Aspergillosis in Poultry: The Hidden Mold Behind Heavy Losses

Pashu Sandesh, 31 March 2026

Km Himani

Assistant Professor, Arawali Veterinary College, Sikar, Rajasthan

Email pf corresponding author- himanidhiman918@gmail.com

Respiratory diseases remain a major challenge in poultry production, and aspergillosis—often called brooder pneumonia—is one of the most overlooked yet economically damaging infections.

Etiology- The disease is caused by opportunistic fungus Aspergillus fumigatus, a fast-growing, thermotolerant mold commonly present in soil, decaying organic matter, and improperly stored feed. Under favorable conditions, the fungus produces large numbers of microscopic airborne spores called conidia, extremely light and easily dispersed through dust particles in poultry houses and hatcheries.

Global Occurrence and Risk Factors- Aspergillosis occurs worldwide and affects many domestic and wild bird species. The disease is most commonly seen in young chicks between one and three weeks of age because their immune systems are still developing. The causative fungus, Aspergillus fumigatus, is widely present in the environment and can easily infect birds under poor management conditions. 

Risk factors such as wet or moldy litter, poor ventilation, high humidity, and contaminated or improperly stored feed favor fungal growth. Overcrowding, poor hatchery sanitation, and weakened immunity due to malnutrition or other infections further increase susceptibility. These conditions allow fungal spores to accumulate in the environment and increase the chances of inhalation by birds.

Transmission- Aspergillosis is mainly transmitted through the inhalation of airborne fungal spores present in the environment. The primary sources of infection include moldy litter, contaminated or improperly stored feed, hatchery dust, soil, and damp bedding materials.

Pathogenesis- After inhalation, the spores of Aspergillus fumigatus pass through the nasal passages and trachea, eventually reaching the bronchi, lungs, and air sacs. In the lungs, immune cells such as macrophages attempt to eliminate the spores through phagocytosis; however, the fungus can resist destruction and continue to multiply. The fungal spores may then penetrate tissues and spread through the bloodstream and lymphatic system to other organs. This leads to different pathological reactions in tissues, including the formation of granulomatous nodules in organs like the lungs and air sacs, diffuse infiltration of fungal hyphae into tissues and blood vessels, or a mixed form where both granulomatous and infiltrative reactions occur within the same tissue. These changes impair normal respiratory function and contribute to disease progression.

Clinical Signs- Aspergillosis may occur in both acute and chronic forms depending on the age of birds and the level of exposure to spores of Aspergillus fumigatus. 

The acute form is mainly seen in young chicks and is characterized by severe respiratory distress, gasping, loss of appetite, weakness, increased thirst, and rapid weight loss, with sudden death occurring in severe cases. 

The chronic form usually affects older birds and develops gradually, showing signs such as progressive emaciation, persistent respiratory difficulty, fever, and diarrhea. In some cases, the infection may extend beyond the respiratory system, causing nervous signs like tremors, paralysis, ataxia, torticollis, and convulsions, along with ocular lesions such as inflammation, photophobia, and mycotic keratitis.

Post-Mortem Findings- The most characteristic lesions of aspergillosis are observed in the lungs and air sacs. The affected organs typically show white to yellowish granulomas or nodules of varying sizes. The air sac membranes become thickened and may contain caseous plaques, while the lungs may appear consolidated with necrotic areas. In advanced cases, gray-green velvety fungal growth indicating sporulation of Aspergillus fumigatus may be visible, which helps in confirming the disease during post-mortem examination.

Diagnosis- Based on a combination of flock history, clinical signs, and laboratory confirmation. Environmental conditions such as moldy litter, contaminated feed, poor ventilation, or recent stress events in the flock often provide important clues. Confirmation is achieved through laboratory investigations, including histopathological examination of tissues from the lungs and air sacs. Special fungal stains such as Periodic acid–Schiff (PAS) and silver stains are commonly used to visualize fungal hyphae in tissue sections. The causative fungus, Aspergillus fumigatus, can also be isolated by culturing samples on Sabouraud’s agar and incubating them at 37°C, where characteristic colonies develop. Additional diagnostic techniques such as radiography may further assist in confirming the infection.

Treatment- Often difficult and costly. The disease often progresses rapidly and fungal lesions can limit the effectiveness of antifungal drugs. Although antifungal agents such as itraconazole, ketoconazole, clotrimazole, fluconazole, and amphotericin B may be used in valuable birds, treatment is rarely practical for large commercial flocks. Among these drugs, itraconazole is commonly considered the preferred option.

Prevention and control- Since treatment options for aspergillosis are limited and often ineffective in large poultry flocks, prevention remains the most effective strategy for controlling the disease. Preventive measures mainly focus on reducing exposure to fungal spores and maintaining proper environmental hygiene in poultry houses. Good hatchery sanitation practices should be followed, and the use of moldy litter or contaminated feed must be strictly avoided. Feed should always be stored in dry, well-ventilated areas to prevent fungal growth. Regular cleaning of feed bins and storage containers, removal of old litter, and replacement with fresh bedding are also essential management practices. In addition, maintaining adequate ventilation in poultry houses and ensuring thorough cleaning and disinfection of hatching equipment help minimize the accumulation and spread of spores of Aspergillus fumigatus in the poultry environment.

Aspergillosis may be invisible in the environment, but its impact on poultry health and farm profitability can be severe. Good hygiene, proper ventilation, and quality feed management are the most reliable defences against this silent fungal threat.