THE MERCK VETERINARY MANUAL
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Overview of Aspergillosis in Poultry

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Aspergillosis is a disease, usually of the respiratory system, of chickens, turkeys, and less frequently ducklings, pigeons, canaries, geese, and many other wild and pet birds. In chickens and turkeys, the disease may be endemic on some farms; in wild birds, it appears to be sporadic, frequently affecting only an individual bird. Severe outbreaks usually occur in birds 7–40 days old. (Also see Aspergillosis and see Aspergillosis.)

Aspergillus fumigatus is a common cause of the disease. However, several other Aspergillus spp may be incriminated.

High mortality rates are seen in chicks and poults that inhale large numbers of spores during hatching in contaminated incubators or when placed on mold-bearing litter. In older birds, infection is caused primarily by inhalation of spore-laden dust from contaminated litter or feed or dusty range areas. Morbidity can be underestimated in finishing flocks until slaughter inspection reveals pulmonary lesions.

Dyspnea, hyperpnea, somnolence and other signs of nervous system involvement, inappetence, emaciation, and increased thirst may be seen. In chicks or poults up to 6 wk old, the lungs are most frequently involved. Airsacculitis is a cause of postmortem condemnation in young mature turkeys intended for food supply. Pulmonary lesions are characterized by white to yellow plaques and nodules a few mm to several cm in diameter; occasionally, mycelial masses may be seen within the air passages on gross examination. The plaques and nodules also may be found in the syrinx, air sacs, liver, intestines, and occasionally the brain. The encephalitic form is most common in turkeys. An ocular form is seen in chickens and turkeys as mycotic keratitis, in which large plaques may be expressed from the medial canthus.

The fungus can be demonstrated by culture or by microscopic examination of fresh preparations. One of the plaques is teased apart and placed on a suitable medium, usually resulting in a pure culture of the organism. Histopathologic examination using a special fungus stain reveals granulomas containing mycelia.

Differential diagnoses include infectious bronchitis, Newcastle disease, infectious laryngotracheitis, mycobacteriosis, colibacillosis, other mycoses (eg, ochroconosis, zygomycosis), and nutritional encephalomalacia.

Treatment of affected birds is generally ineffective. Spontaneous recovery from pulmonary aspergillosis can occur if reexposure to the mold is prevented. Strict adherence to sanitation procedures in the hatchery minimizes early outbreaks. Grossly contaminated or cracked eggs should not be set for incubation, because they enable bacterial and fungal growth and may explode and disseminate spores throughout the hatching machine. Contaminated hatchers should be thoroughly cleaned and fumigated with enilconazole or formaldehyde. Avoiding moldy litter or ranges serves to prevent outbreaks in older birds. Cleaned pens should be sprayed or fumigated with enilconazole following label directions, and all equipment should be cleaned and disinfected.

Last full review/revision September 2014 by Frederic J. Hoerr, DVM, PhD, DACVP, DACPV

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