ACVPM Board Review

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ACVPM Board Review

• Plant -Related Toxicoses

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Introduction

• Osweiler, GD. Toxicology. National Veterinary
  Medical Series. Williams and Wilkins, 1996
• Fowler, M. Poisonous Plants A Veterinary Guide
  to Toxic Syndromes. Iowa State University Press,
  1998 (CD ROM)

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Plant Toxins

• 2? products of plant metabolism
• adjunct mechanism for plant survival
• vary widely in chemical properties

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Factors favoring toxicoses

• adverse climatic conditions
• agricultural practices
• animal management practices
• nutrient deficiencies ? pica
• overgrazing ?inadequate forage, ? weeds
• thirsty or hungry animals in new location
• confinement ? boredom, curiosity

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Recognition depends on

• familiarity with indigenous toxic plants
• knowledge of seasonal variations in concentration
  of toxins
• access to other resources

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Diagnosis

• Were toxic plants consumed?
• History
• Examination of environment, ingesta
• Compatible signs and lesions
• Laboratory diagnostics
• I.D. of toxic plants

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History

• geography - range and habitat of plant
• time of year - are toxic parts of the plant
  available?
• recent changes in pasture or forage?
• recent melting of snow cover, or plant growth
  following flooding?
• overgrazing?

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ID of Toxic Plants

• collect entire plant, including flowering parts
• provide detailed location information
• preserve green plants
• seal in plastic bag and refrigerate
• dry in press for 1-3 days

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General Treatment

• Reduce exposure
• prevent access
• give adequate water and alternative feed
• Detoxification
• emesis or gastric lavage
• activated charcoal
• osmotic cathartics
• (unless specifically contraindicated)

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Prevention

• allow acclimation to new pasture and provide
  alternative feed initially
• avoid overgrazing or withholding water
• dont feed chopped or ground forages containing
  toxic plants
• dont allow access to areas recently sprayed with
  herbicides
• minimize close confinement of pets

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Toxic Principles

• Alkaloids
• contain nitrogen
• most bitter
• Diterpene (phorbol) esters
• Grayanotoxins are diterpenoid
• Rhododendron, Kalmia

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Toxic Principles - Glycosides

• toxin aka glycone linked to sugar
• often not toxic until sugar hydrolyzed off
• bitter, colorless, noncrystalline
• 6 groups

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Toxic Principles - Glycosides

• cyanogenic
• cardiac
• goitrogens
• isothiocyanates
• protoanemonin
• saponins

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Cyanogenic Glycosides

• yield hydrogen cyanide upon hydrolysis
• ruminants highly susceptible
• rumen contains large amounts of ?-glycosidase
• ?-glycosidase hydolyzes the glycoside

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Toxic Principles - Glycosides

• cyanogenic
• cardiac
• goitrogens
• isothiocyanates
• protoanemonin
• saponins

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Cardiac Glycosides

• aka cardioactive glycosides
• interfere with Na/K ATPase
• decrease intracellular K
• high-grade heart block
• increased vagal tone
• cardiac arrthymias

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Toxic Principles - Glycosides

• cyanogenic
• cardiac
• goitrogens
• isothiocyanates
• protoanemonin
• saponins

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Goitrogenic Glycosides

• prevent the accumulation of organic iodide
• ? formation of thyroid hormones
• ? TSH release
• ? size thyroid gland
• (goiter was endemic in the U.S. until the advent
  of iodized salt)

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Toxic Principles - Glycosides

• cyanogenic
• cardiac
• goitrogens
• isothiocyanates
• protoanemonin
• saponins

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Isothiocyanate Glycosides

• irritant oils
• allyl isothiocyanate most common
• found primarily in Cruciferae
• (mustard family)

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Toxic Principles - Glycosides

• cyanogenic
• cardiac
• goitrogens
• isothiocyanates
• protoanemonin
• saponins

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Protoanemonin

• glycoside ranunculin ? protoanemonin upon
  hydrolysis
• volatile yellow oil
• combines with sulfhydryl
• strong vesicant and irritant action on skin and
  mucous membranes

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Toxic Principles - Glycosides

• cyanogenic
• cardiac
• goitrogens
• isothiocyanates
• protoanemonin
• saponins

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Saponins

• produce soapy froth when shaken with water
• irritant to skin and mucous membranes
• nausea and vomiting if swallowed

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Toxic Principles

• Nitrates
• Oxalates
• Gallotannins
• Toxalbumins (phytotoxins)

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Oxalates

• calcium oxalate
• insoluble needle-like crystals
• especially indoor houseplants
• soluble oxalates
• Na or K salts
• Nitrates

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Toxic Principles

• Nitrates
• Oxalates
• Gallotannins
• Toxalbumins (phytotoxins)

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Toxalbumins

• glycoproteins
• highly toxic but not well absorbed from the gi
  tract
• many animal cells contain receptors for certain
  toxalbumins
• e.g., ricin, abrin
• seeds are most concentrated source

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Neurotoxicants

• Increased CNS activity, seizures

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Asclepias (milkweed)

• Narrow-leafed species more toxic
• resinoid- galitoxin
• digitalis-like cardenolides
• all veg parts
• cattle, sheep, horses

• Dx - clinical
• profuse salivation, incoordination, violent
  seizures, bloating/colic
• arrythmias, hypotension, hypothermia, death

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Cicuta maculata, C. douglasii (water hemlock)

• hollow purple-streaked stems, roots like cluster
  of small sweet potatoes
• resinoid- cicutoxin, extremely toxic!
• mainly in roots and base

• Dx - clinical
• acute onset of violent tetanic seizures like
  strychnine poisoning
• salivation, muscle twitching, seizures, champing
  of jaws, coma, death

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Corydalis (fitweed)

• hilly or mountainous W. or Appalachian states,
  rocky/sandy soils high pH
• isoquinolone alkaloid
• all plant parts
• ruminants, esp. sheep

• Dx - clinical
• acute onset of polypnea, tremors, ataxia
• periodic seizures, facial twitching, champing of
  the jaws
• death or recovery in 24 hrs

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Gelsemium sempervirens (yellow jessamine)

• evergreen vine, fragrant yellow, trumpet-shaped
  flowers, SE U.S.
• gelsemine, gelseminine, and related indole
  alkaloids
• all plant parts, honey

• Dx - clinical
• abdominal pain, slow respiration, muscle
  weakness, convulsions, hyperthermia, signs of
  colic
• may die in 24-48 hrs.

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Neurotoxicants

• Incoordination, depression, bizarre behavior,
  agitation

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Aesculus sp. (buckeye, horsechestnut)

• Aesculin - mixture of saponin glycosides
• nuts, bark, leaves, twigs, pollen, nectar
• cattle and horses most susceptible

• Dx - clinical
• incoordination, staggering, hypermetria,
  weakness, falling
• severe gastroenteritis
• nonspecific hepatic and renal congestion

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Astragalus (locoweed) -1

• many species
• Great Plains to Rockies in dry, alkaline soil
• 3 toxic fractions
• fresh plants are toxic, loses toxicity as dries
  except for Se

• cattle and horses may become habituated to
  locoweed and seek it out, even when good forages
  are available
• reserpine may reduce severity in horses, may not
  be safe to ride

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Astragalus (locoweed) -2

• 3 toxic principles
• glycoside - miserotoxin, hydrolyzed in ruminants
  to 3-nitropropanol, releases nitrite
• alkaloid - swainsonine, inhibits ?-mannosidase ?
  neuronal swelling after 2 weeks or more of
  ingestion, passes in milk
• selenium (some sp. accumulate)

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Astragalus (locoweed) -3

• Clinical - miserotoxin
• demyelination of posterior spinal cord ?
  incoordination, hypermetria, ataxia, clicking of
  dewclaws cracker heels
• emphysema (sheep), dyspnea, cyanosis, sudden
  collapse, death may occur 4-24 hrs with large
  doses
• methemoglobinemia

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Astragalus (locoweed) -4

• Clinical - swainsonine
• ataxia, emaciation, staggering, proprioceptive
  deficits
• horses may become belligerent or startle
  violently from small stimuli
• vision may be impaired
• decreased lacrimation, retinal degeneration
• immunosuppression
• abortions mid-late pregnancy, teratogenic effects
  (contracted tendons)
• male infertility d.t. ? spermatogenesis

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Astragalus (locoweed) -5

• Dx. clinical plus lesions
• emaciation, congestive right heart failure,
  pulmonary emphysema, congestion of liver and
  lungs
• myelin degeneration and neuronal vacuolation

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Centaurea solstitialis, C. repens (yellow star
thistle, Russian knapweed) -1

• C. solstitialis w. of Rockies
• C. repens w. of Missouri R.
• toxic principle unknown
• all parts, dried plants toxic

• toxicosis after 30d consumption
• horses most susceptible, also donkeys and mules
• neurologic lesions permanent
• treatment is ineffective

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Centaurea solstitialis, C. repens (yellow star
thistle, Russian knapweed) -2

• Dx - clinical signs and lesions
• hypertonicity of facial muscles (may be
  unilateral), partial to complete paralysis of
  tongue, chewing motions without swallowing,
  inability to eat or drink normally ? emaciation
• nigropallidal encephalomalacia
• ischemia and necrosis of globus pallidus and
  substantia nigra

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Ipomea (morning glory)

• heart-shaped leaves, trumpet flowers, vining
• lysergic acid and other indole alkaloids
  (lysergic acid diethylamide LSD)
• seeds major source, but whole plant toxic

• Dx - clinical
• nausea, mydriasis, hallucinations, decreased
  reflexes, diarrhea, hypotension
• bizarre behavior, barking, disorientation

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Neurotoxicants

• CNS depression

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Eupatorium rugosum (white snakeroot)

• flowers Sept.-Oct.
• east central and northeast US forests
• true toxic principal not identified (formerly
  trematol or trematone)
• veg parts toxic

• toxin passed in milk and may poison nursing
  animals or babies - early settlers died of milk
  sickness
• toxin readily detectable

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Eupatorium rugosum (white snakeroot) -2

• Dx - clinical, lesions, lab
• horses
• depression, weakness, congestive heart failure,
  tremors, posterior weakness within several days
  of ingesting plant
• CHF, myocardial degeneration, necrosis, fibrosis
• hepatic necrosis and lipidosis possible
• cattle
• depression, ataxia, muscle tremors about face,
  neck, flank, hind quarters, coma and death
• constipation, salivation, ketone or acetone on
  breath
• hepatic congestion, lipidosis, NO myocardial
  necrosis

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Isocoma wrightii (rayless goldenrod)

• formerly known as Haplopappus heterophyllus
• low moist areas, SW U.S.
• trematol or trematone
• clinical signs like white snakeroot, except
  myocardial lesions in horses not described

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Stipa robusta (sleepy grass)

• perennial with distinctive twisted awn on flowers
  and seeds
• SW U.S.
• toxic principle unknown
• neurologic depression main effect
• mainly horses affected, cattle resistant
• moderate to severe CNS depression may progress to
  recumbency