Field Post-Mortem & Pathology Guide
Necropsy lesion reference profiles for clinical training and farm screening.
Newcastle Disease (ND) Lesion Profile
Pathogen Type: Avian Paramyxovirus 1 (APMV-1), an enveloped single-stranded RNA virus.
Pathological Lesions:- Petechial (pinpoint) hemorrhages on the mucosal lining and tips of the glands of the proventriculus
- Hemorrhagic or necrotic button-like ulcers in the intestinal mucosa, particularly in the duodenum and cecal tonsils
- Tracheitis with catarrhal or hemorrhagic exudates in the tracheal lumen
- Cloudy or thickened air sac membranes (airsacculitis)
- Congestion of the kidneys and enlargement of the spleen
Transmission: Direct contact with respiratory secretions and feces of infected birds. Highly infectious aerosolization occurs in closed coops. Also spread via fomites (contaminated cages, feed bags, footwear, vehicle tires).
Marek's Disease (MD) Lesion Profile
Pathogen Type: Gallid Alphaherpesvirus 2 (Marek's Disease Virus - MDV), a highly contagious cell-associated herpesvirus.
Pathological Lesions:- Marked enlargement and loss of striations in peripheral nerves, particularly the sciatic, vagus, and brachial nerves (sciatic nerve may be 2-3 times normal thickness)
- Diffuse or nodular lymphoid tumors (lymphomas) in internal organs including the liver, spleen, kidneys, heart, lungs, ovaries/testes, and proventriculus wall
- Atrophy of the Bursa of Fabricius and thymus in chronic stages
Transmission: Inhalation of infective feather dander and dust. MDV is shed in large quantities from the epithelial cells of feather follicles. The virus remains stable and infectious in litter dust for several years.
Coccidiosis Lesion Profile
Pathogen Type: Protozoan parasites of the genus Eimeria (E. tenella, E. necatrix, E. acervulina, E. maxima). Each species infects a specific section of the intestine.
Pathological Lesions:- E. tenella: Severe distension of the cecal pouches filled with frank blood, necrotic debris, or solid core-like plugs. Thickened, hemorrhagic cecal walls.
- E. necatrix: Ballooning and petechiae in the middle third of the small intestine, containing blood-stained fluid.
- E. acervulina: Transverse white ladder-like plaques in the mucosal surface of the duodenum.
Transmission: Ingestion of sporulated oocysts from contaminated litter, feed, or drinking water. Oocysts sporulate (become infective) in warm, moist litter conditions (>25°C and >30% moisture) within 24-48 hours.
Infectious Bursal Disease (IBD / Gumboro) Lesion Profile
Pathogen Type: Infectious Bursal Disease Virus (IBDV), a non-enveloped double-stranded RNA birnavirus. Highly resistant to physical and chemical agents.
Pathological Lesions:- Enlarged, edematous, and yellowish/gelatinous Bursa of Fabricius in early stages (day 3-4), which may contain hemorrhages (resembling a strawberry)
- Bursa undergoes rapid atrophy by day 8, shrinking to less than half its normal size
- Hemorrhages in the breast and thigh muscles due to coagulation defects
- Swollen kidneys with uric acid deposits (nephrosis)
Transmission: Fecal-oral route. Spreads via ingestion of feces, contaminated feed, water, equipment, dust, or insect vectors (specifically the darkling beetle, Alphitobius diaperinus).
Avian Influenza (Bird Flu) Lesion Profile
Pathogen Type: Influenza A virus (Orthomyxoviridae family), categorized as Low Pathogenic (LPAI) or Highly Pathogenic (HPAI) based on viral genetics.
Pathological Lesions:- Severe congestion and hemorrhages in the lungs, trachea, and air sacs
- Subcutaneous gelatinous edema of the head and neck tissues
- Petechial hemorrhages on epicardial fat, proventriculus mucosa, and gizzard lining
- Necrosis and hemorrhages in the pancreas, liver, and spleen
Transmission: Contact with excretions (saliva, nasal discharge, feces) of infected wild waterfowl, which are natural reservoirs. Rapidly spreads via aerosolized droplets, contaminated equipment, clothing, shoes, feed, and water.
Fowl Pox Lesion Profile
Pathogen Type: Fowl Pox Virus (Avipoxvirus), a large, brick-shaped double-stranded DNA virus. Extremely resistant to environmental desiccation.
Pathological Lesions:- Dry form: Hyperplasia of epithelial cells with characteristic eosinophilic intracytoplasmic inclusion bodies (Bollinger bodies) visible on histology.
- Wet form: Croupous, diphtheritic inflammation of the upper digestive and respiratory tracts, leading to necrotic ulcers when membranes are peeled back.
Transmission: Slowly spreading disease transmitted via biting mosquitoes (mechanical vectors), minor skin abrasions, or fighting and feather-pecking. The virus can enter via the respiratory tract in dusty environments.
Infectious Bronchitis (IB) Lesion Profile
Pathogen Type: Infectious Bronchitis Virus (IBV), a single-stranded RNA coronavirus. Exists in numerous serotypes (e.g., Massachusetts, Connecticut, Ark, D274) which do not cross-protect.
Pathological Lesions:- Serous, catarrhal, or caseous exudates in the trachea, nasal passages, and sinuses
- Cloudy air sacs containing yellow foam or caseous plugs
- In nephropathogenic strains: Swollen, pale kidneys with tubules and ureters distended with white urate crystals (urate nephrosis)
- Atrophic, cystic, or fluid-filled oviducts in layers
Transmission: Highly contagious. Spreads via airborne droplets (coughing/sneezing), feces, and contaminated equipment. The incubation period is extremely short (18-36 hours). Spreads through an entire house within days.
Infectious Coryza Lesion Profile
Pathogen Type: Avibacterium paragallinarum, a Gram-negative, pleomorphic bacterium requiring V-factor (NAD) for growth.
Pathological Lesions:- Acute catarrhal inflammation of the nasal passages, infraorbital sinuses, and conjunctiva
- Copious subcutaneous gelatinous edema of the face, eyelids, and wattles
- Congestion of the lungs and catarrhal tracheitis (in severe lower respiratory tract involvement)
Transmission: Direct contact with infected birds, inhalation of airborne droplets (aerosols), or consumption of feed and water contaminated with nasal discharge. Older carrier birds are the primary source of infection.
Chronic Respiratory Disease (CRD / Mycoplasmosis) Lesion Profile
Pathogen Type: Mycoplasma gallisepticum (MG), a cell-wall-less bacterium. Often exacerbated by secondary E. coli or virus infections (Infectious Bronchitis or Newcastle Disease).
Pathological Lesions:- Catarrhal tracheitis, sinusitis, and rhinitis with congestion of mucosal linings
- Thickened, cloudy air sac membranes filled with yellow, caseous (cheesy) exudates (severe airsacculitis)
- Fibrinous pericarditis (heart covered in a yellow-white fibrinous sheet) and fibrinous perihepatitis (liver encapsulated in a yellow film) when secondary E. coli infection occurs
Transmission: Vertical transmission through the hatching egg (transovarian) from carrier breeders to offspring. Horizontal transmission occurs via inhalation of dust, dander, or aerosol droplets, and contact with contaminated equipment, feed, or drinking water.
Fowl Cholera Lesion Profile
Pathogen Type: Pasteurella multocida, a Gram-negative, bipolar-staining bacterium. Highly infectious and resistant to cold temperatures, surviving in soil/litter for weeks.
Pathological Lesions:- Petechial and ecchymotic hemorrhages on the epicardium, gizzard fat, proventriculus, and abdominal membranes
- Enlarged, congested liver with a cooked appearance and numerous small, pinpoint yellow-white necrotic foci
- Acute congestion of lungs, often with consolidation (croupous pneumonia)
- Ruptured egg yolk material in the abdominal cavity leading to yellow fibrinous egg peritonitis (in laying hens)
Transmission: Contact with excretions from the mouth, nose, and eyes of diseased or carrier birds. Also transmitted via contaminated soil, water, feed, and equipment. Wild birds, rodents, cats, and flies act as mechanical vectors.
Pullorum Disease (Salmonellosis) Lesion Profile
Pathogen Type: Salmonella enterica subsp. enterica serovar Pullorum (Salmonella Pullorum), a Gram-negative, non-motile bacterium. Extremely host-adapted to chickens.
Pathological Lesions:- Enlarged, congested, and discolored liver (yellow-brown with pinpoint necrotic spots) and swollen spleen
- Pinpoint gray-white necrotic nodules in the lungs, gizzard muscle wall, heart, and intestinal mucosa
- Unabsorbed yolk sac with thickened, congested blood vessels and cheesy, solidified contents
- White urate deposits in the kidneys and distended ureters
Transmission: Vertical transmission (transovarian) from carrier hens through the egg yolk to chicks. Horizontal transmission occurs via inhalation or ingestion of infected fluff, dust, or feces in incubators, brooders, or litter.
Bumblefoot (Staphylococcal Pododermatitis) Lesion Profile
Pathogen Type: Staphylococcus aureus, a Gram-positive facultative anaerobic bacterium causing chronic ulcerative pododermatitis.
Pathological Lesions:- Ulcerated footpad epidermis with a hard, dark central kerato-necrotic plug or scab
- Cheesy (caseous) fibrous abscess core in the deep plantar tissues
- Tenosynovitis and arthritis of the flexor tendons and hock joint in advanced cases
Transmission: Entry occurs through skin abrasions, mechanical cuts from sharp litter, rough perches, or high pressure on footpads due to wet litter and obesity.
Omphalitis (Navel Ill / Yolk Sac Infection) Lesion Profile
Pathogen Type: Polymicrobial infection caused primarily by Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, and Proteus spp.
Pathological Lesions:- Unabsorbed, enlarged yolk sac with watery, foul-smelling greenish-brown contents
- Severe inflammation and edema of the abdominal wall and umbilical tissue
- Fibrinous peritonitis and congested visceral organs
Transmission: Contamination of the open navel immediately after hatching in contaminated incubators, dirty hatcher trays, or un-sanitized chick boxes.
Fatty Liver Hemorrhagic Syndrome (FLHS) Lesion Profile
Pathogen Type: Non-infectious metabolic disease affecting high-producing layer hens, associated with positive energy balance and high estrogen levels.
Pathological Lesions:- Massive blood clots (hematomas) surrounding the liver and filling the abdominal cavity
- Enlarged, friable, pale yellow-tan liver with high fat content (>50% dry weight)
- Excessive abdominal and visceral fat reserves
Transmission: Metabolic and nutritional origin; not infectious.
Infectious Synovitis (Mycoplasma synoviae - MS) Lesion Profile
Pathogen Type: Mycoplasma synoviae, a small cell-wall-less bacterium causing respiratory and systemic joint infections.
Pathological Lesions:- Viscid cream-colored to grayish exudate in synovial sheaths, hock joints, and footpads
- Enlarged, dark green liver and enlarged spleen in acute systemic phase
- Airsacculitis with cheesy exudates in respiratory cases
Transmission: Transovarian (vertical) from infected breeders to chicks. Transmitted horizontally via aerosols, dust, or contaminated equipment.
Fowl Typhoid (Salmonella gallinarum) Lesion Profile
Pathogen Type: Salmonella enterica serovar Gallinarum (Salmonella gallinarum), a non-motile Gram-negative bacterium causing acute or chronic septicemia.
Pathological Lesions:- Enlarged, dark bronze or greenish-brown liver with a metallic sheen and pinpoint necrotic foci
- Enlarged, dark red spleen and swollen kidneys
- Fibrinous pericarditis and peritonitis
Transmission: Vertical transmission via eggs and horizontal transmission via ingestion of feces, dead carcasses, or contaminated water/feed.
Pullorum Disease (Salmonella pullorum) Lesion Profile
Pathogen Type: Salmonella enterica serovar Gallinarum biovar Pullorum (Salmonella pullorum), a non-motile Gram-negative bacterium causing severe septicemic disease in young chicks and poults.
Pathological Lesions:- Grayish necrotic foci in lungs, liver, gizzard wall, heart muscle, and intestinal wall
- Unabsorbed enlarged yolk sacs containing caseous yellow material
- Cheesy cecal cores and swollen joints containing viscid exudate in chronic survivors
Transmission: Primary vertical transmission via egg yolk; horizontal transmission through chick-to-chick contact in incubators, contaminated feces, down feathers, and brooder equipment.
Blackhead Disease / Histomoniasis (Histomonas meleagridis) Lesion Profile
Pathogen Type: Histomonas meleagridis, a flagellated protozoan parasite harbored within the eggs of the cecal worm Heterakis gallinarum.
Pathological Lesions:- Bilateral enlargement of ceca with thickened walls and yellow-green caseous cores
- Pathognomonic 'bullseye' liver lesions — circular crater-like necrotic areas with yellowish ring margins
- Peritonitis and cecal perforation in severe advanced cases
Transmission: Ingestion of cecal worm eggs (Heterakis gallinarum) or earthworms carrying worm larvae; horizontal transmission via cloacal drinking in turkeys.
Air Sac Mite Infestation (Cytodites nudus) Lesion Profile
Pathogen Type: Cytodites nudus, a minute endoparasitic mite invading the respiratory air sacs, lungs, bronchi, and bone cavities of avian species.
Pathological Lesions:- Pinpoint yellow or cream-colored mobile dots (mites) visible on transparent air sac walls upon necropsy
- Catarrhal cloudiness, inflammation, and excess mucus in bronchi, trachea, and abdominal air sacs
- Secondary bacterial pneumonia and airsacculitis
Transmission: Direct transmission via coughing/sneezing droplets, mutual grooming, and regurgitation of respiratory secretions.