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Dactylariosis

Other Names: Ochroconiasis, Mycotic Encephalitis

Dactylariosis, also known as ochroconiasis, is a sporadic fungal encephalitis of birds caused by the dematiaceous thermophilic fungus, Dactylaria gallopava (synonyms 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, and quails.

D. gallopava is commonly found in warm, acidic environments, including decaying vegetation, excrement, old saw-dust, 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 D. 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.

There is no known treatment for dactylariosis.

Clinical Signs

Incoordination
Paresis and inability to walk
Head tilt
Tremors
Circling
Paralysis
Torticollis (wry neck)

Diagnosis

  • History
  • Clinical signs
  • Fungal culture
  • Necropsy

Reported Cases

  • Case 1: Dactylariosis in a Chickens A farmer obtained bark to be used as wood shavings for bedding from an unknown source. The product was damp upon delivery, and the farmer tried to dry it out before the chicks arrived. Within 9 days of arrival, many of the chicks developed wry neck, made paddling movements with their legs as they lay on their sides, and were unable to stand, toppling over backwards when placed upright. Some had head/neck tremors. Necropsy results revealed gross abnormalities within the brain. Cerebellar oedema and haemorrhage were prominant features in some of the chicks, in others, oedema was also present over the cerebral hemispheres and haemorrhage was noted on the brain stems. The fungus, Dactylaria gallopava was isolated from the brain. Ref

  • Case 2: Dactylariosis in a Trumpeters One of the chicks housed in a zoo exhibit was raised on a substrate containing fir bark mulch over top commercially available potting soil. At 17 days of age, the chick started showing signs of weakness, thought to be mild incidence of head trauma. However, two days later, the bird had developed a head tilt towards the left, and mild ptosis of the lower left palpebra, and was circling towards the left. The bird was treated with injectable dexamthasone (4 mg/kg) once, and trimethoprim (4 mg/kg) and sufadiazine (20 mg/kg) were given subcutaneously twice daily. The bird was found dead the following morning. Necropsy results revealed tan necrotic areas involving the anterior quarter of the brain, fungal culture swabs isolate the fungus, Dactylaria gallopava from the brain, as well as the mulch. Ref

  • Case 3: Dactylariosis in a Snowy owl A 28-day-old captivity-bred snowy owl chick showed a sudden onset of neurological signs, consisting of ataxia, falling over backwards, inability to stand, intermittent wry neck (torticollis) and extensor rigidity of the legs. Radiographs, CBC, blood chemistry, and fecal test were all normal. Five days later, the bird was extremely weak and her signs were worse. She was euthanized. At necropsy, the brain showed extensive malacia, particularly on the left side, with hemorrhage of the meninges. There was widespread invasion with septate, dematiaceous hyphae consistent with D. gallopava. Ref

  • Case 4: Dactylariosis in a Quail 7 to 14 day old chicks on a farm in South Carolina started showing signs of neurological disease. All of the quails showed lateral recumbency and coarse muscular head tremors. Ataxia was observed in some of the less severely affected birds. Ref

Treatment

Supportive care: Isolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.

Support

Prevention

  • Don't reuse old saw dust or wood shavings.
  • Only purchase mulch and wood chips from quality sources.
  • Thoroughly clean egg incubators before hatching more eggs.

Prognosis

Poor, there is no known treatment.

Scientific References

Age Range

All ages can become infected, but chicks between 1 and 5 weeks of age are most susceptible.

Risk Factors

  • Using or reusing old saw-dust and wood shavings.
  • Purchasing wood chips and mulch from poor quality sources.
  • Hot and humid weather conditions
  • Tropical or subtropical climates.
  • Dirty egg incubators.

Seasonality

WinterSpringSummerAutumn

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