Following an isolated episode of protracted mortality in mallards (Anas platyrhynchos) in a wilderness area near Lemhi, Idaho in early December, the U.S. Geological Survey - National Wildlife Health Center in Madison, WI. diagnosed pulmonary aspergillosis in three birds examined.  The report was posted on December 29th on ProMed Mail.

While there is no disputing the diagnosis that is evident on morphological examination and can be confirmed by histopathological examination and culture, the question arises as to why mature ducks apparently feeding on waste grain contaminated with Aspergillus fumigatus should have died showing pulmonary lesions.  Infection of other than hatchlings with A. fumigatus is uncommon in both wildlife and domestic avian species especially by the oral route.  In 1964 Emperor penguins (Aptenodytes forsteri) inappropriately transported from Marion Island in the South Atlantic to an enclosed temperature-controlled aviary at the Pretoria zoo died of pulmonary aspergillosis. Unknown to management, the air-conditioning system was contaminated with A. fumigatus.  The group of twenty birds died over a seven-day period showing mycotic pneumonia with inhalation the most likely route of infection. 

It is questioned whether the affected mallards were latent carriers of aspergillus that may have been activated by some insult including environmental cold stress or a bacterial or viral infection.  Given the resources and competence of the National Wildlife Health Center it is presumed that the three ducks examined were screened for avian influenza, Newcastle disease and other frequently encountered pathogens.  It is questioned why only three ducks were submitted for examination.  Live clinically affected birds together with recently gathered dead ducks from the same population would have provided more material for diagnosticians. To quote an old and wise mentor “there is a world of difference between a diagnosis and the actual problem”.