Phaeohyphomycoses, formally known as dactylariosis and ochroconiasis, is a sporadic fungal encephalitis of birds caused by the dematiaceous thermophilic fungus,
Verruconis gallopava (synonyms
Dactylaria and
Ochroconis gallopava). The disease has mainly been associated with younger birds, 1 to 5 weeks of age, although birds of any age can become infected. It has been described in chickens, turkeys, quails, grey-winged trumpeters, a captive snowy owl, an Eclectus parrot, and a kea.
V. gallopava is commonly found in warm, acidic environments, including decaying vegetation, excrement, old sawdust, and wood shavings. It grows best in low pH conditions (less than 5). Outbreaks of dactylariosis have been associated with contaminated wood chips, mulch, and sawdust litter. Contaminated egg incubators have also been tied to outbreaks.
Chickens become infected with the fungus by inhaling spores released into the air by
V. gallopava. Once infected, the organism targets the bird's central nervous system, resulting in neurological signs such as incoordination, torticollis (wry neck), head tilt, tremors, paralysis, and death.
Gross lesions may be confined to the brain with involvement of both the cerebellum and cerebrum. Lesions have been described as large, hardened, grayish, and circumscribed or as focally extensive areas of prominent red discoloration. Pulmonary granulomas are seen in some cases.
Histologically, lesions are characterized by multifocal to coalescing areas of infiltrates of massive numbers of heterophils, macrophages, and multinucleated giant cells with central areas of necrosis. The dematiaceous hyphae of Dactylaria are readily apparent in hematoxylin and eosin-stained tissue sections. The hyphae typically are scattered throughout the lesion in a random arrangement and are yellow to light brown, septate, irregularly branched, and 1.2–2.4 µm in diameter.
