Evaluation of the formalin-Tween concentration technique for parasitic detection

Abstract

SUMMARYThe formalin-Tween sedimentation method was compared with the formalin-ether sedimentation for parasitic detection. Of a total 297 fecal specimens examined, 72.1% were positive. The formalin-tween technique was effective for ascertaining helminths, particularly Ascaris lumbricoides, Trichuris trichiura and hookworm eggs; however it has less capability for protozoa detection. This method is simple, inexpensive, less time consuming and highly sensitive when detecting the parasitic infection, particularly when focusing on helminth eggs. KEYWORDS:Formalin-tween; Concentration; Detection; Parasite.Parasitic infections are endemic and represent a major public health problem in developing countries 5 . Detection of parasite products in fecal specimens is enhanced by the use of concentration procedures, of which formalin-ether sedimentation 7 is generally used in most clinical parasitology investigation. Not only is this technique reliable for the detection of helminth eggs, larvae and protozoan cysts, but is also thought to provide certain advantages, including less alteration to organisms and increased recovery of Schistosoma and operculated eggs 8 . However, the use of diethyl ether, an essential reagent of this technique, may be hazardous to laboratory personnel, since it is explosive, of potential toxicity such as respiratory irritation, and a cause of cardiovascular depression and narcosis 2,9 . Moreover, it may yield residues of mutagenic peroxides in Salmonella typhimurium strains TA100 and TA102 3 . Therefore, a replacement for diethyl ether has been sought for this technique. YOUNG et al. 9 introduced ethyl acetate as a replacement. Even though ethyl acetate appeared to be an effective reagent for concentrating parasite organisms as well as in maintaining characteristic morphology, the formalin-ethyl acetate method also had some drawbacks. The thickest interface plugs of ethyl acetate were difficult to remove and they sometimes remixed with the concentrated sediment. In addition, they included a confluence of small liquid bubbles, probably composed of remaining insoluble ethyl acetate under the cover slips, or they obscured small parasite organisms 4 .Recently, an alternative sedimentation procedure was reported 6 . A locally common dish-washing detergent was used to replace diethyl ether in this formalin-detergent method, and it gave a slightly better result than the formalin-ether procedure. This method, however, required an overnight sedimentation time and the amount of fine precipitate in the sediment concealed parasite observation. Thus, the other stronger surfactants may help in shortening the procedure and reducing these fine particles. Herein, we developed the formalin-tween sedimentation technique for the detection of parasites in the stool.A total of 297 freshly passed fecal specimens were received from hill-tribe students of the Somdet Prabhudhachinnawong School, SanSai District of Chiang Mai Province, northern Thailand. All specimens were kept in refrigerator set at 4 o C for not more than 7...

Comparing the efficiency of four diagnostic concentration techniques performed on the same group of intestinal parasites

“…As in the present study, previous reports showed that the FTC and FAC techniques are able to detect common human helminth ova including H. nana and A. lumbricoides with an equal or higher sensitivity than currently more widely used methods, such as FEC technique. 9,11,12 This might support the idea that FAC and/or FTC method is generally recommended for the diagnosis of helminth infection including ova of A. lumbricoides and H. nana.…”

“…Our results reinforce those of studies that demonstrate the accuracy achieved by associating the FTC, FGC and FAC techniques in detection of positivity of intestinal parasites. [9][10][11][12] There were differences in recovery of the numbers of positive samples by each technique, however, they varied considerably from one species to another. In this study, all techniques revealed the same intestinal parasite species (E. coli, G. lamblia, A. lumbricoides, H. nana), whereas the FTC and FAC techniques were more sensitive than the FEC and FGC techniques for diagnosing helminth species ova especially more likely to correctly identify H. nana, and the differences were statistically significant.…”

“…7,8 Although several diagnostic methods such as formalin-acetone concentration (FAC), formalin-gasoline concentration (FGC), and formalin-tween concentration (FTC) techniques are available, formalin-ether concentration (FEC) technique is used as a reliable diagnostic method for helminth eggs, larvae, and protozoan cysts in stool specimens for many laboratories in different parts of the world. [9][10][11][12] However, the recovery efficiency of this technique is not as high as had been thought for some intestinal parasites. For example, the FEC method may be suboptimal for the detection of Hymenolepis nana and Iodamoeba, 9,13 T. trichiura eggs 14 and S. stercoralis.…”

Adaptation of Ritchie's Method for Parasites Diagnosing with Minimization of Chemical Products

“…The method that uses formalin polysorbate is significantly superior for the identification of eggs of Ascaris lumbricoides ; it also shows similar sensitivity for the identification of Giardia lamblia , Trichuris trichiura , Entamoeba coli , and Entamoeba histolytica . However, it was less effective in the identification of protozoa like Endolimax nana , and Blastocystis hominis [18]. Another disadvantage of this method was the need to use formalin, only replacing ether by polysorbate.…”

Comparison between three concentration techniques for diagnosing intestinal parasites

“…No reagent employed by the Willis method has any kind of chemical hazards that may endanger the laboratory staff. Some authors demonstrated that less toxic reagents could be used in replacement of ether as a solvent to extract fat and debris, like ethyl acetate (11), acetone (12), or tween (13). A modified version of Ritchie’s method by Régis Anécimo (14) did even replace both formaldehyde and ether by a natural detergent, yet had similar qualitative and quantitative performances in parasite recovery.…”