Swine Swine Dysentery: Diagnosis and Eradication

Swine Dysentery: Diagnosis and Eradication

This article provides syndrome-level guidance for veterinarians and swine health professionals investigating swine dysentery. It covers clinical presentation, diagnostic methods including culture and PCR, antimicrobial therapy considerations, and eradication protocols. The primary pathogen is Brachyspira hyodysenteriae, though other Brachyspira species can produce similar disease. Accurate diagnosis and systematic eradication are essential for control.

At a Glance

Etiology and Pathogen Characteristics

Swine dysentery is caused primarily by Brachyspira hyodysenteriae, a Gram-negative anaerobic spirochete that colonizes the large intestine and induces mucohemorrhagic colitis. The disease is characterized by bloody to mucoid diarrhea in pigs, primarily affecting animals during the growth and finishing stage. The World Organisation for Animal Health recognizes swine dysentery as a disease of significance for international trade and animal health reporting [1]. The Animal Health and Welfare division of the World Organisation for Animal Health provides frameworks for disease surveillance and control [3].

The pathogen produces hemolysins and other virulence factors that damage colonic epithelial cells, leading to inflammation, fluid secretion, and hemorrhage. Brachyspira hyodysenteriae is distinct from other spirochetes that may be confused with it during diagnostic investigation. Early literature described the diagnostic challenge of differentiating Treponema hyodysenteriae (now Brachyspira hyodysenteriae) from other spirochetes that can be present in porcine feces [6]. The Merck Veterinary Manual provides detailed descriptions of clinical signs and diagnostic approaches associated with swine dysentery [2].

Other Brachyspira species, including Brachyspira hampsonii clade I, have been confirmed to cause mucohemorrhagic diarrhea and colitis in experimentally infected pigs [13]. This expands the differential for swine dysentery-like disease and underscores the need for species-level diagnostic confirmation. Characterization of the fecal microbiota of pigs before and after inoculation with Brachyspira hampsonii has provided insights into microbial community changes during infection [14].

Clinical Signs and Disease Presentation

Acute Disease

Acute swine dysentery presents with sudden onset of diarrhea that progresses from soft, watery feces to bloody, mucoid stools. Affected pigs show reduced feed intake, dehydration, and weight loss. Mortality can occur, particularly in untreated cases or when concurrent infections are present. The disease primarily affects pigs during the growth and finishing stage, typically from 8 to 20 weeks of age [10].

Chronic and Subclinical Disease

Chronic infections may present with intermittent diarrhea, reduced growth rates, and variable fecal consistency. Subclinically infected pigs can shed Brachyspira hyodysenteriae without showing overt clinical signs, serving as reservoirs for transmission within and between herds. This carrier state complicates eradication efforts and necessitates comprehensive testing protocols.

Age Groups Affected

Swine dysentery most commonly affects grow-finish pigs. Suckling piglets and adult breeding stock are less frequently affected, though sows can become carriers and introduce infection to naive herds. The control and prevention of Brachyspira hyodysenteriae consists of the administration of antimicrobial drugs, in addition to management and adapted feeding strategies [10].

Diagnostic Approach

Clinical Examination and Herd History

Investigation begins with thorough herd history, including:

• Onset and duration of diarrhea
• Age groups affected
• Mortality and morbidity rates
• Recent introductions or movements
• Previous treatment history and response
• Biosecurity practices

Physical examination of affected pigs should assess hydration status, body condition, and fecal character. Bloody, mucoid feces with a characteristic odor are suggestive but not pathognomonic. The Merck Veterinary Manual provides guidance on clinical examination protocols for swine dysentery [2].

Necropsy Findings

Postmortem examination reveals lesions confined to the large intestine. The cecum and colon show:

• Thickened, edematous walls
• Hyperemia and hemorrhage
• Fibrinous exudate adherent to mucosa
• Contents ranging from watery to bloody with mucus

Histopathology confirms mucohemorrhagic colitis with spirochetes visible on silver stains or immunohistochemistry. The Veterinary Pathology journal has published detailed descriptions of the pathological features of swine dysentery [4].

Laboratory Diagnosis

Culture

Anaerobic culture on selective media (e.g., trypticase soy agar with blood and antibiotics) allows isolation of Brachyspira hyodysenteriae. Colonies show strong beta-hemolysis. Culture is essential for antimicrobial susceptibility testing but requires specialized laboratory capability and takes 3-7 days. The Veterinary Record has published guidance on distinguishing Brachyspira hyodysenteriae from other spirochetes that may be confused during diagnostic investigation [6].

Polymerase Chain Reaction (PCR)

PCR assays targeting species-specific genes (e.g., nox gene for Brachyspira hyodysenteriae) provide rapid, sensitive detection directly from feces or intestinal tissue. PCR can differentiate Brachyspira hyodysenteriae from other Brachyspira species and is the preferred method for herd screening and confirmation. The Monatshefte fur Veterinarmedizin has published diagnostic protocols for swine dysentery [7].

Histopathology and Immunohistochemistry

Tissue sections from affected colon show spirochetes within the mucosa and crypt lumens. Immunohistochemistry using specific antibodies can confirm Brachyspira hyodysenteriae infection. The Tierarztliche Praxis has published diagnostic approaches for swine dysentery [5].

Differential Diagnoses

The genome and transcriptome of the porcine whipworm Trichuris suis have been characterized, providing molecular tools for differential diagnosis [17]. Necrotizing enterocolitis (pig bel) represents another differential consideration in certain geographic regions [15].

Antimicrobial Therapy

Current Options and Resistance Concerns

Antimicrobial therapy has been the mainstay of swine dysentery control. Drugs commonly used include pleuromutilins (tiamulin, valnemulin), macrolides (tylosin, tilmicosin), and others. However, a worldwide re-emergence of swine dysentery has been reported with an increasing number of isolates demonstrating decreased susceptibility to several crucially important antimicrobials. This compromises the ability to eradicate Brachyspira hyodysenteriae from infected pig farms [10].

Antimicrobial Susceptibility Testing

When treatment failure is suspected, culture and susceptibility testing should be performed. Isolates should be tested against a panel of relevant antimicrobials. Results guide drug selection and help identify emerging resistance patterns. The Veterinariia journal has published guidance on swine dysentery treatment approaches [9].

Non-Antibiotic Alternatives

Zinc Chelate Formulations

A novel non-antibiotic zinc chelate (IntraDysovinol 499 mg/mL, IntraCare) has been reported to demonstrate positive effects on fecal quality and consistency, general clinical signs, average daily weight gain, and Brachyspira hyodysenteriae excretion during and after a 6-day oral treatment. A 14-day treatment schedule combined with alternative management measures (including partial depopulation of post-weaning facilities and improved external and internal biosecurity measures) and thorough cleaning and disinfection (including 2% NaOH) of buildings and sows from day 7 of treatment onwards has been evaluated. This alternative approach for Brachyspira hyodysenteriae eradication was assessed on 18 pig farms over a 5-year period, with all enrolled eradication programs evaluated as successful at least 6-9 months after protocol finalization [10].

Competitive Exclusion and Probiotics

Research into animal microbiota reveals relationships between commensal bacteria and enteric pathogens. Metagenomics and culturomics offer opportunities in probiotic research, particularly for diseases where treatment alternatives are limited, such as swine dysentery caused by Brachyspira hyodysenteriae. Studies evaluating the potential ability of isolates from species of interest to outcompete Brachyspira hyodysenteriae have shown that certain isolates can reduce growth of the pathogen by more than one log10 bacteria/mL after 96 hours of co-culture. Species including Intestinibaculum porci, Dorea longicatena, Bifidobacterium thermoacidophilum, Mobilitalea sibirica, Clostridium butyricum, and Parabacteroides goldsteinii have demonstrated reduction of Brachyspira hyodysenteriae growth by more than 2 log10 units. The anti-Brachyspira hyodysenteriae activity of cell-free supernatants suggests mechanisms beyond nutrient competition, with a concentration-dependent reduction observed. Cell-free supernatants from 11 isolates achieved a reduction of over 2 log10 bacteria/mL, with Clostridium butyricum and Paraprevotella clara cell-free supernatants standing out with values of 2-3 log10 bacteria/mL. A pH-dependent effect was disclosed for part of the isolates tested, while Clostridium butyricum, Limosilactobacillus mucosae, Bifidobacterium thermoacidophilum, and Lactiplantibacillus plantarum maintained part of their anti-Brachyspira hyodysenteriae activity [11].

Non-Antimicrobial Compounds

In vitro screening of non-antibiotic components to mitigate intestinal lesions caused by Brachyspira hyodysenteriae, Lawsonia intracellularis, and Salmonella enterica serovar Typhimurium has been conducted. Commercially available non-antimicrobial compounds, including a fungal fermented rye product (compound F), a blend of short and medium chain fatty acids (compound S), a synergistic blend of short and medium chain fatty acids including coated butyrates (compound P), and an extract of carob and thyme (compound D), have been evaluated using an intestinal culture model. These findings represent steps toward finding alternatives to antimicrobial usage in swine production [12].

Eradication Protocols

Principles of Eradication

Successful eradication of swine dysentery requires a systematic approach addressing both the pathogen and its transmission. Key principles include:

• Removal of infected animals or cohorts
• Thorough cleaning and disinfection of facilities
• Treatment of remaining animals to eliminate infection
• Enhanced biosecurity to prevent reintroduction
• Post-eradication monitoring to confirm success

The control of swine dysentery at national level has been demonstrated in Sweden, providing a model for systematic eradication programs [8].

Partial Depopulation Strategy

Partial depopulation of post-weaning facilities reduces the pathogen load and breaks the cycle of reinfection. This approach involves removing all pigs from affected barns or sections, followed by cleaning, disinfection, and a downtime period before repopulation. The zinc chelate eradication study evaluated partial depopulation of post-weaning facilities combined with improved external and internal biosecurity measures [10].

Cleaning and Disinfection

Thorough cleaning and disinfection is critical. Organic matter must be removed before disinfection. Sodium hydroxide (2% NaOH) has been used effectively as a disinfectant against Brachyspira hyodysenteriae. All surfaces, including floors, walls, feeders, and water lines, must be treated. Sows should be washed and treated from day 7 of the treatment protocol onward [10].

Biosecurity Improvements

External biosecurity measures prevent introduction of Brachyspira hyodysenteriae from outside sources. Internal biosecurity measures reduce spread between groups. Key measures include:

• Dedicated footwear and clothing for each barn
• Boot baths with effective disinfectants
• Rodent and bird control
• All-in/all-out management by barn or room
• Cleaning and disinfection of transport vehicles

Post-Eradication Monitoring

Monitoring for at least 6-9 months after protocol finalization is necessary to confirm eradication success. Fecal sampling and PCR testing of high-risk groups (e.g., grow-finish pigs, newly introduced animals) should be conducted at regular intervals. Any recurrence of clinical signs requires immediate investigation. All enrolled eradication programs in the zinc chelate study were evaluated as successful at least 6-9 months after the finalization of the protocol [10].

Records and Measurements

Herd Health Records

Maintain records of:

• Clinical signs observed and dates
• Treatments administered (drug, dose, route, duration)
• Mortality and morbidity rates
• Laboratory results (culture, PCR, histopathology)
• Biosecurity audits and corrective actions

Diagnostic Records

Document:

• Sample types and collection dates
• Laboratory methods used
• Results with species identification
• Antimicrobial susceptibility profiles
• Interpretation and recommendations

Eradication Protocol Records

Record:

• Dates of depopulation, cleaning, disinfection
• Treatment protocols and compliance
• Biosecurity measures implemented
• Monitoring results and dates
• Final outcome assessment

Common Failure Patterns

Incomplete Depopulation

Leaving any infected pigs in the facility allows the pathogen to persist. All pigs in affected groups must be removed or treated according to the protocol. The zinc chelate eradication study emphasized the importance of partial depopulation of post-weaning facilities [10].

Inadequate Cleaning and Disinfection

Organic matter protects Brachyspira hyodysenteriae from disinfectants. Failure to remove all organic material before disinfection is a common cause of eradication failure. The use of 2% NaOH requires thorough pre-cleaning to be effective [10].

Reintroduction from External Sources

Newly introduced pigs, contaminated transport vehicles, or personnel can reintroduce the pathogen. Strict quarantine and testing of incoming animals is essential. Improved external biosecurity measures were a key component of successful eradication protocols [10].

Antimicrobial Resistance

Resistance to pleuromutilins and other key drugs compromises treatment efficacy. Susceptibility testing should guide drug selection, and alternative approaches may be necessary. The worldwide re-emergence of swine dysentery with decreased susceptibility to crucially important antimicrobials has been documented [10].

Carrier Animals

Subclinically infected pigs can shed Brachyspira hyodysenteriae without showing signs. Testing of all animals in affected groups is necessary to identify carriers. The zinc chelate study evaluated Brachyspira hyodysenteriae excretion during and after treatment [10].

Welfare and Safety Context

Animal Welfare Implications

Swine dysentery causes significant pain and distress due to colitis, diarrhea, dehydration, and weight loss. Prompt diagnosis and treatment are essential for welfare. Pigs with severe disease may require euthanasia on welfare grounds. The zinc chelate study reported positive effects on fecal quality and consistency, general clinical signs, and average daily weight gain [10].

Public Health Considerations

Brachyspira hyodysenteriae is not considered a zoonotic pathogen. However, antimicrobial use in swine dysentery control contributes to selection for resistance in the farm environment. Reducing antimicrobial use through alternative strategies benefits both animal and public health. The World Organisation for Animal Health provides frameworks for antimicrobial resistance surveillance [1][3].

Occupational Safety

Personnel handling affected pigs or performing cleaning and disinfection should use appropriate personal protective equipment. Sodium hydroxide (2% NaOH) is caustic and requires careful handling with gloves, eye protection, and proper ventilation. Listeriosis in fattening pigs caused by poor quality silage represents another occupational safety consideration in swine production [16].

Professional Escalation Criteria

Urgent Escalation

Contact a veterinary diagnostic laboratory or swine specialist immediately when:

• High mortality occurs in affected groups
• Treatment fails to control clinical signs within 48-72 hours
• Multiple age groups become affected simultaneously
• Suspected antimicrobial resistance is identified

Routine Escalation

Consult with a swine health specialist when:

• Planning an eradication protocol
• Interpreting complex diagnostic results
• Developing a herd-specific biosecurity plan
• Evaluating non-antibiotic treatment alternatives

Practical Decision Framework for Selecting Eradication Approach

Selecting the appropriate eradication strategy for swine dysentery requires a structured evaluation of farm-specific factors, including herd size, facility design, production flow, antimicrobial susceptibility patterns, and economic constraints. This section provides a practical decision framework that integrates clinical assessment, diagnostic confirmation, treatment selection, and protocol implementation. The framework is designed for veterinarians and swine health professionals to apply systematically when faced with a swine dysentery outbreak or when planning proactive eradication.

Step 1: Initial Farm Assessment and Risk Stratification

Begin with a comprehensive farm assessment that categorizes the operation into one of three risk levels based on disease prevalence, facility type, and management practices. This stratification guides the intensity and duration of the eradication protocol.

Low-Risk Farms

Low-risk farms are those with:

• No clinical signs of swine dysentery in the past 12 months
• Negative PCR or culture results from routine surveillance
• All-in/all-out management by barn or room
• High external biosecurity standards including quarantine for incoming animals
• No recent introductions from herds with unknown health status

For low-risk farms, the primary focus is on maintaining biosecurity and conducting periodic surveillance. The Merck Veterinary Manual recommends routine monitoring of fecal samples from grow-finish pigs at least quarterly to detect subclinical infections [2]. The World Organisation for Animal Health provides frameworks for surveillance that can be adapted to farm-level monitoring [1].

Moderate-Risk Farms

Moderate-risk farms show:

• Intermittent clinical signs in a subset of pens or rooms
• Positive PCR results in fewer than 20% of samples tested
• Continuous flow management in at least part of the facility
• Moderate biosecurity with some gaps in external or internal measures
• History of antimicrobial use for swine dysentery control

These farms require a targeted eradication approach that may include partial depopulation of affected sections, treatment of remaining animals, and enhanced cleaning and disinfection. The zinc chelate eradication study evaluated partial depopulation of post-weaning facilities combined with improved external and internal biosecurity measures as a core strategy for moderate-risk situations [10].

High-Risk Farms

High-risk farms are characterized by:

• Active clinical signs in multiple age groups
• Positive PCR results in more than 20% of samples
• Continuous flow management throughout the facility
• Poor biosecurity with known reintroduction risks
• History of antimicrobial treatment failure or confirmed resistance

High-risk farms require the most intensive eradication protocols, often including complete depopulation of affected barns, extended downtime, and comprehensive cleaning and disinfection. The control of swine dysentery at national level in Sweden demonstrates that systematic, intensive approaches can achieve eradication even in high-prevalence settings [8].

Step 2: Diagnostic Confirmation and Pathogen Characterization

Before selecting a treatment protocol, confirm the presence of Brachyspira hyodysenteriae and characterize the pathogen. This step is critical because other Brachyspira species, including Brachyspira hampsonii clade I, can produce similar clinical signs and require different management approaches [13].

Sample Collection Protocol

Collect fecal samples from at least 10-20 affected pigs per barn or room. For subclinical detection, sample 30-60 pigs from high-risk groups such as grow-finish pigs in continuous flow systems. The Veterinary Record has published guidance on distinguishing Brachyspira hyodysenteriae from other spirochetes that may be confused during diagnostic investigation [6].

Submit samples for:

• PCR targeting the nox gene for Brachyspira hyodysenteriae species confirmation
• Anaerobic culture on selective media for isolation and antimicrobial susceptibility testing
• Histopathology on tissue samples from necropsied pigs if available

Antimicrobial Susceptibility Testing

When culture is successful, request susceptibility testing against a panel including:

• Pleuromutilins (tiamulin, valnemulin)
• Macrolides (tylosin, tilmicosin)
• Other relevant drugs based on regional resistance patterns

A worldwide re-emergence of swine dysentery has been reported with an increasing number of isolates demonstrating decreased susceptibility to several crucially important antimicrobials. This compromises the possibilities to eradicate Brachyspira hyodysenteriae from infected pig farms [10]. Susceptibility results directly inform treatment selection and help identify when non-antibiotic alternatives may be necessary.

Step 3: Treatment Selection Based on Susceptibility and Farm Factors

Use the diagnostic results and farm risk stratification to select the treatment approach. Three primary options exist: antimicrobial therapy, non-antibiotic zinc chelate therapy, or combination approaches.

Antimicrobial Therapy

Antimicrobial therapy is appropriate when:

• Susceptibility testing confirms sensitivity to available drugs
• No history of treatment failure with the selected drug class
• Farm can comply with withdrawal periods and treatment duration
• No regulatory restrictions on antimicrobial use in the region

The Merck Veterinary Manual provides dosing guidelines for approved antimicrobials [2]. Treatment duration should follow label recommendations or veterinary prescription, typically 5-14 days depending on the drug and formulation. Monitor clinical response within 48-72 hours and adjust if no improvement is observed.

Non-Antibiotic Zinc Chelate Therapy

Zinc chelate therapy is indicated when:

• Antimicrobial resistance is confirmed or suspected
• Farm policy aims to reduce antimicrobial use
• Previous antimicrobial treatments have failed
• Regulatory or market requirements restrict antimicrobial use

A novel non-antibiotic zinc chelate (IntraDysovinol 499 mg/mL, IntraCare) has been reported to demonstrate positive effects on fecal quality and consistency, general clinical signs, average daily weight gain, and Brachyspira hyodysenteriae excretion during and after a 6-day oral treatment. A 14-day treatment schedule combined with alternative management measures has been evaluated [10].

Combination Approaches

Combination therapy may be considered when:

• High-risk farm with multiple challenges
• Partial depopulation is not feasible
• Need to address concurrent infections such as ileitis or salmonellosis

In vitro screening of non-antibiotic components to mitigate intestinal lesions caused by Brachyspira hyodysenteriae, Lawsonia intracellularis, and Salmonella enterica serovar Typhimurium has been conducted. Commercially available non-antimicrobial compounds, including fatty acid blends and plant extracts, have been evaluated using an intestinal culture model [12]. These may be used alongside antimicrobial or zinc chelate therapy to support gut health.

Step 4: Protocol Implementation and Monitoring

Implement the selected protocol with clear timelines, responsibilities, and monitoring checkpoints.

Treatment Administration

For antimicrobial or zinc chelate therapy:

• Calculate total dose based on body weight and number of pigs
• Ensure all pigs in affected groups receive the full course
• Document treatment dates, doses, and any adverse reactions
• Monitor feed and water intake during treatment

The zinc chelate eradication study evaluated a 14-day treatment schedule combined with alternative management measures including partial depopulation of post-weaning facilities and improved external and internal biosecurity measures [10].

Cleaning and Disinfection Protocol

Begin cleaning and disinfection from day 7 of treatment onward as described in the zinc chelate study [10]:

1. Remove all organic matter from surfaces
2. Wash with detergent and hot water
3. Apply 2% sodium hydroxide (NaOH) to all surfaces
4. Allow contact time as per disinfectant label
5. Rinse thoroughly after disinfection
6. Allow adequate drying time before repopulation

Sodium hydroxide (2% NaOH) is caustic and requires careful handling with gloves, eye protection, and proper ventilation. All surfaces including floors, walls, feeders, and water lines must be treated. Sows should be washed and treated from day 7 of the treatment protocol onward [10].

Biosecurity Enhancements

Implement or strengthen:

• Dedicated footwear and clothing for each barn
• Boot baths with effective disinfectants at all entry points
• Rodent and bird control programs
• All-in/all-out management by barn or room
• Cleaning and disinfection of transport vehicles
• Quarantine and testing of incoming animals

Improved external and internal biosecurity measures were key components of successful eradication protocols in the zinc chelate study [10].

Step 5: Post-Eradication Monitoring and Confirmation

Monitoring for at least 6-9 months after protocol finalization is necessary to confirm eradication success. All enrolled eradication programs in the zinc chelate study were evaluated as successful at least 6-9 months after the finalization of the protocol [10].

Monitoring Schedule

• Month 1-3: Monthly fecal sampling of high-risk groups (grow-finish pigs, newly introduced animals)
• Month 4-6: Bimonthly sampling
• Month 7-9: Quarterly sampling
• After 9 months: Continue quarterly surveillance indefinitely

Testing Protocol

Collect fecal samples from:

• 30-60 pigs per barn or room for PCR testing
• Any pigs showing clinical signs of diarrhea
• Newly introduced animals before mixing with resident herd

PCR targeting the nox gene for Brachyspira hyodysenteriae is the preferred method for post-eradication monitoring due to its sensitivity and rapid turnaround time. The Veterinary Pathology journal has published detailed descriptions of diagnostic methods for swine dysentery [4].

Criteria for Declaring Eradication Success

Eradication can be considered successful when:

• No clinical signs of swine dysentery observed for at least 6 months
• Negative PCR results from at least three consecutive samplings of high-risk groups
• No positive culture results from any samples
• No reintroduction events identified

Record System for Eradication Protocols

Maintain a structured record system that documents every step of the eradication process. This system serves multiple purposes: tracking progress, identifying failures, supporting regulatory compliance, and providing data for future planning.

Core Record Components

Digital Record Keeping

Use farm management software or spreadsheets to maintain records. Ensure data is backed up and accessible to the veterinarian and farm management. The World Organisation for Animal Health provides frameworks for animal health data management that can be adapted to farm-level record keeping [1][3].

Record Review Schedule

Review records at least monthly during the eradication protocol and quarterly during the monitoring phase. Identify trends, gaps, and areas for improvement. The Tierarztliche Praxis has published diagnostic approaches for swine dysentery that emphasize the importance of systematic record keeping [5].

Troubleshooting Method for Eradication Failures

When eradication fails or clinical signs recur, use a structured troubleshooting method to identify the cause and implement corrective actions.

Step 1: Confirm Diagnosis

Rule out other causes of diarrhea before assuming eradication failure. Differential diagnoses include:

• Salmonellosis: Systemic signs, fever, Salmonella cultured from feces or tissues
• Ileitis (Lawsonia intracellularis): Proliferative lesions in ileum and colon, PCR or histopathology confirmation
• Whipworm (Trichuris suis): Eggs in feces, adult worms visible at necropsy
• Other Brachyspira species: Brachyspira hampsonii, Brachyspira pilosicoli, species-level PCR required

The genome and transcriptome of the porcine whipworm Trichuris suis have been characterized, providing molecular tools for differential diagnosis [17]. Necrotizing enterocolitis (pig bel) represents another differential consideration in certain geographic regions [15].

Step 2: Investigate Treatment Compliance

Review treatment records to determine if:

• All pigs received the full course of treatment
• Doses were calculated correctly based on body weight
• Feed or water intake was adequate during treatment
• No interruptions occurred in treatment administration

Step 3: Assess Cleaning and Disinfection

Evaluate cleaning and disinfection protocols:

• Was all organic matter removed before disinfection?
• Was 2% NaOH applied correctly with adequate contact time?
• Were all surfaces including water lines and feeders treated?
• Was adequate drying time allowed before repopulation?

Organic matter protects Brachyspira hyodysenteriae from disinfectants. Failure to remove all organic material before disinfection is a common cause of eradication failure [10].

Step 4: Identify Reintroduction Sources

Investigate potential reintroduction routes:

• Newly introduced pigs not properly quarantined or tested
• Contaminated transport vehicles
• Personnel moving between farms without changing footwear or clothing
• Rodents or birds carrying the pathogen
• Contaminated feed or water sources

Step 5: Test for Antimicrobial Resistance

If treatment failure is suspected, submit samples for culture and susceptibility testing. Resistance to pleuromutilins and other key drugs compromises treatment efficacy. The worldwide re-emergence of swine dysentery with decreased susceptibility to crucially important antimicrobials has been documented [10].

Step 6: Implement Corrective Actions

Based on the investigation findings, implement targeted corrective actions:

• If treatment compliance was poor: Retrain staff, use alternative delivery methods
• If cleaning was inadequate: Repeat cleaning and disinfection with improved protocols
• If reintroduction occurred: Strengthen biosecurity, quarantine incoming animals
• If resistance is confirmed: Switch to non-antibiotic alternatives or different drug classes

Comparison of Eradication Approaches

Common Failure Patterns and Solutions

Pattern 1: Incomplete Depopulation

Leaving any infected pigs in the facility allows the pathogen to persist. All pigs in affected groups must be removed or treated according to the protocol. The zinc chelate eradication study emphasized the importance of partial depopulation of post-weaning facilities [10].

Solution: Conduct a thorough inventory of all pigs in affected barns before starting the protocol. Use visual inspection and PCR testing to identify all infected groups. Remove or treat every pig in positive groups.

Pattern 2: Inadequate Cleaning and Disinfection

Organic matter protects Brachyspira hyodysenteriae from disinfectants. Failure to remove all organic material before disinfection is a common cause of eradication failure. The use of 2% NaOH requires thorough pre-cleaning to be effective [10].

Solution: Implement a two-step cleaning process: first remove all organic matter with detergent and hot water, then apply disinfectant. Use a checklist to verify all surfaces are treated. Allow adequate contact time and drying.

Pattern 3: Reintroduction from External Sources

Newly introduced pigs, contaminated transport vehicles, or personnel can reintroduce the pathogen. Strict quarantine and testing of incoming animals is essential. Improved external biosecurity measures were a key component of successful eradication protocols [10].

Solution: Establish a quarantine facility for all incoming animals. Test for Brachyspira hyodysenteriae using PCR before mixing with resident herd. Require dedicated footwear and clothing for each barn. Clean and disinfect all transport vehicles.

Pattern 4: Antimicrobial Resistance

Resistance to pleuromutilins and other key drugs compromises treatment efficacy. Susceptibility testing should guide drug selection, and alternative approaches may be necessary. The worldwide re-emergence of swine dysentery with decreased susceptibility to crucially important antimicrobials has been documented [10].

Solution: Submit samples for culture and susceptibility testing before selecting treatment. If resistance is confirmed, switch to non-antibiotic alternatives such as zinc chelate therapy. Consider combination approaches with probiotics or fatty acid blends.

Pattern 5: Carrier Animals

Subclinically infected pigs can shed Brachyspira hyodysenteriae without showing signs. Testing of all animals in affected groups is necessary to identify carriers. The zinc chelate study evaluated Brachyspira hyodysenteriae excretion during and after treatment [10].

Solution: Use PCR testing on fecal samples from all pigs in affected groups, beyond those showing clinical signs. Test at multiple time points to detect intermittent shedders. Consider treating all pigs in positive groups regardless of clinical status.

Professional Escalation Criteria for Eradication Failures

Urgent Escalation

Contact a veterinary diagnostic laboratory or swine specialist immediately when:

• High mortality occurs during or after eradication protocol
• Clinical signs recur within 3 months of protocol completion
• Multiple age groups become affected simultaneously
• Suspected antimicrobial resistance is identified
• Reintroduction from an unknown source is suspected

Routine Escalation

Consult with a swine health specialist when:

• Planning an eradication protocol for a high-risk farm
• Interpreting complex diagnostic results including susceptibility profiles
• Developing a herd-specific biosecurity plan
• Evaluating non-antibiotic treatment alternatives
• Designing a post-eradication monitoring program

The control of swine dysentery at national level in Sweden provides a model for systematic eradication programs that can be adapted to individual farm situations [8]. The World Organisation for Animal Health provides frameworks for disease surveillance and control that support professional decision-making [1][3].

Frequently Asked Questions

What is the primary cause of swine dysentery?

Swine dysentery is primarily caused by Brachyspira hyodysenteriae, a Gram-negative anaerobic spirochete that colonizes the large intestine and induces mucohemorrhagic colitis. The disease is characterized by bloody to mucoid diarrhea in pigs, primarily affecting animals during the growth and finishing stage [10]. Other Brachyspira species, including Brachyspira hampsonii clade I, can also cause similar disease [13].

How is swine dysentery diagnosed?

Diagnosis is based on clinical signs (bloody to mucoid diarrhea in grow-finish pigs), necropsy findings (mucohemorrhagic colitis), and laboratory confirmation. PCR provides rapid species-specific detection from feces or tissue. Culture allows antimicrobial susceptibility testing. Histopathology confirms characteristic lesions. The Merck Veterinary Manual provides detailed diagnostic guidance [2]. Early literature described the diagnostic challenge of differentiating Treponema hyodysenteriae (now Brachyspira hyodysenteriae) from other spirochetes [6].

What are the treatment options for swine dysentery?

Antimicrobial therapy with pleuromutilins, macrolides, or other drugs has been the mainstay of treatment. However, increasing antimicrobial resistance limits options. Non-antibiotic alternatives, including zinc chelate formulations, competitive exclusion probiotics, and fatty acid blends, are under evaluation. A novel non-antibiotic zinc chelate has demonstrated positive effects on fecal quality, clinical signs, weight gain, and pathogen excretion [10].

Can swine dysentery be eradicated from a farm?

Yes, eradication is possible using a systematic approach including partial depopulation, thorough cleaning and disinfection (including 2% NaOH), treatment of remaining animals, enhanced biosecurity, and post-eradication monitoring for at least 6-9 months. A study evaluating this approach on 18 pig farms over a 5-year period reported all enrolled eradication programs as successful at least 6-9 months after protocol finalization [10]. Control of swine dysentery at national level has been demonstrated in Sweden [8].

What is the role of antimicrobial susceptibility testing?

Susceptibility testing identifies which antimicrobials are effective against the specific Brachyspira hyodysenteriae isolate on a farm. This is critical when treatment failure occurs or when resistance to key drugs is suspected. A worldwide re-emergence of swine dysentery has been reported with an increasing number of isolates demonstrating decreased susceptibility to several crucially important antimicrobials [10].

Are there non-antibiotic alternatives for swine dysentery control?

Yes. Zinc chelate formulations have shown positive effects on fecal quality, clinical signs, weight gain, and pathogen excretion [10]. Probiotic candidates with competitive exclusion capacity against Brachyspira hyodysenteriae are being studied, with certain isolates reducing pathogen growth by more than 2 log10 units [11]. Non-antimicrobial compounds including fatty acid blends and plant extracts have been evaluated in vitro [12].

What biosecurity measures prevent swine dysentery?

External biosecurity prevents introduction through quarantine of incoming pigs, cleaning and disinfection of transport vehicles, and control of rodents and birds. Internal biosecurity reduces spread through all-in/all-out management, dedicated footwear and clothing, boot baths, and cleaning and disinfection between groups. Improved external and internal biosecurity measures were key components of successful eradication protocols [10].

How long should post-eradication monitoring continue?

Monitoring should continue for at least 6-9 months after protocol finalization. Regular fecal sampling and PCR testing of high-risk groups, including grow-finish pigs and newly introduced animals, is necessary to confirm eradication success. All enrolled eradication programs in the zinc chelate study were evaluated as successful at least 6-9 months after the finalization of the protocol [10].

Related Veterinary Guides

• Veterinary Clinical Methods Procedures Surgical Interventions
• Swine Respiratory Disease Observation And Diagnostics
• Manure Management For Pig Farms
• Production Records For Pig Farms
• Pig Lameness Monitoring And Flooring Management

References and Further Reading

• World Organisation for Animal Health
• Merck Veterinary Manual. Merck Veterinary Manual.
• Animal Health and Welfare. World Organisation for Animal Health.
• Swine Dysentery.. Veterinary pathology, 2017.
• [Swine dysentery].. Tierarztliche Praxis, 1984.
• Diagnosis of swine dysentery: spirochaetes which may be confused with Treponema hyodysenteriae.. The Veterinary record, 1976.
• [Diagnosis of swine dysentery].. Monatshefte fur Veterinarmedizin, 1971.
• Control of swine dysentery at national level in Sweden.. Acta veterinaria Scandinavica, 2024.
• [Swine dysentery].. Veterinariia, 1975.
• Successful Brachyspira hyodysenteriae Eradication Through a Combined Approach of a Zinc Chelate Treatment and Adapted Management Measures. Pathogens, 2025.
• Exploring the potential for competitive exclusion of commensal probiotic candidates against the insidious swine pathogen Brachyspira hyodysenteriae. Animal Microbiome, 2026.
• In Vitro Screening of Non-Antibiotic Components to Mitigate Intestinal Lesions Caused by Brachyspira hyodysenteriae, Lawsonia intracellularis and Salmonella enterica Serovar Typhimurium. Animals, 2022.
• Confirmation that " Brachyspira hampsonii" clade I (Canadian strain 30599) causes mucohemorrhagic diarrhea and colitis in experimentally infected pigs. BMC Veterinary Research, 2014.
• Characterization of the fecal microbiota of pigs before and after inoculation with "Brachyspira hampsonii". Plos One, 2014.
• Necrotizing enterocolitis (pig bel): A historic and current review. Medizinische Klinik, 2000.
• Listeriosis in fattening pigs caused by poor quality silage - A case report. BMC Veterinary Research, 2018.
• Genome and transcriptome of the porcine whipworm Trichuris suis. Nature Genetics, 2014.

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