Diagnosic Dilemma No. 18 

Contributors: Emeritus Professor John Goldsmid, University of Tasmania

As part of a routine screening of recently arrived refugees for intestinal parasites, faecal samples were sent to the laboratory. Five of the refugees were found to be passing what were initially identified as “hookworm” eggs:
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Fig. 18.1 - Egg from patient 1 (from Sri Lanka) Egg size 60 x 45 µm
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Fig. 18.2 - Egg from patient 2 (from Viet Nam) Egg size 65 x 40 µm
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Fig. 18.3 - Egg from patient 3 (from Democratic Republic of Congo) Size 52 x 35 µm
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Fig. 18.4 - Egg from refugee 4 (from Zimbabwe) Size 80 x 50 µm
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Fig. 18.5 - Eggs from refugee 5 (from Fiji) Size 62 x 44 µm

Question 1: What would be your identification of the eggs from patients 1-5 be?

The photomicrographs in Fig 6 may prove helpful:
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Fig 18.6: Hookworm-like eggs found in human faeces
a = hookworm; b = Ternidens deminutus; c = Trichostrongylus sp; d = Strongyloides fuelleborni

What is your diagnosis?


Patients 1 & 2: This egg is probably a hookworm egg. These eggs normally range in size between about 56-70 x 35-50 µm. The species of hookworm (Necator americanus or Ancyostoma duodenale) cannot be determined from the egg. (Note: Eggs of Oesophagostomum spp cannot be differentiated from those of the hookworms)

Patient 3: This small egg, passed fully developed with a motile larva inside, is probably a Strongyloides fuelleborni egg. These eggs of this species range in size between about 52 - 58 x 35 µm.

Patient 4: The egg passed by this patient falls into a range of about 75 – 85 x 46 – 55 µm. This size range is usually shown by Ternidens deminutus, (also known as the false hookworm as it is often misdiagnosed by laboratory staff as ”hookworm”)

Patient 5: The eggs passed by this refugee are also consistent with the eggs of the hookworm species.

Question 2

The faecal specimens from the 5 patients who were found to be passing “hookworm-like” eggs were further investigated using the Harada-Mori faecal culture technique to elucidate the species of nematode involved. The cultures (1 – 5) are shown in Fig 18.7.
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Fig. 18.7 - Harada-Mori cultures of specimens 1 - 5

After 10 days, the water at the base of the tubes was examined microscopically for filariform larvae of hookworm-like species. Of the 5 cultures, cultures 1,2 and 5 revealed sheathed filariform larvae approx. 600 µm in length as shown in Fig. 18.8:
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Fig. 18.8 - Filariform (infective) larva culture of a specimen provided by patients 1,2 and 5
(Photograph courtesy of McGill University, Canada)

Culture 3 revealed unsheathed larvae approx 500 µm in length with a notched tail as seen in Fig 18.9, but in addition showed free-living adult nematodes as shown in Fig 18.10:
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Fig. 18.9 - Posterior end of larva found in culture of a specimen provided by patient 3
(Photograph courtesy Assoc Prof John Frean, NICD, South Africa)
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Fig. 18.10 - Free-living adult female worm found in culture of a specimen provided by patient 3

Culture 4 revealed sheathed filariform larvae approx 680 µm in length as seen in Fig 18.11
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Fig. 18.11 - Filariform Larva seen in culture of specimen provided by from patient 4

Culture 5 revealed filariform larvae like those shown in Fig 8 but also motile organisms about 400 µm in length, as shown in Fig 18.12
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Fig. 18.12 - Motile organism seen in culture of specimen provided by from patient 5
(Photograph courtssy Assoc Prof Wayne Melrose, James Cook University, Australia)

Question 2:
Given the Hirada Mori culture results above, what would you identifications now be?

The chart below may prove helpful;
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Fig. 18.13:Morphology of infective larvae found in Harada-Mori cultures.
Ad – Ancylostoma duodenale; Na – Necator americanus; T - Trichostrongylus spp; Ss – Strongyloides spp a – post end of S. stercoralis; b - post end of S. fuelleborni; Td – Ternidens deminutus; Rh – Rhabditis (Rhabditella) spp; O sp - Oesophagostomum spp. n – nerve ring; g – genital pore; j - buccal canal junction; mh – mouth spicule


Question 2:
The results of the Harada-Mori larval culture technique, allow a more definitive diagnosis:

Patients 1,2 and 5: Are all confirmed as being infected with hookworm. Careful examination of the larval morphology can allow a species differentiation between A. duodenale and N. americanus.
Patient 3: Confirmed as being infected with Strongyloides as seen by the unsheathed larva with a notched tail. The free-living adult female seen allows confirmation of the species as S. fuelleborni, having the characteristic shape with a constricted waist.
Patient 4: This patient is confirmed by culture from the filariform larva, to be infected with False Hookworm; Ternidens deminutus, which can be identified from the chart provided (Fig 18.13) as “Td”. It is identifiable by the “zigzag” gut and the relatively short tail of the sheath and can be differentiated from the filariform larva of Oesophagostomum (O sp) which has a long tail to the sheath and the shorter tail as seen in Trichostrongylus filariform larvae.
Patient 5: As well as finding hookworm larvae in culture 5, the motile organism seen in the culture 5 is a rotifer – a free-living metazoan varying in length between 200 – 500 µm and found in pools and occasionally as a contaminant in faecal cultures. (However, see Diagnostic Dilemma 10 of this series) It requires no treatment.

I should like to thank the following:
Fig. 18.8 Hookworm filariform larva – courtesy McGill University, Canada.
Fig 18.9 Strongyloides fialriform larva – courtesy Dr John Frean.
Fig 18.12 Rotifer – courtesy Dr Wayne Melrose.

Goldsmid, J.M. The African ‘hookworm’ problem : an overview. In: Parasitic Helminths and Zoonoses in Africa. Eds Macpherson, CNL and Craig, PS, Unwin Hyman . London. 1991. pp 101 – 130.

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