Module 9 unit 4

Question 1

Selective Toxicity

Answer 1

capitalises on the differences in toxic effect between different species, to destroy neoplastic cells, parasites, microbes or pest (feral) animals

Question 2

What is the Principles of pesticide use

Answer 2

•  Selective exposure
- palatability of the bait
OR

•  Selective toxicity…

Question 3

What is Selective toxicity

Answer 3

– the agent is more toxic to the target species than to non target species
– ie LD50 in non target species is significantly higher than in target species

Question 4

How to achieve selective toxicity

Answer 4

– Differences in toxic effect (mechanism of action)

– Differences in toxicokinetics (eg absorption, metabolism, excretion)

Question 5

What is the example of Selective toxicity

Answer 5

Insect Growth Regulators used as topical flea insecticides on dogs eg lufenuron

insecticide imidacloprid

Question 6

What is the mechanism of action for lufenuron

Answer 6

– kill juvenile forms of fleas by disrupting capacity of flea to form chitin (exoskeleton) and hence to moult
– as mammals do not have chitin synthetic pathways, non toxic to mammals

Question 7

What is the mechanism of action for insecticide imidacloprid

Answer 7

– An insect neurotoxin

– Binds more avidly to insect neuro-receptors than mammalian neuro-receptors

Question 8

What is an example of platability of toxicity

Answer 8

Sheep dip contains organophosphate insecticide to control ectoparasites on sheep

•  The selective toxicity for parasites depends on differences in surface absorption of the toxic agent

Question 9

Selective Toxicity of Permethrin

Answer 9

•   Permethrin is used to treat fleas on dogs
•   It is rapidly absorbed by insects and causes rapid “knock down” paralysis of the flea
•   Its selective toxicity depends on toxicokinetics (greater absorption in the flea) and hence higher dose

Question 10

What is the difference in toxicokinetics of permthrin

Answer 10

They have similar mechanism of action but Dose received far greater in insect due to greater surface area to volume ratio of insect and greater absorption through body surface

Question 11

Why you should not treat cats with permethrin

Answer 11

•  Cats self groom and may ingest a greater dose

•   Cats lack capacity to glucuronidate permethrin in hepatic metabolism
•   Permethrin can be highly toxic to cats