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*B33VPI - Biology & Physiology > Common Nematode Infections > Flashcards

Common Nematode Infections Flashcards

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1
Q

What are flatworms also known as? Where do they classify re. Taxonomy?

A
  • Platyhelminths

- Flatworms are the Phylum (one below Kingdom - Animals)

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2
Q

What taxonomic categories are there?

A
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus (capitalized)
  • Species (not capitalized)
King 
Prawn
Curry
Or 
Fat
Goose 
Soup
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3
Q

What are the characteristics of platyhelminths? (flatworms - platy = plateau = flat)

A
  • Flattened dorsoventrally (from back to front)
  • Alimentary canal (oesophagus-stomach-intestines) absent or rudimentary; don’t have a gut, feed through the skin hence flat (mainly take up glucose)
  • Suckers present
  • Hermaphrodites (mostly)
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4
Q

What are tapeworms officially known as? How are they classed re. taxonomy?

A
  • Cestodes

- They are the Class

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5
Q

What are the characteristics of the Tapeworms/cestodes? Give an example.

A
  • Tapelike, segmented
  • No alimentary canal
  • Hermaphrodites (testes + ovaries)
  • Head has hooks or suckers (to attach to intestines)
    E.g. Taenia (genus) saginata (species)
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6
Q

What are the characteristics of nematodes? What is their common name? What is their taxonomic category?

A
  • Roundworms (phylum)
  • Rounded body
  • Complete alimentary canal (mouth at posterior)
  • No suckers
  • Sexually differentiated (M/F; eggs released in faeces)
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7
Q

What are some common geohelminth nematode worm infections? What is their common name?

A
  • Enterobius vermicularis (pinworm/threadworm)
  • Trichuris trichiura (whipworm)
  • Ascaris lumbricoides (giant roundworm)
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8
Q

What is a geohelminth? What is their differential feature? How does infection occur?

A
  • Soil-transmitted helminths (STH)
  • Intestinal nematodes where development takes place outside the body
  • Infection occurs through contact w/parasite eggs or infective larvae in contaminated food, soil or water.
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9
Q

What is the most common chronic infection of humans?

A
  • STHs (soil-transmitted helminths; geohelminths)

- Predominantly in countries w/low hygienic standards

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10
Q

What is the difference between infestation and infection?

A
  • Infestation = for parasitic diseases caused by ectoparasites (ticks, lice, fleas) or worms (helminths)
  • Infection = for disease caused by bacteria, fungi, viruses, protozoa.
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11
Q

What is enterobius vermicularis commonly known as? What are some key facts?
(What is its infection called? How common? Hosts? Multiplication?)

A
  • Pinworm/threadworm (looks like cotton fibres)
  • Infection called enterobiasis
  • Most common type of worm infection in UK
  • Particularly common in children U10 (usually toddlers)
  • Humans are the ONLY hosts (can’t transmit from pets)
  • No multiplication in the body
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12
Q

What is the lifecycle for Enterobius vermicularis (pin/threadworm)?

A

1) Eggs on perianal folds; larvae inside mature within 4-6 hours to viable worm
2) Eggs are itchy; embryonated eggs ingested by human (e.g. during sleep) (faecal - oral)
»> Potentially secondary infection of perianal tissue with itching
3) Larvae hatch in the small intestine
4) Adults in lumen of cecum (beginning of colon)
5) Female gravid migrates to perianal region at night to lay eggs

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13
Q

What are the four modes of transmission for pin/threadworms/enterobius vermicularis, and how common each one is?

A

1) Direct transmission; from anal/perianal region to the mouth, by fingernail contamination, soiled night clothes (most common route)
2) Exposure to viable eggs on soiled bed linen (e.g. can breathe in eggs)
3) Contamination via mouth or nose from contaminated dust
4) Retroinfection; larvae hatch from eggs on anal mucosa, migrating up the bowel (rare, only if high infectious dose)

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14
Q

What are the symptoms of Enterobius vermicularis infection?

A

Pin/threadworm:

  • Pruritus ani; mild to acute painful itching mainly at night, resulting in scratching of perianal region. Can lead to secondary infection if skin integrity is compromised.
  • Vulvitis; inflammation of vulva (worms entering)
  • Insomnia, restlessness, loss of appetite.
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15
Q

What clinical signs do NOT present for Enterobius vermicularis infection? What are the implications?

A

There is neither:
- Anaemia (no blood feeding)
- Eosinophilia (increased eosinophils, but; no blood feed = no immune response)
»> Typical diagnostic factors for worms

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16
Q

How is diagnosis for the nematode Enterobius vermicularis (pin/threadworm) made, given there is no anaemia or eosinophilia? Official vs. non-official way?

A

By copromicroscopical examination of:

  • Faeces
  • Perianal scrapings
  • Swabs from under nails

Frequently Sellotape used in perianal region; eggs adhere to tape. Investigation on consecutive days to enhance sensitivity.

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17
Q

What prophylaxis can be taken against Enterobius vermicularis infestation?

A
  • Trim fingernails (no breaking skin)
  • Wear cotton clothes and gloves during sleep
  • Frequent washing of sheets (60 C) and hands
18
Q

What is the pathology of Enterobius vermicularis? Where do they reside?

A
  • Adult worms reside in the upper colon (caecum; where small intestine meets large)
  • Small ulcerations may develop at site of attachment, resulting in haemorrhages and secondary infections
  • Can cause nonspecific colitis in children (tummy aches)
  • Ectopic infections can cause problems (e.g. in the genital or urinary tract, liver, kidney, spleen, lung)
    »> But these are rare; worm wants to stay in gut.
19
Q

What is the treatment for Enterobius vermicularis?

A

Mebendazole (Ovex); of the benzimidazole class.

  • Well tolerated
  • For over 6 months age
  • Single dose, followed by another dose after 2 weeks (reinfection is v. common)
20
Q

What is Trichuris trichiura commonly known as? What are some key facts?
(How common? Where does it occur? Where does it reside?)

A
  • Whipworm
  • One of the most common geohelminths (500 million infected in 2010)
  • Occurs worldwide, but most prevalent in tropic, humid areas w/inadequate sanitation
  • No transmission in arid areas (dessert/arctic)
  • Resides in the caecum (like Enterobius vermicularis), BUT remain attached to the epithelium by burrowing in epithelial folds/tunnels (unlike pin/threadworm)
21
Q

What is the life cycle of Trichuris trichiura?

A

1) Unembryonated eggs passed in faeces (3,000 to 20,00 per day)
2) In the soil, eggs develop to 2-cell stage, undergoing maturation over 15-30 days (dependent on temperature/humidity, infective upon maturation)
3) Then to advanced cleavage
4) Then eggs embryonated (end of 15-30 days), and are ingested
5) Eggs hatch in the small intestine, releasing larvae
6) Mature adults in the colon (4cm in length), burrowing in the caecum and the ascending colon

22
Q

How does Trichuris trichiura (whipworm) attach itself to colon epithelium?

A
  • Trichuris’ head (anterior end) looks like a whip; real thin, allows burrowing into the intestinal epithelium
  • Posterior end is phat; the “egg factory” of the worm, with eggs in its uterus
23
Q

How is Trichuris trichiura diagnosed?

A
  • Stool examination; detection of eggs by microscopy (Kato-Katz method), where eggs have characteristic ‘lemon’ shape
  • Egg counts; reflect intensity of infection (> 10,000 eggs /g faeces = heavy infection)
  • FLOTAC; flotation chamber technique allowing detection and counting of eggs.
24
Q

What are the symptoms of Trichuris trichiura infection?

A
  • Light infection; asymptomatic
  • Heavy infection; abdominal pain, stool w/mucus, water and blood, rectal prolapse can occur (but rare, mostly in children)
  • Heavy chronic infection in children; severe anemia, growth retardation, impaired cognitive development.
25
Q

What is the pathology of Trichuris trichiura?

A
  • Pathology strongly linked w/worm load (intensity of infection); few worms = little damage
  • Trichuris dysentery syndrome (TDS) associated w/heavy infections; can resemble dysentery caused by other pathogens e.g. some enteric bacteria and Entamoeba histolytica (protozoa)
  • Mucosal damage can promote secondary infection w/other parasites e.g. Entamoeba histolytica or bacteria (e.g. Campylobacter jejuni, Salmonella typhi)
26
Q

What is the treatment for Trichuris trichiura? CIs?

A
  • Same as for Enterobius vermicularis; Mebendazole (Ovex) of the benzimidazoles.
  • CI in pregnancy and hypersensitivity.
27
Q

What are the key facts of Ascaris lumbricoides? What is its common name? How large is it? Where does it mature? Fertility? Morphology?

A
  • Known as roundworm
  • Largest nematode parasitizing the human intestine (20-35 cm)
  • Eggs have long developmental phase outside the host; 21 days at 25 degrees
  • Females have high fertility (obv cause not hermaphrodites); up to 200,000 eggs per day
  • Morphologically indistinguishable from Ascaris suum (pig), but A.suum does not infect humans.
28
Q

What is the life cycle for Ascaris lumbricoides?

A

1) Adult worms live in the lumen of the small intestine
2) Eggs passed in faeces; only fertilised eggs undergo biological development
3) Fertile eggs embryonate, becoming infective after 18 days to several weeks (optimum if moist, warm, shaded soil)
4) Ingestion of infective eggs, larvae hatch
5) Larvae invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs
6) The larvae mature further in the lungs (10 to 14 days), penetrate alveolar walls, ascend the bronchial tree to the throat
7) And are then swallowed. Upon reaching the small intestine, they develop into adult worms, 1).

29
Q

How long does it take for Ascaris lumbricoides to go from ingestion of infective eggs to oviposition by the adult female?

A

Between 2 and 3 months.

30
Q

How long can an Ascaris lumbricoides (roundworm) live for?

A

1 to 2 years.

31
Q

How is Ascaris lumbricoides infestation diagnosed?

A

Copromicroscopic detection (of the faeces) of eggs or passage of worms (dead worms)

32
Q

How is intensity of Ascaris lumbricoides infestation measured? What is defined as a heavy infection?

A
  • Through egg count using: Kato-Katz, McMaster or the newer FLOTAC method (same techniques)
  • > 50,000 eggs/g (epg) in faeces is considered heavy by WHO (as opposed to >10,000 eggs/g w/ Trichuris trichiura)
33
Q

What are the symptoms of Ascaris lumbricoides infection?

A
  • Light infection; asymptomatic
  • Symptoms during lung migration; similar to pneumonia/asthma e.g. persistent cough, SoB, wheezing
  • Intestinal symptoms (may include); severe abdominal pain, fatigue, weight loss
  • Worm can be sometimes found in vomit or stool
34
Q

What is the pathology of Ascaris lumbricoides infection?

A
  • Migrating larvae can cause damage to lungs during migration; potentially causing ‘Löffer syndrome’ (pulmonary eosinophilia) = potentially fatal
  • Larvae can migrate to brain, eyes or retina causing symptoms similar to other migrating parasites e.g. Toxocara canis
  • Adults worms cause little pathology by themselves; but can lead to intestinal obstruction or intussusception in high numbers = potentially fatal.
35
Q

What is intussusception, and which nematode can lead to it?

A
  • Condition where one part of the intestine slides into another, much like a collapsible telescope
  • Intestine blocked as a result
  • Blocks blood flow, leading to ischemia, tissue necrosis within hours, resulting in gut perforation (gut becomes leaky, bacteria enters belly) and peritonitis (inflammation of inner wall of abdomen)
  • Roundworm (Ascaris lumbricoides)
36
Q

How is Ascaris lumbricoides (roundworm) infection treated?

A
  • Mebendazole (benzimidazole); works for all nematodes

- Pyrantel Pamoate (possibly effective)

37
Q

What is Mebendazole’s mechanism of action in combatting Ascaris lumbricoides infection? Dose?

A
  • Binds to a single high affinity site on the β-subunit of tubulin, preventing microtubule infection
  • Affects parasitic functions such as glucose transport/uptake
    > 100mg tablets BD for 3 days (diff. from Enterobius vermicularis; one single dose, repeated two weeks later)
38
Q

What is transmission of nematodes usually associated with?

A

Low hygienic standards and poor sanitation

39
Q

Which nematodes can appear to be asymptomatic?

A
  • Enterobius vermicularis
  • Trichuris trichiura
  • Ascaris lumbricoides
    (All of the above, but heavy infections can lead to serious problems incl. death)
40
Q

How are nematode infections diagnosed?

A

Copromicroscopical examination of eggs (eggs in stool)

*B33VPI - Biology & Physiology (8 decks)

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