Endoparasites Flashcards by Leah Stevenart

What are the main types of parasiticides?

Ectoparasiticides: Kill external parasites

Endoparasiticides: Kill internal parasites.

Endectocides: Kill both internal and external parasites.

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What is the function of anthelmintics

used to treat infections of animals with parasitic worms/helminths

These include flat worms, e.g., flukes (trematodes) and tapeworms (cestodes), and round worms (nematodes)

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What are the classes of anthelmintic drugs

organophosphates
benzimidazoles
Tetrahydropyrimidines/
imidazothiazoles
Salicylanilides
Pyrazinoisoquinolones
Sulphonamide
Hexahydropyrazine
Macrocyclic lactones

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Give examples of Organophosphates as anthelmintics

Dichlorvos
Haloxon
Napthalofos

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Give examples of Benzimidazoles as anthelmintics

Albendazole
Febantel
Fenbendazole
Flubendazole
Mebendazole
Oxfendazole
Oxibendazole
Thiabendazole

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Give examples of Salicylanilides as anthelmintics

Closantel
Rafoxanide

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Give examples of Pyrazinoisoquinolones as anthelmintics

Praziquantel
Epsiprantel

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Give examples of Sulphonamide as anthelmintics

Clorsulon

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Give examples of Tetrahydropyrimidines/
imidazothiazoles as anthelmintics

Levamisole
Morantel
Pyrantel
Oxantel

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Give examples of Hexahydropyrazine as anthelmintics

piperazine and its derivative diethylcarbamazine

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Give examples of Macrocyclic lactones as anthelmintics

Abamectin
Doramectin
Eprinomectin
Ivermectin
Moxidectin
Milbemycin oxime
Selamectin

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What are the main targets for anthelmintics?

Give examples of each.

Beta-tubulin (e.g. benzimidazoles)

Nicotinergic acetylcholine receptor (e.g. Tetrahydropyrimidines/
imidazothiazoles)

GABA receptor and glutamate-gated chloride channels (e.g. Macrocyclic lactones)

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What is the method of action of Benzimidazoles

Bind to β-tubulin, blocking microtubule polymerization, disrupting intracellular homeostasis and energy metabolism.

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Describe the neurological control of endoparasite locomotion

Control of antagonistic neurones

Excitatory (ACh containing) neurones and inhibitory (GABA containing) neurones

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Describe the action of anthelmintics that target GABA receptor and glutamate-gated chloride channel.

Piperazine & Macrocyclic lactones

Piperazine:
Act as GABA agonists - stimulate GABA containing neurones - opens voltage gated channels - hyperpolarisation of neurones - excessive relaxation of muscles => flaccid paralysis

Macrocyclic lactones:
Blocks the response of the cholinergic receptors - alters membrane ion permeability - causes hyperpolarisation => flaccid paralysis
OR
activate glutamate gated chloride channels - influx of Cl- => flaccid paralysis

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Describe the mode of action of anthelmintics that target ACh containing neurones

Tetrahydropyrimidines/ imidazothiazoles:
Agonists of nicotinic acetylcholinergic receptors - changes permeability of post-synaptic membrane - influx of ions => spastic paralysis

What are cyclic octadepsipeptides

Compounds: Emodepside & Nitroxynil

Mechanism: Acts on latrophilin receptors, a class of G-protein coupled receptors (GPCRs), causing flaccid paralysis of pharynx & expulsion of parasites

What are aminoacetonitrile derivatives (AADs), and what is their mode of action?

Compound: Monepental

Mechanism: Targets MPTL-1 receptors (unique type of acetylcholine receptor), causing spastic paralysis & rapid expulsion of parasites

What are Spiroindoles and what is there more of action

Compounds: Derquantel + Abamectin

Mechanism: Acetylcholine antagonism leading to flaccid paralysis, targeting specific nervous system pathways in parasites.

Fill in the mode of action for each of these

ignore years

What role do acetylcholine (ACh) & GABA play in worm paralysis?

ACh (excitatory) causes spastic paralysis.

GABA (inhibitory) causes flaccid paralysis.

Why is risk assessment important in endoparasite control?

Prevent generation of resistant parasite populations

Minimize environmental impacts, including effects on non-target species and ecosystem disruption.

Protect animal health.

What are the 2 main elements of risk in endoparasite control?

Environmental risk: Likelihood of parasite contamination and infectivity

Animal risk: Likelihood of clinical signs due to infection.

What affects how likely an environment is to have high contamination? (environmental risks cattle & sheep)

Affected by:
- Temperature (speed of generation of infective L3)
- Pasture history – how many eggs have been deposited

What affects how likely an environment is to have high infectivity? (environmental risks cattle & sheep)

Affected by moisture – how readily can infective L3 move away from the faeces

What testing methods help us assess environmental risk in cattle & sheep?

Worm egg counts (WECs) Daily live weight gain (DLWG) Combining multiple data points for accuracy.

How can environmental contamination be reduced in cattle and sheep?

Targeted selective treatment (TST), which treats only animals failing weight gain targets, reducing anthelmintic use by up to 52%.

Which cattle & sheep are at highest risk for endoparasites

First-season grazing animals. Ewes during lambing due to reduced immunity (risk primarily for pasture contamination). Animals with poor nutrition or other diseases. Weaned suckler calves For most endoparasites in cattle and sheep, immunity is developed (fluke and haemonchus are exceptions).

How is risk assessed in horses?

Environmental risk: Stocking density, poo picking, pasture rotation, quarantine. Animal risk: Clinical history, age (<5 years or >20 years), testing for worm egg counts and tapeworm antibodies.

What are the canter guidelines?

A framework to assess and manage worm risks in horses.

How is risk assessed in small animals?

Environmental risk: Indoor/outdoor lifestyle, walking areas, travel, regional variations, and history/testing. Animal risk: Age, health, and zoonotic risk (e.g., Toxocara).

How do we manage risk in farm animals?

Targeted selective treatment - 80% of parasites in 20% of population Diagnostics / parasite forecasts Grazing management – high-risk animals on low-risk pastures

How do we manage risk in horses?

Targeted selective treatment Diagnostics Grazing management – poo picking/stocking density

How do we manage risk in small animals?

Detailed history to assess risk +/- testing Treatment of animals with access to outdoors at least every 3 months

What pastures are considered high-risk in spring

Pastures grazed by first season grazing cattle the previous year

What pastures are considered high-risk in summer/autumn

Pastures grazed by cattle earlier in the grazing season

What pastures are considered low-risk in spring

Pastures not grazed previous year, or grazed by other species. Pastures grazed by adults in good health previous year. Newly seeded leys

What pastures are considered low-risk in summer/autumn

Ungrazed hay/silage aftermath Newly sown forage crops Pastures grazed by other species earlier in the season