Explorer Grazing livestock are exposed to terrestrial cyanobacteria

While toxins from aquatic cyanobacteria are a well-recognised cause of disease in birds and animals, exposure of grazing livestock to terrestrial cyanobacteria has not been described. This study identified terrestrial cyanobacteria, predominantly Phormidium spp. , in the biofilm of plants from most livestock fields investigated. Lower numbers of other cyanobacteria, microalgae and fungi were present on many plants. Cyanobacterial 16S rDNA, predominantly from Phormidium spp. , was detected in all samples tested, including 6 plant washings, 1 soil sample and ileal contents from 2 grazing horses. Further work was performed to test the hypothesis that ingestion of cyanotoxins contributes to the pathogenesis of some currently unexplained diseases of grazing horses, including equine grass sickness (EGS), equine motor neuron disease (EMND) and hepatopathy. Phormidium population density was significantly higher on EGS fields than on control fields. The cyanobacterial neurotoxic amino acid 2,4-diaminobutyric acid (DAB) was detected in plant washings from EGS fields, but worst case scenario estimations suggested the dose would be insufficient to cause disease. Neither DAB nor the cyanobacterial neurotoxins β-N-methylamino-L-alanine and N-(2-aminoethyl) glycine were detected in neural tissue from 6 EGS horses, 2 EMND horses and 7 control horses. Phormidium was present in low numbers on plants where horses had unexplained hepatopathy. This study did not yield evidence linking known cyanotoxins with disease in grazing horses. However, further study is warranted to identify and quantify toxins produced by cyanobacteria on livestock fields, and determine whether, under appropriate conditions, known or unknown cyanotoxins contribute to currently unexplained diseases in grazing livestock. Introduction Cyanobacteria are a diverse group of ubiquitous environmental bacteria which can produce a wide array of toxins (cyanotoxins). While exposure to cyanotoxins from aquatic cyanobacterial blooms, scums and mats is a well-recognised cause of neurologic and hepatic disease in birds and animals [1], exposure of grazing livestock to terrestrial, as opposed to aquatic, cyanobacteria has not been previously described. We hypothesised that grazing livestock are exposed to Phormidium spp. since this cyanobacterial genus can grow on turf grasses and golf courses, particularly in favourable weather conditions and following fertiliser application [2-6]. Cyanobacteria including Phormidium spp. can produce a wide range of hepato-, neuroand dermotoxins which cause disease in animals exposed to aquatic cyanobacterial blooms [7-10]. While exposure to anatoxin-a from the benthic cyanobacterium Phormidium favosum has been associated with canine neurotoxicosis [9], toxins from terrestrial Phormidium spp. have not been previously definitively associated with disease. We hypothesised that cyanotoxins from terrestrial Phormidium spp. may trigger or cause currently unexplained diseases of grazing livestock such as equine grass sickness (EGS), a frequently fatal multi-system neuropathy affecting grazing horses, equine motor neuron disease (EMND) and idiopathic hepatopathy. The aims of this study were to: (a) identify and enumerate Phormidium filaments in washings of the biofilm on plants collected from livestock-grazing fields; (b) evaluate spatial and temporal variation in the density of Phormidium filaments; (c) determine whether Phormidium filaments can be detected by microscopy in gastrointestinal contents from grazing horses; and (d) use a genomic approach to identify cyanobacteria in plant washings, equine ileal contents and soil. Additionally, a * Correspondence: Bruce.mcgorum@ed.ac. uk Royal (Dick) School of Veterinary Studies and Roslin Institute, University of Edinburgh, Roslin EH25 9RG, Scotland, UK Full list of author information is available at the end of the article VETERINARY RESEARCH © 2015 McGorum et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. McGorum et al. Veterinary Research (2015) 46:16 DOI 10.1186/s13567-015-0143-x