Aspergillosis in poultry is most often a respiratory tract infection; less frequently, it can affect other organs. It occurs mainly in chickens and turkeys but can affect a wide range of other domestic fowl, wild birds, and pet birds. Affected birds may display respiratory distress, suppressed growth, and general unthriftiness. Diagnosis is made through observation of granulomas, usually in the respiratory tissues, and can be confirmed through fungal culture or histological examination of affected tissue. There is no effective treatment in poultry.
Aspergillosis, also known as brooder pneumonia, is an untreatable fungal disease that most typically presents as a lung infection in young poultry. It can lead to high mortality rates in affected poultry populations. Survivors are typically smaller than normal because of longterm impacts on the cardiovascular system. Although outbreaks of aspergillosis are uncommon, their economic impacts can be substantial for individually affected farms or flocks.
This topic addresses aspergillosis in poultry; for information on aspergillosis in pet birds, see Mycotic Diseases of Pet Birds. Also see Aspergillosis in Animals.
Etiology and Pathophysiology of Aspergillosis in Poultry
Aspergillosis in poultry is caused bysaprophytic, spore-forming, filamentous fungi in the genus Aspergillus.Aspergillus fumigatus is a common cause of aspergillosis; however, several Aspergillus spp may be incriminated, including A flavus and A niger.
Other mold species, such as Rhizopus spp, Mucor spp, and Penicillium spp, can cause disease that is clinically similar to aspergillosis, but such infections are less common.
Infection occurs by inhalation of spores (conidia). Healthy adult birds that inhale small numbers of spores usually do not develop aspergillosis. In young or immunocompromised birds, or when spore numbers are very high, inhaled spores lodge in alveoli, germinate, form hyphae, and invade local vasculature, leading to clinical signs of disease.
Large numbers of spores can form when shavings that are used as bedding get wet and then dry out; if the shavings are then stirred or otherwise disturbed, spores become aerosolized. Inadequate ventilation can also contribute to disease development. Although all birds exposed to large numbers of spores are susceptible to infection, aspergillosis is not transmissible between birds.
Aspergillosis typically affects the respiratory system, although the brain and other tissues can also be affected.
Epidemiology of Aspergillosis in Poultry
Aspergillosis in poultry occurs primarily in chickens and turkeys but can also affect ducklings, pigeons, canaries, geese, and many other wild and pet birds. In chickens and turkeys, the disease can reoccur in farms where animals are housed in suboptimal conditions; in wild birds, it appears to be sporadic, frequently affecting only individual birds that live in moist, moldy environments.
Aspergillus spp are ubiquitous and have a worldwide distribution. These organisms can proliferate and sporulate in feed and bedding.
Severe outbreaks usually occur in birds 7–40 days old whose immune systems have not fully matured.
Mortality rates can be high in chicks and turkey poults that inhale large numbers of mold spores, potentially while hatching or when placed on bedding contaminated with spores.
In older birds, infection is primarily due to inhalation of spore-laden dust from contaminated litter, feed, or dusty range areas. Allowing contaminated bedding to become wet and then dry creates a major risk for both young and mature poultry, because the increased moisture facilitates sporulation of mold present in bedding, and subsequent drying creates the opportunity for aerosolization of infectious spores.
In facilities with reoccurring infection, the air handling system should also be investigated as a source of contamination.
Clinical Findings of Aspergillosis in Poultry
The most common clinical signs of aspergillosis in poultry include the following:
dyspnea
labored breathing
fever
inappetence
emaciation
increased mortality
Less frequently, birds can develop a neurological form of aspergillosis. Clinical signs of the neurological form include torticollis and tremors.
In chickens and turkeys, aspergillosis most frequently affects the lungs and air sacs. Pulmonary lesions are commonly characterized by white to yellow plaques and nodules a few millimeters to several centimeters in diameter. In rare cases, birds may have diffuse pulmonary congestion only. Occasionally, mycelial masses may be present within the respiratory tract on gross examination. (See severe granulomatous fungal pneumonia, diffuse granulomatous fungal airsacculitis, and fungal plaque and nodulesimages.)
Lungs of a turkey poult with severe granulomatous fungal pneumonia, characteristic of aspergillosis. Note the numerous firm, white to yellow fungal granulomas diffusely distributed throughout the lungs (blue arrow) and two nodules in the air sac (green arrows).
Courtesy of Dr. M. E. Lighty.
Thoracic and abdominal air sacs of a turkey poult with diffuse granulomatous fungal airsacculitis, characteristic of aspergillosis. Note the numerous firm, white to tan fungal granulomas (arrows) of varying sizes diffusely distributed throughout the air sacs.
Courtesy of Dr. M. E. Lighty.
Thoracic and abdominal air sacs of a turkey poult with aspergillosis. Note the single, large, flat, white fungal plaque on the lung (blue arrow) and the multiple, smaller, coalescing, firm, white to tan fungal nodules along the inner thigh (green arrow) and within the air sacs (orange arrow). Note also the mild caseous exudate on serosal surfaces within the coelom, indicative of bacterial serositis. The large white structure on the thigh that appears between the blue and green arrows is the head of the femur.
Courtesy of Dr. M. E. Lighty.
Lungs of a turkey poult with severe granulomatous fungal pneumonia, characteristic of aspergillosis. Note the numerous firm, white to yellow fungal granulomas diffusely distributed throughout the lungs (blue arrow) and two nodules in the air sac (green arrows).
Courtesy of Dr. M. E. Lighty.
Thoracic and abdominal air sacs of a turkey poult with diffuse granulomatous fungal airsacculitis, characteristic of aspergillosis. Note the numerous firm, white to tan fungal granulomas (arrows) of varying sizes diffusely distributed throughout the air sacs.
Courtesy of Dr. M. E. Lighty.
Thoracic and abdominal air sacs of a turkey poult with aspergillosis. Note the single, large, flat, white fungal plaque on the lung (blue arrow) and the multiple, smaller, coalescing, firm, white to tan fungal nodules along the inner thigh (green arrow) and within the air sacs (orange arrow). Note also the mild caseous exudate on serosal surfaces within the coelom, indicative of bacterial serositis. The large white structure on the thigh that appears between the blue and green arrows is the head of the femur.
Courtesy of Dr. M. E. Lighty.
In addition, plaques and nodules may be found in the trachea, syrinx, liver, intestines, and occasionally the brain.
Morbidityassociated with aspergillosis can be underestimated in finishing flocks until the time of processing, when airsacculitis can result in postmortem condemnation of poultry intended for the food supply.
An ocular form of aspergillosis occurs in chickens and turkeys as mycotic keratitis. In affected birds, large plaques may be expressed from the medial canthus.
Diagnosis of Aspergillosis in Poultry
Clinical signs
Gross pathological findings
Fungal culture
Histological examination of affected tissue
Diagnosis of aspergillosis in poultry is most often based on clinical signs and gross lesions. For confirmation, the presence of fungus in the affected organs can be demonstrated by fungal culture or by cytological or histological examination of affected tissues.
Common histopathological lesions in poultry with aspergillosis include granulomatous pneumonia with intralesional fungal hyphae and heterophilic infiltrates.
There are several ways to obtain a sample of affected tissue for microscopic examination: a piece of affected tissue may be excised, the lesion(s) may be sampled using a swab, or one of the plaques can be teased apart. Typically, the sample is then placed on Sabouraud dextrose agar or some other medium specific for fungal growth.
Histological examination using a special stain for fungus reveals granulomas containing mycelia. (See fungal granuloma, fungal pneumonia, fungal hyphae [brain], and fungal hyphae [lung] images.)
Photomicrograph of a histological section of lung tissue from a turkey poult with respiratory signs of aspergillosis. The image shows a focal granuloma with multinucleated giant cells (arrow), consistent with fungal pneumonia. H&E stain; scale bar = 50 mcm.
Courtesy of Dr. M. E. Lighty.
Photomicrograph of a histological section of lung tissue from an adult chicken with respiratory signs of aspergillosis. The image shows bronchopneumonia with numerous intralesional, branching, septate fungal hyphae (arrows), consistent with Aspergillus spp. H&E stain; scale bar = 50 mcm.
Courtesy of Dr. M. E. Lighty.
Photomicrograph of a histological section of the cerebellum of a turkey poult with neurological signs of aspergillosis. Note the branching, septate fungal hyphae, consistent with Aspergillus spp. Grocott methenamine silver stain; scale bar = 50 mcm.
Courtesy of Dr. M. E. Lighty.
Photomicrograph of a histological section of lung tissue from a turkey poult with respiratory signs of aspergillosis. Note the branching, septate fungal hyphae, consistent with Aspergillus spp. Grocott methenamine silver stain; scale bar = 50 mcm.
Courtesy of Dr. M. E. Lighty.
Photomicrograph of a histological section of lung tissue from a turkey poult with respiratory signs of aspergillosis. The image shows a focal granuloma with multinucleated giant cells (arrow), consistent with fungal pneumonia. H&E stain; scale bar = 50 mcm.
Courtesy of Dr. M. E. Lighty.
Photomicrograph of a histological section of lung tissue from an adult chicken with respiratory signs of aspergillosis. The image shows bronchopneumonia with numerous intralesional, branching, septate fungal hyphae (arrows), consistent with Aspergillus spp. H&E stain; scale bar = 50 mcm.
Courtesy of Dr. M. E. Lighty.
Photomicrograph of a histological section of the cerebellum of a turkey poult with neurological signs of aspergillosis. Note the branching, septate fungal hyphae, consistent with Aspergillus spp. Grocott methenamine silver stain; scale bar = 50 mcm.
Courtesy of Dr. M. E. Lighty.
Photomicrograph of a histological section of lung tissue from a turkey poult with respiratory signs of aspergillosis. Note the branching, septate fungal hyphae, consistent with Aspergillus spp. Grocott methenamine silver stain; scale bar = 50 mcm.
Courtesy of Dr. M. E. Lighty.
Differential diagnoses for aspergillosis include the following:
colibacillosis (Escherichia coli infection)
other mycoses (eg, ochroconosis, zygomycosis)
oncogenic tumors (eg, Marek's disease, avian leukosis)
Treatment and Control of Aspergillosis in Poultry
No effective treatment
Measures to minimize exposure
Treatment of aspergillosis in affected poultry is generally ineffective. Spontaneous recovery can occur if reexposure to fungus is prevented.
The best strategy for mitigating an aspergillosis outbreak is to remove the birds from the contaminated environment and rehouse them. If that is not possible, the following strategies can help:
removing contaminated materials to limit further exposure of the flock to mold spores
preventing disturbances of contaminated materials to limit further aerosolization of spores
increasing ventilation or air exchange rates to possibly minimize the severity of the outbreak, unless the ventilation system is suspected to be a potential source of mold exposure
For subsequent flocks, strict adherence to cleaning and disinfection procedures for any contaminated environment (eg, hatchery or barn) minimizes the risk of future aspergillosis outbreaks.
Grossly contaminated or cracked eggs should not be set for incubation, because they can enable bacterial and fungal growth. Affected eggs may explode and disseminate spores throughout the incubator.
To prevent aspergillosis outbreaks in poultry, moldy bedding or ranges should not be used. Contaminated surfaces may be sprayed or fumigated with enilconazole or other fungicidal disinfectants in accordance with label directions. Enilconazole must not be used when poultry or eggs are present. The extralabeluse of nitroimidazoles is prohibited in food-producing animals in the US.
Key Points
Aspergillosis in poultry is most often a respiratory disease of young chickens or turkeys; however, other forms of the disease (eg, neurological or ocular) can occur, and all types of birds can be affected.
Diagnosis is based on the observation of typical gross lesions but can be confirmed through fungal culture or cytological or histological examination of tissue.
There is no effective treatment in poultry. The key to control is to minimize exposure of birds to contaminated materials.
For More Information
The Poultry Site: Aspergillosis.
