Mycotoxicosis - Aflatoxicosis and T-2 Toxin (Trichothecene Mycotoxicosis)

Mycotoxicosis refers to a broad class of poultry diseases caused by the ingestion of feed contaminated with toxic secondary metabolites produced by toxigenic fungi. Among the most economically significant mycotoxicoses in commercial poultry are aflatoxicosis, caused by Aspergillus flavus and Aspergillus parasiticus producing aflatoxins (primarily B1, B2, G1, G2), and T-2 toxicosis, caused by Fusarium sporotrichioides and related species producing T-2 toxin, a type A trichothecene. Ochratoxin A, produced by Aspergillus ochraceus and Penicillium verrucosum, is also a common co-contaminant. These toxins induce a spectrum of pathological effects including hepatotoxicity, immunosuppression, coagulopathy, oral and gastrointestinal necrosis, and reduced performance. The disease affects all poultry sectors—broilers, commercial layers, broiler breeders, turkeys, ducks, and backyard flocks—with severity dependent on toxin concentration, duration of exposure, age, and nutritional status. Globally, mycotoxicoses are a major concern due to widespread feed contamination, leading to substantial economic losses from mortality, decreased feed conversion, reduced egg production, and increased susceptibility to infectious diseases.

The primary causative agents are toxigenic fungi and their mycotoxins. Aflatoxins are difuranocoumarin derivatives, with aflatoxin B1 being the most potent hepatocarcinogen and immunosuppressant. Producing fungi include Aspergillus flavus and A. parasiticus, which thrive in warm, humid conditions and contaminate corn, peanuts, and other grains. T-2 toxin is a trichothecene mycotoxin (12,13-epoxytrichothec-9-ene) produced by Fusarium sporotrichioides, F. poae, and F. graminearum. It is a potent protein synthesis inhibitor and causes severe oral and gastrointestinal necrosis. Ochratoxin A is a pentaketide derivative with a chlorinated isocoumarin moiety linked to phenylalanine, produced by Aspergillus ochraceus and Penicillium verrucosum, and is nephrotoxic and immunosuppressive. Other mycotoxins such as fumonisins, zearalenone, and deoxynivalenol (vomitoxin) may also be present but are less commonly implicated in acute outbreaks. The toxins are chemically stable and resistant to heat, surviving feed processing and storage.

Mycotoxicosis is a global problem, with prevalence varying by region and climate. Aflatoxin contamination is more common in tropical and subtropical regions, while T-2 toxin is more prevalent in temperate climates. Broilers are highly susceptible, with acute aflatoxicosis causing mortality up to 20-30% in severe cases, while chronic exposure leads to poor growth and immunosuppression. Layers experience reduced egg production (up to 20-30% drop) and increased eggshell defects. Turkeys are extremely sensitive to aflatoxin B1, with LD50 around 0.5 mg/kg body weight. Ducks are also highly susceptible. Age is a critical factor: young chicks (1-3 weeks) are most vulnerable due to immature detoxification systems. Housing systems with poor feed storage, high humidity, and inadequate ventilation increase risk. Morbidity can be high (up to 100%) in contaminated flocks, but mortality varies. Feed conversion ratio (FCR) may increase by 5-10% in chronic cases. Seasonal patterns exist, with higher contamination in warm, humid months. Biosecurity lapses, such as using moldy feed ingredients, are primary predisposing factors.

Aflatoxin B1 is metabolized by hepatic cytochrome P450 enzymes to the reactive epoxide, which binds to DNA and proteins, causing hepatocyte necrosis, fatty change, and bile duct proliferation. It inhibits protein synthesis, leading to reduced albumin and clotting factor production, resulting in coagulopathy and immunosuppression. Aflatoxin also impairs macrophage function and T-cell immunity, increasing susceptibility to infectious diseases. T-2 toxin inhibits protein synthesis by binding to the 60S ribosomal subunit, causing rapid necrosis of rapidly dividing cells, particularly in the gastrointestinal tract, bone marrow, and lymphoid tissues. It induces oral lesions, gastrointestinal ulceration, and bone marrow suppression, leading to anemia and leukopenia. Ochratoxin A primarily affects the proximal renal tubules, causing nephropathy, and also impairs immune function. All toxins cause oxidative stress, leading to lipid peroxidation and cellular damage. The combined effects result in reduced nutrient absorption, impaired liver function, and systemic toxicity.

Intrinsic factors include genetic susceptibility (e.g., turkeys and ducks are more sensitive to aflatoxin), age (young birds are more susceptible), immune status (immunosuppressed birds are more vulnerable), and high production stress (laying hens and fast-growing broilers). Extrinsic factors include poor feed storage conditions (high moisture, humidity, temperature), use of contaminated feed ingredients (corn, peanuts, cottonseed meal), inadequate ventilation leading to high ammonia and humidity, high stocking density, wet litter, and poor biosecurity. Vaccination failure due to immunosuppression can also predispose to secondary infections. Nutritional deficiencies (e.g., low protein, vitamin E, selenium) exacerbate toxicity.

Clinical signs vary with toxin type, dose, and duration. In acute aflatoxicosis, broilers show depression, huddling, anorexia, pale combs and wattles, and diarrhea (often with blood). Mortality can be sudden. Chronic exposure leads to poor growth, decreased feed intake, poor feathering, and increased susceptibility to infections. Layers exhibit decreased egg production, reduced egg size, poor shell quality (thin, cracked), and increased mortality. T-2 toxicosis is characterized by oral lesions (white plaques, ulcers on the beak, tongue, and palate), reduced feed intake, weight loss, diarrhea, and neurological signs (incoordination, tremors) in severe cases. Ochratoxin A causes polydipsia, polyuria, and renal failure, with dehydration and increased water consumption. In all cases, immunosuppression leads to secondary bacterial and viral infections, complicating the clinical picture.

Differential diagnoses include: 1) Infectious bursal disease (IBD) - causes bursal atrophy and hemorrhages, but no oral lesions; PCR and histopathology differentiate. 2) Newcastle disease (ND) - respiratory and neurological signs, but no oral lesions; HI titers and PCR. 3) Avian influenza (AI) - severe systemic signs, edema, cyanosis; virus isolation and PCR. 4) Fowl cholera (Pasteurella multocida) - septicemia, liver necrosis; bacterial culture. 5) Coccidiosis - intestinal lesions, bloody diarrhea; lesion scoring and oocyst identification. 6) Vitamin A deficiency - oral lesions and hyperkeratosis; histopathology and diet history. 7) Gumboro disease (IBD) - similar immunosuppression; bursal lesions. 8) Mycoplasmosis (MG) - respiratory signs, airsacculitis; serology and PCR. 9) Fatty liver hemorrhagic syndrome - liver lesions in layers; diet and histopathology. 10) Other mycotoxicoses (e.g., ochratoxicosis, fusariotoxicosis) - similar signs; feed analysis for specific toxins.

The diagnostic approach begins with a thorough flock history, including feed source, storage conditions, and recent changes. Clinical signs and gross necropsy findings (e.g., pale, fatty liver, oral lesions, kidney enlargement) raise suspicion. Feed samples should be collected and analyzed for mycotoxins using ELISA, HPLC, or LC-MS/MS. Confirmatory diagnosis involves histopathology of liver, kidney, and oral tissues. Serology and PCR are used to rule out infectious diseases. A step-by-step algorithm: 1) Flock history and clinical signs. 2) Necropsy of representative birds. 3) Feed sampling and mycotoxin analysis. 4) Histopathology. 5) Rule out infectious agents via culture, PCR, and serology. 6) Correlate findings to confirm mycotoxicosis.

Serology: ELISA can detect aflatoxin residues in serum, but is not routine. Molecular diagnostics: PCR for toxigenic fungi in feed. Microbiology: Fungal culture of feed to identify Aspergillus and Fusarium species. Coccidiosis lesion scoring (0-4 scale) may be normal. Mycotoxin feed assays: Aflatoxin B1 levels >20 ppb are concerning; T-2 toxin >500 ppb; ochratoxin A >100 ppb. Blood chemistry: Elevated liver enzymes (AST, ALT, GGT), decreased total protein and albumin, prolonged prothrombin time. CBC: Anemia, leukopenia, thrombocytopenia. Urinalysis (in layers): Increased protein and casts in ochratoxicosis.

Radiography is not typically used for mycotoxicosis, but may reveal skeletal abnormalities in chronic cases (e.g., rickets due to vitamin D deficiency secondary to liver damage). Ultrasonography is not commonly employed. Gross necropsy photography is essential for documenting lesions: pale, swollen liver with petechial hemorrhages; oral ulcers; enlarged kidneys with urate deposits; and bursal atrophy.

Gross necropsy lesions: Aflatoxicosis - pale, fatty, enlarged liver with hemorrhages; gallbladder distension; ascites; kidney pallor. T-2 toxicosis - oral and esophageal ulcers, white plaques, and necrosis; gastrointestinal mucosal congestion and hemorrhage. Ochratoxicosis - enlarged, pale kidneys with urate deposits; dehydration. Histopathology: Aflatoxicosis - hepatic fatty change, hepatocyte necrosis, bile duct hyperplasia, and periportal fibrosis. T-2 toxicosis - necrosis of oral mucosa, intestinal villus blunting, and bone marrow hypoplasia. Ochratoxicosis - proximal tubular degeneration and necrosis, interstitial fibrosis. Immunosuppression is evidenced by lymphoid depletion in bursa and thymus.

There is no specific antidote for mycotoxicosis. Immediate action includes removing contaminated feed and replacing with clean, high-quality feed. Supportive therapy: Administer vitamins (A, D3, E, C, K) and electrolytes in drinking water to mitigate oxidative stress and support liver function. For aflatoxicosis, add liver protectants such as silymarin or activated charcoal (0.5-1% of feed) to bind toxins. For T-2 toxicosis, provide oral rinses with antiseptic solutions (e.g., dilute chlorhexidine) to reduce secondary infections. Antibiotics may be indicated for secondary bacterial infections (e.g., amoxicillin 20 mg/kg body weight orally twice daily for 5 days, or oxytetracycline 20 mg/L drinking water for 3-5 days). Anticoccidials may be needed if coccidiosis is concurrent. In severe cases, depopulation may be necessary. Biosecurity measures should be enhanced to prevent further contamination.

Prognosis depends on toxin level and duration. In acute cases with high toxin concentrations, mortality can be high (20-30%), and recovery is poor. Chronic exposure leads to permanent growth retardation and reduced egg production. With early removal of contaminated feed and supportive care, flocks may recover within 2-4 weeks, but egg production may not return to normal levels. In severe immunosuppression, secondary infections may cause prolonged morbidity. Long-term effects include reduced flock uniformity and increased susceptibility to disease. In cases of severe liver damage, prognosis is guarded.

After an outbreak, monitor feed quality regularly (monthly mycotoxin assays). Implement a comprehensive biosecurity and feed storage program. Conduct serial necropsies and histopathology to assess recovery. Monitor flock performance (body weight, FCR, egg production) for 4-6 weeks. For layers, track egg production and shell quality. Implement a vaccination program review to ensure immunosuppression is not compromising immunity. Clean and disinfect feed bins, mills, and feeders thoroughly. Audit feed suppliers and storage conditions.

Pearls: 1) Always examine the liver and oral cavity in suspected mycotoxicosis. 2) Pale, fatty liver with hemorrhages is classic for aflatoxicosis. 3) Oral ulcers are pathognomonic for T-2 toxicosis. 4) Immunosuppression increases susceptibility to infectious diseases, so rule out concurrent infections. 5) Feed analysis is essential for definitive diagnosis. Pitfalls: 1) Do not overlook mycotoxicosis as a primary cause of poor performance; it is often underdiagnosed. 2) Avoid using contaminated feed; even low levels can cause chronic issues. 3) Do not rely solely on clinical signs; confirm with feed analysis and histopathology. 4) Do not treat with antibiotics without evidence of secondary bacterial infection. 5) Do not ignore the role of mycotoxins in vaccine failures.

There are no specific antidotes. Supportive therapy includes: Vitamin E (100-200 IU/kg feed) and selenium (0.2-0.3 mg/kg feed) as antioxidants. Vitamin C (100-200 mg/L drinking water) to reduce stress. Vitamin K (1-2 mg/kg feed) to support clotting. Activated charcoal (0.5-1% of feed) as a toxin binder. For secondary bacterial infections, use amoxicillin (20 mg/kg body weight orally twice daily for 5 days) or oxytetracycline (20 mg/L drinking water for 3-5 days). For coccidiosis, use amprolium (0.0125% in drinking water for 3-5 days) or toltrazuril (25 mg/L drinking water for 2 days). Vaccines should be administered according to standard protocols, but may need adjustment if immunosuppression is severe. Always observe withdrawal times: amoxicillin 1 day, oxytetracycline 3 days, amprolium 0 days.

Landmark studies have demonstrated the hepatotoxic and immunosuppressive effects of aflatoxin B1 in broilers (Smith et al., 1971). Research by Leeson et al. (1995) showed that chronic aflatoxin exposure reduces growth and feed efficiency. T-2 toxin studies by Wyatt et al. (1973) characterized oral lesions and reduced feed intake. Ochratoxin A research by Huff et al. (1975) established nephrotoxicity. Consensus guidelines from the AAAP and WVPA recommend routine feed testing and use of toxin binders. Meta-analyses indicate that mycotoxin binders (e.g., aluminosilicates) can reduce toxicity by up to 50%. Expert recommendations emphasize prevention through proper feed storage and quality control.