Fecal Sedimentation

Repeated “washing” of fecal material with water presents clean trematode eggs in a small amount of fecal debris. The “washing” is usually accomplished by mixing a large volume of water (200mls) with a small amount of faeces (5 g), letting the suspension stand for at least 10 minutes, decanting most of the supernatant, mixing more water with the sediment, and repeating the process 3-5 times. The eggs are visible in the final sediment.

• 250ml beakers
• Tea strainer or cheesecloth
• Pipette
• Petri dish
• Methylene Blue
• Dissecting microscope

1. Combine 5g of faeces with 200ml water in a 250ml beaker and mix thoroughly.
2. Filter the fecal suspension through a tea strainer or double-layer of cheesecloth into a second beaker.
3. Allow to sediment for 30 minutes.
4. Remove the supernatant very carefully with a pipette.
5. Combine sediment with 200ml water and mix thoroughly.
6. Repeat steps three to five at least 3 times until the supernatant is clear.
7. After removing the supernatant for the last time transfer the sediment to a Petri dish, add a drop of methylene blue, and examine for eggs using a dissecting microscope (the methylene blue stains the background).

There are a number of different sedimentation techniques described in the literature (e.g. ethyl acetate), as well as a commercially available kit – FLUKEFINDER® (https://flukefinder.com/). As with the other fecal examination techniques, it is possible to quantify a sedimentation.

Other than technical difficulties, the major problem with the sedimentation technique is that very small number of eggs, or eggs released sporadically by the adult parasites, may be missed, producing false negative test results.