helminths in faeces
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Helminths in faeces
General considerations
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Parasitic Disease
Number of Infections(millions)
Morbidity (%)
Mortality(number)
(%)
Ascariasis 1,472 23 60,0000.004
Hookworm infections 1,298 12 65,000
0.005Lymphatic filariasis 120 37
Onchocerciasis 18 4.2 45,0000.25
Schistosomiasis 200 10 20,0000.01
Trichuriasis 1,049 21 10,0000.001
Courtesy The Ohio State University
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Bethony J. et al. 2006. Lancet 367:1521-1532.
Soil-transmitted helminth infections: ascariasis, trichuriasis, and
hookworm
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Bethony J. et al. 2006. Lancet 367:1521-1532.
• Ascaris lumbricoides• Trichuris trichiura• Necator americanus and
Ancylostoma duodenale• Strongyloides stercoralis• Enterobius vermicularis• Toxocara canis and
Toxocara cati
• 807-1221 x 106
• 604-795 x 106
• 576-740 x 106
• 30-100 x 106
• 4-28% of children• 2-80% of children
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Bethony J. et al. 2006. Lancet 367:1521-1532.
High worldwide prevalence, except Europe, North America, Australia,
and Japan
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Helminths: morbidity (%) mortality (n)
Ascaris lumbricoides Ancylostoma-Necator Onchocerca volvulus Schistosoma spp. Trichuris trichiura
23 60 000 12 65 000 4.2 45 000 10 20 000 21 10 000
www.biosci.ohio-state.edu/∼parasite/morbidity.html
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Helminths in faeces
• Adult worms (Ascaris lumbricoides, Enterobius vermicularis,...), fragments of worms (proglottids of Taenia saginata,...).
• Eggs and larvae.
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Ascaris lumbricoides Adult male worm, with a curved tail (Unstained).
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Ascaris lumbricoides Adult worm (Unstained).
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Ascaris lumbricoides
Fertile bile-stained egg with a thick, mammillated shell, measuring 55-75 μm (Unstained).
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Strongyloides stercoralis
First stage rhabditoid larva in faeces. The lenght varies from 180 to 380 μm (Unstained).
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Eggs of helminths (worms) in faeces
• Eggs with an operculum: trematodes.
• Eggs with a spine: schistosomes.
• Eggs having hooklets (hexacanth larva of Taenia saginata): cestodes.
• Eggs sometimes containing a larva: nematodes or roundworms.
• Size is essential for identification.
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Ocular micrometer disk
• Each objective must be calibrated with reference material.
• Can be roughly checked with a counting chamber, with RBCs ...
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Courtesy Ash L.R. & Orihel T.C.
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Courtesy CDC
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Concentration procedures
• Are base on differences in specific gravities
• Two most commonly used methods:
– zinc sulfate flottation method
– formalin-ether sedimentation method
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Formalin-Ethyl Acetate (Ether)
Sedimentation Concentration (Modified
Ritchie-Method)
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Specific gravities
• S.G. of Zn-sulfate 33 %: 1.180• S.G. of formol-solution 10 %: 1.019• S.G. of ether: 0.714• S.G. of parasites: Ancylostoma 1.055; Giardia
1.060; Entamoeba histolytica (coli) and Endolimax nana 1.065 - 1.070; Ascaris 1.110; Trichuris 1.150, Chilomastix mesnili 1.180; Ascaris (unfertilized) 1.200 (Bailenger, 1965).
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Editorial Commentary
• One or multiple (three) specimens tested.• Lack of clear evidence.• If testing is worth doing it is worth doing
well.
Jon. E. Rosenblatt. 2006. CID. 42:979-980.
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Estimation of worm burdens through egg counts
• Direct fecal smear of 2 mg (Beaver)• Number of adult worms correlated to
number of eggs present Ascaris lumbricoides 1/2 Trichuris trichiura 10 Ancylostoma duodenale 5 Necator americanus 10 to 20
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Eosinophilia > 10%With helminths,insects (myasis),
not with protozoa excepting Isospora belli and Dientamoeba
fragilis (with pinworms?)
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Charcot-Leyden
Crystals
associated with
eosinophils
found in faeces
or sputum
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Charcot-Leyden
Crystals
associated with
eosinophils
found in faeces
or sputum
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Auto-infectiousEnterobius vermicularis
Hymenolepis nana
Strongyloides stercoralis