Influence of refrigeration and formalin on the floatability of Giardia duodenalis cysts

Giardia duodenalis cysts obtained from fresh fecal samples, fecal samples k ept under refrigeration and fecal samples treated with formalin were studie d as to their floatability on sucrose solutions with the following specific gravities: 1,040 kg/m(3); 1,050 kg/m(3); 1,060 kg/m(3); 1,070 kg/m(3); 1,0 80 kg/m(3); 1,090 kg/m(3); 1,100 kg/m(3); 1,150 kg/m(3); 1,200 kg/m(3); and 1,250 kg/m(3), contained within counting-chambers 0.17 mm high. Cysts that floated on and those settled down as sediments were counted, and had their percentages estimated. Sucrose solutions of 1,200 kg/m3 specific gravity ( the average specific gravity of diluting liquids employed in floatation tec hniques) caused to float 77.7%, 78.4% and 6.6% of the G. duodenalis cysts o btained, respectively, from fresh fecal samples, fecal samples kept under r efrigeration, and fecal samples treated with formalin. Cysts obtained both from fresh fecal samples and fecal samples kept under refrigeration present ed similar results concerning floatability. It was observed, however, that the treatment of feces with formalin diminished the cysts floatability unde r the various specific gravities studied. This results should influence, th e recommendations for transport and storage of fecal samples used for paras itological coproscopy.