[Evaluation of a technique of sedimentation in tubes]

The efficiency of sedimentation in test tubes for the detection of eggs of Ancylostomidae, Trichuris trichiura and Ascaris lumbricoides was tested in 80 mm-high columns of fecal suspensions. Dilutions of 2.0%, 1.5% and 1.0% were tested by using samples containing, respectively, 12.5, 25.0, 50.0, 100.0, 150.0 and 200.0 eggs per gram (epg) of each helminth under study. Efficiency was evaluated in terms of frequency of positive results and eggs per slide of the sediment (0.078 ml). Both the frequencies of positive results and egg counts per slide increased with epg values, but were not apparently dependent from suspension dilutions within the range assessed. Sediments of 1.0% fecal suspensions were positive in 80.0% or more of the cases for epg values of 150.0. It is inferred that dilution values are not critical. Thus, it is not necessary to determine fecal weights or volumes instrumentally. Considering overall results, it may be concluded that 1.0% fecal dilutions should be recommended for best results both in terms transparency of the preparations and chances of recovering eggs, particularly when egg counts are low.

[The evaluation of the specific gravity of Giardia duodenalis and Entamoeba coli cysts]

Cysts of Giardia duodenalis and Entamoeba coli were observed as for floatability in sucrose solutions of different specific gravity, contained in counting-chambers of 0.17 mm height. The cysts that floated and those that sedimented were counted and then calculated the respective percentage. Floatability differences of the cysts of each species were not considerable. Solutions of specific gravity 1,200 kg/m3 made 88.49% of G. duodenalis cysts and 95.71% of E. coli cysts float. The greater values of floatability were associated to specific gravity 1,250 kg/m3 and were 89.15% and 98.59% for cysts of G. duodenalis and E. coli, respectively.

Sedimentation in parasitological coproscopy

A sedimentation technique is described, in which a fecal suspension is placed on top of an aqueous sucrose solution of specific gravity 1.015 g/cm3. Using 100 by 15 mm test tubes, duplicate gravity sedimentation experiments were made using homogenized fecal suspensions (single-columns) and fecal suspensions placed on top of clear columns (double-columns). Egg and cyst counts, and turbidity determinations were made in the sediments obtained after definite time intervals. Most Ascaris lumbricoides, Trichuris trichiura and Ancylostomidae eggs sedimented within 20 minutes in single-and between 30 and 60 minutes in double-columns. Giardia duodenalis cysts required longer periods to sediment in double-than in single-columns; after 180 minutes (the maximum period of observation), double-column sediments produced 60.0% of the counts of single-columns. Double-column sediments were consistently less turbid than single-column ones.