Swine Glässer's Disease: Diagnosis and Management

Glässer's disease is a systemic bacterial infection of swine caused by Haemophilus parasuis, characterized by fibrinous polyserositis, arthritis, and meningitis. This article provides swine veterinarians and herd health managers with syndrome-level investigation guidance covering clinical recognition, postmortem lesion assessment, diagnostic methods including culture and PCR, antimicrobial therapy considerations, and prevention through vaccination and biosecurity. The content is based on approved veterinary references and published research, and is intended to support clinical decision-making within a veterinarian-client-patient relationship.

At a Glance

Etiology and Epidemiology

Haemophilus parasuis is a Gram-negative coccobacillus in the family Pasteurellaceae. The bacterium is an early colonizer of the upper respiratory tract of piglets, typically acquired within the first days of life from the sow. Under conditions of stress, immunosuppression, or concurrent viral infection, the organism can invade the bloodstream and cause systemic disease. The World Organisation for Animal Health (WOAH) includes H. parasuis among significant swine pathogens requiring laboratory surveillance and reporting in some contexts.

Fifteen serovars of H. parasuis have been described based on heat-stable antigen typing, with serovars 1, 5, 10, 12, 13, and 14 considered highly virulent, while serovars 3, 6, 7, 8, 9, and 11 are generally associated with low virulence or non-pathogenic colonization. A study on the prevalence of Haemophilus parasuis serovars among isolates from swine documented the distribution of serovars in clinical cases, confirming that certain serovars are more frequently isolated from systemic disease. Knowledge of the circulating serovars in a herd is important for vaccine selection and interpretation of diagnostic results.

The disease occurs worldwide and is most common in nursery and early grower pigs, typically between 4 and 12 weeks of age. Maternal antibody provides some protection in the first weeks of life, but waning immunity combined with the stress of weaning, mixing, and transport creates a window of susceptibility. Concurrent infection with porcine reproductive and respiratory syndrome virus (PRRSV) or swine influenza virus can potentiate H. parasuis disease by impairing pulmonary macrophage function and disrupting respiratory epithelial barriers.

Clinical Signs and Syndrome Recognition

The clinical presentation of Glässer's disease varies with the virulence of the infecting strain, the immune status of the pig, and the presence of concurrent infections. Acute cases present with sudden onset of fever (40.5 to 42.0 degrees C), depression, anorexia, and reluctance to move. Pigs may show respiratory distress with abdominal breathing, cyanosis of the extremities, and rapid progression to death within 24 to 48 hours.

Arthritis is a hallmark sign, with one or more joints becoming hot, swollen, and painful. Affected pigs may sit on their hindquarters or walk stiffly. When meningitis develops, neurological signs include tremors, incoordination, paddling movements, nystagmus, and recumbency. Mortality in untreated acute outbreaks can exceed 50 percent.

Subacute and chronic cases present with milder signs including poor growth, intermittent lameness, and low-grade fever. These pigs may have fibrinous adhesions in the pleural or peritoneal cavities that are only detected at slaughter or necropsy. Chronic polyserositis can lead to pericarditis, pleuritis, and peritonitis that reduce growth performance and increase carcass condemnation at slaughter.

The differential diagnosis for polyserositis in swine includes other bacterial pathogens. Pasteurella multocida polyserositis in growing-finishing pigs has been documented as a cause of similar fibrinous serositis. Mycoplasma hyorhinis is another important cause of polyserositis and arthritis in nursery and grower pigs, and altered nasal microbiota composition has been associated with development of polyserositis by Mycoplasma hyorhinis. Streptococcus suis can cause meningitis and arthritis that clinically resembles Glässer's disease. A case of pericarditis caused by Mycoplasma hyorhinis in a weaned piglet further illustrates the need for laboratory differentiation. Even enteric pathogens such as Salmonella Agona have been reported to cause polyserositis, meningoencephalitis, arthritis and omphalitis in pigs, underscoring the importance of definitive diagnosis.

Postmortem Lesions

Necropsy is a critical component of Glässer's disease investigation. The characteristic gross lesion is fibrinous polyserositis, with yellow to white fibrinous exudate covering the pleural, pericardial, and peritoneal surfaces. The exudate may be thin and serofibrinous in acute cases or thick and organized in chronic cases.

The pericardium often shows a bread and butter appearance with fibrinous deposits on both the visceral and parietal surfaces. The pleural cavity may contain serosanguinous fluid with fibrin strands. The peritoneum can have fibrinous adhesions between abdominal organs. Joints, particularly the carpal, tarsal, and stifle joints, contain increased synovial fluid that may be turbid or blood-tinged, with fibrin clots visible in the joint capsule.

In cases with meningitis, the meninges are congested and may have a cloudy or purulent exudate over the brainstem and cerebellum. The cerebrospinal fluid is often turbid. Lung lesions are not a consistent feature of Glässer's disease, but concurrent pneumonia from other pathogens may be present.

Experimental reproduction of Haemophilus parasuis infection in swine has confirmed that clinical signs, bacteriological findings, and morphologic lesions are consistent with field cases, validating the use of necropsy findings for diagnosis. The distribution and character of fibrinous exudate should be recorded systematically, including the extent of involvement of each serosal surface.

Diagnostic Methods

Sample Collection and Submission

Proper sample collection is essential for laboratory confirmation of Glässer's disease. Samples should be collected from acutely affected pigs that have not been treated with antimicrobials, as prior therapy can reduce culture sensitivity. For live pigs, joint fluid aspirated from swollen joints and cerebrospinal fluid from the atlanto-occipital space are the preferred samples. Blood culture may be attempted but has lower sensitivity.

At necropsy, swabs of serosal surfaces, pericardial fluid, joint fluid, and meningeal exudate should be collected. Tissues for culture include lung, liver, spleen, and brain. Samples for PCR can be collected on sterile swabs placed in transport medium or as fresh tissue in sterile containers. Formalin-fixed tissues are suitable for histopathology but not for culture.

Bacterial Culture

Haemophilus parasuis is a fastidious organism that requires nicotinamide adenine dinucleotide (NAD, also called V factor) for growth. Culture media such as chocolate agar, trypticase soy agar with 5 percent sheep blood and a Staphylococcus nurse streak, or specialized NAD-supplemented media are required. The organism grows as small, translucent, non-hemolytic colonies after 24 to 48 hours of incubation at 37 degrees C in 5 to 10 percent CO2.

Culture sensitivity is reduced by prior antimicrobial therapy, improper sample handling, or overgrowth by contaminating organisms. Samples should be transported to the laboratory within 24 hours, preferably on transport swabs with appropriate medium. If delays are expected, samples should be refrigerated but not frozen.

Polymerase Chain Reaction

PCR assays for H. parasuis offer higher sensitivity than culture, particularly for samples from treated pigs or those with low bacterial loads. Real-time PCR assays targeting the 16S rRNA gene or species-specific genes can detect the organism directly from clinical samples. PCR can also be used for genotyping, including ERIC-PCR genotypic characterization of Haemophilus parasuis isolates, which provides information on strain diversity within a herd.

PCR does not provide antimicrobial susceptibility data, so culture should still be attempted when possible. PCR results should be interpreted in conjunction with clinical signs and lesions, as the organism can be detected in the upper respiratory tract of healthy carrier pigs.

Serotyping

Serotyping of H. parasuis isolates is important for epidemiological investigation and vaccine selection. The traditional heat-stable antigen typing method uses a panel of rabbit antisera to identify serovars 1 through 15. However, a significant proportion of isolates may be non-typeable, and cross-reactions between serovars can occur. Molecular serotyping methods using multiplex PCR are increasingly used and can improve typing success rates.

Knowledge of the serovars circulating in a herd guides vaccine selection, as commercial bacterins provide serovar-specific protection. Autogenous vaccines can be developed for serovars not covered by commercial products. The association between serum resistance and systemic disease in Haemophilus parasuis has been demonstrated, with virulent strains showing greater resistance to complement-mediated killing.

Serology

Serological testing for H. parasuis has limited diagnostic value for individual animals due to the high prevalence of antibodies in carrier pigs and the lack of correlation between antibody titers and protection. Serology may be useful at the herd level to assess exposure patterns and to monitor the effectiveness of vaccination programs. Paired serum samples collected from the same age group over time can demonstrate seroconversion associated with clinical disease.

Histopathology

Histological examination of affected tissues can support the diagnosis. Fibrinous serositis with infiltration of neutrophils and macrophages is characteristic. In the meninges, there is suppurative meningitis with fibrin deposition. Gram-negative coccobacilli may be visible within lesions using Gram stain or immunohistochemistry. Histopathology is particularly useful when culture results are negative due to prior antimicrobial therapy.

Antimicrobial Therapy

Treatment Principles

Early and aggressive antimicrobial therapy is essential for reducing mortality in acute Glässer's disease outbreaks. The choice of antimicrobial should be based on culture and susceptibility testing of isolates from the affected herd whenever possible. Empirical therapy should be initiated while awaiting laboratory results, using drugs with known activity against H. parasuis.

The organism is generally susceptible to penicillins, cephalosporins, fluoroquinolones, tetracyclines, and potentiated sulfonamides. However, antimicrobial resistance patterns vary geographically and between herds. Injectable formulations are preferred for acutely ill pigs that are not eating or drinking. Water-soluble medications can be used for group treatment when individual injection is impractical.

Treatment Protocols

Treatment protocols should be developed in consultation with a veterinarian and tailored to the specific herd situation. Factors to consider include the severity of clinical signs, the number of pigs affected, the availability of different drug formulations, and withdrawal periods for slaughter. The Merck Veterinary Manual provides general guidance on antimicrobial selection for swine respiratory and systemic diseases.

For individual pigs with severe signs, parenteral therapy is indicated. The route of administration (intramuscular, subcutaneous, or intravenous) depends on the drug formulation and the condition of the pig. Severely dehydrated or moribund pigs may require intravenous fluids and supportive care.

Group treatment through water medication can be effective for controlling outbreaks when a large number of pigs are at risk. Water consumption should be monitored to ensure adequate dosing, and medicated water should be the only source of drinking water during the treatment period. Feed medication is less reliable for acute disease because sick pigs often stop eating.

Treatment Failure and Resistance

Treatment failure can occur due to antimicrobial resistance, inadequate dosing, delayed treatment, or the presence of concurrent infections. If clinical response is poor within 48 hours, re-evaluation of the diagnosis and susceptibility testing is warranted. The emergence of resistant strains can be minimized by using appropriate drug concentrations, completing the full course of treatment, and avoiding routine prophylactic use of critically important antimicrobials.

Withdrawal Periods

All antimicrobials used in food animals have established withdrawal periods that must be observed to prevent violative residues in meat. Withdrawal periods vary by drug, formulation, route of administration, and dosage. The veterinarian prescribing the treatment is responsible for ensuring that withdrawal periods are communicated to the producer and observed before animals are sent to slaughter. Records of treatment dates, drugs used, dosages, and withdrawal periods must be maintained.

Vaccination and Prevention

Commercial Bacterins

Commercial bacterins for H. parasuis are available in many countries and are typically administered to sows to provide passive immunity to piglets through colostrum, or directly to piglets to stimulate active immunity. Most commercial vaccines contain inactivated whole cells of several common serovars, but the specific serovars included vary by product.

Vaccination of sows 2 to 4 weeks before farrowing boosts colostral antibody levels, providing protection to piglets during the first weeks of life. Piglet vaccination is typically given at 3 to 4 weeks of age, with a booster 2 to 3 weeks later. The timing of vaccination should be adjusted based on the age at which clinical disease typically occurs in the herd.

Autogenous Vaccines

When commercial vaccines do not cover the serovars circulating in a herd, autogenous (custom) vaccines can be prepared from isolates obtained from the affected herd. Autogenous vaccines are produced under USDA license or equivalent regulatory authority and must be used under the direction of a veterinarian. The process involves isolating H. parasuis from clinical cases, confirming the serovar, and having a licensed biologics company produce the vaccine.

Autogenous vaccines offer the advantage of serovar-specific protection but require time for production and may not be immediately available during an outbreak. They are most useful for herds with recurrent disease caused by serovars not covered by commercial products.

Vaccine Limitations

Vaccination does not prevent colonization of the upper respiratory tract by H. parasuis, and carrier pigs can still shed the organism. Protection is serovar-specific, and cross-protection between serovars is limited. Vaccine efficacy can be reduced by maternal antibody interference, immunosuppression from concurrent infections, or improper vaccine handling and administration.

Biosecurity and Management

Biosecurity measures to prevent introduction of H. parasuis into a herd include quarantine of incoming stock, testing of replacement animals, and control of fomites and personnel movement. The organism is transmitted by direct contact and aerosol over short distances, so strict isolation of new arrivals is important.

Within a herd, management practices that reduce stress and improve immunity can decrease the incidence of clinical disease. These include:

• All-in/all-out production to break the cycle of infection
• Adequate ventilation to reduce respiratory challenge
• Temperature control in nursery facilities
• Minimizing mixing and sorting of pigs
• Providing clean, dry bedding
• Ensuring adequate colostrum intake by newborn piglets
• Controlling concurrent diseases, especially PRRSV and swine influenza

Monitoring and Surveillance

Regular monitoring for clinical signs of Glässer's disease should be part of the herd health program. Records of mortality, treatment rates, and necropsy findings should be maintained and reviewed to detect changes in disease patterns. Diagnostic testing of pigs that die or are euthanized for poor performance can identify subclinical disease.

Serological monitoring can assess the effectiveness of vaccination programs and identify gaps in immunity. PCR testing of tonsil swabs from different age groups can determine the prevalence of carriage and the serovars present in the herd.

Records and Measurements

Clinical Records

Accurate records are essential for managing Glässer's disease outbreaks and evaluating control measures. The following data should be recorded for each outbreak:

• Date of onset and duration
• Age group affected
• Number of pigs affected and mortality rate
• Clinical signs observed
• Treatments administered, including drug, dose, route, and duration
• Necropsy findings
• Laboratory results
• Vaccination history of affected pigs

Treatment Records

Individual pig treatment records should include:

• Pig identification (ear tag, tattoo, or pen card)
• Date and time of treatment
• Drug name and concentration
• Dose administered
• Route of administration
• Withdrawal period
• Person administering treatment
• Outcome (recovered, died, euthanized)

Group treatment records should document:

• Dates of treatment
• Drug and concentration in water or feed
• Estimated daily consumption
• Number of pigs treated
• Withdrawal period

Mortality Records

Mortality records should be maintained by age group and cause. Pigs that die suddenly or are euthanized for suspected Glässer's disease should be necropsied and recorded separately from other causes of death. Monthly mortality rates should be calculated and compared to baseline levels to detect outbreaks early.

Laboratory Records

Laboratory results should be filed and reviewed regularly. The following information should be recorded for each diagnostic submission:

• Date of submission
• Sample type and number of samples
• Tests requested
• Results (culture, PCR, serotyping, histopathology)
• Antimicrobial susceptibility profile
• Interpretation and recommendations

Common Failure Patterns

Delayed Diagnosis

The most common failure in managing Glässer's disease is delayed diagnosis. Early signs such as fever and depression are non-specific and may be attributed to other causes. By the time polyserositis and arthritis are evident, the outbreak may be well established. Regular necropsy of pigs that die unexpectedly, especially in the nursery phase, can improve early detection.

Inadequate Treatment

Treatment failure often results from using inappropriate antimicrobials, incorrect dosing, or too short a treatment duration. Sick pigs may not consume adequate amounts of medicated water or feed, so injectable therapy is preferred for severely affected animals. Treatment should continue for at least 3 to 5 days after clinical signs resolve to prevent relapse.

Vaccine Mismatch

Using a commercial vaccine that does not contain the serovars circulating in the herd is a common cause of vaccine failure. Serotyping of isolates from clinical cases should be performed before selecting a vaccine. If commercial vaccines are not protective, autogenous vaccines should be considered.

Concurrent Infections

Glässer's disease often occurs in combination with other respiratory or systemic infections. PRRSV, swine influenza, Mycoplasma hyopneumoniae, and Streptococcus suis are common coinfections that complicate diagnosis and treatment. Control of concurrent diseases is essential for effective management of H. parasuis.

Environmental Stress

Poor environmental conditions such as cold drafts, high ammonia levels, overcrowding, and poor sanitation increase the risk of clinical disease. Even with effective vaccination and treatment, disease will recur if environmental stressors are not addressed.

Welfare and Safety Context

Animal Welfare

Glässer's disease causes significant pain and distress due to polyserositis, arthritis, and meningitis. Affected pigs experience fever, difficulty breathing, lameness, and neurological signs. Prompt diagnosis and treatment are essential for welfare reasons. Pigs with severe arthritis or meningitis that do not respond to treatment should be euthanized humanely to prevent prolonged suffering.

The World Organisation for Animal Health (WOAH) provides standards for animal welfare in livestock production systems, including requirements for disease prevention and control. The WOAH Animal Health and Welfare framework emphasizes the importance of biosecurity, surveillance, and timely veterinary intervention to minimize disease impact.

Food Safety

Antimicrobial use in food animals must be managed to prevent violative residues in meat and to minimize the development of antimicrobial resistance. All treatments must be recorded, and withdrawal periods must be observed. The veterinarian is responsible for ensuring that treatment protocols comply with regulatory requirements.

Occupational Safety

Handling sick pigs carries risks of injury from bites, kicks, and crushing. Needle stick injuries are a hazard during injection. Personnel should be trained in safe animal handling techniques and proper needle disposal. Personal protective equipment including gloves and boots should be worn when handling sick pigs or performing necropsies.

Professional Escalation Criteria

Urgent Veterinary Consultation

The following situations require immediate veterinary consultation:

• Sudden increase in mortality in nursery or grower pigs
• Multiple pigs with neurological signs
• Outbreak not responding to empirical therapy within 48 hours
• Suspected foreign animal disease (always rule out African swine fever and classical swine fever)
• Need for diagnostic testing to confirm diagnosis
• Development of antimicrobial resistance suspected

Routine Veterinary Consultation

The following situations should be discussed with a veterinarian during routine herd health visits:

• Recurrent Glässer's disease outbreaks
• Evaluation of vaccination protocols
• Interpretation of diagnostic results
• Development of biosecurity plans
• Review of treatment records and antimicrobial use
• Assessment of environmental risk factors

Regulatory Reporting

In some jurisdictions, certain swine diseases are reportable to animal health authorities. While H. parasuis is not typically a reportable disease, the veterinarian should be aware of local reporting requirements. Any suspicion of a foreign animal disease must be reported immediately.

Practical Decision Framework for Glässer's Disease Outbreak Investigation and Response

Managing a Glässer's disease outbreak requires a structured approach that integrates clinical observation, diagnostic sampling, treatment decisions, and preventive adjustments. Without a systematic framework, response efforts can become reactive and inconsistent, leading to higher mortality and prolonged disease impact. The following decision framework is designed for herd health managers and veterinarians to apply during suspected or confirmed outbreaks, with clear decision points based on observable findings and laboratory results.

Outbreak Recognition and Initial Assessment

The first step in any outbreak response is recognizing that an unusual disease event is occurring. A Glässer's disease outbreak should be suspected when mortality in nursery or early grower pigs exceeds baseline levels by more than 50 percent over a 48-hour period, or when multiple pigs present with fever, lameness, or neurological signs. The Merck Veterinary Manual emphasizes that early recognition is critical for successful intervention, as delayed treatment significantly worsens prognosis.

Upon suspicion of an outbreak, the following initial assessment should be completed within 4 hours:

• Count the number of affected pigs and calculate the attack rate (affected pigs divided by total pigs in the group)
• Record the age range of affected pigs
• Note the predominant clinical signs (fever, lameness, neurological signs, respiratory distress)
• Check treatment records for any recent antimicrobial use
• Review vaccination history for the affected group
• Assess environmental conditions including ventilation, temperature, stocking density, and hygiene

This initial assessment determines the urgency of response and guides the next steps. If the attack rate exceeds 10 percent or neurological signs are present, immediate veterinary consultation is required.

Diagnostic Sampling Decision Tree

The decision to collect diagnostic samples and which samples to collect depends on the clinical presentation and the availability of laboratory services. The following decision tree guides sample selection:

Scenario A: Acute deaths with polyserositis at necropsy

• Collect swabs from pleural, pericardial, and peritoneal surfaces for culture and PCR
• Collect joint fluid from any swollen joints
• Collect brain tissue if neurological signs were observed
• Submit fresh lung, liver, and spleen for culture
• Submit formalin-fixed tissues from serosal surfaces, brain, and joint capsule for histopathology

Scenario B: Live pigs with arthritis but no neurological signs

• Aspirate joint fluid from the most swollen joint using aseptic technique
• Collect blood culture if pig is febrile
• Collect tonsil swab for PCR to assess carriage status

Scenario C: Live pigs with neurological signs

• Collect cerebrospinal fluid from the atlanto-occipital space
• Collect joint fluid if arthritis is also present
• Collect blood culture

Scenario D: Chronic or subclinical disease with poor growth

• Collect tonsil swabs from multiple pigs for PCR
• Collect serum for serology to assess exposure patterns
• Necropsy any pigs that die or are euthanized for poor performance

Samples should be collected from at least three to five acutely affected pigs that have not received antimicrobial therapy in the previous 48 hours. The World Organisation for Animal Health (WOAH) recommends that diagnostic samples be transported to the laboratory within 24 hours under refrigeration to maintain organism viability.

Treatment Decision Matrix

Treatment decisions should be based on the severity of clinical signs, the number of pigs affected, and the availability of antimicrobials. The following matrix provides guidance for different outbreak scenarios:

Mild outbreak (less than 5 percent affected, mild lameness, no neurological signs)

• Individual injectable therapy for affected pigs using a penicillin or ceftiofur
• Monitor response within 24 hours
• If no improvement, collect diagnostic samples and consider water medication for the group

Moderate outbreak (5 to 15 percent affected, fever, lameness, some recumbency)

• Individual injectable therapy for severely affected pigs
• Water medication for the entire group using an approved antimicrobial
• Collect diagnostic samples from untreated pigs before starting group medication
• Monitor water consumption to ensure adequate dosing

Severe outbreak (more than 15 percent affected, neurological signs, high mortality)

• Immediate veterinary consultation
• Individual injectable therapy for all affected pigs
• Water medication for the entire group
• Collect diagnostic samples before treatment if possible
• Consider euthanasia for pigs with severe neurological signs that are unlikely to recover

The choice of antimicrobial should be guided by local susceptibility patterns. If susceptibility data are not available, a penicillin, ceftiofur, or potentiated sulfonamide is a reasonable empirical choice. Treatment should continue for a minimum of 3 to 5 days after clinical signs resolve.

Vaccination Decision Framework

Vaccination decisions should be based on the serovars circulating in the herd, the age at which disease occurs, and the effectiveness of current vaccination protocols. The following framework guides vaccination strategy:

Step 1: Determine circulating serovars

• Submit isolates from clinical cases for serotyping
• If serotyping is not available, use PCR-based genotyping methods
• Compare results to the serovars included in commercial vaccines

Step 2: Assess current vaccination protocol

• Review vaccination timing relative to disease onset
• Check vaccine handling and administration practices
• Evaluate maternal antibody interference if vaccinating piglets

Step 3: Select vaccination strategy

• If commercial vaccine covers circulating serovars and disease occurs after 6 weeks of age: vaccinate piglets at 3 to 4 weeks with a booster at 6 weeks
• If commercial vaccine covers circulating serovars but disease occurs before 6 weeks: vaccinate sows 2 to 4 weeks before farrowing to boost passive immunity
• If commercial vaccine does not cover circulating serovars: develop an autogenous vaccine from herd isolates
• If multiple serovars are circulating: consider a combination of commercial and autogenous vaccines

Step 4: Monitor vaccine effectiveness

• Track mortality and treatment rates after vaccination
• Collect serum samples to assess antibody response
• Repeat serotyping if disease recurs

Biosecurity Decision Points

Biosecurity measures should be implemented based on the risk of introduction and spread within the herd. The following decision points guide biosecurity actions:

Preventing introduction

• Quarantine all incoming stock for a minimum of 30 days
• Test replacement gilts for H. parasuis carriage using tonsil swab PCR
• Require vaccination of incoming stock against circulating serovars
• Control visitor access and provide dedicated boots and coveralls

Controlling spread within the herd

• Implement all-in/all-out production by room or barn
• Clean and disinfect facilities between groups
• Use dedicated equipment for each room
• Minimize pig movement between groups
• Control rodents and other potential fomites

Managing an active outbreak

• Isolate affected pigs in a separate hospital pen
• Use dedicated boots and coveralls for the affected area
• Treat affected pigs last to avoid spreading infection to healthy pigs
• Increase ventilation in the affected area
• Reduce stocking density if possible

Monitoring and Evaluation Protocol

After implementing control measures, ongoing monitoring is essential to evaluate effectiveness and detect changes in disease patterns. The following protocol should be followed:

Daily monitoring during an outbreak

• Record number of new cases and deaths
• Assess clinical response to treatment
• Monitor water and feed consumption
• Check environmental conditions

Weekly monitoring after outbreak resolution

• Calculate mortality rate for the affected group
• Compare to baseline mortality rates
• Review treatment records for antimicrobial use
• Assess growth performance of recovered pigs

Monthly monitoring for herd health

• Review necropsy records for any pigs that die
• Submit tonsil swabs from different age groups for PCR surveillance
• Review serology results if available
• Update vaccination protocols based on surveillance data

Record System for Outbreak Management

A standardized record system is essential for tracking outbreaks and evaluating control measures. The following records should be maintained for each outbreak:

Outbreak record form

• Date outbreak identified
• Barn or room number
• Age group and number of pigs
• Number of pigs affected and died
• Clinical signs observed
• Samples collected and results
• Treatment protocol used
• Vaccination history
• Environmental conditions
• Biosecurity measures implemented
• Outcome and lessons learned

Individual pig treatment log

• Pig identification
• Date and time of treatment
• Drug name and dose
• Route of administration
• Withdrawal period
• Person administering treatment
• Outcome

Group treatment log

• Dates of treatment
• Drug and concentration
• Estimated daily consumption
• Number of pigs treated
• Withdrawal period

Laboratory results log

• Date of submission
• Sample type and number
• Tests requested
• Results
• Antimicrobial susceptibility profile
• Interpretation and recommendations

These records should be reviewed during routine herd health visits and used to adjust prevention and control strategies.

Common Failure Patterns in Outbreak Response

Several common failure patterns can undermine outbreak response efforts. Recognizing these patterns allows for corrective action:

Failure Pattern 1: Delayed recognition

• Signs: Outbreak is identified only after mortality has been high for several days
• Cause: Lack of daily mortality monitoring, failure to necropsy dead pigs
• Correction: Implement daily mortality checks and necropsy all pigs that die unexpectedly

Failure Pattern 2: Inadequate diagnostic sampling

• Signs: Laboratory results are inconclusive or negative despite clinical signs
• Cause: Samples collected from treated pigs, improper sample handling, insufficient sample number
• Correction: Collect samples from untreated pigs, use proper transport media, submit multiple sample types

Failure Pattern 3: Treatment failure due to resistance

• Signs: Poor clinical response within 48 hours of treatment
• Cause: Antimicrobial resistance, inadequate dosing, wrong drug choice
• Correction: Submit isolates for susceptibility testing, adjust drug selection based on results

Failure Pattern 4: Vaccine mismatch

• Signs: Disease occurs despite vaccination
• Cause: Vaccine does not contain circulating serovars, improper vaccine handling, maternal antibody interference
• Correction: Serotype isolates, select appropriate vaccine, adjust vaccination timing

Failure Pattern 5: Environmental stress perpetuating disease

• Signs: Disease recurs in successive groups despite vaccination and treatment
• Cause: Poor ventilation, cold drafts, high ammonia, overcrowding
• Correction: Address environmental deficiencies before expecting vaccination or treatment to be effective

Professional Escalation Criteria

The following situations require escalation to a veterinarian or diagnostic laboratory:

Immediate veterinary consultation required

• Mortality exceeds 20 percent in any group
• Neurological signs present in multiple pigs
• No response to empirical therapy within 48 hours
• Suspected foreign animal disease (always rule out African swine fever and classical swine fever)
• Need for regulatory reporting

Routine veterinary consultation recommended

• Recurrent outbreaks despite vaccination
• Need for autogenous vaccine development
• Interpretation of complex diagnostic results
• Development of herd-specific biosecurity plans
• Review of antimicrobial use patterns

Laboratory escalation criteria

• Culture-negative cases with typical lesions
• Atypical serovar patterns
• Suspected mixed infections requiring specialized testing
• Need for genotyping to understand strain diversity

The World Organisation for Animal Health (WOAH) provides standards for disease surveillance and reporting that should be followed when escalating cases to regulatory authorities. The WOAH Animal Health and Welfare framework emphasizes the importance of timely reporting and collaboration with veterinary authorities to control significant swine diseases.

Practical Implementation Steps

To implement this decision framework on farm, the following steps should be taken:

1. Train personnel on outbreak recognition and initial assessment procedures
2. Develop a standard operating procedure for diagnostic sample collection
3. Establish relationships with a diagnostic laboratory and understand their submission requirements
4. Create treatment protocols in consultation with a veterinarian
5. Maintain a stock of appropriate antimicrobials for emergency use
6. Implement a record system for tracking outbreaks and treatments
7. Review the framework annually and update based on herd experience and new research

The decision framework should be adapted to the specific conditions of each herd, including facility design, management practices, and disease history. Regular review of outbreak records and outcomes will identify areas for improvement and refine the framework over time.

Frequently Asked Questions

What is the difference between Glässer's disease and Haemophilus parasuis infection?

Glässer's disease refers specifically to the systemic form of H. parasuis infection characterized by fibrinous polyserositis, arthritis, and meningitis. Haemophilus parasuis infection can also occur as a subclinical colonization of the upper respiratory tract without causing disease. The term Glässer's disease is reserved for the clinical syndrome with systemic lesions.

How is Glässer's disease transmitted between pigs?

Transmission occurs through direct contact with respiratory secretions from carrier pigs. Piglets typically acquire the organism from the sow within the first days of life. The bacterium can survive for short periods in the environment but does not persist long outside the host. Aerosol transmission over short distances is possible, but fomites and personnel movement are more important routes of spread between groups.

Can Glässer's disease be treated successfully?

Yes, with early and appropriate antimicrobial therapy, many affected pigs recover. Treatment success depends on the virulence of the strain, the immune status of the pig, and the timeliness of intervention. Severely affected pigs with advanced meningitis or extensive polyserositis have a poorer prognosis. Group treatment through water medication can control outbreaks when individual treatment is not feasible.

Why does Glässer's disease occur most often in nursery pigs?

Nursery pigs are most susceptible because maternal antibody levels decline after weaning, and the pig's own immune system is not fully mature. The stress of weaning, transport, and mixing with pigs from other litters increases susceptibility. Concurrent infections such as PRRSV are common in this age group and can potentiate H. parasuis disease.

How long does Haemophilus parasuis survive in the environment?

The organism is fragile and does not survive for extended periods outside the host. Survival time depends on temperature, humidity, and exposure to disinfectants. In general, the bacterium survives for hours to days on surfaces but is readily killed by common disinfectants including quaternary ammonium compounds, bleach, and phenolics. Thorough cleaning and disinfection of facilities between groups is important for control.

Is there a vaccine for Glässer's disease?

Yes, commercial bacterins are available in many countries. These vaccines contain inactivated whole cells of several common serovars. Protection is serovar-specific, so the vaccine should contain serovars that match those circulating in the herd. Autogenous vaccines can be produced for herds with serovars not covered by commercial products. Vaccination of sows to provide passive immunity to piglets is a common strategy.

Can pigs recover from Glässer's disease without treatment?

Some pigs with mild disease may recover without antimicrobial therapy, but mortality is high in untreated acute cases. Pigs that recover may have chronic lesions such as pericarditis, pleuritis, or joint adhesions that affect growth performance and carcass quality. Treatment is recommended for all pigs showing clinical signs to reduce mortality and improve welfare.

How is Glässer's disease differentiated from other causes of polyserositis?

Differentiation requires laboratory testing. Mycoplasma hyorhinis causes similar polyserositis and arthritis but can be distinguished by culture, PCR, or serology. Pasteurella multocida and Streptococcus suis can also cause polyserositis. Histopathology with special stains and immunohistochemistry can help identify the causative agent. Mixed infections are common, so testing for multiple pathogens is recommended.

Related Veterinary Guides

• Swarm Prevention And Management
• Swine Respiratory Disease Observation And Diagnostics
• Manure Management For Pig Farms
• Pig Lameness Monitoring And Flooring Management
• Pig Farm Odor Management And Neighbor Relations

References and Further Reading

• World Organisation for Animal Health
• Merck Veterinary Manual. Merck Veterinary Manual.
• Animal Health and Welfare. World Organisation for Animal Health.
• Haemophilus parasuis: new trends on diagnosis, epidemiology and control.. Veterinary microbiology, 2004.
• Update on the diagnosis of Haemophilus parasuis infection in pigs and novel genotyping methods.. Veterinary journal (London, England : 1997), 2007.
• Experimental reproduction of Haemophilus parasuis infection in swine: clinical, bacteriological, and morphologic findings.. Journal of veterinary diagnostic investigation : official publication of the American Association of Veterinary Laboratory Diagnosticians, Inc, 1995.
• ERIC-PCR genotypic characterization of Haemophilus parasuis isolated from Brazilian swine.. Brazilian journal of microbiology : [publication of the Brazilian Society for Microbiology], 2011.
• Prevalence of Haemophilus parasuis serovars among isolates from swine.. American journal of veterinary research, 1992.
• Serum-resistance in Haemophilus parasuis is associated with systemic disease in swine.. Veterinary journal (London, England : 1997), 2008.
• Polyserositis, meningoencephalitis, arthritis and omphalitis due to Salmonella Agona infection in a pig. Journal of Comparative Pathology, 2025.
• Pasteurella multocida polyserositis in growing-finishing pigs. Journal of Comparative Pathology, 2023.
• Altered nasal microbiota composition associated with development of polyserositis by mycoplasma hyorhinis. Pathogens, 2021.
• A case of pericarditis caused by Mycoplasma hyorhinis in a weaned piglet. Porcine Health Management, 2021.
• Characterization and application of monoclonal antibodies against Mycoplasma hyorhinis pyruvate dehydrogenase E1 complex subunit alpha. Applied Microbiology and Biotechnology, 2016.
• Characterization of neurologic disease-associated Streptococcus suis strains within the United States swine herd and use of diagnostic tools. Journal of Clinical Microbiology, 2024.

This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.