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Parasite
organism that lives in or on another organism at its expense
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Ectoparasites
live on surface of animal's body; like ticks; cause infestations
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Endoparasites
live inside the animal's body; cause infections
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Diagnosis of parasites
- - sometimes on surface of animals
- - other times need to exam a fecal sample (eggs/larvae released in feces)
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Ideal parasiticide
- - selectively toxic
- - no resistance
- - economical
- - effective against all stages
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Helminths
- - drugs that treat= antihelminthics
- - include nematodes and platyhelminths
- - not protozoa
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Nematodes
- - cylindrical and nonsegmented
- - generally inhabit GIT
- - filarial nematodes are a special group
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Platyhelminths
- - flat worms
- - include cestodes (tapeworms) and trematodes (flukes)
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Protozoa
- - single cell, not helminth
- - include coccidia, toxoplasmosis
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Routes of infection of hookworms
- - infective larvae penetrate skin
- - infective larvae enter host transplacentally
- - host ingests infective larvae in food, colostrum, or milk
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6 groups of antinematodal drugs
- 1. benzimidiazoles
- 2. tetrahydropyrimidines
- 3. piperazines
- 4. organophosphates
- 5. imidazothiazoles
- 6. macrocyclic lactones (macrolides)
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Benzimidazoles
- - include thiabendazole (has some antifungal properties), oxibendazole (equine past deworm), fenbendazole (Panacur), albendazole, Febantel (pro benizimadole)
- - low toxicity
- - attacks proteins necessary for cell divisions in parasites
- - problems with resistance
- - targets microtubules of all
- - liquid gran powder past
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Tetrahydropyrimidines
- - pyrantel- 2 forms
- - suspension
- - highly effective against hookworms and roundworms
- - only targets adults
- - classified as cholinergic agonist
- - parasympathomimetic ( targets ACh neurotransmitter, contractions)
- - if parasite is freely living and not attached it will be expelled
- - only acts within GI tract
- - also used in people with pinworms; horses get pinworms too
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Piperazines
- - GABA agonists
- - OTC
- - roundworms
- - narrow spectrum
- - normal side effect: bolus of worms through vomit or defecation
- - MA: pump protein--> pump out Cl- --> into cell depolarize --> expel worm
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Organophosphates
- - used for ectoparasites
- - narrow range of safety
- - MA by irreversibly inhibiting acetylcholinesterase
- - end up with cholinergic signs: paralysis
- - cats more prone to OP toxicity-- dip
- - antidote for toxicity = atropine
- - used a lot in large animal pour-ons, powders
- - cholinergic crisis = salivation, lacrimation, urinating, diarrhea
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Imidazothiazoles
- - only levamisol in large animals
- - cholinergic agonist; stimulating --> paralysis
- - same toxic side effects as OP
- - used in poultry
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Macrocyclic lactones (macrolides)
- - endectocide; broad spectrum against nematodes and get ectoparaistes like mites and lice
- - include avermectins and milbemycins
- - not effective against cestodes or trematodes
- - MA: induce spastic paralysis through GABA receptor at high concentrations
- - some effect at glutamate ion channels: hyperpolarization of parasite; muscle spasms; cannot move; parasites are washed away or attacked by immune cells
- - cause paralysis of pharygeal muscles of parasites
- - worms lack CNS
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Acaricide
- - kills mites by paralyzing pharyngeal muscles
- - toxicity causes mutation of transporter proteins
- - accumulation = hyperpolarization and neurological problems
- - ivermectin hazardous to collies, australian shepherds, and sheep dogs
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Heartworm
- -once/month preventative = low dose; not effective for L1/L4
- - significant disease in right side of heart leading to CHF
- - diagnosed by snap test or x-ray through enlargement of right side of heart
- - expensive to treat= arsenic cmpds for adult worms; restrained for 1-2 months to prevent thromboembolism
- - treatment also depends on if microfilaria is being produces
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Immiticide
heartworm adulticide; deep intramuscular injection (back muscles)
- melarsomine dihydrochloride
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Treat microfilaria after 1-2 months of clearing adults with
macrocyclic lactones at high doses (extra label)
there is a risk of neurotoxicity with no antidote
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Ivermectin
antinematidal in large animals; given by injection and in horses given orally only
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Resistance
occurs when a greater # of individuals in a population are resistant or no longer affected by the medication; permanent
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Cestodes (tapeworms)
- - affects both small and large animals
- - not affected by macrocyclic lactones
- - thin end (head); proglottins (segments) packed full of eggs and passed in feces when shedding
- - each egg has immature head of tapeworm
- - suckers on head attach to mucosa of sm. intestine and absorb nutrients
- - parthenogenesis (need no mate)
- - infection through ingestion
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Anticestodal drugs
- - attack the attachment site (scolex= head), causing paralysis, and worm gets purged through feces
- - causes an increase in calcium ion permeability, parasite loses calcium with is necessary for muscle contraction and relaxation
- - includes Praziquantel (Droncit), Epsiprantel (Cestex)
- - oral tablets
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Trematodes (flukes)
- - fasciola hepatica
- - great economic impact in cattle
- - unsegmented parasitic flat worms, visible to naked eye (1 cm in length)
- - lead to liver condemnation, unthriftiness and loss of condition in cattle
- - cysts in liver, adults reside in these cysts
- - intermediate host = snail
- - ingestion when grazing on pastures near ponds or natural water supply
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Anti-trematodals
- - includes praziquantel (used in sm animals to treat lung flukes), albendazole, and curatrem (colorsulon; main)
- - inhibits the energy production system of these parasits (glycolysis)
- - given by drench (oral solution)
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Protozoans
class of organisms, single celled, eukaryotic
include giardia, coccidia, and sarcocystis neurona
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Coccidia
- - intestinal protozoa; causes GI problems in young animals, diarrhea, scours in calves
- - problem in poultry
- - prevent by decreasing stocking #'s and increasing sanitization
- - parasite invade cell that line sm intestine, replicate, cell ruptures, release in lumen, infect other cells, and cells are not able to absorb nutrients which causes the diarrhea
- - treat with coccidistats: monensin which effects metabolism of protozoa
- - narrow spectrum: corid (amprolium) in large animal and sulfa antibiotic (albon) in cats and dogs
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Giardia
- - zoonotic disease, infect sm. intestine, epithelial stage
- - have flagella
- - diagnose with fecal elisa tests
- treat with fembendazol (panacur)
- - can treat with antimicrobial agent= flagel (metronidazole) but not approved yet; can lead to nausea/vomiting at high levels (neurotoxin); unpalatable for cats, effective against anaerobic microbes
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Sarcocystis neurona
- - protozoal disease cusing EPM (equine protozoal myolitis)
- - affects CNS of host
- - intermediate host = armadilos, raccoons, skunk
- - Definitive host = opposums
- - Dead end host = horse
- - drug: ponazuril which inhibits nuclear division in parasite (cocciostatic)
- - EPM: nurological signs, prevalent, muscle atrophy, lameness, CSF test, expensive
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Antiprotozoals
- - Albon (sulfadimethoxine)
- - Panacur (fenbendazole)
- - Flagyl (metronidazole)
- - Marquis (ponazuril)
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Treat Ectoparasites with
- - Organophosphates and carbamates
- - pyrethrins and pyrethroids
- - macrolides
- - imidacloprid
- - frontline (Fipronil)
- - capstar (nitempyram)
- - program (lufeneron)
- - mitaban, preventic (amitraz)
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Organophosphates and carbamates
- - Developed as nerve gas originally
- - Dips
- - Toxicity signs: (parasympathetic over stimulation), Hypersalivation, Defacation, Pupils dilation (mydriasis), Epiphora, will progress to muscle tremors/seizures
- - Mechanism of action: irrevesibly inhibit acetylcholinesterase causing paralysis; parasite falls off or is destroyed
- - Cats very sensitive; Antidote: atropine
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Pyrethrins and Pyrethroids
- - safe; applied external (spray or dip)
- - Pyrethrins: natural products, toxic to fish, not a good kill effect on adults but great knockdown effect; MA: open Na+ channels in insects causing hyperpolarization
- Pyrethroids: synthetic; used as a room defogger to kill larval stages; cant penetrate eggs; good kill effect; can cause toxicity in cats; use on adult animals
- Insect growth regulators to prevent molting can be added--- mimic effect of juvenile growth hormone
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Macrolides
- - Include selomectic (active ingredient in Revolution)
- - In ruminants by injection; horses= paste; drench; topically
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Imidacloprid
- - Topically-- between shoulder blades; not absorbed systemically; Trifexis
- - Advantix in dogs has pyrethrin added; Advantage in cats
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Fipronil
- - Not absorbed systemically
- - Interferes with nicotinic insect receptors
- - Gets into sebaceous gland --> 30 day absorbed
- - Nontoxic even if animals accidentally ingest
- - Alopecia or hair loss at site
- - Need a couple days to be absorbed and avoid touching area
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Nitempyram
- - oral
- - Kill adult fleas; absorbed systemically
- - Animals have to get bitten
- - Works well for maggot infestation in animals
- - Can be used in fly-strike in rabbits
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Lufeneron
- - chewable tablet
- - Inhibits insect growth by interfering with chitin
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Amitraz
- - Preventic collar --> if ingested causes coma and lead to death; trim excess collar
- - Mitaban dip-- only approved product to treat demodectic mange in dogs (not all dogs respond to it); caused by demodex canis
- - CANNOT BE USED IN CATS
- - Miticidal; effective against ticks too
- - Highly toxic if ingested
- - Staff must wear personal protective equipment
- - Alpha2 receptor agonist (depresses norepinephrine)
- - See depression and sedation
- - MAO inhibitor (recycling norepi)
- - Antidote --> yohimbe
- - Milbomycin works better than ivermectin
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Mange
- - Demodectic: Live in hair follicles; causes hair loss; inflammation; severe skin infestation; bacterial infection; Genetic: neuter or spayed a must
- - Another type of mange is sarcoptic mange: burrows under skin into dermis; treat with ivermectin
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