A field evaluation of formalin–gasoline technique in the concentration of stool for detection of intestinal parasites

Abstract

A field evaluation of the formalin-gasoline procedure to detect parasite ova, cysts, or larvae from 470 fecal specimens (comprising both fresh and formalin-preserved stool samples) was compared with that of the formalin-ether sedimentation technique. Parallel concentrates with diethyl ether and gasoline were prepared for each specimen, and the species and appearance of recovered parasite species were determined. Of 470 total specimens, 206 (43.83%) were found to be positive for parasites in one or both concentration techniques. Gasoline was comparable to diethyl ether in the recovery of parasite eggs, cysts, and larvae, so that the formalin-gasoline and the formalin-diethyl ether sedimentation techniques detected 165 and 156 positive of total specimens, respectively. In this study, gasoline proved to be as good as diethyl ether in concentrating parasite eggs and cysts, as well as in maintaining characteristic morphology. However, gasoline was considerably superior to diethyl ether in detecting larvae of Strongyloides stercoralis. Parallel examination of total stool samples by the routine formalin-ether (original) and by the formalin-gasoline techniques resulted in identical distribution of positive slides and morphology of recovered parasite species. However, the easy availability of gasoline (wherever gas stations are present) and its low cost in comparison to ether makes gasoline superior to ether for use in concentration of stools by the sedimentation method in laboratories, including laboratories with limited material resources and also laboratories present in small cities and rural health centers.