Helminths in faeces

General considerations

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

Bethony J. et al. 2006. Lancet 367:1521-1532.

Soil-transmitted helminth infections: ascariasis, trichuriasis, and

hookworm

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

Bethony J. et al. 2006. Lancet 367:1521-1532.

High worldwide prevalence, except Europe, North America, Australia,

and Japan

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

Helminths in faeces

• Adult worms (Ascaris lumbricoides, Enterobius vermicularis,...), fragments of worms (proglottids of Taenia saginata,...).

• Eggs and larvae.

Ascaris lumbricoides Adult male worm, with a curved tail (Unstained).

Ascaris lumbricoides Adult worm (Unstained).

Ascaris lumbricoides

Fertile bile-stained egg with a thick, mammillated shell, measuring 55-75 μm (Unstained).

Strongyloides stercoralis

First stage rhabditoid larva in faeces. The lenght varies from 180 to 380 μm (Unstained).

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.

Ocular micrometer disk

• Each objective must be calibrated with reference material.

• Can be roughly checked with a counting chamber, with RBCs ...

Courtesy Ash L.R. & Orihel T.C.

Courtesy CDC

Concentration procedures

• Are base on differences in specific gravities

• Two most commonly used methods:

– zinc sulfate flottation method

– formalin-ether sedimentation method

Formalin-Ethyl Acetate (Ether)

Sedimentation Concentration (Modified

Ritchie-Method)

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).

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.

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

Eosinophilia > 10%With helminths,insects (myasis),

not with protozoa excepting Isospora belli and Dientamoeba

fragilis (with pinworms?)

Charcot-Leyden

Crystals

associated with

eosinophils

found in faeces

or sputum

Charcot-Leyden

Crystals

associated with

eosinophils

found in faeces

or sputum

Auto-infectiousEnterobius vermicularis

Hymenolepis nana

Strongyloides stercoralis