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The identification of gross lesions produced by toxins by equine practitioners is often the first step in formulating a diagnostic plan.
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Two structural toxicoses of the nervous system in horse which produce gross lesions are equine nigropallidal encephalomalacia (ENPE) and equine leukoencephalomalacia (ELM).
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The most common toxin responsible for liver failure in horses is pyrrolizidine alkaloid (PA).
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Red maple toxicosis and chronic sorghum poisoning produce detectable gross lesions within the
Toxicology for the Equine Practitioner
Section snippets
Key points
Toxins affecting the nervous system
Toxins affecting the nervous system can be categorized into two main groups based on mechanism of toxicoses: structural toxicoses and functional toxicoses. Toxins affecting the structure of the nervous system may harm one or more of three components (neurons, axons, or myelin) resulting in a neuropathy, axonopathy, or myelinopathy, respectively. Structural toxicoses commonly result in detectable lesions at the gross and/or microscopic level, which facilitate their diagnosis. However, functional
Toxins affecting the liver and biliary system
The liver is highly susceptible to toxins because of its role in excretion of xenobiotics. Toxins taken orally reach the liver through the portal system and are metabolized by a group of enzymes known as mixed-function oxidases. These enzymes usually increase the water solubility of metabolized compounds but occasionally produce more toxic metabolites. Depending on the dose and the duration of exposure the toxic injury results in hepatic necrosis, fibrosis, bile duct proliferation,
Toxins affecting the urinary system
The kidney is a primary target for toxicity because of its high perfusion. Toxins affecting the kidney can be categorized into two groups: exogenous toxins and endogenous toxins. Exogenous toxins include a long list of chemicals, drugs, plants, and metals, whereas endogenous toxins include hemoglobin myoglobin and bilirubin. Both endogenous and exogenous toxins cause tubular necrosis with proximal convoluted tubules being most susceptible. With the exception of hemoglobinuric nephrosis, acute
Toxins affecting the cardiovascular system
Drugs, chemicals, and plants can produce toxic effects on the heart. Common equine myocardial toxicoses in North America include ionophore antimicrobials (eg, monensin, lasalocid), blister beetles (discussed later), many plants, and rarely mycotoxins. Most plant toxicoses affecting the equine myocardium result in sudden onset of clinical signs and fall into the alkaloid and glycoside groups. An alkaloid is a nitrogen base containing organic compound that has a pharmacologic effect in animals
Bister Beetle (Cantharidin) Toxicosis
The Meloidae family of blister beetles contains more than 200 species of beetles within North America, which contain the toxin cantharidin at different levels. Beetles are often killed and trapped within hay during harvesting.40 Because beetles swarm for mating purposes, large numbers can be trapped with a single flake of hay. Cantharidin is produced by mature males and is passed to females during copulation, which later incorporates it into eggs to deter feeding by other insects. The minimum
References (48)
- et al.
Repin-induced neurotoxicity in rodents
Exp Neurol
(1998) - et al.
Characterization of the role of glutathione in repin-induced mitochondrial dysfunction, oxidative stress and dopaminergic neurotoxicity in rat pheochromocytoma (PC12) cells
Neurotoxicology
(2004) - et al.
Toxic effects of solstitialin A 13-acetate and cynaropicrin from Centaurea solstitialis L. (Asteraceae) in cell cultures of foetal rat brain
Neuropharmacology
(1992) - et al.
Neuropathological assessment of Parkinson's disease: refining the diagnostic criteria
Lancet Neurol
(2009) - et al.
Fumonisins: toxicokinetics, mechanism of action and toxicity
Animal Feed Science and Technology
(2007) - et al.
Inhibition of sphingolipid biosynthesis by fumonisins. Implications for diseases associated with Fusarium moniliforme
J Biol Chem
(1991) - et al.
Increases in serum sphingosine and sphinganine and decreases in complex sphingolipids in ponies given feed containing fumonisins, mycotoxins produced by Fusarium moniliforme
J Nutr
(1992) Pyrrolizidine alkaloid-containing toxic plants (Senecio, Crotalaria, Cynoglossum, Amsinckia, Heliotropium, and Echium spp.)
Vet Clin North Am Food Anim Pract
(2011)- et al.
Pharmacokinetics, pharmacodynamics, metabolism, toxicology and residues of phenylbutazone in humans and horses
Vet J
(2013) Veterinary toxicology basic and clinical principles
(2007)
Inactivation of the cytotoxic activity of repin, a sesquiterpene lactone from Centaurea repens
Chem Res Toxicol
Nigropallidal encephalomalacia in horses caused by ingestion of weeds of the genus Centaurea
J Am Vet Med Assoc
Nigropallidal encephalomalacia in horses fed Russian knapweed–Centaurea repens L
Am J Vet Res
Toxic equine parkinsonism: an immunohistochemical study of 10 horses with nigropallidal encephalomalacia
Vet Pathol
Natural co-occurrence of fumonisins and zearalenone in cereals and cereal-based foods from eastern and southern Africa
J Agric Food Chem
Senecio spp poisoning in cattle in southern Brazil
Vet Hum Toxicol
Pyrrolizidine alkaloidosis in Argentinian cattle caused by Senecio selloi
Vet Hum Toxicol
Toxicity of threadleaf groundsel (Senecio douglasii var longilobus) to cattle
Am J Vet Res
Toxicity of Riddell's groundsel (Senecio riddellii) to cattle
Am J Vet Res
Toxicity of pyrrolizidine alkaloids from Riddell groundsel (Senecio riddellii) to cattle
Am J Vet Res
Stability of pyrrolizidine alkaloids in hay and silage
J Agric Food Chem
Effects on cattle and their calves of tansy ragwort (Senecio jacobaea) fed in early gestation
Am J Vet Res
Crotalaria juncea intoxication in horses
Vet Hum Toxicol
Pyrrolizidine alkaloids: genotoxicity, metabolism enzymes, metabolic activation, and mechanisms
Drug Metab Rev
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Molecular toxicology and carcinogenesis of fumonisins: a review
2020, Journal of Environmental Science and Health, Part C: Toxicology and Carcinogenesis