# Differential Diagnosis of Skin Lesions in Poultry: Infectious and Management Causes


## Key Takeaways

- Differentiating poultry skin lesions requires correlating lesion morphology (vesicle, scab, ulcer, nodule) and distribution (focal vs. generalized) with flock signalment (age, production class) and mortality patterns. For instance, Marek's disease often presents with follicular nodules in birds aged 8-20 weeks, while contact dermatitis affects weight-bearing surfaces in young broilers due to litter quality issues.
- Viral etiologies like Marek's disease and avian leukosis are distinguished by lesion characteristics and age of onset; Marek's disease typically involves follicular lesions and nerve enlargement, while avian leukosis presents with more diffuse skin thickening or nodular infiltration in older birds, often with bursal tumors. Histopathology is the reference standard for definitive diagnosis.
- Bacterial and fungal dermatitis commonly arise secondary to skin trauma or poor environmental conditions, presenting as moist dermatitis, scabbing, or dry, scaly lesions. Bacterial infections often involve *Staphylococcus aureus* or *E. coli*, while fungal dermatitis may be seen in high-humidity environments.
- Parasitic infestations, such as by mites or lice, are characterized by pruritus, self-trauma, feather loss, and scabbing, particularly around the vent and thighs. The presence of pruritus and identification of the parasite are key diagnostic indicators.
- Management-related causes like ammonia scald and contact dermatitis result from prolonged exposure to irritants in litter, leading to erythema, ulceration, and scabbing on contact surfaces. These are preventable through proper litter management and ventilation.
- Highly pathogenic avian influenza (HPAI) can manifest with edema, cyanosis, and hemorrhage of the comb and wattles, but absence of these classic signs does not rule out infection, especially when progressive mortality is observed. Prompt reporting to animal health authorities is critical.

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This article provides a diagnostic framework for veterinarians evaluating skin lesions in commercial and smallholder poultry flocks. It distinguishes infectious, parasitic, and management-related causes using lesion morphology, distribution, flock signalment, and progression patterns. The content assumes familiarity with poultry anatomy, necropsy technique, and basic flock medicine, and it supports clinical reasoning when the presenting complaint is dermatitis, feather loss, scabbing, or ulceration of the skin.

The differential diagnosis of poultry skin lesions spans viral, bacterial, fungal, parasitic, nutritional, and environmental causes. Many conditions produce overlapping gross appearances, and a lesion that suggests a single etiology in an individual bird may represent a different process when viewed at flock level. This article prioritizes the clinical and pathological features that separate these entities, with attention to the diagnostic value of lesion location, bird age, and the presence or absence of systemic signs. The scope excludes treatment protocols and biosecurity interventions, which are covered elsewhere.

The practicing veterinarian should approach these cases with a structured workup: characterize the lesion, determine its distribution across the flock, establish the age and production class affected, and correlate skin findings with mortality, feed intake, and behavior. This foundation supports the differential tables and decision pathways presented in subsequent sections.

## At a Glance

| Parameter | Diagnostic Significance | Key Distinguishing Feature |
|---|---|---|
| Lesion distribution | Focal versus generalized | Marek's disease often follicular, contact dermatitis affects weight-bearing surfaces |
| Bird age | Narrows viral versus management causes | Marek's disease peaks at 12 to 24 weeks, management dermatitis occurs in young broilers |
| Mortality pattern | Separates infectious from environmental | Highly pathogenic avian influenza produces progressive mortality, management causes rarely fatal |
| Lesion morphology | Vesicle, scab, ulcer, or nodule | Vesicles suggest viral infection, ulcers suggest contact or bacterial origin |
| Flock history | Feed, litter, stocking density | Ionophore toxicity and ammonia scald have characteriztic management histories |
| Systemic involvement | Skin-only versus multi-organ | Avian leukosis and Marek's disease often show visceral lesions |
| Pruritus presence | Parasitic versus non-parasitic | Mites and lice cause self-trauma, bacterial dermatitis does not |

## Skin Structure and Lesion Biology in Poultry

Avian skin differs from mammalian skin in ways that directly affect lesion expression. The epidermis is thin, the dermis is poorly vascularized, and the absence of sebaceous glands alters the response to irritants. Feather follicles are deeply embedded and highly vascular, making them a route for systemic viral spread and a site of predilection for neoplastic infiltration. The comb and wattles are densely vascularized and poorly insulated, which explains their prominence in vascular and ischemic conditions.

The skin's response to injury is limited to a narrow range of gross patterns: erythema, vesiculation, scabbing, ulceration, nodule formation, and feather loss. These patterns are not pathognomonic for any single agent. The diagnostic task is to match the pattern with the epidemiological context. For example, follicular nodules in an adolescent layer flock point toward Marek's disease, whereas the same gross appearance in a broiler flock at three weeks of age is more consistent with bacterial folliculitis or a management-related irritant.

## Viral Causes of Skin Lesions

### Marek's Disease

Marek's disease is caused by a cell-associated alphaherpesvirus and produces characteriztic skin lesions, particularly in the feather follicle epithelium. Gross findings include raised, nodular, or plaque-like lesions at feather follicles, often with associated erythema or scabbing. The skin form of Marek's disease is one of several clinical presentations, and its recognition matters because skin lesions may be the only external sign in an otherwise healthy-looking bird.

The differential diagnosis between Marek's disease and avian leukosis has historically relied on pathological criteria. Age at presentation, nerve and eye involvement, bursal atrophy in Marek's disease versus bursal tumor growth in lymphoid leukosis, and the pattern of visceral involvement are the principal distinguishing features. Histological confirmation is recommended for individual diagnosis, but herd-level diagnosis based on gross pathology is considered reliable when these criteria are applied systematically, as described in the German-language study on pathological-anatomical diagnosis of Marek's disease and lymphoid leukosis.

### Avian Leukosis

Avian leukosis viruses, particularly the lymphoid leukosis subgroup, can produce skin manifestations, though these are less common than visceral tumors. The retroviruses responsible for avian osteopetrosis also cause proliferative diaphyseal thickening, and the same viral family can induce cutaneous lymphoid infiltration. Skin lesions in avian leukosis are typically less follicular than those of Marek's disease and more often present as diffuse thickening or nodular infiltration. Age at onset is generally later, and bursal involvement is characteriztic.

### Highly Pathogenic Avian Influenza

Highly pathogenic avian influenza (HPAI) can produce edema, cyanosis, and hemorrhagic lesions of the comb, wattles, and shanks. However, the gross lesions observed in field outbreaks do not always match textbook descriptions. In the 2003 H7N7 epidemic in the Netherlands, the first five infected flocks lacked the expected hemorrhagic changes, edema, and cyanosis, which delayed recognition. The lesson for the clinician is that the absence of classic skin signs does not exclude HPAI, and increased progressive mortality should prompt consideration of this diagnosis even when skin lesions are atypical or absent.

## Bacterial and Fungal Causes

Bacterial dermatitis in poultry most commonly involves *Staphylococcus aureus*, *Escherichia coli*, and *Clostridium* species. These infections typically arise secondary to skin trauma, poor litter quality, or immunosuppression. Gross findings include moist dermatitis, scabbing, and ulceration, often on the breast, abdomen, and feet. Cellulitis in broilers presents as a diffuse subcutaneous thickening and discoloration of the lower abdomen and thigh, frequently detected at processing.

Fungal dermatitis is less common but should be considered in flocks with poor ventilation and high humidity. Lesions are typically dry, scaly, and poorly demarcated, affecting the face, comb, and wattles. The diagnosis is supported by skin scraping and cytology, with culture reserved for refractory cases.

## Parasitic Causes

Ectoparasites produce skin lesions through direct feeding, irritation, and self-trauma. The northern fowl mite (*Ornithonyssus sylviarum*) and the chicken mite (*Dermanyssus gallinae*) cause pruritus, feather loss, and scabbing, particularly around the vent, tail, and back. Lice infestations produce similar signs but are more often visible on the bird. Scaly leg mite (*Knemidocoptes mutans*) causes distinctive proliferative crusting of the shanks and feet.

The key diagnostic feature of parasitic skin disease is the presence of pruritus and the identification of the parasite on the bird or in the environment. Skin lesions without pruritus are unlikely to be primarily parasitic.

## Management and Environmental Causes

### Contact Dermatitis and Ammonia Scald

Contact dermatitis of the breast, hocks, and feet results from prolonged exposure to wet, compacted litter. The pathogenesis involves chemical irritation from ammonia and fecal material, followed by secondary bacterial infection. Lesions begin as erythema and progress to ulceration and scabbing. Flock-level risk factors include high stocking density, poor ventilation, and litter moisture above 25 to 30 percent. The condition is almost entirely preventable through litter management, and its presence indicates an environmental failure instead of an infectious outbreak.

### Ionophore Toxicity

Ionophore toxicity, while primarily a neuromuscular and cardiac condition, can produce skin changes secondary to recumbency and self-trauma. The clinical syndrome includes anorexia, diarrhea, dyspnea, ataxia, and recumbency, with pathological findings of focal degenerative cardiomyopathy and skeletal muscle necrosis. Skin lesions in affected birds are pressure sores and abrasions from prolonged recumbency instead of primary dermatological disease. The diagnosis rests on feed history and the characteriztic muscle and cardiac pathology, as clinical signs and lesions are not pathognomonic.

## Diagnostic Workup: History, Flock Signalment, and Lesion Mapping

The diagnostic sequence begins before the first bird is examined. Flock history should establish age, breed, vaccination status, feed source and delivery dates, litter type and condition, stocking density, ventilation settings, and recent changes in management. Age is the single most discriminating signalment variable. Marek's disease typically produces skin lesions in birds between 8 and 20 weeks of age, whereas avian leukosis manifests later, usually after sexual maturity, a distinction supported by the pathologico-anatomic criteria used in herd diagnosis of the two neoplasms. Highly pathogenic avian influenza should be considered at any age but becomes a leading differential when mortality rises sharply over 48 to 72 hours.

Lesion mapping requires a standardized approach. Examine the bird in good light, preferably natural daylight, and record the distribution of lesions on a body diagram. Note whether lesions are confined to feathered skin, unfeathered skin, or both. Distinguish primary lesions, such as vesicles, papules, and nodules, from secondary changes, including crusts, excoriations, and ulceration. The presence of feather loss, broken feathers, or fecal soiling of the vent and caudal abdomen directs attention toward management-related dermatitis instead of systemic viral disease.

Live bird examination should include assessment of gait, posture, and neurologic status. Marek's disease frequently presents with asymmetric leg weakness or paralysis in addition to skin lesions, and the skin tumors themselves may be palpable as firm, raised nodules in feather follicles. Respiratory signs, cyanosis of comb and wattles, and edema of the head suggest highly pathogenic avian influenza, although the 2003 H7N7 epidemic in the Netherlands demonstrated that these classic hemorrhagic and edematous changes may be absent in some outbreaks, and increased progressive mortality alone warranted suspicion.

## Necropsy and Sample Selection

Postmortem examination should be performed promptly on freshly euthanized or recently dead birds. Examine the skin before plucking, then remove feathers over affected areas to assess the full extent of lesions. Record the distribution of subcutaneous hemorrhage, edema, or necrosis. Internal examination should include the peripheral nerves, particularly the sciatic and brachial plexuses, the bursa of Fabricius, liver, spleen, and bone marrow. Nerve enlargement with loss of striation supports Marek's disease, while bursal tumors with a lobulated, fleshy appearance support avian leukosis.

Sample selection depends on the differential list. For suspected viral neoplasia, collect affected skin, nerve, bursa, and liver into 10% neutral buffered formalin for histopathology. For suspected highly pathogenic avian influenza, collect tracheal and cloacal swabs into viral transport medium and submit them to the appropriate diagnostic laboratory, following the reporting requirements of the relevant animal health authority. For bacterial dermatitis, collect swabs from beneath the crust or from the leading edge of the lesion for aerobic culture and antimicrobial susceptibility testing. For suspected ionophore toxicity, submit a representative feed sample for assay, since clinical signs and lesions are not pathognomonic and confirmatory diagnosis requires laboratory testing to identify the specific ionophore involved.

## Differential Prioritization Table

The following table organizes the primary differential diagnoses by lesion morphology, distribution, and the diagnostic tests that discriminate among them. Use this table in conjunction with flock history and signalment to rank differentials before laboratory submission.

| Lesion Description | Typical Distribution | Key Signalment or History | Primary Differentials | Discriminating Diagnostic Tests |
|---|---|---|---|---|
| Firm raised nodules, often involving feather follicles, with or without neurologic signs | Feathered skin, especially neck, wings, and legs | Birds 8 to 20 weeks old | Marek's disease | Histopathology of skin, nerve, and viscera, PCR for Marek's disease virus |
| Diffuse or nodular skin thickening, sometimes ulcerated, in mature birds | Variable, often trunk and limbs | Adult birds, especially layers | Avian leukosis | Histopathology, bursal involvement on necropsy, virus isolation or PCR |
| Edema, cyanosis, and hemorrhage of comb and wattles, sudden mortality spike | Unfeathered skin of head | Any age, rapid flock spread | Highly pathogenic avian influenza | Virus isolation, RT-PCR, antigen detection, notify animal health authority |
| Moist, erythematous, ulcerated skin of plantar surface of feet or caudal keel | Contact surfaces: footpads, hocks, keel | Broilers on wet or ammoniated litter | Contact dermatitis, ammonia scald | Necropsy, litter moisture and ammonia assessment, bacterial culture of secondary infection |
| Crusty, thickened skin with feather loss and self-trauma | Vent, thighs, back, wings | Any age, associated with poor nutrition or stress | Nutritional deficiency, cannibalism, ectoparasites | Skin scraping, feather examination, diet history |
| Acute onset of ataxia, recumbency, and death with skin pallor or cyanosis | None specific, skin changes secondary to circulatory failure | Any age, recent feed change | Ionophore toxicity | Feed assay for ionophores, histopathology of skeletal muscle and myocardium |

## Diagnostic Testing and Interpretation

Histopathology remains the reference standard for distinguishing Marek's disease from avian leukosis. Marek's disease produces pleomorphic lymphoid infiltrates in skin, nerves, and viscera, with the bursa typically atrophied instead of tumorous. Avian leukosis produces uniform lymphoblastic populations with bursal tumors and visceral involvement. When histopathology is unavailable, the combination of age, nerve involvement, and bursal status provides sufficient reliability for herd-level diagnosis, accepting a small number of individual misclassifications.

Molecular testing adds sensitivity and specificity. PCR for Marek's disease virus can detect viral DNA in skin and feather pulp, which is useful when formalin-fixed tissue is the only sample available. For highly pathogenic avian influenza, RT-PCR on respiratory and cloacal swabs is the primary diagnostic modality, and a positive result triggers statutory reporting. Bacterial culture should be interpreted in the context of lesion morphology, since secondary bacterial infection of any skin wound is common and does not establish a primary diagnosis.

Feed analysis for ionophores is indicated when clinical signs include acute mortality, ataxia, and recumbency, and when necropsy reveals skeletal muscle necrosis or congestive heart failure. Because ionophore toxicosis mimics other causes of acute death, feed assay is required for confirmation, and the specific ionophore involved must be identified.

## Documentation and Reporting

Record all findings in a standardized format that includes flock identification, date, age, breed, lesion distribution diagram, necropsy findings, and laboratory submissions. Photograph representative lesions before and after plucking. Maintain a chronological log of mortality and morbidity rates, since the temporal pattern of disease progression is often more diagnostic than a single examination. The incidence rates of morbidity and mortality in smallholder poultry flocks can vary widely, from 2.02 to 58.43 cases per 1000 chicken-week at risk for morbidity and 0.21 to 58.18 for mortality, so documenting the trajectory of disease within a flock provides essential context for interpretation.

Reporting obligations differ by jurisdiction and by disease. Highly pathogenic avian influenza is a notifiable disease in most countries, and the veterinarian should be familiar with the reporting pathway of the relevant animal health authority. For other conditions, documentation supports herd-level monitoring and helps distinguish recurrent management problems from introduced infectious disease. The choice of diagnostic tests and the depth of investigation will vary with the production system, the economic value of the flock, and the availability of laboratory services, and the practitioner should tailor the workup accordingly.

## Recognized Complications and Early Detection

Skin lesions in poultry flocks can progress beyond the integument. Secondary bacterial infection of traumatised skin, particularly with *Staphylococcus aureus* or *Escherichia coli*, produces cellulitis and septicemia that amplify mortality beyond the primary cause. Detect this early by monitoring daily mortality curves, a rising slope that precedes visible lesion spread suggests systemic invasion. Examine the subcutis of culled birds for gelatinous exudate or caseous cores, findings that confirm cellulitis and shift the working diagnosis from a purely cutaneous process to a systemic bacterial disease.

Vaccine-associated complications merit specific attention. Marek's disease vaccination protects against tumor formation but does not prevent infection, and very virulent strains can break through vaccine immunity. Early detection relies on recognizing the age distribution of lesions. Marek's disease tumors typically appear from 8 to 20 weeks, whereas avian leukosis tumors present later, usually after 16 weeks, and the two differ in bursal involvement as established in herd-level pathological diagnosis [Beyer et al., criteria for differential diagnosis of Marek's disease and lymphoid leukosis](https://pubmed.ncbi.nlm.nih.gov/7212936/). A flock with vaccine breaks shows rising mortality with visceral and cutaneous tumors in vaccinated birds, a pattern that warrants laboratory confirmation instead of a simple vaccine failure assumption.

Highly pathogenic avian influenza can present with minimal skin changes. The 2003 H7N7 epidemic in the Netherlands demonstrated that comb and wattle edema, cyanosis, and hemorrhage were often absent in early outbreaks, and increased progressive mortality was the most consistent signal [Elbers et al., lessons from the first five HPAI outbreaks](https://pubmed.ncbi.nlm.nih.gov/15529997/). Detect this early by tracking mortality against expected baselines for the production stage and by submitting birds for postmortem examination whenever mortality exceeds two consecutive days of elevation.

## Common Diagnostic Errors and Corrective Actions

Less experienced clinicians frequently attribute all skin lesions to ectoparasites without examining the distribution pattern. Lice and mites produce lesions concentrated on the vent, thighs, and under the wings, whereas contact dermatitis affects the plantar surface of the hocks and the sternum. Correct this by mapping lesions on a body diagram before reaching a diagnosis.

A second error is over-reliance on gross appearance for viral differentiation. Marek's disease and avian leukosis can be distinguished reliably at necropsy when age, nerve involvement, bursal changes, and skin lesions are considered together as part of herd diagnosis, but individual birds can be misleading [Beyer et al., herd-level pathological diagnosis](https://pubmed.ncbi.nlm.nih.gov/7212936/). Submit affected birds for histopathology when the flock pattern is ambiguous.

Ionophore toxicity is frequently missed because the skin lesions are secondary to recumbency instead of primary. The clinical picture of anorexia, ataxia, and recumbency with focal skeletal muscle necrosis may be mistaken for a neurological infection, and the associated skin abrasions distract from the muscle pathology [Novilla, ionophore toxic syndrome](https://pubmed.ncbi.nlm.nih.gov/1621367/). Correct this by examining the pectoral and leg muscles for pale streaking and by reviewing feed records for mixing errors.

| Observation | Likely cause | Discriminating check |
|---|---|---|
| Rising mortality, no skin lesions | HPAI, ionophore toxicity | Mortality curve analysis, feed records, muscle histology |
| Vent and thigh lesions | Ectoparasites | Direct examination, fecal flotation |
| Plantar hock lesions | Contact dermatitis | Litter moisture, ammonia levels |
| Tumors in birds under 20 weeks | Marek's disease | Nerve enlargement, bursal atrophy, histopathology |
| Tumors in birds over 20 weeks | Avian leukosis | Bursal tumor, histopathology |

## Limitations of Current Evidence

The evidence base for poultry skin lesion diagnosis is uneven. Much of the published work derives from specific production systems and geographic regions, and extrapolation to other settings carries risk. The longitudinal study from Ethiopian smallholder farms, for example, identified disease patterns in intensive and semi-intensive systems with particular breed mixes, and those findings may not transfer directly to large-scale commercial operations [Hailegebreal et al., epidemiological investigation of morbidity and mortality in smallholder poultry farms](https://pubmed.ncbi.nlm.nih.gov/35992007/). Breed differences in disease resistance, including responses to bacterial challenge, are documented but the genetic mechanisms are incompletely characterized [Dar et al., comparative RNA-Seq analysis of Salmonella disease resistance](https://pubmed.ncbi.nlm.nih.gov/36064074/).

Expert opinion still differs on the value of gross necropsy versus histopathology for Marek's disease diagnosis. Some authorities accept herd-level gross diagnosis as sufficient, while others require histological confirmation for every case. The evidence supports gross diagnosis as reliable for herd decisions but acknowledges that individual misdiagnosis occurs [Beyer et al., reliability of pathological diagnosis](https://pubmed.ncbi.nlm.nih.gov/7212936/). Practitioners should match diagnostic rigour to the consequence of error, a breeding flock with a suspected leukosis virus requires laboratory confirmation, whereas a commercial broiler flock with classic Marek's lesions may not.

## Referral, Consultation, and Regulatory Reporting

Referral to a diagnostic laboratory is warranted when mortality exceeds expected baselines, when lesions are atypical, when a notifiable disease is suspected, or when the economic consequence of misdiagnosis is high. Histopathology, virus isolation, and PCR-based testing require laboratory infrastructure that most practices do not possess.

Regulatory reporting obligations vary by jurisdiction. Highly pathogenic avian influenza is notifiable in most countries, and the clinical signs may be subtle, so a low threshold for reporting is appropriate [Elbers et al., lessons from the first five HPAI outbreaks](https://pubmed.ncbi.nlm.nih.gov/15529997/). Veterinary practitioners should consult their national veterinary authority or the WOAH terrestrial animal health standards for current reporting requirements [WOAH terrestrial animal health code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). Regional guidance from bodies such as the USDA APHIS or FAO can clarify local surveillance expectations [USDA APHIS animal health information](https://www.aphis.usda.gov/livestock-poultry-disease), [FAO animal production and health](https://www.fao.org/animal-production/en/).

Consult a poultry specialist or diagnostic pathologist early when the flock pattern does not fit a familiar disease, when lesions are progressive despite management correction, or when the differential includes both infectious and toxic causes. Early consultation reduces the risk of prolonged flock losses and improves the quality of samples submitted for laboratory testing.

## Frequently Asked Questions

### How should I prioritize differentials when laboratory confirmation is delayed or unavailable?

When laboratory access is limited, prioritize by flock mortality trajectory, lesion distribution, and signalment. Rapidly rising mortality with cyanotic combs or wattles should trigger immediate suspicion of highly pathogenic avian influenza, even when hemorrhagic lesions are absent, as the 2003 Dutch H7N7 outbreaks demonstrated [clinical findings from the Netherlands H7N7 epidemic](https://pubmed.ncbi.nlm.nih.gov/15529997/). Marek's disease remains the leading differential for cutaneous lymphoid tumors in young layers, while avian leukosis typically presents in older birds with visceral involvement [pathological criteria for Marek's disease and lymphoid leukosis](https://pubmed.ncbi.nlm.nih.gov/7212936/). Management-related lesions such as contact dermatitis usually affect the plantar surface and breast in broilers with litter quality problems. Submit frozen tissues and fixed samples for later testing, and document photographic evidence systematically.

### What minimum equipment is needed for a useful field necropsy of skin lesions?

A sharp knife, scissors, forceps, and a clean cutting surface suffice for gross examination. Collect skin lesions with surrounding normal tissue into 10% neutral buffered formalin at a 1:10 tissue-to-fixative ratio. For viral testing, place fresh samples of skin, spleen, liver, and kidney in separate sterile containers kept cold but not frozen. Examine the sciatic and brachial nerves, bursa of Fabricius, and viscera in every bird, since visceral lesions often discriminate between Marek's disease and avian leukosis [pathological criteria for Marek's disease and lymphoid leukosis](https://pubmed.ncbi.nlm.nih.gov/7212936/). If a microscope is unavailable, photograph gross lesions with a scale bar and preserve samples for histopathology at a referral laboratory.

### How does the diagnostic approach differ between commercial broilers and smallholder backyard flocks?

Commercial broilers present with uniform genetics, controlled environment, and consistent feed, which narrows differentials toward management factors such as litter moisture and ammonia. Smallholder flocks in intensive or semi-intensive systems face higher morbidity and mortality risks from infectious diseases, with incidence rates varying widely between farms [epidemiological investigation of improved breed chickens in Ethiopia](https://pubmed.ncbi.nlm.nih.gov/35992007/). In backyard flocks, mixed infections are common, vaccination status is often unknown, and nutritional deficiencies may coexist with infectious causes. Lesion mapping across multiple birds becomes essential because individual variation is greater. Consider endemic diseases that may be controlled or absent in commercial operations, and account for breed susceptibility differences when interpreting resistance or susceptibility patterns [Salmonella disease resistance gene expression in poultry](https://pubmed.ncbi.nlm.nih.gov/36064074/).

### What records should I maintain for skin lesion cases that may require regulatory reporting?

Maintain a flock-level record that includes daily mortality counts, lesion distribution diagrams, feed batch numbers, water source, litter management history, and vaccination records. Photograph representative lesions and gross necropsy findings. Record the date of first clinical signs, the progression pattern, and the number of birds affected. For suspected notifiable diseases such as highly pathogenic avian influenza, document the timeline of clinical observations and any movement of birds, personnel, or equipment [USDA APHIS animal disease information](https://www.aphis.usda.gov/livestock-poultry-disease). Keep these records for at least the duration required by local veterinary authorities, and be prepared to share them with regulatory veterinarians. Accurate contemporaneous records also support retrospective diagnosis when laboratory results arrive after clinical resolution.

### How do I communicate skin lesion findings to a producer who wants immediate treatment decisions?

Frame the conversation around the diagnostic plan instead of speculative treatment. Explain that skin lesions have multiple causes with overlapping appearances, and that treatment without diagnosis risks worsening the problem, particularly if a viral or toxic cause is present. Describe the lesions in plain terms, such as scabs, swelling, or reddening, and relate them to likely causes based on the flock history. For suspected ionophore toxicity, emphasize that clinical signs and lesions are not pathognomonic and that feed analysis is required for confirmation [ionophore toxic syndrome in poultry](https://pubmed.ncbi.nlm.nih.gov/1621367/). Provide a clear timeline for sample submission and results, and outline what management changes can be implemented immediately without compromising the diagnostic workup.

### When should I refer a skin lesion case to a diagnostic laboratory or specialist?

Refer when mortality exceeds expected baseline for the production stage, when lesions are progressive despite management correction, or when gross findings suggest a notifiable disease. Submit samples to a diagnostic laboratory whenever the economic impact of the flock loss justifies the cost, which is most commercial operations. Referral is also appropriate when lesions are atypical, when multiple flocks are affected, or when regulatory reporting may be required. International standards for disease surveillance and reporting apply to poultry health events, and early laboratory involvement supports both flock health and trade-related obligations [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). Do not delay referral while attempting to rule out every management cause, since some infectious diseases progress rapidly and early samples improve diagnostic yield.

## Related Clinical & Scientific Guides

* [Rumen Health Assessment in Dairy Cows: Clinical and Subclinical Indicators](/knowledge/veterinary-medicine/food-animal-medicine/rumen-health-assessment-dairy-cows-clinical-subclinical-indicators)
* [Mastitis Control Programs in Dairy Herds: Monitoring and Prevention](/knowledge/veterinary-medicine/food-animal-medicine/mastitis-control-programs-dairy-herds-monitoring-prevention)
* [Swine Nutrition and Health: Feed-Related Disease Diagnosis](/knowledge/veterinary-medicine/food-animal-medicine/swine-nutrition-health-feed-related-disease-diagnosis)


## References and Further Reading

- [Epidemiological investigation of morbidity and mortality of improved breeds of chickens in small holder poultry farms in selected districts of Sidama Region, Ethiopia.](https://pubmed.ncbi.nlm.nih.gov/35992007/). 2022.
- [Human-Aided Movement of Viral Disease and the Archaeology of Avian Osteopetrosis.](https://pubmed.ncbi.nlm.nih.gov/29104410/). 2017.
- [[Studies on the reliability of hard diagnosis of Marek's disease and lymphoid leukosis of chickens on the basis of pathologic-anatomical findings].](https://pubmed.ncbi.nlm.nih.gov/7212936/). 1980.
- [The highly pathogenic avian influenza A (H7N7) virus epidemic in The Netherlands in 2003--lessons learned from the first five outbreaks.](https://pubmed.ncbi.nlm.nih.gov/15529997/). 2004.
- [The veterinary importance of the toxic syndrome induced by ionophores.](https://pubmed.ncbi.nlm.nih.gov/1621367/). 1992.
- [Comparative RNA-Seq analysis reveals insights in Salmonella disease resistance of chicken, and database development as resource for gene expression in poultry.](https://pubmed.ncbi.nlm.nih.gov/36064074/). 2022.
- [USDA APHIS Animal Health Information](https://www.aphis.usda.gov/livestock-poultry-disease). USDA APHIS.
- [FAO Animal Production and Health](https://www.fao.org/animal-production/en/). FAO.
- [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual.

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> This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.