Glässer's Disease
LEVELS: Highly unlikely; No human illness; Already in the herd; Laboratory-dependent; Moderate; Negligible; Some; Available but inconsistent
| Register id | glaesserella_parasuis |
| Type | bacteria |
| Scientific name | Glaesserella parasuis |
| NCBI taxid | 738 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Glaesserella parasuis, until recently called Haemophilus parasuis, causes Glässer's disease — inflammation of the membranes lining the chest and abdomen, the joints and the brain. The organism is a normal inhabitant of the pig's upper airway and is present in herds worldwide; piglets pick it up from the sow within days of birth. Disease appears when that balance is disturbed, typically in four- to eight-week-old pigs as maternal immunity fades, after mixing, transport or other stress, or when pigs meet a strain they have not seen before. Peracute cases are found dead; acute cases run a high fever, breathe hard, develop swollen painful joints and may show nervous signs. Morbidity and mortality are usually 5–10% but rise sharply alongside PRRSV, PCV2 or influenza. Fifteen serovars are recognised and they differ greatly in virulence, with the strains that invade the body genetically distinct from those that merely live in the nose. That diversity is the practical problem: immunity is largely serovar-specific, so commercial bacterins protect against what is in them and farms often need an autogenous vaccine made from their own isolate.
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. ch50 HAS NO PUBLIC HEALTH SECTION, which is itself informative in a book whose chapters give one to every agent with a human question -- ch43 gives APP one in order to say there is no risk, ch48 gives Erysipelothrix one, ch44 gives Bordetella one. What ch50 says instead, in 50.3: "DOMESTIC PIGS AND WILD BOARS ARE THE ONLY KNOWN HOSTS FOR THIS BACTERIUM." No human infection with G. parasuis is described anywhere.
How this level was decided
Level 1. The chapter states host restriction to Sus scrofa outright, so there is no route to a person to assess. This is a structured silence of the strongest kind: the same authors and the same book raise public health whenever there is a question, and here they instead say the host range is two forms of one species.
C2 Zoonotic impact
Severity of human illness caused by the agent
No human illness: Agent does not cause illness in people
Basis. ch50 50.3: "Domestic pigs and wild boars are THE ONLY KNOWN HOSTS for this bacterium." No human illness with G. parasuis is described anywhere in the chapter.
How this level was decided
Level 1, following C1. Under C2 as rescoped, pigs are not a source of human illness with this agent because it does not infect people.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Already in the herd: Present in most herds, or carried by pigs themselves, so there is no introduction event to prevent
Basis. ch50 50.3: "GLAESSERELLA PARASUIS IS A MEMBER OF THE NORMAL RESPIRATORY MICROBIOTA AND IS UBIQUITOUS IN SWINE HERDS WORLDWIDE. COLONIZATION OF THE UPPER RESPIRATORY TRACT OF PIGLETS BY G. PARASUIS OCCURS SOON AFTER BIRTH THROUGH CONTACT WITH THE SOW... As many as four to five strains can be isolated from a herd at a given time, and UP TO 16 DIFFERENT STRAINS were isolated in a single farm during one production cycle." 50.9 on whether exclusion is even wanted: "ALTHOUGH ELIMINATION OF G. PARASUIS FROM A HERD IS DIFFICULT due to early maternal colonization of neonatal piglets, it may be achieved through cesarean derivation into pig-free premises. HOWEVER, EXCEPT IN CIRCUMSTANCES WHERE STANDARDS OF BIOSECURITY ARE EXCEPTIONAL, ELIMINATION IS NOT RECOMMENDED BECAUSE SUCH HERDS ARE HIGHLY SUSCEPTIBLE TO SEVERE OUTBREAKS IF EXPOSED."
How this level was decided
Level 1, and it is the worked example at this level. The piglet acquires it from its dam within days of birth, a single farm can carry sixteen strains at once, and the chapter advises AGAINST elimination even where it is technically possible, because a naive herd is a worse place to be. There is no introduction event to prevent, and the profession has decided there should not be one.
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
Basis. ch50 50.7: "The clinical signs and lesions described for G. parasuis systemic infection ARE NOT PATHOGNOMONIC of this agent, and other agents must be included in a differential diagnosis" -- nonhaemolytic E. coli, Mycoplasma hyorhinis, Streptococcus suis, Erysipelothrix and Mycoplasma hyosynoviae are all listed. On confirmation: "G. PARASUIS IS A FASTIDIOUS MICROORGANISM WITH LIMITED SURVIVAL AT ROOM TEMPERATURE AND SPECIAL REQUIREMENTS FOR IN VITRO GROWTH. The chances of isolating G. parasuis can be considerably improved by utilizing swabs with Amies transport media and submitting samples under refrigeration... WHILE G. PARASUIS ISOLATION CAN BE A DIFFICULT TASK, IT IS IMPORTANT TO OBTAIN AN ISOLATE for antibiotic sensitivity assessment and typing. PCR IS A SENSITIVE AND SPECIFIC METHOD TO DETECT G. PARASUIS... PCR detects G. parasuis even when the organism is no longer viable, and it represents a great advantage in sensitivity compared to bacterial isolation." The trap: "considering that G. parasuis is A COLONIZER OF THE UPPER RESPIRATORY TRACT OF HEALTHY PIGS, DETECTION OF THIS MICROORGANISM IN THE NASAL CAVITY AND TRACHEA DOES NOT IMPLY DISEASE DEVELOPMENT."
How this level was decided
Level 2. Polyserositis in a nursery pig raises half a dozen agents and the chapter lists them, so this is not level 1; and a validated PCR at any regional diagnostic laboratory confirms it, which is the level 2 label. NOTE THE TWO PRACTICAL TRAPS, both of which produce wrong answers rather than no answer, and both of which belong in a brief: the organism is fastidious and dies in transit, so a negative culture from a warm overnight swab means nothing; and a positive from the nose means colonisation, not disease, so the sample must come from the lesion.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l3, signficance varies by farm, season, cofactors but no question in general terms it is a consequential disease, at least intermittently, on most farms"
Basis. ch50 50.1: "Glasser's disease occurs in swine populations around the world, IRRESPECTIVE OF HEALTH STATUS, and outbreaks of this ECONOMICALLY SIGNIFICANT DISEASE may be linked to stress-associated events, including coinfections and moving and comingling animals. IN THE UNITED STATES, IT IS CONSIDERED ONE OF THE MAIN INFECTIOUS PROBLEMS IN THE NURSERY, ALSO AFFECTING GROWING PIGS AND SOWS (Holtkamp et al. 2007)." 50.9 on the losses: "commingling of pigs from different sources and ages is AN IMPORTANT CAUSE OF INCREASED MORTALITY DUE TO GLASSER'S DISEASE and should be avoided when possible", and "VACCINATION IS AN EFFECTIVE MEASURE TO PREVENT MORTALITY." No dollar figure is given.
How this level was decided
INFERRED. Level 3 -- losses that measurably increase cost of production but remain manageable within normal farm operations. The chapter names it one of the main infectious problems in the US nursery, in a US-specific citation, which is exactly what the standing note SCORING/production_cost_impact asks for; and the loss is mortality plus the vaccination and antibiotic programme that holds it down. NOT LEVEL 4: this is a disease the industry manages routinely with sow and piglet vaccination and all-in/all-out flow, not one that threatens the viability of a unit. NOT LEVEL 2: nursery mortality is not a short-lived loss, and the chapter calls the disease economically significant in its opening paragraph.
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 impact on markets"
Basis. G. parasuis is ubiquitous in US swine herds and is normal respiratory microbiota (ch50 50.3), and no trade measure, movement restriction or consumer response to a Glasser's disease diagnosis is recorded anywhere in the chapter.
How this level was decided
INFERRED. Level 1 under the standing note SCORING/market_impact: an organism universally present and routinely diagnosed in US pigs, with no market move ever observed.
C7 Treatment potential
Potential for treatment to improve outcomes
Some: Treatment exists but is inconsistent, requires extralabel use, or works only in some circumstances
Basis. ch50 50.9: "ANTIBIOTIC TREATMENT REMAINS AN ESSENTIAL CONTROL MEASURE IN THE FACE OF SEVERE OUTBREAKS of G. parasuis systemic infection. INJECTABLE TREATMENTS TEND TO BE MORE EFFECTIVE THAN WATER OR FEED MEDICATION, since pigs clinically affected... are less likely to ingest the required antibiotic dose via food and water intake. Nonsteroidal anti-inflammatory treatment may assist recovery." On whether it keeps working: "Antibiotic susceptibility profiles ARE VARIABLE IN DIFFERENT COUNTRIES... whereas HIGH RATES OF RESISTANCE to commonly used antibiotics are reported for Chinese and Spanish isolates... IN THE UNITED STATES, THE ODDS OF RESISTANCE FOR A RANGE OF ANTIMICROBIALS, INCLUDING CEPHALOSPORINS, FLUOROQUINOLONES, PENICILLINS, AND MACROLIDES, WERE SHOWN TO HAVE INCREASED ANNUALLY BETWEEN 2006 AND 2016 (Hayer et al. 2020)."
How this level was decided
Level 2. Treatment exists, is essential, and is used -- but it works only in some circumstances, which is the level 2 clause: the sick pig will not drink or eat, so oral routes fail and injection is needed animal by animal; and US resistance to every major class rose annually across a decade of surveillance. THE LABEL QUESTION IS NOT PUT TO YOU, because it could not change the answer: the inconsistent-efficacy clause holds level 2 whatever a label says, and it would matter only if the pass were arguing level 1.
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
Basis. ch50 50.9: "VACCINATION IS AN EFFECTIVE MEASURE TO PREVENT MORTALITY. Programs are based on sow vaccination for preventing preweaning disease among suckling pigs, peri-weaning vaccination where disease occurs post weaning, and vaccination as part of acclimatization programs for incoming breeding stock. COMMERCIALLY AVAILABLE BACTERIN VACCINES ARE BASED ON SEROVAR 5, COMBINED SEROVARS 4 AND 5, OR COMBINED SEROVARS 1 AND 6 for use in sows and pigs. ALL THESE PRODUCTS SHOW LIMITED CROSS-PROTECTION TO HETEROLOGOUS STRAINS." 50.8.2: "Complete protection against challenge is usually obtained with HOMOLOGOUS vaccination, whereas PARTIAL protection is generally observed with heterologous challenges... CROSS-PROTECTION BETWEEN DIFFERENT SEROVARS AND EVEN WITHIN THE SAME SEROVAR IS VARIABLE AND DIFFICULT TO PREDICT." Autogenous vaccines are used for acclimatisation.
How this level was decided
Level 2, and the chapter writes the label for us. Commercial bacterins are available in the US and prevent mortality, so this is not level 3, and the disease plainly warrants vaccinating, so it is not the "not needed" half of level 1. What holds it at level 2 is stated twice: all commercial products show limited cross-protection to heterologous strains, and cross-protection is variable and difficult to predict even WITHIN a serovar -- in an organism where one farm can carry sixteen strains at once.
Levels and evidence are generated from data/assignments/glaesserella_parasuis.yml; the overview is authored in data/overviews/glaesserella_parasuis.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.