History

Early 1990's

There is good evidence that AVM was first observed in Woodlake, NC (Lake Surf) in October and November 1990. One American coot was found with paralyzed legs, two were found with general lethargy, and two others were found dead. These dead birds were taken to the Robbins Animal Disease Diagnostic Laboratory (Robbins, North Carolina) which reported abnormal histology in the cerebrum of one specimen, and softening and demyelination in the brain of the other. Preserved specimens from these birds were not retained by the diagnostic lab, so there is no way to confirm if these birds had the characteristic AVM brain lesions documented at DeGray Lake, Arkansas. However, the observation of coots with paralysis and myelin lesions at a site where AVM has now been documented suggests the disease had the earliest recorded onset at Lake Surf. (Augspurger et al 2003).

Winter of 1994-1995

AVM was first diagnosed during the winter of 1994-1995 at DeGray Lake in Arkansas when 29 bald eagles were found dead or dying (Thomas et al. 1998). The following winter, at nearby Lake Ouachita and Lake Hamilton, 26 more sick or dead eagles were recovered. Scientists from the National Wildlife Health Center (NWHC), Madison, Wisconsin, USA conducted epidemiological studies and performed diagnostic evaluations of recovered carcasses (Thomas et al. 1998). No association was found with infectious agents, pesticides, herbicides, or heavy metals. No consistent gross lesions or abnormalities were found except for lesions in the brain, most pronounced in the white matter of the CNS. Several chemicals have been associated with this specific type of lesion, including triethyltin, bromethalin, isonicotinic acid hydrochloride, and hexachlorophene, but none were detected in tissues of affected birds.


Sick coot


Winters of 1997-8 and 1998-99

AVM was documented in 1997-8 outside of Arkansas in coots at Woodlake, NC and Lake Juliette, GA. The following winter AVM was documented in coots again at Woodlake and Lake Juliette, and at several more locations: Lake J. Strom Thurmond on the Georgia-South Carolina border, Lake Murray, and Par Pond on the Savannah River Site, both in South Carolina. In addition to coots, AVM was documented in 2 ring-neck ducks (Aythya collaris), 6 mallards (Anas platyrhynchos) and 2 bufflehead ducks (Bucephala albeola) at Woodlake (Augspurger et al. 2003). Mallard duck and coot field release trials at Woodlake demonstrated that the disease was contracted on site and that birds could get sick very quickly. Some sentinel mallards became neurologically imparied within five days of release on Woodlake during an active disease time period (late fall) (Rocke, et al 2002, Augspurger et al 2003).


Mallard ducks

Winters of 2000-01 and 2001-02

The largest AVM-bald eagle mortalities, outside of Arkansas, occurred at Thurmond during the winters of 2000-2001 and 2001-2002, when 23 carcasses were recovered. During active disease surveillance on Thurmond, AVM was diagnosed in 16 Canadian geese (Branta canadensis), 2 great-horned owls (Bubo virginianus), and 1 killdeer (Charadrius vociferus) (Fischer et al. 2006). Feeding studies with non-releasable red-tailed hawks fed AVM positive coots confirmed that the predators could get AVM by ingesting prey positive for the disease (Fischer, et al 2003). Field monitoring of AVM positive locations documented the high abundance of a novel epiphytic cyanobacterium in the order Stigonematales during active disease (Wilde, et al. 2005).


Great Horned Owl

Winters of 2004 to 2006

Another period of higher eagle mortality at Thurmond was during the winters from 2004-2006, when there were 17 more AVM bald eagle deaths. To date, AVM has been the confirmed or suspected cause of 54 bald eagles mortalities at this reservoir. Three more dead eagles were also recovered from DeGray Lake (AR) during 2005. Sentinel mallard feeding trials on a small farm pond linked invasive hydrilla and dense coverage of a new species of Stigonematalan cyanobacteria to AVM (Wilde, et al. 2005).


Davis Pond mallard duck trial 2005

Winters of 2007 to present

During this time period, there were three new sites where dead AVM positive eagles were recovered. These locations were all in the western piedmont region of Georgia; Lake Horton, Lake Varner, and Troupe County, near West Point Lake.


Hydrilla in new AVM site, Lake Varner, GA