Caseous Lymphadenitis in Sheep and Goats: Diagnosis, Abscess Management, and Flock Control

Caseous lymphadenitis (CLA) is a chronic, contagious bacterial disease of sheep and goats caused by Corynebacterium pseudotuberculosis. The infection typically presents as abscesses in peripheral lymph nodes, but internal abscesses in the lungs, liver, kidneys, and other organs are common and often go undetected until slaughter or necropsy. For veterinarians, the primary challenges are confirming the diagnosis, managing abscesses to minimize environmental contamination, and implementing flock-level control measures that reduce prevalence over time. This article provides a practical framework for diagnosing CLA, treating abscesses, and controlling the disease within flocks, based on current veterinary literature and clinical experience.

At a Glance: Caseous Lymphadenitis in Sheep and Goats

Etiology and Pathogenesis

Corynebacterium pseudotuberculosis is a gram-positive, facultative intracellular rod that produces a potent exotoxin, phospholipase D, which is a major virulence factor. The bacterium survives within macrophages and can persist in the environment for extended periods, particularly in dried pus. The organism enters the body through skin wounds, including those from shearing, ear tagging, fighting, or contaminated needles. After entry, it is transported via lymphatics to regional lymph nodes, where it causes abscess formation. The abscess wall is thick and fibrous, containing caseous (cheese-like) pus that is typically greenish-white and layered. Over time, abscesses may rupture spontaneously, releasing large numbers of bacteria into the environment and onto other animals.

The Merck Veterinary Manual provides detailed information on the etiology and pathogenesis of CLA in small ruminants. The World Organisation for Animal Health (WOAH) also includes CLA in its list of notifiable diseases and provides guidance on diagnostic methods and control measures.

Clinical Signs and Disease Presentation

Peripheral Lymph Node Abscesses

The most recognizable form of CLA is abscessation of superficial lymph nodes. The most commonly affected nodes are the submandibular, parotid, prescapular, and prefemoral lymph nodes. Abscesses are firm, non-painful swellings that gradually enlarge over weeks to months. They may eventually rupture, discharging thick, greenish-white pus. In goats, abscesses are often more fluctuant and may rupture earlier than in sheep. Affected animals may show no systemic signs unless abscesses are large or multiple.

Internal Abscesses

Internal CLA is a significant cause of production loss and mortality. Abscesses can develop in the lungs, liver, kidneys, spleen, and other organs. Clinical signs are often vague and include chronic weight loss, poor growth, decreased milk production, and intermittent fever. Respiratory signs such as cough, nasal discharge, and dyspnea may occur with pulmonary abscesses. Internal abscesses are frequently found at slaughter or necropsy, and they represent a major economic loss for producers. The Merck Veterinary Manual notes that internal abscesses are common and often undiagnosed antemortem.

Differential Diagnoses

Peripheral abscesses should be differentiated from other causes of lymph node enlargement, including:

• Abscesses caused by other bacteria (e.g., Trueperella pyogenes, Staphylococcus aureus, Streptococcus spp.)
• Lymph node hyperplasia due to local infection
• Tumors (rare in small ruminants)
• Actinobacillosis (wooden tongue) in sheep

Caseous lymphadenitis is the most common cause of chronic lymph node abscesses in sheep and goats. A study published in the Journal of Veterinary Research on isolation and molecular identification of Corynebacterium pseudotuberculosis and Trueperella pyogenes from cutaneous abscesses in dairy cattle farms highlights the importance of laboratory confirmation for accurate diagnosis.

Diagnosis

Sample Collection and Culture

Definitive diagnosis requires isolation of C. pseudotuberculosis from abscess pus. Collect pus aseptically from an unruptured abscess or from the deep portion of a lanced abscess. The organism is a slow-growing, gram-positive rod that requires 24 to 48 hours of incubation on blood agar. It produces small, dry, white colonies that are catalase-positive and urease-negative. The World Organisation for Animal Health (WOAH) provides detailed diagnostic methods for CLA.

PCR

Polymerase chain reaction (PCR) assays targeting the phospholipase D gene are available and provide rapid, specific identification. PCR can be performed on pus samples and is particularly useful when culture is negative due to prior antibiotic treatment or sample contamination.

Serology

Enzyme-linked immunosorbent assay (ELISA) tests detect antibodies against C. pseudotuberculosis exotoxin. Serology is useful for flock screening to identify subclinically infected animals. However, serology has limitations: it may not detect early infections (seroconversion takes 2 to 4 weeks), and some infected animals may remain seronegative. Serology is best used as a herd-level tool instead of for individual diagnosis.

Imaging

Ultrasound can be used to detect internal abscesses in the thorax and abdomen. Thoracic ultrasound may reveal pulmonary abscesses, pleural effusion, or mediastinal lymph node enlargement. Abdominal ultrasound can identify liver and kidney abscesses. Radiography is less sensitive but may show pulmonary abscesses or mediastinal lymphadenopathy.

Abscess Management

Lancing and Drainage

Lancing and drainage is the most common treatment for peripheral abscesses. The procedure should be performed with strict biosecurity to prevent environmental contamination. Steps include:

1. Restrain the animal securely.
2. Clip and surgically prepare the skin over the abscess.
3. Make a stab incision at the most dependent part of the abscess using a sterile scalpel blade.
4. Drain the pus into a container for disposal. Do not allow pus to contact the ground, bedding, or other animals.
5. Flush the abscess cavity with a dilute antiseptic solution (e.g., 1% povidone-iodine or 0.1% chlorhexidine). Do not use harsh chemicals that may damage tissue.
6. Pack the cavity with sterile gauze if necessary to keep it open for drainage.
7. Dispose of all contaminated materials (gloves, gauze, pus) in a sealed bag for incineration or deep burial.

The wound should be checked daily and flushed as needed until healing is complete. Most abscesses heal within 2 to 4 weeks.

Surgical Excision

Surgical excision of the entire abscess and surrounding fibrous capsule is an alternative for accessible abscesses, particularly in valuable animals. This approach reduces the risk of recurrence and environmental contamination. The procedure requires general anesthesia or heavy sedation and local anesthesia. The abscess is dissected out en bloc, and the wound is closed primarily if possible. Excision is more invasive and costly than lancing but may be preferred for show animals or breeding stock.

Antibiotic Therapy

Antibiotics have limited efficacy in treating CLA because the bacterium is intracellular and the abscess wall is poorly penetrated. Systemic antibiotics are generally not recommended for peripheral abscesses. However, they may be considered for internal abscesses or for animals with multiple abscesses. The choice of antibiotic should be based on culture and sensitivity testing. Commonly used antibiotics include penicillin, tetracyclines, and macrolides, but resistance patterns vary. The Journal of the American Veterinary Medical Association published a comparison of three treatment regimens for sheep and goats with caseous lymphadenitis, which may guide clinical decisions.

Alternative Treatments

Brazilian Green Propolis has been investigated as a therapeutic agent for the post-surgical treatment of caseous lymphadenitis in sheep. A study published in Frontiers in Veterinary Science evaluated its use and found it may have benefits in wound healing and reducing bacterial load. However, this is not a standard treatment and should be considered experimental.

Treatment Failure and Recurrence

Treatment failure is common, particularly with lancing alone. Recurrence rates are high because the fibrous capsule may not be completely removed, and bacteria can persist in the cavity. Animals that fail to respond to treatment or develop new abscesses should be culled to reduce the source of infection for the flock.

Flock Control

Culling

Culling affected animals is the most effective method for reducing CLA prevalence in a flock. Animals with peripheral abscesses should be removed from the flock as soon as possible. Animals with internal abscesses are difficult to identify antemortem, but those with chronic weight loss, poor production, or positive serology should be considered for culling. The Veterinary Clinics of North America: Food Animal Practice published a review on the control of caseous lymphadenitis that discusses culling strategies.

Vaccination

Vaccines for CLA are available in some countries. They are typically bacterins or toxoids that stimulate immunity against the exotoxin. Vaccination can reduce the incidence and severity of abscesses but does not prevent infection entirely. The Applied Microbiology and Biotechnology journal published a review on vaccines for caseous lymphadenitis, discussing current and future strategies. Vaccination is most effective when combined with other control measures, such as culling and biosecurity.

Biosecurity

Biosecurity measures are essential to prevent introduction and spread of CLA. Key practices include:

• Quarantine new animals for at least 30 days and examine them for abscesses.
• Test new animals serologically before introducing them to the flock.
• Use separate equipment (shears, needles, ear taggers) for infected and clean groups.
• Disinfect equipment between animals, especially shearing blades.
• Avoid overcrowding and reduce skin injuries.
• Properly dispose of pus and contaminated materials.
• Maintain clean, dry bedding to reduce environmental contamination.

Testing and Segregation

Serological testing can identify subclinically infected animals. Positive animals should be segregated from the clean flock and either culled or managed separately. Testing should be repeated at regular intervals (e.g., every 6 to 12 months) to monitor the effectiveness of control measures. The goal is to eventually have a seronegative flock.

Environmental Management

C. pseudotuberculosis can survive in the environment for months, particularly in dried pus. Contaminated pens, feeders, and waterers should be cleaned and disinfected. The organism is susceptible to common disinfectants, including bleach (1:10 dilution), chlorhexidine, and iodophors. However, organic matter (pus, manure) protects the bacteria, so thorough cleaning is essential before disinfection.

Records and Measurements

Maintaining accurate records is critical for monitoring CLA control. The following data should be recorded:

• Individual animal identification
• Date and location of abscess detection
• Treatment administered and outcome
• Serological test results
• Culling decisions and dates
• New animal introductions and quarantine results

These records allow the veterinarian and producer to track the prevalence of CLA over time and evaluate the effectiveness of control measures.

Common Failure Patterns

Several common mistakes undermine CLA control efforts:

• Incomplete drainage: Leaving pus in the abscess cavity leads to recurrence.
• Poor biosecurity: Allowing pus to contaminate the environment or equipment spreads infection.
• Failure to cull: Keeping chronically infected animals perpetuates the disease.
• Inadequate quarantine: Introducing new animals without testing or observation brings in new strains.
• Overreliance on antibiotics: Antibiotics are not effective for peripheral abscesses and may select for resistance.
• Ignoring internal abscesses: Animals with internal abscesses continue to shed bacteria and infect others.

Welfare and Safety Context

CLA causes pain and discomfort, particularly when abscesses are large or multiple. Ruptured abscesses can lead to secondary infections and fly strike. Internal abscesses cause chronic disease and suffering. From a welfare perspective, early detection and treatment are important. However, treatment should not be prolonged in animals that do not respond, as this prolongs suffering. Culling is often the most humane option for chronically affected animals.

For veterinarians and producers, there is a zoonotic risk. C. pseudotuberculosis can cause lymphadenitis in humans, particularly in those with compromised immune systems. Proper hygiene, including wearing gloves and washing hands after handling abscesses, is essential.

Professional Escalation Criteria

Veterinarians should consider referral or consultation in the following situations:

• Abscesses that do not respond to standard treatment
• Suspected internal abscesses requiring advanced imaging (CT, MRI)
• Flocks with high prevalence that do not respond to control measures
• Cases where regulatory or export implications exist (e.g., for breeding stock)
• Suspected antimicrobial resistance requiring specialized testing

Practical Decision Framework for CLA Abscess Management: A Stage-Based Approach

Managing caseous lymphadenitis abscesses in sheep and goats requires a structured decision process that accounts for abscess location, stage, animal value, and flock status. A stage-based framework helps veterinarians and producers make consistent, evidence-informed choices instead of relying on ad hoc treatment decisions that may increase environmental contamination or treatment failure. This section presents a practical decision framework organized by abscess stage, a record system for tracking individual abscess outcomes, a troubleshooting method for non-healing abscesses, and a comparison of management approaches for different production scenarios.

Abscess Stage Classification and Corresponding Management Decisions

Caseous lymphadenitis abscesses progress through distinct stages that influence management options. Recognizing these stages allows the clinician to select the most appropriate intervention while minimizing the risk of spreading Corynebacterium pseudotuberculosis to other animals and the environment.

Stage 1: Early developing abscess (days 1 to 14 after infection)

The early abscess presents as a firm, warm, slightly painful swelling in a lymph node region. The overlying skin is intact, and there is no fluctuation on palpation. At this stage, the abscess contains a developing core of necrotic tissue and bacteria surrounded by a thin fibrous capsule. The Merck Veterinary Manual notes that early abscesses may be difficult to distinguish from lymph node hyperplasia due to local infection.

Management options for Stage 1 abscesses include:

• Observation with daily palpation to monitor progression
• Surgical excision if the abscess is accessible and the animal is valuable
• No lancing or drainage at this stage because the pus is not yet liquefied and drainage will be incomplete

Surgical excision of early abscesses removes the entire developing lesion before it matures and ruptures. This approach reduces the risk of environmental contamination compared to lancing a mature abscess. The procedure requires general anesthesia or heavy sedation and local anesthesia. The abscess and surrounding fibrous capsule are dissected out en bloc, and the wound is closed primarily if possible. Excision is more invasive and costly than lancing but may be preferred for show animals, breeding stock, or animals in flocks with low CLA prevalence where eradication is the goal.

Stage 2: Mature fluctuant abscess (days 14 to 28 after infection)

The mature abscess is characterized by a soft, fluctuant swelling with thinning overlying skin. The abscess may have a visible point of impending rupture. The pus inside is thick, greenish-white, and layered, containing high concentrations of C. pseudotuberculosis. This stage represents the highest risk for environmental contamination because spontaneous rupture is imminent.

Management options for Stage 2 abscesses include:

• Lancing and drainage with strict biosecurity
• Surgical excision if the abscess is accessible and the animal is valuable
• No systemic antibiotics because they do not penetrate the abscess wall effectively

Lancing and drainage is the most common treatment for mature peripheral abscesses. The procedure should be performed with strict biosecurity to prevent environmental contamination. Steps include:

1. Restrain the animal securely.
2. Clip and surgically prepare the skin over the abscess.
3. Make a stab incision at the most dependent part of the abscess using a sterile scalpel blade.
4. Drain the pus into a container for disposal. Do not allow pus to contact the ground, bedding, or other animals.
5. Flush the abscess cavity with a dilute antiseptic solution (e.g., 1% povidone-iodine or 0.1% chlorhexidine). Do not use harsh chemicals that may damage tissue.
6. Pack the cavity with sterile gauze if necessary to keep it open for drainage.
7. Dispose of all contaminated materials (gloves, gauze, pus) in a sealed bag for incineration or deep burial.

The wound should be checked daily and flushed as needed until healing is complete. Most abscesses heal within 2 to 4 weeks. The Journal of the American Veterinary Medical Association published a comparison of three treatment regimens for sheep and goats with caseous lymphadenitis, which may guide clinical decisions regarding post-lancing care.

Stage 3: Ruptured or draining abscess

The ruptured abscess has an open wound discharging pus into the environment. This stage represents the highest risk for flock transmission because large numbers of bacteria are released onto the animal's skin, bedding, and equipment. The wound may be contaminated with environmental bacteria, and secondary infection with Trueperella pyogenes or other organisms is common.

Management options for Stage 3 abscesses include:

• Wound cleaning and debridement
• Flushing with dilute antiseptic solution
• Systemic antibiotics if secondary infection is present, based on culture and sensitivity testing
• Isolation of the animal to prevent contact with other animals
• Culling if the abscess is large, multiple, or recurrent

The Veterinary Clinics of North America: Food Animal Practice published a review on the control of caseous lymphadenitis that discusses the importance of isolating animals with ruptured abscesses. Animals with draining abscesses should be housed separately from the main flock until the wound is completely healed and no longer discharging pus.

Stage 4: Chronic or recurrent abscess

The chronic abscess has been present for more than 4 weeks despite treatment, or the animal develops new abscesses at different lymph node sites. Chronic abscesses often have thick fibrous capsules that are difficult to penetrate with antiseptic solutions. Recurrent abscesses indicate that the animal is unable to clear the infection and may have internal abscesses that are seeding new peripheral sites.

Management options for Stage 4 abscesses include:

• Culling the animal to remove the source of infection from the flock
• Surgical excision of the entire abscess and capsule if the animal is valuable and the abscess is accessible
• Diagnostic imaging (ultrasound) to evaluate for internal abscesses
• No further lancing or drainage because this only temporarily addresses the clinical sign without resolving the underlying infection

Culling is the most effective option for chronic or recurrent abscesses. The Veterinary Clinics of North America: Food Animal Practice review on control of caseous lymphadenitis emphasizes that keeping chronically infected animals perpetuates the disease within the flock and undermines control efforts.

Decision Matrix for Abscess Management

The following decision matrix integrates abscess stage, animal value, and flock status to guide management choices. This matrix is intended for use by veterinarians and producers in consultation with their veterinarian.

This matrix reflects the principle that culling is the most effective method for reducing CLA prevalence, as discussed in the Veterinary Clinics of North America: Food Animal Practice review on control of caseous lymphadenitis. For high-value animals in low-prevalence flocks, surgical excision offers the best chance of removing the infection without contaminating the environment.

Record System for Tracking Individual Abscess Outcomes

A systematic record system allows the veterinarian and producer to track abscess outcomes over time and identify animals that are not responding to treatment. The following record system is designed for use on farm with minimal paperwork.

Individual Abscess Record Card

Each animal with a CLA abscess should have a record card that includes:

• Animal identification (ear tag number, name, or other unique identifier)
• Date of abscess detection
• Abscess location (e.g., left submandibular, right prescapular)
• Abscess stage at detection (Stage 1, 2, 3, or 4)
• Treatment performed (lancing, excision, flushing, antibiotics)
• Date of treatment
• Outcome at 7 days (healing, not healing, new abscesses)
• Outcome at 14 days (healed, draining, new abscesses)
• Outcome at 28 days (healed, chronic, recurrent)
• Final disposition (culled, sold, retained)

Flock-Level Abscess Log

A flock-level log should summarize abscess data for all affected animals. This log allows the veterinarian to calculate:

• Abscess incidence (number of new abscesses per month)
• Treatment success rate (percentage of abscesses healed at 28 days)
• Recurrence rate (percentage of animals with new abscesses within 6 months)
• Culling rate (percentage of affected animals culled)

These metrics provide objective data for evaluating the effectiveness of the CLA control program. If the treatment success rate is below 50% or the recurrence rate is above 30%, the veterinarian should reassess the management protocol and consider more aggressive culling.

Troubleshooting Method for Non-Healing Abscesses

Non-healing abscesses are a common frustration in CLA management. The following troubleshooting method provides a systematic approach to identifying and addressing the causes of treatment failure.

Step 1: Assess drainage adequacy

Incomplete drainage is the most common cause of non-healing abscesses. The abscess cavity may have loculations (pockets of pus separated by fibrous tissue) that are not drained by a single incision. Palpate the abscess cavity after drainage to identify any remaining firm areas. If loculations are present, make additional stab incisions at the most dependent points of each loculation. Flush the cavity thoroughly with dilute antiseptic solution to remove all pus and debris.

Step 2: Evaluate for foreign body or necrotic tissue

Foreign bodies (e.g., plant material, dirt, suture material) can prevent healing by providing a nidus for bacterial persistence. Explore the abscess cavity with a sterile gloved finger or blunt probe to identify any foreign material. Remove any foreign bodies and debride necrotic tissue. The Merck Veterinary Manual notes that foreign bodies are a common cause of chronic abscesses in small ruminants.

Step 3: Consider secondary infection

Secondary infection with Trueperella pyogenes, Staphylococcus aureus, or other bacteria can complicate CLA abscesses. Collect a sample of pus for culture and sensitivity testing. If secondary infection is confirmed, treat with an appropriate antibiotic based on sensitivity results. The Journal of Veterinary Research published a study on isolation and molecular identification of Corynebacterium pseudotuberculosis and Trueperella pyogenes from cutaneous abscesses, highlighting the importance of identifying mixed infections.

Step 4: Assess for internal abscesses

Animals with non-healing peripheral abscesses may have internal abscesses that are seeding new infections. Perform thoracic and abdominal ultrasound to evaluate for internal abscesses in the lungs, liver, kidneys, and other organs. If internal abscesses are detected, the prognosis for recovery is poor, and culling is recommended. The Veterinary Clinics of North America: Food Animal Practice review on caseous lymphadenitis in small ruminants discusses the high prevalence of internal abscesses in chronically infected animals.

Step 5: Evaluate the animal's immune status

Animals that are immunosuppressed due to concurrent disease, poor nutrition, or stress may not heal abscesses effectively. Evaluate the animal's body condition score, fecal egg count, and overall health status. Address any underlying health problems before attempting further abscess treatment. Animals that fail to heal despite adequate drainage and appropriate treatment should be culled.

Comparison of Management Approaches for Different Production Scenarios

The optimal approach to CLA abscess management varies depending on the production system, flock size, and disease prevalence. The following comparison outlines the advantages and limitations of different management approaches for common production scenarios.

Approach 1: Aggressive culling (recommended for low-prevalence flocks)

In flocks with low CLA prevalence (less than 5% of animals affected), aggressive culling of all affected animals is the most effective strategy for eradication. Animals with peripheral abscesses are culled immediately. Animals with positive serology are culled or segregated and retested. This approach requires a commitment to testing and culling over several years but can result in a CLA-free flock.

Advantages:

• Rapid reduction in disease prevalence
• Elimination of the environmental reservoir of bacteria
• Potential for eradication

Limitations:

• High cost of culling affected animals
• Loss of genetic material
• Requires accurate diagnostic testing

Approach 2: Treatment and selective culling (recommended for moderate-prevalence flocks)

In flocks with moderate CLA prevalence (5% to 20% of animals affected), treatment of peripheral abscesses combined with selective culling of chronic or recurrent cases can reduce prevalence over time. Animals with Stage 2 abscesses are lanced and drained. Animals with Stage 4 abscesses are culled. Serological testing is used to identify subclinically infected animals for segregation or culling.

Advantages:

• Lower immediate cost than aggressive culling
• Allows retention of valuable breeding stock
• Gradual reduction in prevalence

Limitations:

• Slower progress toward eradication
• Risk of environmental contamination during treatment
• Requires consistent record keeping and follow-up

Approach 3: Symptomatic treatment only (not recommended for control)

In flocks with high CLA prevalence (greater than 20% of animals affected), some producers may choose to treat abscesses symptomatically without attempting to reduce prevalence. This approach involves lancing and draining abscesses as they appear, with no culling or testing. While this approach may be perceived as less expensive in the short term, it perpetuates the disease and may lead to increasing prevalence over time.

Advantages:

• Low immediate cost
• Minimal management changes

Limitations:

• Does not reduce disease prevalence
• High risk of environmental contamination
• Poor welfare outcomes for chronically affected animals
• May lead to export restrictions or loss of market access

The Veterinary Clinics of North America: Food Animal Practice review on control of caseous lymphadenitis emphasizes that symptomatic treatment alone is not an effective control strategy and should be avoided in flocks where disease reduction is a goal.

Practical Implementation Steps for the Decision Framework

Implementing the stage-based decision framework requires a systematic approach that integrates clinical examination, record keeping, and communication with the producer. The following steps provide a practical guide for veterinarians.

Step 1: Classify each abscess by stage

At each examination, classify the abscess as Stage 1, 2, 3, or 4 based on the criteria described above. Record the stage on the individual abscess record card.

Step 2: Apply the decision matrix

Use the decision matrix to select the appropriate management option based on abscess stage, animal value, and flock status. Discuss the options with the producer and obtain informed consent before proceeding with treatment.

Step 3: Perform treatment with strict biosecurity

Whether lancing, draining, or excising, perform the procedure with strict biosecurity to prevent environmental contamination. Use disposable gloves, collect pus in a sealed container, and disinfect the treatment area after the procedure.

Step 4: Schedule follow-up examinations

Schedule follow-up examinations at 7, 14, and 28 days after treatment. At each follow-up, assess the wound for healing, drainage, and new abscess formation. Record the outcome on the individual abscess record card.

Step 5: Escalate to culling if treatment fails

If the abscess has not healed by 28 days, or if new abscesses develop at other sites, recommend culling the animal. Explain to the producer that continued treatment is unlikely to be successful and that the animal represents a source of infection for the rest of the flock.

Step 6: Review flock-level data regularly

Review the flock-level abscess log at least every 6 months to assess the effectiveness of the CLA control program. Calculate incidence, treatment success rate, recurrence rate, and culling rate. If these metrics are not improving, consider more aggressive culling or consultation with a veterinary specialist.

Professional Escalation Criteria for Abscess Management

Veterinarians should consider referral or consultation in the following situations related to abscess management:

• Abscesses that do not respond to standard treatment after 28 days
• Suspected internal abscesses requiring advanced imaging (CT, MRI)
• Flocks with high prevalence that do not respond to control measures
• Cases where regulatory or export implications exist (e.g., for breeding stock)
• Suspected antimicrobial resistance requiring specialized testing
• Animals with multiple recurrent abscesses that may have internal disease

The World Organisation for Animal Health provides guidance on diagnostic methods and control measures for CLA that may be useful in complex cases.

Practical Decision Framework for CLA Abscess Management: A Stage-Based Approach

Managing caseous lymphadenitis abscesses in sheep and goats requires a structured decision process that accounts for abscess location, stage, animal value, and flock status. A stage-based framework helps veterinarians and producers make consistent, evidence-informed choices instead of relying on ad hoc treatment decisions that may increase environmental contamination or treatment failure. This section presents a practical decision framework organized by abscess stage, a record system for tracking individual abscess outcomes, a troubleshooting method for non-healing abscesses, and a comparison of management approaches for different production scenarios.

Abscess Stage Classification and Corresponding Management Decisions

Caseous lymphadenitis abscesses progress through distinct stages that influence management options. Recognizing these stages allows the clinician to select the most appropriate intervention while minimizing the risk of spreading Corynebacterium pseudotuberculosis to other animals and the environment.

Stage 1: Early developing abscess (days 1 to 14 after infection)

The early abscess presents as a firm, warm, slightly painful swelling in a lymph node region. The overlying skin is intact, and there is no fluctuation on palpation. At this stage, the abscess contains a developing core of necrotic tissue and bacteria surrounded by a thin fibrous capsule. The Merck Veterinary Manual notes that early abscesses may be difficult to distinguish from lymph node hyperplasia due to local infection.

Management options for Stage 1 abscesses include:

• Observation with daily palpation to monitor progression
• Surgical excision if the abscess is accessible and the animal is valuable
• No lancing or drainage at this stage because the pus is not yet liquefied and drainage will be incomplete

Surgical excision of early abscesses removes the entire developing lesion before it matures and ruptures. This approach reduces the risk of environmental contamination compared to lancing a mature abscess. The procedure requires general anesthesia or heavy sedation and local anesthesia. The abscess and surrounding fibrous capsule are dissected out en bloc, and the wound is closed primarily if possible. Excision is more invasive and costly than lancing but may be preferred for show animals, breeding stock, or animals in flocks with low CLA prevalence where eradication is the goal.

Stage 2: Mature fluctuant abscess (days 14 to 28 after infection)

The mature abscess is characterized by a soft, fluctuant swelling with thinning overlying skin. The abscess may have a visible point of impending rupture. The pus inside is thick, greenish-white, and layered, containing high concentrations of C. pseudotuberculosis. This stage represents the highest risk for environmental contamination because spontaneous rupture is imminent.

Management options for Stage 2 abscesses include:

• Lancing and drainage with strict biosecurity
• Surgical excision if the abscess is accessible and the animal is valuable
• No systemic antibiotics because they do not penetrate the abscess wall effectively

Lancing and drainage is the most common treatment for mature peripheral abscesses. The procedure should be performed with strict biosecurity to prevent environmental contamination. Steps include:

1. Restrain the animal securely.
2. Clip and surgically prepare the skin over the abscess.
3. Make a stab incision at the most dependent part of the abscess using a sterile scalpel blade.
4. Drain the pus into a container for disposal. Do not allow pus to contact the ground, bedding, or other animals.
5. Flush the abscess cavity with a dilute antiseptic solution (e.g., 1% povidone-iodine or 0.1% chlorhexidine). Do not use harsh chemicals that may damage tissue.
6. Pack the cavity with sterile gauze if necessary to keep it open for drainage.
7. Dispose of all contaminated materials (gloves, gauze, pus) in a sealed bag for incineration or deep burial.

The wound should be checked daily and flushed as needed until healing is complete. Most abscesses heal within 2 to 4 weeks. The Journal of the American Veterinary Medical Association published a comparison of three treatment regimens for sheep and goats with caseous lymphadenitis, which may guide clinical decisions regarding post-lancing care.

Stage 3: Ruptured or draining abscess

The ruptured abscess has an open wound discharging pus into the environment. This stage represents the highest risk for flock transmission because large numbers of bacteria are released onto the animal's skin, bedding, and equipment. The wound may be contaminated with environmental bacteria, and secondary infection with Trueperella pyogenes or other organisms is common.

Management options for Stage 3 abscesses include:

• Wound cleaning and debridement
• Flushing with dilute antiseptic solution
• Systemic antibiotics if secondary infection is present, based on culture and sensitivity testing
• Isolation of the animal to prevent contact with other animals
• Culling if the abscess is large, multiple, or recurrent

The Veterinary Clinics of North America: Food Animal Practice published a review on the control of caseous lymphadenitis that discusses the importance of isolating animals with ruptured abscesses. Animals with draining abscesses should be housed separately from the main flock until the wound is completely healed and no longer discharging pus.

Stage 4: Chronic or recurrent abscess

The chronic abscess has been present for more than 4 weeks despite treatment, or the animal develops new abscesses at different lymph node sites. Chronic abscesses often have thick fibrous capsules that are difficult to penetrate with antiseptic solutions. Recurrent abscesses indicate that the animal is unable to clear the infection and may have internal abscesses that are seeding new peripheral sites.

Management options for Stage 4 abscesses include:

• Culling the animal to remove the source of infection from the flock
• Surgical excision of the entire abscess and capsule if the animal is valuable and the abscess is accessible
• Diagnostic imaging (ultrasound) to evaluate for internal abscesses
• No further lancing or drainage because this only temporarily addresses the clinical sign without resolving the underlying infection

Culling is the most effective option for chronic or recurrent abscesses. The Veterinary Clinics of North America: Food Animal Practice review on control of caseous lymphadenitis emphasizes that keeping chronically infected animals perpetuates the disease within the flock and undermines control efforts.

Decision Matrix for Abscess Management

The following decision matrix integrates abscess stage, animal value, and flock status to guide management choices. This matrix is intended for use by veterinarians and producers in consultation with their veterinarian.

This matrix reflects the principle that culling is the most effective method for reducing CLA prevalence, as discussed in the Veterinary Clinics of North America: Food Animal Practice review on control of caseous lymphadenitis. For high-value animals in low-prevalence flocks, surgical excision offers the best chance of removing the infection without contaminating the environment.

Record System for Tracking Individual Abscess Outcomes

A systematic record system allows the veterinarian and producer to track abscess outcomes over time and identify animals that are not responding to treatment. The following record system is designed for use on farm with minimal paperwork.

Individual Abscess Record Card

Each animal with a CLA abscess should have a record card that includes:

• Animal identification (ear tag number, name, or other unique identifier)
• Date of abscess detection
• Abscess location (e.g., left submandibular, right prescapular)
• Abscess stage at detection (Stage 1, 2, 3, or 4)
• Treatment performed (lancing, excision, flushing, antibiotics)
• Date of treatment
• Outcome at 7 days (healing, not healing, new abscesses)
• Outcome at 14 days (healed, draining, new abscesses)
• Outcome at 28 days (healed, chronic, recurrent)
• Final disposition (culled, sold, retained)

Flock-Level Abscess Log

A flock-level log should summarize abscess data for all affected animals. This log allows the veterinarian to calculate:

• Abscess incidence (number of new abscesses per month)
• Treatment success rate (percentage of abscesses healed at 28 days)
• Recurrence rate (percentage of animals with new abscesses within 6 months)
• Culling rate (percentage of affected animals culled)

These metrics provide objective data for evaluating the effectiveness of the CLA control program. If the treatment success rate is below 50% or the recurrence rate is above 30%, the veterinarian should reassess the management protocol and consider more aggressive culling.

Troubleshooting Method for Non-Healing Abscesses

Non-healing abscesses are a common frustration in CLA management. The following troubleshooting method provides a systematic approach to identifying and addressing the causes of treatment failure.

Step 1: Assess drainage adequacy

Incomplete drainage is the most common cause of non-healing abscesses. The abscess cavity may have loculations (pockets of pus separated by fibrous tissue) that are not drained by a single incision. Palpate the abscess cavity after drainage to identify any remaining firm areas. If loculations are present, make additional stab incisions at the most dependent points of each loculation. Flush the cavity thoroughly with dilute antiseptic solution to remove all pus and debris.

Step 2: Evaluate for foreign body or necrotic tissue

Foreign bodies (e.g., plant material, dirt, suture material) can prevent healing by providing a nidus for bacterial persistence. Explore the abscess cavity with a sterile gloved finger or blunt probe to identify any foreign material. Remove any foreign bodies and debride necrotic tissue. The Merck Veterinary Manual notes that foreign bodies are a common cause of chronic abscesses in small ruminants.

Step 3: Consider secondary infection

Secondary infection with Trueperella pyogenes, Staphylococcus aureus, or other bacteria can complicate CLA abscesses. Collect a sample of pus for culture and sensitivity testing. If secondary infection is confirmed, treat with an appropriate antibiotic based on sensitivity results. The Journal of Veterinary Research published a study on isolation and molecular identification of Corynebacterium pseudotuberculosis and Trueperella pyogenes from cutaneous abscesses, highlighting the importance of identifying mixed infections.

Step 4: Assess for internal abscesses

Animals with non-healing peripheral abscesses may have internal abscesses that are seeding new infections. Perform thoracic and abdominal ultrasound to evaluate for internal abscesses in the lungs, liver, kidneys, and other organs. If internal abscesses are detected, the prognosis for recovery is poor, and culling is recommended. The Veterinary Clinics of North America: Food Animal Practice review on caseous lymphadenitis in small ruminants discusses the high prevalence of internal abscesses in chronically infected animals.

Step 5: Evaluate the animal's immune status

Animals that are immunosuppressed due to concurrent disease, poor nutrition, or stress may not heal abscesses effectively. Evaluate the animal's body condition score, fecal egg count, and overall health status. Address any underlying health problems before attempting further abscess treatment. Animals that fail to heal despite adequate drainage and appropriate treatment should be culled.

Comparison of Management Approaches for Different Production Scenarios

The optimal approach to CLA abscess management varies depending on the production system, flock size, and disease prevalence. The following comparison outlines the advantages and limitations of different management approaches for common production scenarios.

Approach 1: Aggressive culling (recommended for low-prevalence flocks)

In flocks with low CLA prevalence (less than 5% of animals affected), aggressive culling of all affected animals is the most effective strategy for eradication. Animals with peripheral abscesses are culled immediately. Animals with positive serology are culled or segregated and retested. This approach requires a commitment to testing and culling over several years but can result in a CLA-free flock.

Advantages:

• Rapid reduction in disease prevalence
• Elimination of the environmental reservoir of bacteria
• Potential for eradication

Limitations:

• High cost of culling affected animals
• Loss of genetic material
• Requires accurate diagnostic testing

Approach 2: Treatment and selective culling (recommended for moderate-prevalence flocks)

In flocks with moderate CLA prevalence (5% to 20% of animals affected), treatment of peripheral abscesses combined with selective culling of chronic or recurrent cases can reduce prevalence over time. Animals with Stage 2 abscesses are lanced and drained. Animals with Stage 4 abscesses are culled. Serological testing is used to identify subclinically infected animals for segregation or culling.

Advantages:

• Lower immediate cost than aggressive culling
• Allows retention of valuable breeding stock
• Gradual reduction in prevalence

Limitations:

• Slower progress toward eradication
• Risk of environmental contamination during treatment
• Requires consistent record keeping and follow-up

Approach 3: Symptomatic treatment only (not recommended for control)

In flocks with high CLA prevalence (greater than 20% of animals affected), some producers may choose to treat abscesses symptomatically without attempting to reduce prevalence. This approach involves lancing and draining abscesses as they appear, with no culling or testing. While this approach may be perceived as less expensive in the short term, it perpetuates the disease and may lead to increasing prevalence over time.

Advantages:

• Low immediate cost
• Minimal management changes

Limitations:

• Does not reduce disease prevalence
• High risk of environmental contamination
• Poor welfare outcomes for chronically affected animals
• May lead to export restrictions or loss of market access

The Veterinary Clinics of North America: Food Animal Practice review on control of caseous lymphadenitis emphasizes that symptomatic treatment alone is not an effective control strategy and should be avoided in flocks where disease reduction is a goal.

Practical Implementation Steps for the Decision Framework

Implementing the stage-based decision framework requires a systematic approach that integrates clinical examination, record keeping, and communication with the producer. The following steps provide a practical guide for veterinarians.

Step 1: Classify each abscess by stage

At each examination, classify the abscess as Stage 1, 2, 3, or 4 based on the criteria described above. Record the stage on the individual abscess record card.

Step 2: Apply the decision matrix

Use the decision matrix to select the appropriate management option based on abscess stage, animal value, and flock status. Discuss the options with the producer and obtain informed consent before proceeding with treatment.

Step 3: Perform treatment with strict biosecurity

Whether lancing, draining, or excising, perform the procedure with strict biosecurity to prevent environmental contamination. Use disposable gloves, collect pus in a sealed container, and disinfect the treatment area after the procedure.

Step 4: Schedule follow-up examinations

Schedule follow-up examinations at 7, 14, and 28 days after treatment. At each follow-up, assess the wound for healing, drainage, and new abscess formation. Record the outcome on the individual abscess record card.

Step 5: Escalate to culling if treatment fails

If the abscess has not healed by 28 days, or if new abscesses develop at other sites, recommend culling the animal. Explain to the producer that continued treatment is unlikely to be successful and that the animal represents a source of infection for the rest of the flock.

Step 6: Review flock-level data regularly

Review the flock-level abscess log at least every 6 months to assess the effectiveness of the CLA control program. Calculate incidence, treatment success rate, recurrence rate, and culling rate. If these metrics are not improving, consider more aggressive culling or consultation with a veterinary specialist.

Professional Escalation Criteria for Abscess Management

Veterinarians should consider referral or consultation in the following situations related to abscess management:

• Abscesses that do not respond to standard treatment after 28 days
• Suspected internal abscesses requiring advanced imaging (CT, MRI)
• Flocks with high prevalence that do not respond to control measures
• Cases where regulatory or export implications exist (e.g., for breeding stock)
• Suspected antimicrobial resistance requiring specialized testing
• Animals with multiple recurrent abscesses that may have internal disease

The World Organisation for Animal Health provides guidance on diagnostic methods and control measures for CLA that may be useful in complex cases.

Frequently Asked Questions

What is the most common cause of lymph node abscesses in sheep and goats?

Corynebacterium pseudotuberculosis is the most common cause of chronic lymph node abscesses in sheep and goats. Other bacteria, such as Trueperella pyogenes and Staphylococcus aureus, can also cause abscesses but are less common.

How is caseous lymphadenitis transmitted between animals?

Transmission occurs through direct contact with pus from ruptured abscesses. The bacteria enter through skin wounds, including those from shearing, ear tagging, fighting, or contaminated needles. Indirect transmission via contaminated equipment or environment is also possible.

Can caseous lymphadenitis be cured with antibiotics?

Antibiotics have limited efficacy for peripheral abscesses because the bacteria are intracellular and the abscess wall is poorly penetrated. Systemic antibiotics may be considered for internal abscesses, but treatment should be guided by culture and sensitivity testing. Lancing and drainage is the primary treatment for peripheral abscesses.

What is the best way to diagnose caseous lymphadenitis in a flock?

Culture and PCR of pus from abscesses provide a definitive diagnosis. Serology (ELISA) is useful for flock screening to identify subclinically infected animals. Ultrasound can detect internal abscesses.

How long does Corynebacterium pseudotuberculosis survive in the environment?

The bacteria can survive for months in dried pus and contaminated environments. Proper cleaning and disinfection are essential to reduce environmental contamination.

Is there a vaccine for caseous lymphadenitis?

Vaccines are available in some countries. They can reduce the incidence and severity of abscesses but do not prevent infection. Vaccination should be combined with other control measures, such as culling and biosecurity.

Should I cull animals with caseous lymphadenitis?

Culling affected animals is the most effective method for reducing CLA prevalence. Animals with peripheral abscesses should be removed from the flock. Animals with internal abscesses or chronic weight loss should also be considered for culling.

Can humans get caseous lymphadenitis from sheep or goats?

Yes, C. pseudotuberculosis can cause lymphadenitis in humans, particularly in those with compromised immune systems. Proper hygiene, including wearing gloves and washing hands after handling abscesses, is essential to prevent zoonotic transmission.

Related Veterinary Guides

• Goat Health Management Vaccination Biosecurity Disease Prevention
• Dairy Sheep Production Systems Breeds Milking And Flock Management
• Veterinary Clinical Methods Procedures Surgical Interventions
• Beef Cattle Backgrounding Management
• Beef Cattle Manure Management

References and Further Reading

• www.acvim.org
• Merck Veterinary Manual. Merck Veterinary Manual.
• Animal Health and Welfare. World Organisation for Animal Health.
• Control of caseous lymphadenitis.. The Veterinary clinics of North America. Food animal practice, 2011.
• Comparison of three treatment regimens for sheep and goats with caseous lymphadenitis.. Journal of the American Veterinary Medical Association, 2009.
• Caseous lymphadenitis in small ruminants.. The Veterinary clinics of North America. Food animal practice, 2001.
• Brazilian Green Propolis as a Therapeutic Agent for the Post-surgical Treatment of Caseous Lymphadenitis in Sheep.. Frontiers in veterinary science, 2019.
• Treatment of ovine caseous lymphadenitis.. The Veterinary record, 2006.
• Vaccines for caseous lymphadenitis: up-to-date and forward-looking strategies.. Applied microbiology and biotechnology, 2021.
• Isolation and Molecular Identification of Corynebacterium pseudotuberculosis and Trueperella pyogenes from Cutaneous Abscesses in Dairy Cattle Farms Around Tehran. Journal of Veterinary Research, 2022.

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