An extract of Hydrilla verticillata and associated epiphytes induces avian vacuolar myelinopathy in laboratory mallards

Abstract

Avian vacuolar myelinopathy (AVM) is a neurological disease affecting bald eagles (Haliaeetus leucocephalus), American coots (Fulica americana), waterfowl, and other birds in the southeastern United States. The cause of the disease is unknown, but is thought to be a naturally produced toxin. AVM is associated with aquatic macrophytes, most frequently hydrilla (Hydrilla verticillata), and researchers have linked the disease to an epiphytic cyanobacterial species associated with the macrophytes. The goal of this study was to develop an extraction protocol for separating the putative toxin from a hydrilla-cyanobacterial matrix. Hydrilla samples were collected from an AVM-affected reservoir (J. Strom Thurmond Lake, SC) and confirmed to contain the etiologic agent by mallard (Anas platyrhynchos) bioassay. These samples were then extracted using a solvent series of increasing polarity: hexanes, acetone, and methanol. Control hydrilla samples from a reference reservoir with no history of AVM (Lake Marion, SC) were extracted in parallel. Resulting extracts were administered to mallards by oral gavage. Our findings indicate that the methanol extracts of hydrilla collected from the AVM-affected site induced the disease in laboratory mallards. This study provides the first data documenting for an "extractable" AVM-inducing agent.

Sensitivity of freshwater molluscs to hydrilla-targeting herbicides: providing context for invasive aquatic weed control in diverse ecosystems

“…Hydrilla (Hydrilla verticillata, Hydrocharitaceae) is a non-native aquatic invasive weed that was introduced into the United States in Florida in the early 1950s and has spread rapidly throughout the country, especially in the southeast (Gordon & Thomas 1997). Included on the Federal Noxious Weed List (USDA APHIS 2012), hydrilla can form vast monocultures, shade out native vegetation (FWC 2013), alter water quality parameters including dissolved oxygen (Pesacreta 1988), and can serve as a vector for a neurotoxic cyanobacteria that has been linked to avian vacuolar myelinopathy in several water birds and their predators (e.g., bald eagle Haliaeetus leucocephalus and great horned owl Bubo virginianus; Wiley et al 2008;Williams et al 2009). Hydrilla produces numerous vegetative propagules (e.g., tubers, turions, and shoot fragments), and is frequently dispersed by humans via boat motors, trailers, and angling gear.…”

ALTERNATE FOOD-CHAIN TRANSFER OF THE TOXIN LINKED TO AVIAN VACUOLAR MYELINOPATHY AND IMPLICATIONS FOR THE ENDANGERED FLORIDA SNAIL KITE (ROSTRHAMUS SOCIABILIS)

“…After 7 d of feeding, the snail tissues were removed from the shells, coarsely chopped, frozen, and lyophilized to facilitate delivery and increase palatability in the chicken feeding trial. The uncharacterized AVM neurotoxin has been previously shown to be stable and active after freezing and lyophilization (Wiley et al 2009). …”

“…hydrillicola (from JSTL) for 24 d. The birds received 35-40 mg hydrilla per gram of body weight (bw) per day in addition to 30 mg/g bw commercial poultry diet per day (Table 1). Treatment diet measurements were based on previous feeding studies ( LewisWeis et al 2004;Wiley et al 2009). This initial trial was necessary to ensure the AVM toxin was present in the vegetation collection before proceeding with the snail feeding trial (Birrenkott et al 2004;Wiley et al 2007).…”

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

“…These dense, invasive aquatic macrophyte beds provide ideal substrate for attachment by epiphytic cyanobacteria capable of toxin production and should be considered when evaluating risk of harmful algae in water supply lakes and reservoirs (Wilde et al 2005, Mohamed & Al-Shehri 2010. Feeding trials and field surveys support the hypothesis that birds ingest an unknown neurotoxin produced by this novel epiphytic cyanobacterial species colonizing the aquatic plants (Birrenkott et al 2004, Wilde et al 2005, Wiley et al 2009, Haynie et al 2013. Identification of this cyanobacterial species is critical in order to advance neurotoxin isolation and characterization work that is currently underway.…”