Faeces - ova, cysts and parasites

Last updated: Sunday, 21, May, 2006

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Item Process
Specimen

Fresh faeces; a single specimen of diarrhoeal stool is adequate for the detection of commonly occurring protozoal infections, a second specimen may be required if infection with helminths (worms) is suspected.

Investigation for amoebic colitis requires the immediate examination of mucosal scrapings or secretions, freshly obtained at endoscopy.

Sticky tape preparation from perianal skin for Enterobius vermicularis.

Examination for microsporidia must be specifically requested.

Method

Microscopy (wet film, special stains) for protozoa (trophozoites and cysts), helminths and ova.

EIA for some organisms eg, Giardia intestinalis, Cryptosporidium.

Culture for hookworm and Strongyloides stercoralis (only if specifically requested).

Macroscopic and histological identification of complete worms.

Application

Investigation of persistent or severe diarrhoea or colitis, especially in immunosuppressed patients.

Investigation of unexplained anaemia or significant eosinophilia.

Occasionally useful in patients with unexplained perineal pruritus.

Interpretation

Presence of white or red cells is significant and indicates mucosal inflammation.

Diagnosis of amoebic colitis requires the presence of Entamoeba histolytica trophozoites containing ingested red cells.

Detection of cysts of Entamoeba histolytica/dispar may represent asymptomatic carriage of the organism.

Cysts or trophozoites of Giardia intestinalis confirm a diagnosis of giardiasis.

Oocysts of Cryptosporidium sp and microsporidia can be identified with special staining techniques; their presence may indicate active infection or carriage.

The presence of characteristic ova can identify infection with:
hookworms and other roundworms (nematodes) eg, Enterobius vermicularis in sticky tape preparations, Ascaris lumbricoides;
flat flukes (trematodes) eg, Fasciola hepatica, Clonorchis sinensis;
tape worms eg, Taenia saginata, Taenia solium.

Occasionally complete worms are passed, enabling specific identification of the adult worm.

Reference

Hines J and Nachamkin I. Clin Infect Dis 1996; 23: 1292-1301.