Parasitic Nematodes Flashcards
What are parasitic nematodes also known as?
Helminthes
What are drugs used against parasitic worms called (as a group)?
Anthemintics
What are the groups of drugs that have been created to treat parasitic nematode infections in the 1960s?
Benzimidazoles (1960s)
What is the general target for all current anthelmitics?
Mainly neuromuscular junction
Example of an imidazothiazole
Levamisole
Example of a macrocyclic lactone
Invermectin
Example of a spiroindole
Paraherquamide
What do benzimidazoles target?
inhibit cellular transport and energy metabolism -> impair locomotion and reproduction
What do imidazothiazoles target?
nicotine receptor antagonists -> muscle paralysis
What do macrocyclic lactones target?
ligand-gated ion channels -> paralysis of nematode pharyngeal and body wall muscle
What do spiroindoles target?
competitive cholinergic antagonist -> cause paralysis
Challenges to treatment of parasitic nematode infections
multiple life cycle stages complex body plan protective cuticle mutlicellular abundant and high reproduction capacity some stages metabolically inactive - resistant
Challenges with drug treatment
Resistance
Reliance
Denser stock (livestock)
Movement of livestock
Solutions to challenges with drug treatment
Ensure effective treatment Reduce reliance Combination drugs Correct dose Quarantine
Parasite response to the immune response (host)
Suppress TH1 response (inflammatory)
Activate TH2 response (anti-inflammatory)
Also secrete other substances
Genomic targets for future drug treatment
differential gene expression sites (between parasite and host)
disease-causing genes
Three types of gastrointestinal worm with greatest impact on human health and fitness
Ascaris
Trichuris (whipworm)
Necator and Ancylostoma (hookworm)
Two parasitic worms that have a big impact on farming of animals
Haemonchus
Trichinella
How do Ascaris and Trichuris infect their hosts (human)?
eggs passed in faeces - contaminate -> ingested
At which stage of their respective lifecycles are Ascaris and Trichuris infective to humans?
Eggs (embryogenesis in soil)
How do hookworms (Necator and Ancylostoma) infect their hosts (human)?
L3 larvae penetrate skin on foot
-> bloodstream->lung-> oesophagus-> intestinal epithelium
How can Ascaris, Trichuris (whipworm), Necator and Ancylostoma (hookworm) infections be diagnosed?
eggs in faeces
How does Haemochus infect their hosts?
L3 larvae are ingested, on grass eaten
What is the host of the parasitic worm Haemonchus?
sheep and goats
What is the significance of the parasitic worm Haemonchus?
most abundant sheep parasite globally
Why are parasitic worms so important to the farming of animals?
reduces productivity of cattle, sheep and goats
Brief life cycle of whipworms (Trichuris) and Ascaris
faeces -> soil -> mouth -> small intestine -> …
Brief life cycle of Necator and Ancylostoma
faeces -> soil -> foot -> lungs -> oesophagus -> small intestine -> …
What is the significance of parasitic worm infections in terms of human health and fitness?
Disability adjusted life years
- may not kill, but disable = reduction in productivity
Methods for control of Trichinella
Effective public veterinary health programme
Farm management practices (rodent control + hygiene
Mandatory meat inspection
Public health information
Brief life cycle of Haemonchus
direct life cycle (no vector)
faeces(eggs) -> soil (L1-L2) -> infect host (L3) -> abomasum (L3-adult)
Risk factors for infection by Haemonchus
young - 1st grazing season old genetics environmental factors exposure levels (conc. of eggs on grass)
Methods for control of Haemonchus
monitoring mixed grazing (young and mature) alternating stock (sheep/cattle) stocking density pasture composition - anthelmintic plants, e.g. chicory
Why might trichinella be of particular concern in terms of pig meat consumption?
It is a zoonotic parasite.
At which stage of its life cycle does trichinella infect?
L1 larvae (encysted larvae in striated muscle)
Why is trichinella re-emerging?
wild reservoirs
political upheaval - i.e. Eastern Europe in the 1990s
changes in animal husbandry
global trade
EU trade (Eastern Europe has natural reservoirs)
What are the hosts of trichenella?
humans
pigs (domestic)
other predatory/scavenging animals
Brief life cycle of trichinella
meat -> mouth -> small intestine (larvae to adults) -> larvae in mucosa -> encysted larvae in striated muscle
Point of diagnosis for trichinella
striated muscle
What are the groups of drugs that have been created to treat parasitic nematode infections in the 1970s?
Imidazothiazoles
What are the groups of drugs that have been created to treat parasitic nematode infections in the 1980s?
Macrocyclic lactones
What are the groups of drugs that have been created to treat parasitic nematode infections in the 2000s?
Spiroindoles
