Experimental Vacuolar Myelinopathy in Red-Tailed Hawks

Abstract

Avian vacuolar myelinopathy (AVM) was recognized in 1994 as a cause of wild bird mortality when 29 bald eagles (Haliaeetus leucocephalus) succumbed to the disease at DeGray Lake, Arkansas (USA). The cause of AVM and its source remain undetermined despite extensive diagnostic and research investigations. Two years later, when AVM killed 26 eagles in the same area in Arkansas, it became apparent that American coots (Fulica americana) had identical neurologic signs and lesions, and it was hypothesized that eagles acquired AVM via ingestion of affected coots. In order to test this hypothesis, we fed coot tissues (brain, liver, kidney, muscle, fat, and intestinal tract) to rehabilitated, non-releasable red-tailed hawks (Buteo jamaicensis). Five hawks received tissues from coots with AVM lesions, and one hawk received tissues from coots without brain lesions that had been collected at a site where AVM never has been documented. All hawks received 12-70 g/day (mean = 38 g) of coot tissues for 28 days. All six hawks remained clinically normal during the study. The birds were euthanatized on day 29 and microscopic lesions of AVM were found in all hawks that received tissues from affected coots, but not in the hawk that received tissues from unaffected coots. This marks the first time that AVM has been produced in birds under laboratory conditions and proves that birds of prey can acquire AVM via ingestion of tissues from affected coots.

A novel epiphytic cyanobacterium associated with reservoirs affected by avian vacuolar myelinopathy

“…Birds of prey contract the disease via ingestion of AVM-positive waterfowl tissue (Fischer et al, 2003). A strong association has been observed between the occurrence of AVM, H. verticillata (hydrilla) and certain potentially toxic, epiphytic cyanobacteria on hydrilla (Wilde et al, 2005).…”

Experimental Feeding of Hydrilla verticillata Colonized by Stigonematales Cyanobacteria Induces Vacuolar Myelinopathy in Painted Turtles (Chrysemys picta)

“…Spinal cord was also sectioned transversely, resulting in 3–5 sections that were placed into a second cassette. Formalin fixed tissues were routinely processed, embedded, and stained as previously described for the chickens and were subsequently examined by a pathologist with experience in chelonian histopathology following previously described methods [9]. Subsequently one treatment and one control turtle were randomly selected for EM examination at the Electron Microscopy Laboratory at the University of Georgia [5].…”

“…The UCB grows in high abundance on Hydrilla ( Hydrilla verticillata ), a widespread invasive exotic plant, although it can also grow on several native aquatic plant species [6]. Birds may acquire the toxin(s) directly by ingesting plants that are colonized with the UCB or indirectly by feeding on herbivorous prey such as invertebrates [8] or other bird species that have fed on plants that are colonized with the UCB [9]. Affected birds develop microscopic vacuoles in the white matter of the central nervous system.…”

Avian Vacuolar Myelinopathy Outbreaks at a Southeastern Reservoir

“…Coots with clinical signs of AVM were collected using hand net or shotgun with number 6 steel shot. Additionally, coots with no apparent clinical signs were randomly collected using a shotgun because AVM lesions have been found in the brains of birds without clinical signs (Larson et al, 2002;Fischer et al, 2003). From December 2000 through February 2001, several mammals from areas on the Georgia side of the reservoir were collected using box traps and snares.…”