Summary
The use of a concentration method by clinical laboratories is essential to increase the sensitivity of finding ova, cysts and larvae in faecal specimens as they may be too scanty to be seen by direct microscopy. The Ridley-Allen modified formol ether sedimentation technique is the method of choice for routine use by most clinical laboratories. This procedure utilises filtration of a faecal suspension followed by solvent extraction and centrifugation. It requires several pieces of apparatus and can present potential COSHH problems.
Parasep, a commercial kit for faecal concentration, developed by the company Intersep, is an enclosed, single use disposable system which minimises the pieces of apparatus used and is a less hazardous procedure of comparable efficiency to the standard method.
A comparison between the open and enclosed systems using ether or ethyl acetate with Triton-X as the solvent extraction gave a similar recovery of parasites and negligible interference in the amount of debris present in the deposit. There was, however, a significant increase in the recovery of certain parasites namely Taenia species and Hymenolepis nana, and in some specimens stored in 10% formalin at 4°C containing ova of Ascaris lumbricoides and Toxocara canis, when ethyl acetate was used.