Vacuolar Myelinopathy (VM) Research by Dr. Susan Wilde

Vacuolar Myelinopathy (VM) is the most significant unknown cause of eagle mortality in the history of the United States.

WHAT IS VACUOLAR MYELINOPATHY (VM)?

Vacuolar Myelinopathy, formerly known as Avian Vacuolar Myelinopathy (AVM), is a neurological disease affecting birds of prey, waterfowl, amphibians, reptiles, fishes, and potentially mammals in the Southeastern United States. VM is caused by Aetokthonotoxin, produced by the Aetokthonos hydrillicola cyanobacterium. Cyanobacteria are primarily found on Hydrilla (Hydrilla verticillata). This is an ongoing issue for wildlife associated with our southeastern U.S. reservoirs.

This web page is designed to bring research conducted by various federal and state agencies and universities into one location to update states already affected by VM bird deaths and encourage lake managers in other locations to observe their reservoirs for disease potential.

Origins

The disease was first documented in the winter of 1994-1995 at DeGray Lake, Arkansas, and has since been confirmed in four additional states: Texas, Georgia, North Carolina, and South Carolina. VM is responsible for the death of more than 100 bald eagles and thousands of coots. Necropsies of the birds revealed lesions in the white matter of the brain.

What we know

After several potential sources of VM were ruled out, including sediment and water pollution, researchers focused on harmful cyanobacterial blooms In the reservoirs where VM bird deaths have occurred.

There is very little cyanobacteria growing freely in the water column, but invasive aquatic plants are abundant. These aquatic plants harbor epiphytic cyanobacteria of several species. Coordinated efforts, which included federal agencies, several local agencies and universities, ultimately led to the discovery of the novel cyanobacteria, A. hydrillicola as the cause of VM.

A. hydrillicola produces two toxins, a neurotoxin and a cytotoxin.

• The neurotoxin, now known as aetokthonotoxin, was discovered using a combination of bioassays and high-pressure liquid chromatography. These studies revealed that aetokthonotoxin is the brominated neurotoxin responsible for VM.
• The properties of this cytotoxin, and their potential role in VM, are currently being investigated.

Aetokthonotoxin can be transferred through the food chain. Waterfowl, amphibians, fish, or snails that consume A. hydrillicola can pass the toxin to tertiary consumers like bald eagles and red-tailed hawks. Both primary consumers and tertiary consumers can develop VM. Several species from a wide variety of genera can develop VM, but further research is needed to determine if mammals are susceptible to aetokthonotoxin.

CURRENT PROJECTS

Wood duck surveillance

For the study, we plan to use game cameras, I-buttons, water quality sensors, and water /hydrilla/prey/eggs/adult collections to monitor wood ducks in control sites with no history of vacuolar myelinopathy and locations with VM in wildlife. All the GADNR wood duck boxes are already in the ArcGIS system, and we will contribute additional site-specific assessments to test our hypothesis that AETX could influence not only nesting success but also present a risk to hunters consuming these adults.  We will determine contamination levels in wood duck eggs, dead hatchlings (from unsuccessful nests), and adult tissues from control vs. VM locations.

LAMP assay

This study will focus on application of LAMP (Loop-Mediated Isothermal Amplificaton) to in-field detection of the cyanobacteria, Aetokthonos hydrillicola, that produces Aetokthonotoxin (neurotoxin) that causes vacuolar myelinopathy (VM). It will use previous primer development to produce a protocol that will allow for in-field genetic detection of the gene cluster within Aetokthonos hydrillicola that causes the production of Aetokthonotoxin (AETX). The protocol will be used to determine potential areas where the cyanobacteria could exist in the field (i.e. hydrilla leaves, tubers of the Hydrilla, soil in the reservoirs, pine needles of the surrounding trees). The goal of this project is to develop a protocol that can be used and replicated by other researchers and management to easily identify areas of potential VM risk.

VM outreach

The Wilde Lab is working to educate the public about Aetokthonos hydrillicola and Aetokthonotoxin (AETX), which causes vacuolar myelinopathy in animals. We have found that AETX bioaccumulates in animals in the food chain and is not only dangerous for primary consumers but increasing levels of predators as well. Our education outreach is planned for teachers and students as well as hunters and anglers. We are using ambassador animals, plant samples, and a classroom activity designed to educate and demonstrate how AETX moves through the food chain and the environment.

Mouse trials

The Wilde lab is in the beginning stages of investigating the neurologic effects of Aetokthonos hydrillicola toxin (AETX) on the vertebrate brain. We will use laboratory mice in this experiment, and dose them with AETX in three groups at differing acute toxicity levels.

Semi-aquatic mammals and AETX

This study will investigate VM and the effects of AETX in common southeastern semi-aquatic mammals – particularly beavers (Castor canadensis) and river otters (Lontra canadensis). Researching these species will help us better understand how AETX could be affecting mammals that directly interact with the toxin in their environment, as well as if it is accumulating up the food chain. This project is still in the planning stage and will begin in spring 2023.

Distribution of suitable habitat for Aetokthonos Hydrillicola

This study has related known occurrences of Aetokthonos hydrillicola to various environmental datasets to estimate the probability that individual waterbodies provide suitable habitat. Results will be used to inform future sampling and landscape-scale management activities aimed at controlling the spread of VM disease. Future goals will include the addition of more occurrence data and expansion of model boundaries to include more areas.

Trophic transfer of Aetokthonotoxin and exposure risk

Aetokthonotoxin can be transferred through the food web. This study will determine the potential for AETX to biomagnify in fishes. A reservoir in Georgia that had an invasion of hydrilla, with the associated A. hydrillicola, stocked triploid sterile grass carp to manage the invasion. Fish of all species and a variety of size ranges were subsequently collected to quantify the toxin concentration in muscle tissue using HPLC-MS/MS. This study will use the fish tissue to compare the toxin concentration to the trophic level of fish as determined by stable isotopes. These results will be used to estimate the amount of AETX predators will be exposed to when consuming fish from reservoirs with A. hydrillicola present.

Sorption coefficients of Aetokthonotoxin and other cyanotoxins

To continue studying aetokthonotoxin effectively, we aim to define the sorption coefficients of aetokthonotoxin to water, dissolved organic carbon (DOC), sediments, and plastics. A sorption coefficient is the concentration of a chemical substance absorbed or adsorbed to another substance. Kow, or the sorption coefficient of a substance in water versus oil, informs us on the hydro/lipophilicity of aetokthonotoxin. Koc and Kd quantify the sorption of a substance to DOC and sediments versus water. The Koc and Kd will provide an idea of how persistent aetokthonotoxin is in the environment. The sorption coefficient of aetokthonotoxin to plastic versus water will allow us to understand the potential for plastics to transport the toxin. Defining these sorption coefficients will enhance our ability to hypothesize interactions of aetokthonotoxin in the environment. 

Recent and Select Publications

• Gerrin, W. L., Haram, B., Jennings, C. A., Brandon, G., & Wilde, S. B. (2021). Factors affecting movement and habitat use of grass carp in a mainstem reservoir. FISHERIES MANAGEMENT AND ECOLOGY, 29(1), 100-103. doi:10.1111/fme.12517
• Breinlinger, S., Phillips, T. J., Haram, B. N., Mares, J., Yerena, J. A. M., Hrouzek, P., ... Wilde, S. B. (2021). Hunting the eagle killer: A cyanobacterial neurotoxin causes vacuolar myelinopathy. SCIENCE, 371(6536), 1335-+. doi:10.1126/science.aax9050
• Haram, B. N., Wilde, S. B., Chamberlain, M. J., & Boyd, K. H. (2020). Vacuolar myelinopathy: waterbird risk on a southeastern impoundment co-infested with Hydrilla verticillata and Aetokthonos hydrillicola. BIOLOGICAL INVASIONS, 22(9), 2651-2660. doi:10.1007/s10530-020-02282-w
• Matteson, C. T., Jackson, C. R., Batzer, D. P., Wilde, S. B., & Jeffers, J. B. (2020). Nitrogen and Phosphorus Gradients from a Working Farm through Wetlands to Streams in the Georgia Piedmont, USA. WETLANDS, 40(6), 2139-2149. doi:10.1007/s13157-020-01335-z
• Weber, S. J., Mishra, D. R., Wilde, S. B., & Kramer, E. (2020). Risks for cyanobacterial harmful algal blooms due to land management and climate interactions. SCIENCE OF THE TOTAL ENVIRONMENT, 703, 14 pages. doi:10.1016/j.scitotenv.2019.134608
• Kumar, A., Cooper, C., Remillard, C. M., Ghosh, S., Haney, A., Braun, F., ... Mishra, D. R. (2019). Spatiotemporal monitoring of hydrilla [Hydrilla verticillata (L. f.) Royle] to aid management actions. WEED TECHNOLOGY, 33(3), 518-529. doi:10.1017/wet.2019.13
• Maerz, J., Wilde, S., Terrell, V., Haram, B., Trimmer, R. C., Nunez, C., ... Diamond, S. L. (2019). Seasonal and plant specific vulnerability of amphibian tadpoles to the invasion of a novel cyanobacteria. Biological Invasions, 21, 821-831. doi:10.1007/s10530-018-1861-6
• Brannen, P., Scherm, H., Brewer, M., Wilde, S., & Richardson, E. (2019). Orange cane blotch of commercial blackberry in the southeastern United States. Plant Health Progress, 20, 67-69. doi:10.1094/PHP-10-18-0065-BR
• Marzolf, N., Golladay, S., McCormick, P., Covich, A., & Wilde, S. (2018). Inter- and intra-annual apple snail egg mass dynamics in a large southeastern US reservoir. HYDROBIOLOGIA, 811(1), 155-171. doi:10.1007/s10750-017-3475-x
• Shivers, S. D., Golladay, S. W., Waters, M. N., Wilde, S. B., Ashford, P. D., & Covich, A. P. (2018). Changes in submerged aquatic vegetation (SAV) coverage caused by extended drought and flood pulses. LAKE AND RESERVOIR MANAGEMENT, 34(2), 199-210. doi:10.1080/10402381.2017.1413457
• Shivers, S. D., Golladay, S. W., Waters, M. N., Wilde, S. B., & Covich, A. P. (2018). Rivers to reservoirs: hydrological drivers control reservoir function by affecting the abundance of submerged and floating macrophytes. HYDROBIOLOGIA, 815(1), 21-35. doi:10.1007/s10750-018-3532-0
• Kumar, A., Wilde, S. B., & Mishra, D. (2018). Spatio-Temporal Monitoring of Hydrilla to Aid Management Actions. WEED TECHNOLOGY.
• Fouts, K. L., Poudyal, N. C., Moore, R., Herrin, J., & Wilde, S. B. (2017). Informed stakeholder support for managing invasive Hydrilla verticillata linked to wildlife deaths in a Southeastern reservoir. LAKE AND RESERVOIR MANAGEMENT, 33(3), 260-269. doi:10.1080/10402381.2017.1334017
• Barnard, M. A., Porter, J. W., & Wilde, S. B. (2017). Utilizing Spirogyra grevilleana as a Phytoremediatory Agent for Reduction of Limnetic Nutrients and Escherichia coli Concentrations. AMERICAN JOURNAL OF PLANT SCIENCES, 08(05), 1148-1158. doi:10.4236/ajps.2017.85075
• Dodd, S. R., Haynie, R. S., Williams, S. M., & Wilde, S. B. (2016). Alternate food-chain transfer of the toxin linked to avian vacuolar myelinopathy and implications for the endangered Florida snail kite (Rostrhamus sociabilis). Journal Of Wildlife Diseases, 52(2), 335-344. doi:10.7589/2015-03-061
• Greenfield, D. I., Duquette, A., Goodson, A., Keppler, C. J., Williams, S. H., Brock, L. M., ... Wilde, S. B. (2014). The Effects of Three Chemical Algaecides on Cell Numbers and Toxin Content of the Cyanobacteria Microcystis aeruginosa and Anabaenopsis sp.. ENVIRONMENTAL MANAGEMENT, 54(5), 1110-1120. doi:10.1007/s00267-014-0339-2
• Wilde, S. B., Johansen, J. R., Wilde, H. D., Jiang, P., Bartelme, B. A., & Haynie, R. S. (2014). Aetokthonos hydrillicola gen. et sp. nov.: Epiphytic cyanobacteria on invasive aquatic plants implicated in Avian Vacuolar Myelinopathy. PHYTOTAXA, 181(5), 243-260. doi:10.11646/phytotaxa.181.5.1
• Haynie, R. S., Bowerman, W. W., Williams, S. K., Morrison, J. R., Grizzle, J. M., Fischer, J. M., & Wilde, S. B. (2013). Triploid Grass Carp Susceptibility and Potential for Disease Transfer when used to Control Aquatic Vegetation in Reservoirs with Avian Vacuolar Myelinopathy. JOURNAL OF AQUATIC ANIMAL HEALTH, 25(4), 252-259. doi:10.1080/08997659.2013.833556
• Byers, J. E., McDowell, W. G., Dodd, S. R., Haynie, R. S., Pintor, L. M., & Wilde, S. B. (2013). Climate and pH Predict the Potential Range of the Invasive Apple Snail (Pomacea insularum) in the Southeastern United States. PLOS ONE, 8(2), 9 pages. doi:10.1371/journal.pone.0056812
• Wilde, S. B., Murphy, T. M., Hope, C. P., Habrun, S. K., Kempton, J., Birrenkott, A., ... Lewitus, A. J. (2005). Avian vacuolar myelinopathy linked to exotic aquatic plants and a novel cyanobacterial species. ENVIRONMENTAL TOXICOLOGY, 20(3), 348-353. doi:10.1002/tox.20111