Equine Intoxications Flashcards
Obj: Familiarity with more common equine intoxications
Obj: Understand risk and clinical manifestation for common toxins
Obj: Establish diagnosis, treatment and prognosis
What is Nigropallidal Encephalomalacia? Cause? symptoms? diagnostics? treatment? prognosis?
- Affects Equids
- Caused by 2,3-dihydro-3, 5-dihydroxy-6-methyl-4[H]-pyran-4-1
-
yellow star thistle (Centaurea melitensis)
- CA, OR, Western US
- Russian knapweed (Acroptilon repens)
-
yellow star thistle (Centaurea melitensis)
- Continuous ingestion at 80-200% BW for weeks to months
- Symptoms:
- Bilaterally symmetric lesions
- Non-progressive focal necrosis of globus pallidus or substantia nigra
- Facial hypertonicity increases w/ food being offered - inability to prehend
- Poor BCS
- Bilaterally symmetric lesions
- Dx - MRI for antemortem
- Tx - None
- Poor prognosis for recovery or survival
What is Tremetol? sources?
- Fat soluble, high molecular weight alcohol
- toxic at 1-10% of BW and is cumulative!
- White snakeroot (Eupatorium rugosum)
- Rayless goldenrod (Isocoma wrightii)
What damage does Tremetol cause in horses? signs/symptoms
- Affects Heart, Kidneys, gut, lungs
- Toxins concentrate in milk
- Do not give milk to offspring
- CBC/Chem/UA: (consistent w/ muscle necrosis)
- elevated CK, AST
- Hematuria
- Hemoglobinuria
- proteinuria
- acidosis
- hyperglycemia
- Signs/symptoms:
- Weight loss
- Tremors, ataxia
- Depression
- Cardiac arrhythmias
- Recumbency
- Skeletal muscle and myocardial streaking and necrosis
- Death
What other toxin can cause similar signs to Tremetol poisoning, and needs to be ruled out for Dx?
Ionophore contamination
How is Tremetol poisoning managed?
- Symptomatic treatment
- Supportive care
- Attempt to evacuate GIT
- Administer mineral oil or activated charcoal
- Diuresis
- Examine all herd mates
- prognosis is poor to grave
What is Red Maple Toxicity? source? signs?
- Seasonal toxicity - Fall
- after trimming trees or storm
- Wilted Red Maple leaves
- Hematologic toxicity
- acute severe anemia (intravascular hemolysis)
- methemoglobinemia
- Signs: Tachypnea, Tachycardia
- Depressed
- anorexic
- Signs of Intravascular hemolysis (red/brown urine)
- Cyanotic
- Death
- CBC/Chem/Blood:
- hematacrit drops to 10%
- numerous Heinz bodies
What are the differentials for Red Maple Toxicity?
- Phenothiazine toxicity
- Wild onion
- IMHA, EIA
- Drug hypersensitivity
- Ehrlichiosis, Piroplasmosis
- Endotoxemia
- Hepatic failure
How is Red Maple Toxicity managed? prognosis?
- Stabilize
- Blood transfusion
- Anti-inflammatories
- Antibiotics
- Oxygen insufflation
- Environmental evaluation for affected herd mates
- Guarded prognosis
What plants contain Cardiac Glycoside?
- Foxglove (Digitalis purpurea)
- Oleander (Nerium oleander)
- Azaleas (Rhododendron spp.)
how much foxglove is lethal to horses?
~0.05% BW (~0.25kg)
How is Cardiac Glycoside intoxication managed?
- Supportive:
- IV fluids
- Avoid calcium and potassium containing fluids
- Analgesics: NSAIDS (Flunixin meglumine or phenylbutazone)
- Antioxidants: Vit E, DMSO
- IV fluids
What is the difference between primary and secondary photosensitization?
- Primary - Plant directly causes photosensitization
- Ex: St. John’s wort (Hypericum perforatum)
- Secondary -
- plant causes hepatic disease
- severe hepatic disease leads to phylloerythrin accumulation in skin → photosensitization
- Ex: Ragwort (Senecio spp)
- plant causes hepatic disease
How are cases of photosensitization managed?
- Rule out significant hepatic disease
- if hepatic disease is present - treat as primary disorder
- Determine if/wat plants are in the pasture
- Remove patient from direct sunlight
- Lesions should heal in 2-3 weeks
- Topical silver sulfadiazine (SSD) - soothing and antimicrobial
What is Pyrrolizidine alkaloid toxicity?
- Source: Senecio spp, crotalaria spp
- Ingestion of toxic plant causing hepatic damage
- alkaloid transformed to toxic pyrrole
- Reactive metabolites bind cell molecules and cross link DNA preventing mitosis
- Signs:
- Poor BCS
- Icterus
- Chem - consistent w/ primary hepatic disease
- Elevated GGT, AST, ALP
- reduced hepatic function: bile acids
- Histo:
- Megalocytosis
- Bridging Fibrosis
- Guarded prognosis
What fungus may infect hay, forage, or grain? what do they cause?
- Rhizoctonia leguminicola - Slobber toxin
- Neotyphodium coenphialum - Fescue toxicosis
- Fusarium proliferatum - Leukoencephalomalacia (ELEM)
what are the neurotoxins in Yellow Star thistle?
- aspartic acid
- glutamic acid
- sesquiterpene lactones:
- solstitialin A 13- acetate
- cynaropicrin
- dopaminergic neurotoxin (2,3 dihydro-3, 5 dihydroxy-6-methyl-4 (H) pyran-4-1) similar to the compound that induced Parkinson’s in People has been isolated
What affect does yellow star thistle have on the nervous system?
- Destroys dopaminergic nigrostriatal pathway
- coordinates and inhibits the cerebral cortex pathways that control prehension and chewing of food (CN V, VII, IX)
How is slobber toxin treated?
- removal of infected forage from the diet
What toxin is found in tall fescue grass (Festuca arundinacea)
- Endophytic fungus - Neotyphodium coenophialum
- Produces ergopeptine alkaloids - primarily ergovaline
What endocrine abnormalities are seen with Fescue Toxicosis?
- Depressed prolactin secretion
- Depressed fetal cortisol secretion
- Elevated circulating estradiol concentration
- suppressed final stages of gesation
What are the clinical signs of Equine Fescue Toxicosis?
- Delayed gestation
- Thickened placenta
- impaired lactogenesis
- Poor fetal maturity
How is Fescue Toxicosis managed?
- Remove mares from pasture 90 days before foaling
- Treat with D2 antagonist - Domperidone 1mg/kg q24h
- during pregnancy until foaling
- after delivery if milk production is poor
What is the toxin responsible for Moldy Corn Toxicity?
- Mycotoxin - Fumonisin B1, B2, B3
- interferes with sphingolipid metabolism which disrupts endothelial cell walls and basement membranes
What lesions are seen with Moldy Corn Toxicosis?
- Long term, low dose
- Leukoencephalomalacia - liquefactive necrosis and degeneration of the cerebral white matter
- High dose
- liver toxicity
What are the signs of Moldy Corn Toxicosis?
- CNS signs predominate:
- blindness
- hypermetria
- depression
- disorientation
- Serum Chemistry for hepatic enzymes
What is the treatment for Moldy Corn Toxicosis
- Supportive care
- Prognosis is guarded to grave
What are the signs of Ionophore intoxication in horses?
- Anorexia
- Colic
- Acute death
- Weakness
- Myocarditis
- Congestive heart failure
- DCM
What is the MOA of Ionophore Intoxication?
- Lipid soluble transports monovalent cations preferentially across cell membranes
- Monensin is very potent in transporting Na+ across lipid membranes
- Proton exchange for sodium, leading to acidosis and potassium loss
- High intracellular sodium leads to secondary intracellular calcium overload
- This leads to mitochondrial swelling, catecholamine release, and increased myocardial cell and diaphragm cell contractility
- early positive ionotropyh
- later negative inotropy and contracture
- Results include skeletal muscle and cardiac muscle dysfunction with potential failure
How is Ionophore Toxicosis diagnosed
- History
- Feed evaluation (stomach contents)
- Liver and Muscle enzymes
- ALP, CK, AST
- Cardiac isoenzymes
- Troponin I
- CK-MB, LDH-HBD
- Cardiac evaluation
- ECG
- Echocardiogram
- Reduced fractional shortenting
- +/- thoracic radiographs
How are cases of Ionophore Toxicosis treated?
- Remove suspected feed
- Mineral oil or activated charcoal
- no digoxin or calcium
- Supportive
What would be the presentation of a horse with a low level of ionophore exposure
- Exercise intolerance
- cough
- weight loss
- congestive heart failure
What is the toxin in Blister Beetles?
Cantharidin
What issues does Cantharidin Toxicosis cause?
- Pseudomembranous inflammation of GIT
- hemorrhagic cystitis
- occult blood in urine
- Myocarditis and necrosis
How is Cantharidin toxicosis managed?
- Empty stomach, activated charcoal
- IV fluid for hypocalcemia
- Plasma transfusion for Hypoproteinemia
