Common Nematode Infections (Pins, Threads, Giants) (Franco Falcone) Flashcards
What order of classification is given in taxonomy?
Kingdom Phylum Class Order Family Genus Species
(King Prawn Curry Or Fat Goat Soup
What kingdom do nematodes belong to?
Animals
What phylum are nematodes?
Phylum is nematoda (round worms)
What is the taxonomy of a platyhelminth?
They are a flatworm phylum
What classes fall under the phylum of platyhelminth?
Cestodes (tapeworm)
Trematodes (flukes)
What kind of structure / body do nematoda have?
Roundworms; rounded bodyplan, complete alimentary canal, no suckers, sexually differentiated.
What kind of structure / body do cestodes have?
Tapeworms; tapelike and segmented, no alimentary canal, surface areas large to maximise absorption.
Hermaphrodites
Head has hooks or suckers
What kind of structure / body do platyhelminths have?
Flatworms; flattened dorsoventrally, alimentary canal rudimentary or absent. Suckers present, hermaphrodites mainly.
Name three common worm infections of the intestines?
Enterobius vermicularis
Trichuris trichiura
Ascaris lumbricoides
They are geohelminth nematodes.
What are geohelminths?
Soil-transmitted helminths (STHs) are intestinal nematodes that undergo part of their development outside the body.
How do geohelminths cause infection?
Infection occurs through contact with parasite eggs or infective larvae in contaminated food or soil.
In which countries are geohelminths common? Consider how they are infective / transmitted?
Countries with general poor hygiene or sanitation
What is a common name given to Enterobius vermicularis?
Pinworm or threadworm
What is the infection with Enterobius vermicularis called?
Oxyuriasis (old taxonomy) or enterobiasis
What animals are the hosts of Enterobius vermicularis?
Humans are the only hosts
Do Enterobius vermicularis replicate in the body?
There is no multiplication in the body
EV
What are the four modes of transmission for pinworms?
- Direct transmission from anal/perianal region to the mouth by fingernail contamination and soiled night clothes
- Exposure to viable eggs on soiled be clothes and other objects
- Contamination via mouth or nose from contaminated dust
- Retroinfection: larvae hatch from eggs on anal mucosa and migrate back up the bowel. (only in cases of large larvae population.)
What are the symptoms of Enterobius vermicularis infection?
Pruritus ani. Mild to acute painful itching, mainly at night resulting in scratching of the perianal region. This can lead to secondary infections if the skin is compromised.
Vulvitis ; in women, if worms enter the vulva
Insomnia, restlessness, loss of appetite
There is neither anaemia or eosinophilia as no feeding occurs.
EV
How is Enterobius vermicularis diagnosed?
Copromicroscopal examination of the faeces, perianal scrapings, swabs under nails.
Sellotape
EV
What prophylactic measures can be taken when dealing with Enterobius vermicularis?
Trim fingernails, wear cotton clothes and gloves during sleep, frequent washing of hands and bed sheets etc.
EV
Where do adult pinworm/threadworms reside in the body?
Upper colon
Small ulcerations can occur at the site of attachment, resulting in haemorrhages and secondary infections. Can cause nonspecific colitis in children.
EV
What is ectopic infection and how can it cause problems?
Male or female genital tract or urinary tract, but also liver, kidney, spleen, lung. Quite rare but more serious. The gut is a favorable site for parasites so the most common residence.
What is the drug of choice for the treatment of Enterobius vermicularis?
Mebendazole is a benzimidazole
In children over 6 months
Given as a single dose, can be repeated after 2 weeks if reinfection occurs
What is Trichiuris trichiura?
Whip worm (head tiny, posterior extremity (eggs released) larger)
TT
In what countries is Trichuris trichiura most common?
Tropic humid areas with inadequeate sanitation (there is no transmission in arid areas)
TT
Where does Trichuris trichiura worm reside?
In the caecum, (upper colon) where they remain attached to the epithelium by burrowing into epithelial folds / tunnel.
TT
How is Trichuris trichiura infection diagnosed?
Stool examination: detection of eggs by microscopy using the Kato-Katz method. Eggs look like lemons, two terminal polar plugs
Egg counts reflect the intensity of infection
>10,000 eggs per gram = intense infection
FLOTAC is a new flotation chamber technique that can detect and count eggs.
TT
What are the symptoms of Trichuris trichiura?
Light infections are generally asymptomatic
Heavy infection can cause abdominal pain, stool containing mucus, water and/ore blood.
Rectal prolapse can occur in heavy infection (it is rare).
Heavy chronic infection in children can result in severe anaemia, growth retardation and impaired cognitive development.
TT
What determines the pathology of Trichuris trichiura?
Strongly associated with worm load.
TT
What is Trichuris dysentery syndrome (TDS): associated with heavy infections?
Resembles dysentery caused by other pathogens e.g. some enteric bacteria and Entamoeba histolytica.
TT
What is the drug of choice in the treatment of Trichuris trichiura?
Mebendazole is a benzimidazole
It is contraindicated in pregnancy or if patients are allergic.
AL
What is Ascaris lumbricoides?
Giant worm
AL
What length can Ascaris lumbricoides grow?
20-35cm
AL
Where do eggs devlelop?
Outside of the host and for long phases
AL
Female power
200,000 eggs per day
AL
What is Ascaris suum?
Pig worm
AL
How to pig roundworm (Ascaris suum) eggs develop?
Identical to human roundworm but can’t infect humans
- immature outer sticky shell
- immature egg without the sticky shell, naked
- mature embryonated egg (live worm inside, if ingested, infected.)
AL
How is Ascaris lumbricoides diagnosed?
Copromicroscopic detection of eggs passed in faeces
Intensity of infection can be assessed by egg count via Kato-Katz or new FLOTAC method.
>50,000 eggs per gram is heavy infection
AL
What are the symptoms of Ascaris lumbricoides infection?
Light infection usually asymptomatic
Symptoms during lung migration may be similar to pneumonia or asthma, a persistent cough, SOB, wheezing
Intestinal symptoms may include abdominal pain, fatigue, weight loss.
Sometimes worms can be found in vomit or stool
AL
What is Löffler syndrome?
Migrating larvae can cause damage to lungs, they can cause Löffler syndrome which can be fatal.
In some cases the larva can migrate to the brain, eyes, retina causing other symptoms.
AL
What is intestinal obstruction or intussusception?
In high populations of worms, obstruction can be caused, Intussusception is caused when the intestine slides into itself, much like a collapsable teloscope. This can block bloodflow and cause ischaemia, leading to necrosis, gut perforation and peritonitis within hours.
AL
How is Ascaris lumbricoides treated? Drug of choice? Mechanism of action?
Mebendazole is the treatment of choice (a benzimidazole).
Mebendazole binds to a single high affinity binding site of the B subunit of tubulin, preventing microtubule formation. This affects parasitic function such as glucose uptake/transport.
AL
What is Levamisole?
A thiazole, can be used in treatment but is not licensed in the UK. Where mebendazole cannot be given it is an alternative treatment. Nicotinic acetylcholine receptor agonist, causes the continued stimulation of parasitic worm muscles leading to paralysis.
