ectoparasiticides

chemical control and applications

act systemically or via skin contact - parenterally, orally or topically

dogs and cats = spot-ons, chewable tablets, collars, environment, infectable

livestock = ear tags(cattle), pour-ons, spot-ons, injectable, dip, oral e.g drinking water(poultry)

equine = sprays, pour-ons, oral

ectoparasticide R&D and regulation

different regulatory requirements worldwide

discovery, research and development is lengthy and expensive process

• R&D to demonstrate efficacy, develop formulation, dosage

• demonstrate safety, quality and efficacy to obtain market authorisation

implications for veterinarians - prescribing under cascade

products not classed as veterinary medicinal products have not undergone same level of testing

veterinary medicines vs biocides - different testing requirements

market authorisation may be withdrawn 

major classes of ectoparasticides 

organochlorines

organophosphates

synthetic pyrethroids

macrocyclic lactones

neonicotinoid

phenylpyrazole

isoxazolines

formamidine

insect growth regulators

organochlorines(OCs)

e.g DDT

• global malaria eradication programme but resistance 

• highly toxic - bioaccumulation, food chain, immune impairement and others

banned in many countries - UK - 1984, USA - 1972

organophosphates(OPs)

e.g diazinon

delivery = plunge dip - sheep only

targets - blowfly, lice, mites, ticks, keds

mode of action - acetylcholine released from insect nerve ending, normally inactivated by acetylcholinesterase. OPs bind to AChE, acetyl choline builds up = paralysis

safety = lipid soluble, high toxicity to humans

synthetic pyrethroids(SPs)

e.g permethrin, cypermethrin, deltamethrin

delivery = ear tags, pour-on, spray-on, collars

targets = flies, lice, ticks

mode of action = excites cell membranes by maintaining depolarisation, Na+ channels stay open = paralysis 

safety = repellency and rapid kill, not residual, low mammalian toxicity

contraindications = permethrin toxicity in cats 

macrocyclic lactones(MLs) - endectocides

e.g ivermectin, doramectin, moxidectin, selamectin

delivery = IM or SC injection, spot-on, pour-on

targets = broad spectrum - mites, lice,bots, warbles, fleas 

endectocidal class of drugs 

mode of action = stimulate GABA(inhibitory neurotransmitter) release from nerve endings, enhancing binding to its receptors in post- synaptic motor neurone membrane, increasing flow Cl- = paralysis 

safety = safe, GABA neurotransmission confined to CNS in mammals, large molecules don’t readily cross blood-brain barrier 

lipophillic = systemic slow release, persistent, extended protection(some products)

contraindication = collies(and other breeds) sensitive to ivermectin(mdr1 gene). long meat and milk withdrawl 

neonicotinoid

imidacloprid

delivery = spot-on

targets = fleas, T.canis

mode of action = binds to nicotinic ACh receptors in insect nervous system = paralysis 

safety = toxic to aquatic invertebrates, toxic to bees, agriculture use restricted across the EU

phenylpyrazole

fipronil

delivery = spot-on, spray

targets = fleas, ticks

mode of action = blocks GABA transmitter = paralysis 

safety = toxic to fish and bees

lipophillic, diffuses into sebaceous glands of hair follicules which act as resevoir = long residual activity 

formamidine

amitraz -generally now unavailable

delivery = wash, impregnated strips  

targets = demodectic mange in dogs

mode of action = interacts with octopamine receptors, hyperexcitation = paralysis 

safety = some dogs are sensitive 

contraindications = toxic to horses and cats 

superseded by other products licensed for this parasite

also available for varroa mite treatment in honey bees 

isoxazolines

fluralaner, afoxolaner, lotilaner

delivery = chewable tablets and spot-ons, now injectable 

targets = fleas, ticks, mites

mode of action = GABA and glutamate recpetor antagonist = paralysis 

safety = safe, although enviromental/invertebrae toxicity not fully established 

novelty = fluralaner and afoxolaner kills fleas within 8 hrs and ticks within 48hrs. active for 3 months. lotilaner kills fleas within 2hrs and ticks within 12 hrs = can prevent borrelia and babesia transmission 

bispyrazoles

tigolaner

newer drug, licensed in cats

delivery = spot on

targets = fleas, ticks, mites

mode of action - GABA and glutamate 

insect growth regulators(IGRs)

chitin inhibitors

• cyromazine, dicyclanil, diflubenzuron, lufenuron 

• delivery = spot-on, injection, pour-on

• targets = blowflies, fleas

• mode of action = chitin inhibitor, prevent egg hatch and moulting. cyromazine protects against blowflies for ~14w

juvenile hormone analogues 

• methoprene

• delivery = spot-on

• targets = fleas

• mode of action = mimics the prohormone ecdysone which keeps fleas young

classes by modes of action