Layer Chicken Disease DDx (Organ-wise)

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Respiratory System Infectious Bronchitis (IB): Symptoms: Coughing, sneezing, tracheal rales, nasal discharge, conjunctivitis, swollen sinuses, reduced egg production/quality (misshapen, soft-shelled). Post-mortem: Tracheitis, mucoid exudate in trachea, airsacculitis, kidney lesions (nephropathogenic strains). DDx: Newcastle Disease, Avian Influenza, Mycoplasmosis, Laryngotracheitis. Newcastle Disease (ND): Symptoms: Respiratory distress (gasping, coughing), nervous signs (tremors, paralysis, torticollis), diarrhea, sudden death, severe drop in egg production. Post-mortem: Haemorrhages in proventriculus, intestines, tracheal exudate. DDx: Avian Influenza, Infectious Bronchitis, Laryngotracheitis. Avian Influenza (AI): Symptoms: Severe respiratory signs, facial swelling, cyanosis of comb/wattles, nervous signs, sudden death, sharp drop in egg production. Post-mortem: Hemorrhages, edema, necrosis in various organs. DDx: Newcastle Disease, Fowl Cholera. Infectious Laryngotracheitis (ILT): Symptoms: Severe dyspnea, coughing blood-stained exudate, gasping, head shaking. Post-mortem: Hemorrhagic tracheitis, caseous plugs in trachea/larynx. DDx: Newcastle Disease, Infectious Bronchitis. Mycoplasmosis (Chronic Respiratory Disease - CRD): Symptoms: Chronic cough, rales, nasal discharge, conjunctivitis, swollen infraorbital sinuses. Post-mortem: Airsacculitis (foamy exudate), pericarditis, perihepatitis (often with E. coli). DDx: Infectious Bronchitis, E. coli infection. Digestive System Coccidiosis: Symptoms: Diarrhea (often bloody), ruffled feathers, depression, emaciation, reduced feed intake. Post-mortem: Thickened, inflamed intestinal wall; specific lesions in different parts of the intestine depending on Eimeria species. DDx: Necrotic Enteritis, Worm infestations. Necrotic Enteritis: Symptoms: Sudden death, depression, dark diarrhea, reduced growth/egg production. Post-mortem: Fibrinonecrotic enteritis, particularly in small intestine, 'Turkish towel' appearance of mucosa. DDx: Coccidiosis, Salmonellosis. Salmonellosis (Pullorum/Fowl Typhoid): Symptoms: Often asymptomatic in adult layers, but can cause reduced egg production, diarrhea, lameness, sudden death. Chicks show high mortality. Post-mortem: Enlarged liver/spleen, necrotic foci in liver, enteritis, unabsorbed yolk sac in chicks. DDx: E. coli infection, Omphalitis (in chicks). E. coli Infection (Colibacillosis): Symptoms: Peritonitis, salpingitis, airsacculitis, omphalitis, cellulitis. Can cause reduced egg production and mortality. Post-mortem: Fibrinous exudate on serosal surfaces (liver, heart, air sacs), peritonitis, enlarged oviduct. DDx: Mycoplasmosis (for airsacculitis), Fowl Cholera (for peritonitis/salpingitis). Reproductive System Egg Drop Syndrome (EDS '76): Symptoms: Sudden drop in egg production, eggs become pale, soft-shelled, or shell-less. Birds remain otherwise healthy. Post-mortem: Flaccid oviduct, edema of uterine wall, atrophy of ovarian follicles. DDx: Infectious Bronchitis (nephropathogenic strains), Mycotoxicosis, heat stress. Infectious Bronchitis (IB - reproductive form): Symptoms: Reduced egg production, poor egg quality (misshapen, rough, thin or soft shells, watery albumen). Post-mortem: Persistent oviduct lesions, cystic oviducts, undeveloped oviducts in pullets exposed early. DDx: EDS '76, Mycoplasmosis, stress factors. Fowl Cholera: Symptoms: Acute septicemia causing sudden death, facial swelling, lameness, diarrhea, reduced egg production. Chronic forms lead to localized infections (joints, wattles, oviduct). Post-mortem: Petechial hemorrhages, necrotic foci on liver, peritonitis, salpingitis. DDx: E. coli infection, Newcastle Disease (acute). Salpingitis/Peritonitis: Symptoms: Reduced egg production, distended abdomen ('penguin stance'), depression, sudden death. Post-mortem: Inflamed, distended oviduct filled with caseous material or inspissated yolk, fibrinous exudate in abdominal cavity. DDx: E. coli, Fowl Cholera, Mycoplasmosis, trauma, foreign body. Nervous System Marek's Disease (MD): Symptoms: Paralysis of legs/wings (classic form), ocular lesions ('grey eye'), tumors in internal organs. Post-mortem: Enlarged nerves (sciatic, brachial, vagus), tumors in liver, spleen, kidney, gonads, skin. DDx: Newcastle Disease (nervous form), Avian Encephalomyelitis, Lymphoid Leukosis. Newcastle Disease (ND - nervous form): Symptoms: Tremors, torticollis (twisted neck), opisthotonos, paralysis. Often accompanied by respiratory and digestive signs. Post-mortem: Similar to respiratory/digestive forms; no specific gross nervous lesions for diagnosis without lab. DDx: Marek's Disease, Avian Encephalomyelitis, Vitamin E deficiency. Avian Encephalomyelitis (AE): Symptoms: Ataxia, tremors (especially head/neck), paralysis, dullness, prostration. In layers, can cause a transient drop in egg production and hatchability. Post-mortem: No gross lesions visible. Microscopic brain lesions. DDx: Newcastle Disease, Marek's Disease, Vitamin E deficiency. Musculoskeletal/Integumentary System Marek's Disease (MD - skin form): Symptoms: Feather follicle tumors (skin leukosis). Post-mortem: Enlarged feather follicles with tumors. DDx: Fowl Pox (wet form, but lesions are different), external parasites. Fowl Pox: Symptoms: Dry Pox: Warty lesions on unfeathered skin (comb, wattles, eyelids). Wet Pox: Diphtheritic membranes in mouth, larynx, trachea. Post-mortem: Characteristic pox lesions. DDx: Marek's Disease (skin form - different lesion type), Vitamin A deficiency (wet form). Staphylococcosis: Symptoms: Bumblefoot (swollen footpads), arthritis, septicemia. Post-mortem: Abscesses in joints/footpads, osteomyelitis. DDx: Mycoplasmosis (arthritis), Fowl Cholera (arthritis). Immune System/Generalized Infectious Bursal Disease (IBD - Gumboro): Symptoms: Depression, ruffled feathers, watery diarrhea, dehydration, high mortality in young chicks. In layers, immunosuppression without overt clinical signs, leading to secondary infections and poor vaccine response. Post-mortem: Swollen, edematous, hemorrhagic bursa of Fabricius (early), then atrophied bursa. Hemorrhages in thigh/breast muscles, kidney lesions. DDx: Coccidiosis, Marek's Disease (immunosuppression). Lymphoid Leukosis (LL): Symptoms: Chronic wasting, depression, enlarged abdomen, often no specific clinical signs until advanced. Occurs in older birds. Post-mortem: Smooth, diffuse or nodular tumors in liver, spleen, bursa (follicular), kidney, heart. Bursa lesions typically diffuse. DDx: Marek's Disease (tumors), Reticuloendotheliosis. Mycotoxicosis: Symptoms: Reduced feed intake, poor growth, reduced egg production, immunosuppression, increased susceptibility to other diseases, liver damage, hemorrhages. Post-mortem: Enlarged, friable liver (often fatty), pale kidneys, gizzard erosions, oral lesions. DDx: Nutritional deficiencies, other immunosuppressive diseases.