GLAESSERELLA PARASUIS (GLÄSSER'S DISEASE)
LEVELS: Highly unlikely: No controls necessary; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission; Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s); Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals; Negligible: Little or no market disruption when disease occurs on one or more farms; High risk: Resistance to antibacterial or antiviral treatments is, or can be expected to be a common problem; High risk: Antibacterial or antiviral treatments commonly used on affected groups, or for prophylaxis; Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations; Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent; Not feasible: Eradication extremely unlikely
OVERVIEW
Glaesserella parasuis (formerly Haemophilus parasuis) is a gram-negative bacterium in the family Pasteurellaceae that causes Glässer's disease, characterized by fibrinous polyserositis, polyarthritis, and meningitis. The organism is ubiquitous in swine herds worldwide and is a member of the normal upper respiratory microbiota; colonization of piglets occurs soon after birth through contact with the sow. G. parasuis strains are highly heterogeneous and classified into 15 serovars, with serovars 4, 5/12, 7, 1, and 13 most prevalent. Strains vary markedly in virulence—systemic isolates (serovars 5/12, 13, 7) differ genetically from nasal isolates. Clinical disease primarily affects 4-8 week old pigs following decay of maternal immunity, stress, or exposure to new strains through commingling. Peracute cases may result in sudden death; acute disease presents with high fever (41.5°C), respiratory signs, swollen joints, and neurological signs. Morbidity and mortality typically range 5-10% but vary with concurrent stressors and viral coinfections (PRRSV, PCV2, IAV). Protection is primarily antibody-mediated but cross-protection between serovars is limited. Commercial bacterin vaccines based on serovars 4, 5, and others provide protection against homologous challenge but limited heterologous protection; autogenous vaccines using farm-specific systemic isolates are often needed.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
G. parasuis is not a foodborne zoonotic pathogen. "Domestic pigs and wild boars are the only known hosts for this bacterium." There are no reports of human illness from pork consumption or any other route.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
G. parasuis is strictly host-specific with no zoonotic potential. "Domestic pigs and wild boars are the only natural hosts for G. parasuis." While guinea pig and mouse models can be used experimentally, there is no natural infection or disease in humans or other species.
EFFECTIVENESS OF ON-FARM BIOSECURITY IN PREVENTING FARM-TO-FARM TRANSMISSION
Level: Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission
G. parasuis transmission is controllable through management practices: (1) Direct contact transmission: "Transmission of G. parasuis occurs through contact with carrier or diseased pigs and susceptible animals"; (2) Commingling risk: "mixing pigs from different origins and ages is a risk factor for transmission"; (3) Environmental lability: "G. parasuis is very labile in the environment"; (4) Disinfectant susceptibility: "efficacy of several formulations, including chloramine-T and quaternary ammonium compounds, has been reported"; (5) Management controllable: Sourcing compatible stock, avoiding commingling, and vaccination effectively control disease.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s)
Diagnosis requires laboratory confirmation with some challenges: (1) Non-pathognomonic signs: "The clinical signs and lesions described for G. parasuis systemic infection are not pathognomonic"; differential includes E. coli, M. hyorhinis, S. suis; (2) Fastidious organism: "G. parasuis is a fastidious microorganism with limited survival at room temperature and special requirements for in vitro growth"; (3) Sample handling critical: "The chances of isolating G. parasuis can be considerably improved by utilizing swabs with Amies transport media and submitting samples under refrigeration"; (4) PCR available: "PCR is a sensitive and specific method to detect G. parasuis"; "PCR detects G. parasuis even when the organism is no longer viable"; (5) Systemic samples needed: "Considering that G. parasuis is a colonizer of the upper respiratory tract of healthy pigs, detection...in the nasal cavity and trachea does not imply disease"; systemic isolates should be pursued; (6) Virulence differentiation: LS-PCR can discriminate virulent from avirulent isolates.
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals
Glässer's disease causes substantial economic losses: (1) Major nursery problem: "In the United States, it is considered one of the main infectious problems in the nursery, also affecting growing pigs and sows"; (2) Morbidity/mortality: "Morbidity and mortality rates...usually range from 5 to 10% in conventional farms"; (3) Sudden death: Peracute disease "may result in sudden death without characteristic gross lesions"; (4) Chronic sequelae: "Animals with mild to moderate clinical signs usually survive the acute phase...and may develop a chronic stage characterized by rough hair, reduced growth rate, and lameness"; (5) Stress-associated outbreaks: "outbreaks of this economically significant disease may be linked to stress-associated events, including coinfections and moving and comingling animals."
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Negligible: Little or no market disruption when disease occurs on one or more farms
No trade implications: (1) Not regulated: Glässer's disease is not a reportable or trade-restricted disease; (2) Endemic worldwide: "Glässer's disease occurs in swine populations around the world, irrespective of health status"; (3) Nursery disease: Primarily affects young pigs; resolves before market age.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: High risk: Resistance to antibacterial or antiviral treatments is, or can be expected to be a common problem
Antimicrobial resistance is increasing and varies geographically: (1) Regional variation: "Antibiotic susceptibility profiles are variable in different countries and reflect the selection of drugs used in each region"; (2) High resistance in some regions: "high rates of resistance to commonly used antibiotics are reported for Chinese and Spanish isolates"; (3) Increasing resistance: "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"; (4) Mobile genetic elements: "Resistance to tetracycline, beta-lactam antibiotics, and multidrug resistance has been linked to plasmids and also integrative conjugative elements"; (5) Some regions still susceptible: "Danish, British, and Australian isolates are reported as broadly susceptible to most antibiotics."
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: High risk: Antibacterial or antiviral treatments commonly used on affected groups, or for prophylaxis
Disease management has historically relied heavily on antimicrobials: (1) Widespread use: "Antibiotics are widely used to prevent and control G. parasuis disease"; (2) Treatment essential in outbreaks: "Antibiotic treatment remains an essential control measure in the face of severe outbreaks"; (3) Prophylactic use discouraged: "The use of blanket prophylactic antibiotics in neonatal piglets is no longer recommended"; (4) Stewardship needed: "Strong antimicrobial stewardship is crucial to preserve this approach for initial control of outbreaks"; (5) Non-antimicrobial alternatives: "increasing pressure to reduce reliance on antibiotics...puts more emphasis on vaccination strategies."
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Treatment is effective when implemented early: (1) Injectable preferred: "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"; (2) Supportive care: "Nonsteroidal anti-inflammatory treatment may assist recovery"; (3) Resistance complicates selection: Susceptibility testing important given regional resistance patterns; (4) Timing critical: Peracute cases may die before treatment possible.
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Vaccines provide protection but cross-protection is limited: (1) Commercial vaccines: "Commercially available bacterin vaccines are based on serovar 5, combined serovars 4 and 5, or combined serovars 1 and 6"; (2) Limited cross-protection: "All these products show limited cross-protection to heterologous strains"; (3) Live attenuated available: "A live-attenuated serovar 5 strain is available in North America with cross-protection claimed for serovars 4 and 13"; (4) Autogenous vaccines important: "Autogenous vaccines, defined as farm-specific products generated from disease-associated isolates, are effective in protecting susceptible pigs"; (5) Proper isolate selection critical: "it is essential to use typing methods to ensure that all the appropriate systemic isolates are incorporated into the vaccine preparation by sampling from systemic rather than respiratory locations"; (6) Maternal immunity: "Pigs from vaccinated sows tended to have a lower amount and reduced variety of G. parasuis strains."
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Not feasible: Eradication extremely unlikely
Eradication is not feasible due to ubiquitous carriage: (1) Normal microbiota: "Glaesserella parasuis is a member of the normal respiratory microbiota and is ubiquitous in swine herds worldwide"; (2) Early colonization: "Colonization of the upper respiratory tract of piglets by G. parasuis occurs soon after birth through contact with the sow"; (3) Multiple strains per farm: "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"; (4) Elimination possible but risky: "elimination of G. parasuis from a herd is difficult...it may be achieved through cesarean derivation into pig-free premises. However...such herds are highly susceptible to severe outbreaks if exposed."