Ectoparasiticides Flashcards
What are the most common groups of ectoparasites? Why is treatment important?
- INSECTS - fleas, lice, lice
- ARACHNIDS - ticks, mites
they can transmit disease and cause allergic dermatitis
What are the 3 main characteristics of the ideal ectoparasiticides?
- an effective repellent and adulticide with persistence in the blood or skin surface
- formulation that is stable to sunlight and water/shampooing
- high efficacy with low toxicity to host
What is the feeding behavior of fleas and ticks?
FLEAS - engorge with with a blood meal from the host from 5 mins to 1 hr of infestation
TICKS - engorge longer periods
What are the main 3 mechanisms of action of ectoparasiticides?
- affect ectoparasite nervous system - AChE inhibitor, Na+ channel blocker, nAChR inhibitor, GABA/glutamate receptor Cl- channel inhibitor
- ectoparasite repellant
- block insect growth and development
What formulation is considered the safest ectoparasiticide? Most convenient?
powders - must be applied frequentyl
spot-on - ease of use and efficacy
How should shampoo ectoparasiticides be used? How do sprays compare?
little residual effect and must stay on the skin for at least 10 minutes
residual effect depends on active compound and concentration
What phenylpyrazole is commonly used as an ectoparasiticide? What 3 parasites does it work best on? What is it not effective against?
Fipronil (Frontline)
- adult fleas
- all stages of brown dog tick, American dog tick, Lone Star tick, and deer ticks
- biting fleas
preventing fleas from biting and feeding
What additional action does the formulation Frontline Plus have? What is fipronil approved for use in?
efficacy against flea eggs and larvae
dogs and cats > 8 weeks
What is the mechanism of action of Fipronil (Frontline)?
noncompetitively inhibits GABA-induced ion influx by targeting GABA-regulated Cl- channels, blocking Cl- influx and causing neural hyperexcitation, paralysis, and death
(500x selective toxicity to insects over mammals)
What are 3 signs of Fipronil (Frontline) toxicity?
- hyperactivity
- hyperexcitability
- convulsions
(wide margin of safety, non-teratogenic)
What 3 neonicotinoids are commonly used as ectoparasiticides? What is the mechanism of action?
- Imidacloprid (Advantage)
- Spinosad (Comfortis)
- Nitenpyram (Capstar)
competitive inhibition at the postsynaptic nicotinic acetylcholine receptors (nAChR); don’t bund effectively to nicotinic receptors in mammals
What biphasic response is characteristic of neonicotinoids?
increased frequency of spontaneous discharge followed by a complete block to nerve propagation
What parasite does Imidacloprid (Advantage) have efficacy against? What does it have limited activity against? What animals is it approved for use in?
adult and larval fleas (kills within 1 hour or exposure)
ticks
dogs and cats > 4 months
What formulation is Advantage Multi? What 4 additional effect does it have?
Imidacloprid + moxidectin —> dogs and cats
fleas, heartworm prevention, intestinal worms, ear mites
What does Spinosad (Comfortis) work best against? What is it not labeled for use against?
prevention and treatment of adult fleas in dogs and cats (works within 30 mins of exposure)
ticks
What is the mechanism of action of macrocyclic lactones?
act on glutamate-gated chloride channels (GluCl) and GABA receptors, inducing reduction of motor activity and causing flaccid paralytic effects on pharynx and somatic musculature
What ectoparasiticide effects does Ivermectin have in swine, cattle, dogs, and cats/kittens?
SWINE - lice, mange mites
CATTLE - horn flies, grubs, biting and sucking lice, mites, ticks
DOGS - otodectic, sarcoptic, notoedric, and demodectic mange
CATS/KITTENS - adult ear mites
In what species is Eprinomectin used as an ectoparasiticide? What parasites is it used against?
beef and dairy cattle
horn flies, biting and sucking lice, mites
What 2 species is Doramectin commonly used as an ectoparasiticide? What parasites is it used against?
BEEF CATTLE - horn flies, grubs, biting and sucking lice, mites, ticks, screwworms
SWINE - sucking and mange mites
In what species is Moxidectin used as an ectoparasite? What parasites is it used against?
dairy and beef cattle
horn flies, grubs, biting and sucking lice, mites, and ticks
In what species is Selamectin used as an ectoparasite? What parasites is it used against? What additional use does it have?
dogs and cats
ear mites, adult fleas, sarcoptic mange, ticks
prevents the hatching of flea eggs
In what species is Milbemycin oxime used as an ectoparasite? What parasite is it used against?
cats and kittens (> 4 weeks)
ear mites
What 4 isoxazolines are used as ectoparasiticides? What is their mechanism of action?
- Sarolaner (Simparica)
- Afoxolaner (NexGuard)
- Fluralaner (Bravecto)
- Lotilaner (Credelio)
inhibit GABA-gated and glutamate-gated chloride ion channels, resulting in irreversible hyperexcitation in targeted parasites
What 2 types of parasites do Isoxazolines work against?
- fleas —> Ctenocephalides felis and canis
- ticks —> Dermacentor reticulatus and veriabilis, Ixodes ricinus and scapularis, Rhipicephalus sanguineus, Amblyomma americanum andmaculatum,
What are the 4 major species of ticks that are vectors of bacterial diseases in the US?
- Dermacentor: Rickettsia rickettsii (Rocky Mountain spotted fever)
- Ixodes: Borrelia burgdorferi (Lyme)
- Dermacentor, Amblyomma, Rhipicephalus: Ehrlichia, Babesia
What makes Isoxazolines so safe?
very selective for flea and tick CNS GABA receptors over mammalian receptors
What are pyrethrins? What parasites are they used against?
extracts from chrysanthemum flowers (synthetic = pyrethroids)
- fleas
- flies
- lice
- cheyletiella
- otodectes
- mosquitoes
What is the mechanism of action of pyrethrins?
disrupt neurological function by prolonging the opening of Na+ channels, resulting in repetitive membrane depolarization
(insect sodium channels can be 100x more sensitive than mammalian channels)
How do pyrethroids compare to pyrethrins?
- synthetic analogs with same MOA
- more resistant to breakdown
- extremely selective for insects
What is the most commonly used pyrethroid?
3rd generation pyrethroid, Permethrin
What unique property do both pyrethrin and pyrethroids contain?
repellents
- avoids infection while treating current infestations
- good for patients with allergies sensitive to simply contact with parasites
What species is spot-on Permethrin used on? What is included in its K9 Advantix II formulation? What additional properties will it have?
up to 65% - dogs, NO CATS (lack glucuronidation enzymes)
Imidacloprid + Permethrin + Pyriproxyfen - manage fleas, ticks, mosquitos, lice, and biting flies
What formulations of Permethrin are approved for use in dogs and cats?
sprays, shampoos, and dusts at lower concentrations (0.05%)
How is Permethrin used in food animals?
sprays and pour-ons with short withdrawal times provided they are correctly applied
How are pyrethrins and pyrethroids absorbed dermally?
LIMITED —> very lipophilic and have large molecular weights, making it difficult to entirely cross the keratin and intercellular lipids of the stratum corneum
When is it common for pyrethrin and pyrethroid toxicity to occur? How does it present? How is it treated?
following ingestion from grooming or percutaneous absorption
salivation, tremors, and seizures (like OP and CM)
no specific antidote —> symptomatic treatment including bathing
What are the 2 groups of insect growth regulators?
- juvenile-hormone analogs (JHAs)
- insect development inhibitors (IDIs)
What are 4 approved juvenile-hormone analogs? What are the commonly formulated with? What is their mechanism of action?
- Methoprene
- Pyriproxyfen
- Fenoxycarb
- Cyromazine
- adulticides
falsely signal the organism (ticks, fleas, flies) to remain in its immature egg or larval stage
What is the main uses of Methoprene and Pyriproxyfen? What are they commonly formulated with?
control horn flies n cattle
sprays, spot-ons, collars for dogs and cats
Methoprene + Pyriproxyfen + fipronil = Frontline Gold spot-on
What type of drugs act as insect development inhibitors (IDIs)? What is their mechanism of action?
Benzoylphenyl urea compounds - Diflubenzuron, Lufenuron (Program)
interfere with the development of the exoskeleton by inhibiting chitin synthesis or deposition also required for flea eggshells
