGHT ALSO EXPLAIN THE INFREQUENT PRESENTATION OF MCF IN PIGS", though a case is recorded in a Vietnamese pot-bellied pig kept near sheep and goats in a zoological garden. 31.5.10, the whole of prevention and control: "Despite the low rate of porcine MCF in Europe and North America, it is important to DISCOURAGE CONTACT BETWEEN PIGS AND SHEEP to minimize any infections."
How this level was decided
MOVED L5 -> L2 on 2026-09-03. This is the pass coming round to Eric's ruling of 2026-09-02 rather than a fresh judgment -- he had already corrected the cell to level 2 ("by default putting pigs indoors will exclude agent from farm"), and applying the exclusion test across the whole level 5 block reaches the same answer here: the reservoir is the US sheep flock, the route is nose-to-nose or aerosol from lambs, and not housing pigs beside sheep closes it. His correction is now a no-op rather than an override, which is the right state for a ruling the evidence has caught up with.
EARLIER REASONING, kept because it is the evidence read: MOVED L5 -> L2 on 2026-09-03. This is the pass coming round to Eric's ruling of 2026-09-02 rather than a fresh judgment -- he had already corrected the cell to level 2 ("by default putting pigs indoors will exclude agent from farm"), and applying the exclusion test across the whole level 5 block reaches the same answer here: the reservoir is the US sheep flock, the route is nose-to-nose or aerosol from lambs, and not housing pigs beside sheep closes it. His correction is now a no-op rather than an override, which is the right state for a ruling the evidence has caught up with.
EARLIER REASONING, kept because it is the evidence read: Level 5, and FLAGGED AS A LEVEL 2 OR 5 JUDGMENT, because two rules Eric has set point in opposite directions and the answer decides how the register treats a whole family of entries. LEVEL 5 IS SCORED FOR CONSISTENCY WITH THREE ENTRIES OF IDENTICAL STRUCTURE. Anthrax, Listeria and Trichinella all sit at C3 level 5 with C5 level 1: a permanent US reservoir outside the pig industry, essentially no disease in modern herds, and no farm or industry action that removes the reservoir. This entry is that structure exactly -- the reservoir is the US sheep flock, sheep are unharmed carriers, no pig-industry action touches them, and the pig is a dead-end host. THE CASE FOR LEVEL 2 is his clarification of 2026-09-02, that the ladder is five tiers of one biosecurity programme and housing indoors is its first rung: an indoor US herd never meets a lamb, the chapter's only control advice is to keep pigs away from sheep, and that is a siting decision rather than a programme. He ruled vesicular exanthema to level 3 on comparable reasoning -- an ever-present marine reservoir whose only bridge to pigs is a feed practice. IF LEVEL 2 IS RIGHT HERE, anthrax, Listeria and Trichinella need re-reading with it, which is why the cell is flagged rather than quietly scored low.
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. ch31 31.5.4: cases are few, and this "MAY REFLECT THE LIMITED AVAILABILITY OF MOLECULAR DIAGNOSTIC ASSAYS and the possibility that a considerable number of cases may not be recognized due to abortive forms with full clinical recovery". 31.5.1: "Porcine MCF is a very rare, POORLY DOCUMENTED disease of swine. The small number of reported cases of MCF is mainly based on the fact that the CLINICAL SIGNS CAN BE SUBTLE AND NONSPECIFIC AND DIAGNOSTIC TOOLS ARE NOT GENERALLY AVAILABLE." 31.5.8: the differential is "AD in particular, but also classical swine fever, African swine fever, porcine enterovirus (teschovirus) infection, PCV2 infection, and rabies"; "since lesions found at necropsy are NOT SUFFICIENTLY SPECIFIC for an etiologic diagnosis, HISTOPATHOLOGY INCLUDING MOLECULAR TESTS IS NECESSARY to confirm MCF". WOAH recognises histopathology as the definitive test in cattle; a competitive inhibition ELISA using mAb 15A exists, a direct ELISA has been developed, and conventional and real-time PCR assays "allow sensitive confirmation of the presence of OvGHV2 in infected pigs". 31.5.2: "there is NO PERMISSIVE CELL CULTURE SYSTEM for OvGHV2."
How this level was decided
Level 3. Validated assays plainly exist -- two ELISA formats and both conventional and real-time PCR, with an internationally recognised histopathological standard behind them -- so this is not level 4. What puts it at level 3 rather than level 2 is the chapter's own explanation for why so few cases are reported: the diagnostic tools are not generally available, and it names that as a reason cases are missed. An assay held at reference and research level, for a disease whose signs are subtle and whose differential opens with pseudorabies and African swine fever, is the level 3 label. The virus cannot be cultured, so isolation is not a fallback.
C5 Production cost
Financial impact on the infected farm's cost of production
Negligible: No measurable effect on cost of production
Basis. ch31 31.5.1: "PORCINE MCF IS A VERY RARE, POORLY DOCUMENTED DISEASE OF SWINE... COMPARED WITH OTHER HERPESVIRAL DISEASES OF PIGS, PORCINE MCF DOES NOT POSE A SIGNIFICANT THREAT TO THE PORCINE POPULATION, EVEN IF UNDERDIAGNOSED IN THE FIELD." "For decades, overt disease in swine seemed to be limited to Norway, but has since occurred in Finland, Sweden, and North America", as individual reports. 31.5.6: in affected individuals the disease is severe -- "the clinical course of the disease is usually short, WITH DEATH GENERALLY OCCURRING AFTER 2-4 DAYS", with high persistent fever, and "pregnant sows may abort before death occurs". 31.5.4 also allows that some cases recover: "abortive forms with full clinical recovery".
How this level was decided
Level 1, on the chapter's own assessment rather than on an inference: it says in terms that porcine MCF does not pose a significant threat to the porcine population, and it says so while allowing that the disease is underdiagnosed. The individual pig that gets MCF usually dies, but the reported world literature is a handful of cases and small clusters. No measurable effect on cost of production. This is scored level with anthrax, Listeria and Trichinella, all of which are severe in the individual animal, essentially absent from modern herds, and level 1 here -- the same family this entry belongs to on C3.
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, no evidence to suggest infection will have a market impact"
Basis. A very rare sporadic disease of individual pigs, with no trade measure, movement control or consumer response recorded anywhere in section 31.5, and no notifiability described for the porcine form.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact, a disease that has been diagnosed in North American pigs without any market move on record is level 1. There is a precedent to reason from here rather than a void -- cases have occurred in North America and nothing followed -- so this is the scoreable side of the line the note draws.
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. No treatment for porcine MCF is described anywhere in chapter 31. 31.5.9: "Prophylactic immunization is not available." 31.5.10 offers only avoidance: "it is important to discourage contact between pigs and sheep to minimize any infections." 31.5.6: the clinical course is short, with death generally occurring after 2-4 days, though 31.5.4 allows "abortive forms with full clinical recovery".
How this level was decided
Level 1, on Eric's Trichinella boundary rather than on the recovery clause. He drew it on 2026-09-02: where an agent can be kept off a farm by management, there is no imperative to develop a treatment for pigs, and that is what separates Trichinella at level 1 from Mycobacterium avium complex at level 2. Porcine MCF is more excludable than Trichinella -- it needs pigs and sheep in the same airspace, which US confinement production does not produce -- and the chapter's own control advice is exactly that avoidance. The disease is severe in the individual pig and there is nothing to give it, but the criterion asks whether a treatment would be worth developing, and for a disease this rare and this avoidable it would not.
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. ch31 31.5.9, the whole immunity section: "PROPHYLACTIC IMMUNIZATION IS NOT AVAILABLE." 31.5.1: porcine MCF "does not pose a significant threat to the porcine population". 31.5.2: there is no permissive cell culture system for OvGHV2, which is the practical obstacle to building one.
How this level was decided
Level 1 on the "not needed" clause of the 2026-08-28 rewording. There is no vaccine and no prospect of one -- the virus cannot even be grown -- so the whole question is whether the disease would justify vaccinating, and a very rare condition that the chapter says is not a significant threat, and that is avoided by not housing pigs beside sheep, does not. Level 3 is reserved for a genuine gap where the disease would warrant a product, and this is not that.
Levels and evidence are generated from data/assignments/ovine_gammaherpesvirus_2_porcine_malignant_catarrhal_fever.yml; the overview is authored in data/overviews/ovine_gammaherpesvirus_2_porcine_malignant_catarrhal_fever.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.