Common Nematode Infections (Pins, Threads, Giants) (Franco Falcone)

Question 1

What order of classification is given in taxonomy?

Answer 1

Kingdom Phylum Class Order Family Genus Species

(King Prawn Curry Or Fat Goat Soup

Question 2

What kingdom do nematodes belong to?

Answer 2

Animals

Question 3

What phylum are nematodes?

Answer 3

Phylum is nematoda (round worms)

Question 4

What is the taxonomy of a platyhelminth?

Answer 4

They are a flatworm phylum

Question 5

What classes fall under the phylum of platyhelminth?

Answer 5

Cestodes (tapeworm)

Trematodes (flukes)

Question 6

What kind of structure / body do nematoda have?

Answer 6

Roundworms; rounded bodyplan, complete alimentary canal, no suckers, sexually differentiated.

Question 7

What kind of structure / body do cestodes have?

Answer 7

Tapeworms; tapelike and segmented, no alimentary canal, surface areas large to maximise absorption.
Hermaphrodites
Head has hooks or suckers

Question 8

What kind of structure / body do platyhelminths have?

Answer 8

Flatworms; flattened dorsoventrally, alimentary canal rudimentary or absent. Suckers present, hermaphrodites mainly.

Question 9

Name three common worm infections of the intestines?

Answer 9

Enterobius vermicularis
Trichuris trichiura
Ascaris lumbricoides
They are geohelminth nematodes.

Question 10

What are geohelminths?

Answer 10

Soil-transmitted helminths (STHs) are intestinal nematodes that undergo part of their development outside the body.

Question 11

How do geohelminths cause infection?

Answer 11

Infection occurs through contact with parasite eggs or infective larvae in contaminated food or soil.

Question 12

In which countries are geohelminths common? Consider how they are infective / transmitted?

Answer 12

Countries with general poor hygiene or sanitation

Question 13

What is a common name given to Enterobius vermicularis?

Answer 13

Pinworm or threadworm

Question 14

What is the infection with Enterobius vermicularis called?

Answer 14

Oxyuriasis (old taxonomy) or enterobiasis

Question 15

What animals are the hosts of Enterobius vermicularis?

Answer 15

Humans are the only hosts

Question 16

Do Enterobius vermicularis replicate in the body?

Answer 16

There is no multiplication in the body

Question 17

EV

What are the four modes of transmission for pinworms?

Answer 17

1. Direct transmission from anal/perianal region to the mouth by fingernail contamination and soiled night clothes
2. Exposure to viable eggs on soiled be clothes and other objects
3. Contamination via mouth or nose from contaminated dust
4. Retroinfection: larvae hatch from eggs on anal mucosa and migrate back up the bowel. (only in cases of large larvae population.)

Question 18

What are the symptoms of Enterobius vermicularis infection?

Answer 18

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.

Question 19

EV

How is Enterobius vermicularis diagnosed?

Answer 19

Copromicroscopal examination of the faeces, perianal scrapings, swabs under nails.
Sellotape

Question 20

EV

What prophylactic measures can be taken when dealing with Enterobius vermicularis?

Answer 20

Trim fingernails, wear cotton clothes and gloves during sleep, frequent washing of hands and bed sheets etc.

Question 21

EV

Where do adult pinworm/threadworms reside in the body?

Answer 21

Upper colon
Small ulcerations can occur at the site of attachment, resulting in haemorrhages and secondary infections. Can cause nonspecific colitis in children.

Question 22

EV

What is ectopic infection and how can it cause problems?

Answer 22

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.

Question 23

What is the drug of choice for the treatment of Enterobius vermicularis?

Answer 23

Mebendazole is a benzimidazole
In children over 6 months
Given as a single dose, can be repeated after 2 weeks if reinfection occurs

Question 24

What is Trichiuris trichiura?

Answer 24

Whip worm (head tiny, posterior extremity (eggs released) larger)

Question 25

TT | In what countries is Trichuris trichiura most common?

Answer 25

Tropic humid areas with inadequeate sanitation (there is no transmission in arid areas)

Question 26

TT | Where does Trichuris trichiura worm reside?

Answer 26

In the caecum, (upper colon) where they remain attached to the epithelium by burrowing into epithelial folds / tunnel.

Question 27

TT | How is Trichuris trichiura infection diagnosed?

Answer 27

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.

Question 28

TT | What are the symptoms of Trichuris trichiura?

Answer 28

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.

Question 29

TT | What determines the pathology of Trichuris trichiura?

Answer 29

Strongly associated with worm load.

Question 30

TT | What is Trichuris dysentery syndrome (TDS): associated with heavy infections?

Answer 30

Resembles dysentery caused by other pathogens e.g. some enteric bacteria and Entamoeba histolytica.

Question 31

TT | What is the drug of choice in the treatment of Trichuris trichiura?

Answer 31

Mebendazole is a benzimidazole | It is contraindicated in pregnancy or if patients are allergic.

Question 32

AL | What is Ascaris lumbricoides?

Answer 32

Giant worm

Question 33

AL | What length can Ascaris lumbricoides grow?

Answer 33

20-35cm

Question 34

AL | Where do eggs devlelop?

Answer 34

Outside of the host and for long phases

Question 35

AL | Female power

Answer 35

200,000 eggs per day

Question 36

AL | What is Ascaris suum?

Answer 36

Pig worm

Question 37

AL | How to pig roundworm (Ascaris suum) eggs develop?

Answer 37

Identical to human roundworm but can't infect humans 1. immature outer sticky shell 2. immature egg without the sticky shell, naked 3. mature embryonated egg (live worm inside, if ingested, infected.)

Question 38

AL | How is Ascaris lumbricoides diagnosed?

Answer 38

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

Question 39

AL | What are the symptoms of Ascaris lumbricoides infection?

Answer 39

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

Question 40

AL | What is Löffler syndrome?

Answer 40

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.

Question 41

AL | What is intestinal obstruction or intussusception?

Answer 41

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.

Question 42

AL | How is Ascaris lumbricoides treated? Drug of choice? Mechanism of action?

Answer 42

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.

Question 43

AL | What is Levamisole?

Answer 43

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.