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
