Control of Ectoparasites Flashcards
what are the reasons to control ectoparasites (5)
- debilitating irritant to host
- source of infestation –> animals and humans
- vectors of disease
- economic loss
- compromise animal welfare
why are ectoparasites difficult to control
- large seasonal increases in populations –> tick population increases in spring/autumn, blowflies increase in late spring and early summer, midges peak in summer and autumn
- infestations can be highly contagious –> stocking density, location - transport
- can be widespread in the environment –> although some are more localized
what are the basic strategies to control ectoparasites (7)
- deployment and application of drugs to kill and repel insects and arachnids (all)
- legislation to report and treat (scab and warble)
- quarantine and treatment of incoming stock (scab)
- treatment of all in contact animals (sarcoptic mange)
- treatment of the local environment/habitat (flea allergic demodecosis)
- vaccines against ectoparasites (rhipicephalus tick)
- mechanical removal –> traps and vacuums (tetse fly and fleas)
what are the pharmological interventions to prevent ectoparasite infestation
selective toxicity –> target a feature of the parasite that is different from the host
what is selective toxicity
target specific ion channels that are in the CNS of vertebrates but in the PNS of ectoparasites
what are the mechanisms of action of selective toxicity
- exploit the fact that metabolism is slower in insects than endotherms
- target receptors that vertebrates do not have
- have greater affinity for equivalent ectoparasite receptor
- target proteins, like chitin, that vertebrates lack
- bio-activation of the drug in the gut of the insect to kill parasite
what are the methods of delivery of ectoparasiticides
- ear tags, tapes, collars for farm animal species
- pour on for large and small animals
- spot on solutions
- collars for cats and dogs
- dips
- oral tablets or suspensions
- sprays
- injectable
what is the mechanism of action of organophosphates
selective inhibition of acetyl cholinesterase –> accumulation of acetyl choline in synaptic celft –> neuromuscular paralysis
what is the spectrum of organophosphates
ticks and mites; flies, feals and lice
what is the toxicity of organophosphates
safely margin is limited for animals and man and products carry operator warnings –> certificate of competence for OP dip
what are the mechanism of action of pyrethrins and pyrethroids
prevent closure of presynaptic voltage gated sodium channels
nerves cannot repolarize
cause paralysis
what is the spectrum of pyrethrins and pyrethroids
lice, fleas, flies, keds
what is the toxicity of pyrethrins and pyrethroids
low if given orally, fish and some aquatic invertebrates are highly sensitive
dip formulations banned
how is pyrethrins and pyrethroids selectively toxic
rate of metabolism is more rapid in vertebrates
how is permethrin toxic in cats
life threatening toxocosis
spot ons for dogs applied to cats
high surface/weight ratio –> elevated dose
lower detoxification/excretion
can cause tremors, twitches, hyperthermia, seizures
how is permethrin toxicity in cats treated
methocarbamol i.v (centrally acting muscle relaxant)
seizure control; barbiturates, diazepam, inhalant anaesthetics
dermal decontamination by bathing
what are examples of avermectins and milbemycins
invermectin, doramectin, selamectin, moxidectin, milbemycin
what is the action of avermectins and milbemycins
bind to glutamate gated (ectos) or GABA gated chloride channels (host)
what is the toxicity of avermectins and milbemycins
sensitive animals including some dog species, kittens, some species of birds, turtles, fish and reptiles
what is toxicosis of ivermectin
contraindicated in some species and some dog breeds
unable to pump out drug from CNS
toxicosis syndrome, dilation of pupil, depression, tremor, ataxia, vomiting, salivation, coma
what are uses of avermectins and milbemycins
- invermectin: very many formulations –> Ivomec
- selamectin: stronghold (spot on, dogs and cats)
- doramectin: dectomax (cattle, sheep, pigs)
- moxidectin: cydectin (sheep and cattle) with imidacloprid (advocate)
what are examples of neonicotinoids
nitenpyram and imidacloprid
what is the mechanism of action of neonicotinoids
block nicotinic receptors
inhibits cholinergic transmission causing paralysis and death
what is the spectrum of neonicotinoids
fleas/lice in cats, dogs rabbits, ferrets
what is the toxicity of neonicotinoids
low but toxic to bees
what are the trade names of neonicotinoids
nitenpyram –> Capstar
imidacloprod –> Advantage
imidacloprid + permethrin –> advantix (fleas, ticks, lice)
imidaclorpid + moxidectin –> advocate (sarcoptic mange, demodecosis)
what is the effect of cyromazine and methoprene
insect growth regulators (IGR)
effect deposition of chitin in cuticle
what are the uses of cyromazine and methoprene
blowfly strike –> domestic rabbits –> reargard (cyromazine)
blowfly strike –> sheep –> clik/clikzin pour on (dicyclanil)
what is the withdrawal period of cyromazine and methoprene
7 days for meat
not to be used in sheep producing milk for human use
what is juvenile hormone (methoprene) used for
fleas, ticks and biting lice (dogs and cats)
spot ons –> kill adult fleas and inhibit development of egg
larvae and pupae
what is an example of benzoyl urea derivative
lufenuron
what is the mechanism of action of benzoyl urea derivative
inhibits chitin synthase in fleas
also kills eggs and larvae
what is the pharmacokinetics
absorption improved in presence of food
highly lipophylic and accumulates in adipose tissue
what is the administration of benzoyl urea derivative
oral suspension or tablets (monthly with food)
injectable for cats (six monthly)
what is the mechanism of action of fipronil
an antagonist to GABA and glutamate gated chloride channels
greater affinity for insect receptors
reservoir in skin
what are examples of fipronil
frontline
what is the spectrum of fipronil
fleas, ticks, biting lice in cats and dogs
kills adults before eggs are laid
combined with IGR (methoprene): frontline plus; fiprotec combo; fleascreen combo for flea control
what is the toxicity of fipronil
toxic to some gallinaceous birds and some fish
what is oxadiazine insecticides
indoxacarb
sodium channel blocker
needs bioactivation
adult fleas
what is an amidine
amitraz is the class member used for ectoparasites
what is the mechanism of action of amidines
alpha2 receptor antagonist –> stimulates alpha adrenergic receptors
octopamine receptor antagonist –> alters brain function
leads to insect hyperactivity, paralysis and death
also detaching behaviour; inhibition of oviposition; reduces egg hatchability
what are examples of amidines
aludex
what is a strategy to sheep scab control
sheep scab is difficult control –> highly contagious –> control needs 100% efficiency –> residual activity > 17 days
how is sheep scab treated
effective treatment by plunge dipping –> organophosphate dip kills 24 hours, residual effect –> 28 days
sheep in dip for atleast 60 seconds –> head immersed twice –> operator/environmental issues
injectables:
ivermectin (2, no residual) –> move to mite free environment
doramectin (1, 14-17 days residual) –> move to mite free environment
moxidectin 2% (1, 60 days residual)
emerging resistance of mite to Mls recently reported
mobile dipping contractors increasingly being used
what does scab control require
all in contact animals must be properly treated
minimize impact of outbreak –> inform neighbours of risk –> coordinate treatment across farms
promote biosecurity –> good fencing, all incoming animals, quarantine, test and treat for 3 weeks
recognize common grazing as high risk infection
what are pyrethroid products and their uses
permethrin: Advantix for dogs, Auriplak tag for cattle, Flypor pour on cattle, Xenex spot on for small furries
Cypermethrin: Crovet sheep, Dysect cattle and sheep, Excis pour on salmon, Deosect horses spray
Deltamethrin: AMX salmon, Butox swish cattle, Coopers spot on cattle and sheep, Scalibor collar large dogs
Flumethrin: Bayvarol strips, against varroa mites
