Introduction

Aspergillosis is a common disease of many waterfowl species and eider ducks are particularly sensitive to these pathogens. Aspergillus fumigatus is a ubiquitous saprophytic fungus which can cause severe granulomatous air sacculitis and pneumonia in birds. By the time a bird develops clinical signs, the disease is usually advanced and treatment is often unrewarding. Prevention and early detection offer the best chance for long term survival.

Materials and Methods

Twenty-four Pacific eider duck eggs (Somateria mollissima), confiscated by the U.S. Fish and Wildlife Service, were placed in the care of The Wildlife Conservation Society to provide facilities for incubation, hatching and care. Following hatch, the birds were maintained in an indoor air conditioned facility with access to a fresh water pool. Within six months, ducklings began to develop symptoms of aspergillosis. Clinical signs included various degrees of dyspnea (open mouth breathing, increased respiratory rate), decreased appetite, weight loss, and isolation from the group. A presumptive diagnosis of aspergillosis was based upon clinical signs, radiographic lesions and leukocytosis. Further diagnostic testing included Aspergillus ELISA serology (The Gabbert Raptor Center, College of Veterinary Medicine, St. Paul, MN 55108) serum protein electrophoresis (EPH), fungal culture and antifungal sensitivity of fungal isolates. Selected individuals were evaluated by computerized axial tomography (CAT Scan) and bronchoscopy to determine the location and extent of disease. Full postmortem examination including gross necropsy and histopathology were performed on all birds which died.

Birds with clinical signs (weight range 1.4-1.8 kg) were divided into two treatment groups (I & II). Intraosseous catheters were placed in the ulna of birds from Group I using a 20 gauge 1.5 inch spinal needle". These ducks were treated twice daily with intraosseous and intratracheal amphotericin-B (3.5mg and 3.Omg respectively) and with oral 5-fluorocytosine (250mg). Birds in Group II were aerosolized with enilconazole (Imaverol, Janssen Pharmaceutica, Beerse, Belgium) for 10-15 minutes twice daily. These ducks were placed in a large plastic covered chamber, 400mg of enilconazole was mixed with 30cc of water and was vaporized from a hot plate.

Clinically healthy birds (weight range 1.9-2.3 kg) were also separated into two groups (A & B). Group A was prophylactically treated with itraconazole-impregnated synthetic grit. These birds were orally dosed every seven days with 3 grams of 11% itraconazole grit. Medication impregnated synthetic grit for sustained release dosing is presently being investigated by the author (Stetter) as part of a larger research project. Group B received no medications.

Results

Birds in Group I showed clinical improvement during treatment. Signs of dyspnea resolved and the birds' activity and appetite markedly improved. Birds in Group II also demonstrated clinical improvement but their improvement was slower and less dramatic than that of group I. Birds in both treatment groups were periodically reevaluated with radiographs, CBC, EPH and Aspergillus ELISA titers. After treatment for 21 - 35 days, laparoscopy was performed on birds in groups I and II to help assess treatment efficacy. Severe diffuse granulomatous air sacculitis was noted in the eider ducks from groups I and II. Due to the severity of lesions noted after 3-5 weeks of treatment, these animals were humanely euthanized. Necropsy findings in all birds revealed multifocal-to-coalescing mycolic air sacculitis and pneumonia. Two individuals also demonstrated severe diffuse amyloidosis of the liver and kidneys.

The median white blood cell counts of the clinically ill birds in Groups I was markedly elevated compared to the nonclinical eiders (Groups A & B). The leukocytosis in Group I birds decreased during therapy but remained higher than nonclinical birds (Table 1). At the onset of illness, Group II birds had mild leukocytosis which markedly increased during therapy.

Elevated Aspergillus ELISA titers (>0.40) correlated with clinical disease and moderately elevated titers (0.2-0.4) may be useful in detecting subclinical disease states. ELISA titers measured in group I showed a dramatic decline during therapy. Group II ducks were not serologically tested pretreatment. Two symptomatic ducks, prior to treatment, demonstrated low Aspergillus titers in the face of severe disease.

Table 1

Radiographic air sac and pulmonary lesions were seen in clinically affected birds. A marked thickening of the abdominal air sacs was noted in all cases. Less commonly, discrete pulmonary lesions could be visualized radiographically. These radiographic lesions remained static or showed mild improvement during treatment.

Serum electrophoresis patterns in symptomatic birds were different as compared to the asymptomatic animals. The A/G ratios from asymptomatic birds ranged from 0.96-0.7. A decreased albumen/globulin ratio (A/G) was seen in affected animals. A/G ratios in aspergillosis infected birds ranged from 0.22-0.54. Changes in the electrophoretic pattern were noted when individual ducks became clinically ill and during the course of therapy.

Computerized axial tomography provided a high quality image of the normal and pathological anatomy. Precise location of lesions and extent of disease were demonstrated. Bronchoscopy was a useful diagnostic sampling tool for culture and cytology. Tracheal lesions were uncommon in these eider ducks and direct visualization of aspergillomas would not have been possible via bronchoscopy. The Aspergillus fumigatus organism isolated via bronchoscopy was sensitive to amphotericin-B, 5-flourocytosine and Itraconazole.

Mortality rates between groups A & B were not significantly different. Each group experienced a 55% mortality rate.

Discussion\Conclusions

Eider ducks are particularly susceptible to aspergillosis. Sixty six percent of the ducks died of aspergillosis within 8 months of hatching. Initial diagnosis was easily made by signalment and clinical signs. Hematologic parameters, radiographs, bronchoscopy, protein electrophoresis, Aspergillus ELISA titer, fungal culture and CAT scan were all useful, to various degrees, in confirming the diagnosis and in monitoring the efficacy of treatment. ELISA testing may be beneficial in identifying sub-clinically ill birds before the clinical signs have developed. The ELISA test measures serum anti-Aspergillus antibody levels'. A false negative test may represent an inability of the hosts' immune system to mount an adequate response due to the animal's severe disease state. Repeated serological tests and a rising titer are more useful at determining an active infection than a single sample.

Serum electrophoresis proved to be a useful, nonspecific indicator of disease. Specific globulin peaks in the EPH can be used to determine the chronicity of inflammatory diseases. The A/G ratio noted in asymptomatic eider ducks was similar to those values reported in mallard ducks.

Treatment of aspergillosis with various antifungal protocols helped alleviate clinical signs but failed to resolve the granulomatous lesions. Aspergillosis infected eider ducks undergoing antifungal chemotherapy showed clinical pathological evidence of improvement as measured by the CBC, EPH and Aspergillus titer. This was more evident in birds treated with parenteral antifungal medications (Group I) than those birds treated with aerosolization therapy (Group II).

Prophylactic antifungal therapy was attempted using itraconazole-impregnated synthetic grit. The survival rate was not improved by this means of dosing. The pharmacokinetics for this type of dosing has yet to be determined. The efficacy of itraconazole-impregnated synthetic grit as a therapeutic o preventative treatment modality should not be excluded on the basis of this very limited study. Itraconazole has been used successfully in treating aspergillosis in mammals and birds.

Aspergillosis continues to be a major cause of morbidity and mortality in many avian species. Adequate husbandry and prevention are the most important factors in reducing its incidence. Certain avian species are exquisitely susceptible to aspergillosis and even under the most rigorous management, clinical illness will occur. Early identification and treatment of such birds or prophylactic treatment of all birds may decrease the incidence of aspergillosis in eider ducks.

Acknowledgements

We would like to thank Christine Sheppard (Curator of Ornithology) and Susan Maher (Senior Avian Keeper) for their interest and assistance with these projects. We would also like to thank the veterinary technicians and animal maintainers at the Wildlife Health Center for their hard work and support.

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