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Intestinal nematodes Flashcards

(41 cards)

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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

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A

Benzimidazole or oxantel

18
Q

Ascaris lumbricoides - distribution

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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

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A

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

20
Q

Ascaris lumbricoides - lifecycle

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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

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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

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A

Eosinophilia 10%
Stool OCP

23
Q

Ascaris lumbricoides - egg appearances

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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

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A

Benzimidazoles = albendazole, mebendazole

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

25
Hookworms [necator americanus/ancylostoma duodenale] - distribution
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
Hookworms [necator americanus/ancylostoma duodenale] - adult worms
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
Hookworms [necator americanus/ancylostoma duodenale] - lifecycle
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
Hookworms [necator americanus/ancylostoma duodenale] - transmission
Penetration of unbroken skin Oral infestion on unwashed vegetation [more common with ancylostoma]
29
Hookworms [necator americanus/ancylostoma duodenale] - eggs
6pum Delicate wall - thin wall
30
Hookworms [necator americanus/ancylostoma duodenale] - how to distinguish from strongyloides stercoralis L1 larvae
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
Hookworms [necator americanus/ancylostoma duodenale] - clinical
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
Hookworms [necator americanus/ancylostoma duodenale] -diagnosis
Clinical - abdominal discomfort, anaemia, eosinophilia Eggs in feces
33
Hookworms [necator americanus/ancylostoma duodenale] - treatment
Benzimidazoles - albendazole, mebendazole Iron therapy for anaemia
34
Strongyloides stercoralis - distribution
Worldwide - but most common in warm moist climates Prevalence generally increases with age Can be fatal in immunocompromised patients
35
Strongyloides stercoralis - adult worms
Only female worms found in humans Small 2mm Females reproduce parthenogenetically - asexual reproduction
36
Strongyloides stercoralis - lifecycle
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
Strongyloides stercoralis - autoinfection
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
Strongyloides stercoralis - hyperinfection syndrome
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
Strongyloides stercoralis - clinical features
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
Strongyloides stercoralis - diagnosis
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
Strongyloides stercoralis - treatment
Ivermectin = 1st line Albendazole = 2nd line

LSHTM (47 decks)

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