Avian Vacuolar Myelinopathy
In November 1994 to December 1994, twenty-three bald eagles died due to an unknown cause (Fischer 1995). In November 1996, American coots were also found dead or dieing due to this mysterious disease (Fischer 1997). Labeled Coot and Eagle Brain Lesion Syndrome, it was changed to Avian Vacuolar Myelinopathy when it was discovered to affect other species as well. It has become the most significant unknown cause of eagle mortality in the history of the United States. Avian Vacuolar Myelinopathy causes lesions in the white matter of the brain and the spinal cord of an affected bird (USACE). What causes Avian Vacuolar Myelinopathy remains a mystery even to this day. Avian Vacuolar Myelinopathy is an avian disease that is believed to be caused by a neurotoxin of unknown origin. It causes lesions in the white matter of the brain and in the spinal cord of affected birds. Dead Avian Vacuolar Myelinopathy birds appear to be in good body condition and have no visible external or internal changes with the exception of microscopic neural lesions. Electron Microscopy is used to confirm the disease, but can only be used on fresh specimens that have not been frozen. The clinical signs of a bird affected with Avian Vacuolar Myelinopath
Because Avian Vacuolar Myelinopathy affects the nervous system, specimens that have been frozen or are in an advanced state of decomposition cannot be used for an accurate diagnosis of the disease. Birds killed due to Avian Vacuolar Myelinopathy appear to be in good body condition and have no internal or external changes with the exception of the microscopic brain lesions. Tests have been conducted for a wide range of known toxins such as pesticides and heavy metals, and have resulted in no significant findings. Chemicals that are known to create similar brain lesions have been tested for and the results were negative. A naturally occurring or man-made toxin is believed to be the most probable cause of the lesions. Many research efforts have been or are being employed to determine the cause of Avian Vacuolar Myelinopathy. The only similarities found between the sights with affected birds are that the sites are man-made impoundments, have relatively good water quality, the presence of macrophytic and epiphytic aquatic vegetation, and wintering populations of water birds and eagles (USACE). The Southeastern Cooperative Wildlife Disease Study conducted a study of the distribution of Avian Vacuolar Myelinopathy during the 1998 migratory season (Fischer, 1998). Coots at more than forty sites in fifteen states were observed for signs of Avian Vacuolar Myelinopathy. The disease was detected in coots from eight locations in Arkansas, Georgia, North Carolina, and South Carolina. Coots with lesions resembling mild Avian Vacuolar Myelinopathy were found at one location in Texas. Many of the birds collected with brain lesions did not show the neurologic signs associated
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