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LSHTM > Intestinal nematodes > Flashcards

Intestinal nematodes Flashcards

1
Q

Enterobius vermicularis - distribution

A

Temperate > tropical countries
Broadest geographic range of any helminth
Common in school-aged children

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2
Q

Enterobius vermicularis - number of cases worldwide

A

300 million

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3
Q

Enterobius vermicularis - transmission

A

Eggs directly infectious - faecal-oral
[Not soil transmitted]

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4
Q

Enterobius vermicularis - lifecycle

A

Simple direct life cycle
Ingestion of eggs
Eggs hatch in small intestine
larvae move to large intestine - mature into adults [2-6 weeks]
Adults in lumen of caecum and sexually reproduce
Female lays eggs around anus nightly

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5
Q

Enterobius vermicularis - eggs

A

In cross-section = lateral alae
50-60um
Elongated/oval shape
Double wall

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6
Q

Enterobius vermicularis - clinical features

A

Pruritis ani
Disturbed sleep, loss of apetite

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7
Q

Enterobius vermicularis - diagnosis

A

Adults sometimes seen on surface of stool
Eggs found by tape method

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8
Q

Enterobius vermicularis - treatment

A

Single dose:
-Mebendazole
-Albendazole
-Pyrantel [kills adults]

Reinfection common - treatment repeated after 2-4 weeks

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9
Q

Trichuris trichiura [whipworm] - distribution

A

More common in tropical countries
Highest prevalence in Africa, Latin America, SE Asia
Peak prevalence in children

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10
Q

Trichuris trichiura [whipworm] - number infected

A

1 billion infected
100,000 significant disease
Low mortality

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11
Q

Trichuris trichiura [whipworm] - adult worms

A

2-5cm long
Whip-like appearance

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12
Q

Trichuris trichiura [whipworm] - lifecycle

A

Ingestion of embryonated egg
Larvae hatches in small intestine - develop into adults in 8 weeks
Adults - caecum and ascending colon - live >2 years
Male and females mate - females produce eggs
Eggs in environment:
-Need shade and moisture to become infective in soil = 2weeks at 30c, up to 6 months at 15c
-Eggs remain infective for 12 months

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13
Q

Trichuris trichiura [whipworm] - transmission

A

Ingestion of eggs

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14
Q

Trichuris trichiura [whipworm] - clinical features

A

Worms burrow into mucosal epithelium causing small haemorrhages and inflamamtion

Abdominal discomfort

Heavy infection:
-Oedematous vascularised mucosa
-Haemorrhage - can cause anaemia
-Damage to mucosa - increased risk of bacterial infection or invasion of E histolytica
-Diarrhoea
-Rectal prolapse

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15
Q

Trichuris trichiura [whipworm] - diagnosis

A

Eggs in stool by:
-Direct smear/direct wet mount
-Kato Katz thick smear

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16
Q

Trichuris trichiura [whipworm] - eggs

A

Lemon shaped
50-55um
Translucent polar plugs
Smooth yellow brown colour [stained by bile]
‘tea tray’

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17
Q

Trichuris trichiura [whipworm] - treatment

A

Benzimidazole or oxantel

18
Q

Ascaris lumbricoides - distribution

A

Common in tropics and temperate regions with adequate moisture
Peak prevalence in children
1.5 billion infections worldwide

19
Q

Ascaris lumbricoides - adult worms

A

15-40cm
Live 1 year on average
Female = 20-40cm
Males = 15-30cm [posterior end is tightly curled]

20
Q

Ascaris lumbricoides - lifecycle

A

Infestion of infective egg
Larvae hatch in small intestine
Larvae [L3 larvae] penetrate intestinal wal and enter circulation - migrate to lungs
Ascend bronchial tree and swallowed into GI tract
Develops into adult worm in small intestine
Male and female mate - producing eggs [9-10 weeks after ingestion] = 200,000 eggs/day/worm
Unsegmented egg in soil embryonates to L2/3 infective stage = in 2 weeks at 30c
Eggs are very resistant to dessication, can survive 8 years in environment

21
Q

Ascaris lumbricoides - clinical

A

Lungs = Loeffler’s
Intestine = abdominal discomfort, diarrhoea, malabsorption
Rarely - intestinal obstruction

Ectopic infection - wandering worms = appendix, bile ducts, pancreatic ducts

22
Q

Ascaris lumbricoides - diagnosis

A

Eosinophilia 10%
Stool OCP

23
Q

Ascaris lumbricoides - egg appearances

A

Fertile egg ‘corticated’:
-45-75um
-Knobbly surface
-Double wall

Fertile egg ‘decorticated’:
-Smooth surface
-Double wall

Infertile egg:
-Oval
-80-85um
-Dark and knobbly

24
Q

Ascaris lumbricoides - treatment

A

Benzimidazoles = albendazole, mebendazole

Can be used with piperazine = causes flaccid paralysis reducing risk of obstruction

25
Q

Hookworms [necator americanus/ancylostoma duodenale] - distribution

A

Warm moist climates - limited by humidity and temperature requirements [23-28c] of infective stages

1.3 billion infection with 60,000 feaths = mortality mainly in infants

Necator most common = across tropical belt
Ancylostoma = SE Asia and North african

26
Q

Hookworms [necator americanus/ancylostoma duodenale] - adult worms

A

1cm

Lifespan:
-Necator = up to 10 years
-Ancylostoma = up to 5 years

Buccal capsule:
-Necator = 2 cutting blades
-Ancylostoma = 2 pairs of cutting teeth

27
Q

Hookworms [necator americanus/ancylostoma duodenale] - lifecycle

A

Filariaform larva penetrates skin using an elastase and enter circulation
Ascend bronchial tree in lungs until swallowed into intestine
Adult male and females in small intestine - female release eggs
Eggs hatches in soil in 24-48hrs at 25c
L1 rhabditiform larvae feeds on bacteria - L2 - L3 [infective after 8-10 days]
-Lives few weeks, does not feed

28
Q

Hookworms [necator americanus/ancylostoma duodenale] - transmission

A

Penetration of unbroken skin
Oral infestion on unwashed vegetation [more common with ancylostoma]

29
Q

Hookworms [necator americanus/ancylostoma duodenale] - eggs

A

6pum
Delicate wall - thin wall

30
Q

Hookworms [necator americanus/ancylostoma duodenale] - how to distinguish from strongyloides stercoralis L1 larvae

A

Stool:
-Fresh hookworm stool has eggs - but old stool may have hatched L1
-Fresh strongyloides stool - contains L1 larvae

Buccal invagination:
-Hookworm = long buccal invagination
-Strongyloides = short buccal invagination

31
Q

Hookworms [necator americanus/ancylostoma duodenale] - clinical

A

Skin - pruritusm erythematous papules

Lungs - dry cough, Loefflers - 1-2 weeks post-exposure

GI - blood loss causes anaemia and hypoalbuminaemia
Ancylostoma = 150ul/worm/day
Necator = 50ul/worm/day

32
Q

Hookworms [necator americanus/ancylostoma duodenale] -diagnosis

A

Clinical - abdominal discomfort, anaemia, eosinophilia

Eggs in feces

33
Q

Hookworms [necator americanus/ancylostoma duodenale] - treatment

A

Benzimidazoles - albendazole, mebendazole

Iron therapy for anaemia

34
Q

Strongyloides stercoralis - distribution

A

Worldwide - but most common in warm moist climates
Prevalence generally increases with age
Can be fatal in immunocompromised patients

35
Q

Strongyloides stercoralis - adult worms

A

Only female worms found in humans
Small 2mm
Females reproduce parthenogenetically - asexual reproduction

36
Q

Strongyloides stercoralis - lifecycle

A

Direct lifecycle:
-Parthenogenetic female in small intestine produce eggs which immediately hatch to L1 rhabditiform larva
-1-4 days in soil develop to L3 filariform larva
-L3 larvae penetrate skin
-Undergoes heart-lung migration and swallowed into gut

Indirect [heterogonic] lifecycle:
-Adult female in small intestine produce eggs which immediately hatch to L1 rhabditiform larva
-Develop into male and female free-living adults in soil
-mate and exchange genetic material
-Female hatches L1 larvae - eventually dvelop into L3

37
Q

Strongyloides stercoralis - autoinfection

A

Internal autoinfection:
-Precocious development of L1 to L3 within the gut and L3 invasion of gut mucosa

External autoinfection:
-L3 in faeces contaminating perianal regions can penetrate the same host

38
Q

Strongyloides stercoralis - hyperinfection syndrome

A

Cases can occur following immunosuppressive therapy - notably steroids

2 predisposing factors = steroids, Human T-lymphotropic virus type 1 infection [HTLV-1]

Clinical features:
-Lung = respiratory distress, pulmonary haemorrhage

-Intestine = submucosal damage = oedematous mucosa, ulceration and bacteria - gram negative bacterial sepsis

39
Q

Strongyloides stercoralis - clinical features

A

Skin:
-initial penetration = itchy dermatitis
-Autoinfecting L3 = larva currens [10cm/hr] - highly pruritic

Lung:
-Loefflers

Intestine:
-Acute phase = upper abdominal pain, diarrhoea, mucous, high eosinophilia
-Chronic phase = asymptomatic, chronic colitis, raised total serum IgE, eosinophilia lower than acute phase

40
Q

Strongyloides stercoralis - diagnosis

A

Serial stool examinations [excretion of larvae is intermittent and at a low level]

Direct faecal smear
Culture methods = charcoal culture, nutrient agar plate
Immunodiagnosis = serology [cross-react with other helminth]

41
Q

Strongyloides stercoralis - treatment

A

Ivermectin = 1st line
Albendazole = 2nd line

LSHTM (47 decks)

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