Endoparasites Flashcards
What are the main types of parasiticides?
Ectoparasiticides: Kill external parasites
Endoparasiticides: Kill internal parasites.
Endectocides: Kill both internal and external parasites.
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)
What are the classes of anthelmintic drugs
organophosphates
benzimidazoles
Tetrahydropyrimidines/
imidazothiazoles
Salicylanilides
Pyrazinoisoquinolones
Sulphonamide
Hexahydropyrazine
Macrocyclic lactones
Give examples of Organophosphates as anthelmintics
Dichlorvos
Haloxon
Napthalofos
Give examples of Benzimidazoles as anthelmintics
Albendazole
Febantel
Fenbendazole
Flubendazole
Mebendazole
Oxfendazole
Oxibendazole
Thiabendazole
Give examples of Salicylanilides as anthelmintics
Closantel
Rafoxanide
Give examples of Pyrazinoisoquinolones as anthelmintics
Praziquantel
Epsiprantel
Give examples of Sulphonamide as anthelmintics
Clorsulon
Give examples of Tetrahydropyrimidines/
imidazothiazoles as anthelmintics
Levamisole
Morantel
Pyrantel
Oxantel
Give examples of Hexahydropyrazine as anthelmintics
piperazine and its derivative diethylcarbamazine
Give examples of Macrocyclic lactones as anthelmintics
Abamectin
Doramectin
Eprinomectin
Ivermectin
Moxidectin
Milbemycin oxime
Selamectin
What are the main targets for anthelmintics?
Beta-tubulin (e.g. benzimidazoles)
Nicotinergic acetylcholine receptor (e.g. Tetrahydropyrimidines/
imidazothiazoles)
GABA receptor and glutamate-gated chloride channels (e.g. Macrocyclic lactones)
What is the method of action of Benzimidazoles
Bind to β-tubulin, blocking microtubule polymerization, disrupting intracellular homeostasis and energy metabolism.
Describe the neurological control of endoparasite locomotion
Control of antagonistic neurones
Excitatory (ACh containing) neurones and inhibitory (GABA containing) neurones
Describe the action of anthelmintics that target GABA receptor and glutamate-gated chloride channel
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
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
