Intestinal nematodes Flashcards
Enterobius vermicularis - distribution
Temperate > tropical countries
Broadest geographic range of any helminth
Common in school-aged children
Enterobius vermicularis - number of cases worldwide
300 million
Enterobius vermicularis - transmission
Eggs directly infectious - faecal-oral
[Not soil transmitted]
Enterobius vermicularis - lifecycle
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
Enterobius vermicularis - eggs
In cross-section = lateral alae
50-60um
Elongated/oval shape
Double wall
Enterobius vermicularis - clinical features
Pruritis ani
Disturbed sleep, loss of apetite
Enterobius vermicularis - diagnosis
Adults sometimes seen on surface of stool
Eggs found by tape method
Enterobius vermicularis - treatment
Single dose:
-Mebendazole
-Albendazole
-Pyrantel [kills adults]
Reinfection common - treatment repeated after 2-4 weeks
Trichuris trichiura [whipworm] - distribution
More common in tropical countries
Highest prevalence in Africa, Latin America, SE Asia
Peak prevalence in children
Trichuris trichiura [whipworm] - number infected
1 billion infected
100,000 significant disease
Low mortality
Trichuris trichiura [whipworm] - adult worms
2-5cm long
Whip-like appearance
Trichuris trichiura [whipworm] - lifecycle
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
Trichuris trichiura [whipworm] - transmission
Ingestion of eggs
Trichuris trichiura [whipworm] - clinical features
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
Trichuris trichiura [whipworm] - diagnosis
Eggs in stool by:
-Direct smear/direct wet mount
-Kato Katz thick smear
Trichuris trichiura [whipworm] - eggs
Lemon shaped
50-55um
Translucent polar plugs
Smooth yellow brown colour [stained by bile]
‘tea tray’
Trichuris trichiura [whipworm] - treatment
Benzimidazole or oxantel
Ascaris lumbricoides - distribution
Common in tropics and temperate regions with adequate moisture
Peak prevalence in children
1.5 billion infections worldwide
Ascaris lumbricoides - adult worms
15-40cm
Live 1 year on average
Female = 20-40cm
Males = 15-30cm [posterior end is tightly curled]
Ascaris lumbricoides - lifecycle
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
Ascaris lumbricoides - clinical
Lungs = Loeffler’s
Intestine = abdominal discomfort, diarrhoea, malabsorption
Rarely - intestinal obstruction
Ectopic infection - wandering worms = appendix, bile ducts, pancreatic ducts
Ascaris lumbricoides - diagnosis
Eosinophilia 10%
Stool OCP
Ascaris lumbricoides - egg appearances
Fertile egg ‘corticated’:
-45-75um
-Knobbly surface
-Double wall
Fertile egg ‘decorticated’:
-Smooth surface
-Double wall
Infertile egg:
-Oval
-80-85um
-Dark and knobbly
Ascaris lumbricoides - treatment
Benzimidazoles = albendazole, mebendazole
Can be used with piperazine = causes flaccid paralysis reducing risk of obstruction
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
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
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
Hookworms [necator americanus/ancylostoma duodenale] - transmission
Penetration of unbroken skin
Oral infestion on unwashed vegetation [more common with ancylostoma]
Hookworms [necator americanus/ancylostoma duodenale] - eggs
6pum
Delicate wall - thin wall
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
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
Hookworms [necator americanus/ancylostoma duodenale] -diagnosis
Clinical - abdominal discomfort, anaemia, eosinophilia
Eggs in feces
Hookworms [necator americanus/ancylostoma duodenale] - treatment
Benzimidazoles - albendazole, mebendazole
Iron therapy for anaemia
Strongyloides stercoralis - distribution
Worldwide - but most common in warm moist climates
Prevalence generally increases with age
Can be fatal in immunocompromised patients
Strongyloides stercoralis - adult worms
Only female worms found in humans
Small 2mm
Females reproduce parthenogenetically - asexual reproduction
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
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
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
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
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]
Strongyloides stercoralis - treatment
Ivermectin = 1st line
Albendazole = 2nd line
