The Role of Epiphytic
Cyanobacteria as the Potential Causative Agent of Avian Vacuolar
AVM: The recovery and
conservation of bald eagles (Haliaeetus
leucocephalus) has been
contested due to a newly identified fatal bird disease: Avian Vacuolar
Myelinopathy (AVM). Since the discovery of the disease in 1994, AVM has
caused mortality in at least 99 bald eagles, and unknown numbers of
American coots, Canada geese, great horned owls, mallards, and other
various species of bird throughout the southeastern US. Since its
discovery at DeGray Lake in Arkansas, AVM has been found in Arkansas,
TX, NC, SC, and GA (Fischer et al. unpublished data).
Learn about AVM and South Carolina;s bald eagles at the SCDNR
bald eagle page.
Linkage: A strong association has been observed between
the occurrence of AVM, Hydrilla verticillata (hydrilla), and certain
potentially toxic, epiphytic cyanobacteria on hydrilla. The correlation
has led to the hypothesis that these epiphytes are the source of the
neurotoxin causing AVM. Hydrilla is an invasive, exotic macrophyte that
has been problematic in freshwater systems in the US since the 1960’s.
During 2001-2002, the unidentified cyanobacteria was present on the
surface of hydrilla at every site where AVM has been diagnosed, but was
not found in areas where AVM was not observed.
It is hypothesized that the proposed toxin of the
cyanobacteria is bioaccumulated through the food chain from waterfowl
(coots and other waterfowl) ingesting the cyanobacteria growing on the
hydrilla. AVM positive coots become symptomatic and are easier for
birds of prey to capture. Eagles may ingest a larger number of
AVM-positive waterfowl resulting in quicker and more prevalent deaths.
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