Investigation of the Link Between Avian Vacuolar Myelinopathy and a Novel Species of Cyanobacteria Through Laboratory Feeding Trials

Abstract

Avian vacuolar myelinopathy (AVM) is a neurologic disease affecting Bald Eagles (Haliaeetus leucocephalus), American Coots (Fulica americana), and other birds in the southeastern United States. The cause of the disease has not yet been determined, although it is generally thought to be a natural toxin. Previous studies have linked AVM to aquatic vegetation, and the current working hypothesis is that a species of cyanobacteria growing epiphytically on that vegetation is producing a toxin that causes AVM. Surveys of epiphytic communities have identified a novel species of cyanobacteria in the order Stigonematales as the most likely suspect. The purpose of this study was to further examine the relationship between the suspect Stigonematales species and induction of AVM, by using animal feeding trials. Adult Mallards and domestic chickens were fed aquatic vegetation from two study sites containing the suspect cyanobacterial epiphyte, as well as a control site that did not contain the Stigonematales species. Two trials were conducted. The first trial used vegetation collected during mid-October 2003, and the second trial used vegetation collected during November and December 2003. Neither treatment nor control birds in the first trial developed AVM lesions. Ten of 12 treatment Mallards in the second trial were diagnosed with AVM, and control birds were not affected. This study provides further evidence that the novel Stigonematales species may be involved with AVM induction, or at the least it is a good predictor of AVM toxin presence in a system. The results also demonstrate the seasonal nature of AVM events.

Triploid Grass Carp Susceptibility and Potential for Disease Transfer when used to Control Aquatic Vegetation in Reservoirs with Avian Vacuolar Myelinopathy

“…Treatment and control hydrilla were collected at depths ranging from 0.5 to 1.4 m, stored frozen at −20 • C, and then thawed and used as needed during the feeding trials. Laboratory investigations using field-collected frozen hydrilla with the UCB caused AVM in mallards (Wiley et al 2007).…”

“…The UCB grows as an epiphyte on both native and nonindigenous aquatic plants but grows more densely on nonindigenous SAV, often covering up to 95% of the leaves' surface area (Wilde et al 2005). Collections of SAV from reservoirs that were confirmed to contain the UCB were observed to cause AVM in mallards Anas platyrhynchos during laboratory feeding studies, whereas vegetation without the UCB did not cause AVM (Birrenkott et al 2004;Wiley et al 2007). The putative toxin was efficiently extracted with methanol and caused AVM in a mallard gavage trial, but it could not be characterized analytically due the extract's crude nature (Wiley et al 2008).…”

Aetokthonos hydrillicola gen. et sp. nov.: Epiphytic cyanobacteria on invasive aquatic plants implicated in Avian Vacuolar Myelinopathy

“…Four additional sites were considered at risk based on the presence of hydrilla and dense colonization by the epiphyte. In order to evaluate whether the AVM disease was occurring in birds, intensive surveys, sentinel field trials, and laboratory-feeding trials were conducted as previously reported in Wilde et al (2005), Fischer et al (2006), Wiley et al (2007) and Haynie et al (2013). Submerged aquatic plant samples were collected from within one meter of the top of the canopy from all locations during September-December.…”

Cyanobacterial (blue-green algae) toxins

“…The algal species is in the order Stigonematales and is found on the surface of Hydrilla verticillata, aquatic vegetation commonly found in wetlands in the southeastern United States (Wiley et al, 2007). BMAA is a neurotoxic amino acid that has been associated with the pathogenesis of human amyotrophic lateral sclerosis-parkinsonismdementia complex of Guam (Guam ALS-PD) and lathyrism.…”