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Test results have confirmed that the 8,000 mallards found dead in South Dakota earlier this winter died from respiratory fungal infections, likely picked up when the birds ate moldy grain. The die-off occurred over several days in January and February near Lake Oahe in the Pierre, S.D., area. The U.S. Geological Survey's National Wildlife Health Center (NWHC) tested some birds and determined respiratory infections likely were to blame. A sample of thirteen dead mallards were sent to NWHC for diagnostic necropsy. Initial results indicated that at least two of eight died due to aspergillosis, a respiratory tract infection caused by the inhalation of spores produced by fungi. Asperillosis has been known to cause previous mallard die-off events, including an event that occurred near Pierre in 1985. Further testing, including histopathology analysis of lung tissues, later confirmed that two of the other six mallards also died from a fungal respiratory infection, possibly caused by a different genus of fungi. Scientists at NWHC are continuing tests to try to identify the fungal pathogen associated with disease in these birds. Fungi can also cause avian morality by producing toxins (mycotoxins) that target the liver; however, lab results did not indicate mortality from liver disease. Officials said the mallards most likely developed the fungal respiratory infections after being exposed to moldy corn found at a nearby feedlot and in the digestive tracts of some ducks. However, lab findings did not definitively determine the source of fungi that infected the mallards. The fungal disease found in the ducks isn't considered contagious to other birds, and humans are'nt considered susceptible unless they have an immune system deficiency or develop an allergic reaction, which is rare. More information on aspergillosis and other fungal diseases is available in the National Wildlife Health Center "Field Manual of Wildlife Diseases" available at http://www.nwhc.usgs.gov/publications/field_manual/index.jsp).