Use of a saline gradient for the diagnosis of schistosomiasis

Abstract

Faecal exams are widely used for the diagnosis of intestinal helminth infections because microscopic findings of parasitic structures typically assure reliable and accurate identification of the parasites. Although several types of qualitative and quantitative methods exist for stool examination (Lutz 1919, Hastings-Willis 1921, Faust & Melency 1924, Hoffman et al. 1934, Stoll 1946, Ritchie 1948, Sapero et al. 1951, Kato & Miura 1954, Blagg et al. 1955, Bell 1963, Katz et al. 1972, some of these techniques have operational limitations, including high cost, complexity, low sensitivity and/or reproducibility. These limitations may restrict their respective uses in large-scale surveys in the field.A method commonly used in epidemiological studies due to its relative simplicity and low cost is the quantitative Kato-Katz faecal smear technique (Katz et al. 1972). Katz et al. (1970) showed the limit of sensitivity for this method to be 20 eggs per gram of faeces by recovering Schistosoma mansoni eggs that were added to negative human faecal samples. This exam is considered to be the gold standard for diagnosing schistosomiasis mansoni as per the World Health Organization (WHO 1993). Although this method is widely used, the Kato-Katz test might lack sensitivity in situations of low worm burden, low endemicity and in cases of evaluation post treatment (Ferrari et al. 2003). To overcome these limitations, it is necessary to increase the number of stool samples, which may increase costs and possibly cause logistic difficulties in epidemiological surveys (Enk et al. 2008).Alternative approaches based on antibody, antigen and DNA detection are of potential application, but when the financial and infrastructural difficulties of most endemic countries are taken into consideration, these techniques become unsatisfactory (WHO 2006b). Perhaps as an opposite effect of successful control programs worldwide, the diagnosis of schistosomiasis still needs a more sensitive and low-cost tool for detecting light infections in the field (WHO 2006a). Recently, two novel methods have been proposed. Teixeira et al. (2007) developed a highly sensitive method (named Helmintex) for identifying S. mansoni eggs in large amounts of faeces. Faecal samples of 30 g were processed through a sequence of spontaneous sedimentation, sieving and the Ritchie method and then incubated with or without lectins. This was followed by isolation through interaction with paramagnetic beads and microscopic inspection. The other method consists of a hatching device containing a collecting container for the detection of miracidia (Jurberg et al. 2008). Although hatching methods are highly sensitive, they have an obvious limitation because the faecal samples must be fresh at the moment of the exam. On the other hand, the miracidia suspension fixed in 10% formaldehyde solution could be examined for at least 15 days after the fixation without a statistically significant loss of the miracidia number.In an attempt to develop more sensitive diagnostic tools for schistosomia...

The combination of three faecal parasitological methods to improve the diagnosis of schistosomiasis mansoni in a low endemic setting in the state of Ceará, Brazil

“…Because the eggs had a higher density, they remained on the surface of the porous plate. The final sediment was then transferred to glass slides and examined under a light field microscope and the eggs were counted (Coelho et al 2009). …”

Performance of POC-CCA® in diagnosis of schistosomiasis mansoni in individuals with low parasite burden

“…For the saline gradient technique (25) , feces were filtered through a nylon screen (150µm), and quantification was performed using a metal plate. For each stool sample, two aliquots of 500mg were each homogenized with 3mL of 0.85% saline and poured into separation columns.…”

“…Currently, the ability of POC-CCA® to diagnose schistosomiasis mansoni in different settings in Brazil is being evaluated. Our aim was to compare the performance of POC-CCA® in a Brazilian population from a low-endemicity area with that of two traditional parasitological techniques, the conventional Kato-Katz technique (3) and the saline gradient technique (25) . The results of this study can provide technical evidences to recommend the incorporation of POC-CCA® in the Brazilian Schistosomiasis Program Control.…”

Comparison of the Kato-Katz and Helmintex methods for the diagnosis of schistosomiasis in a low-intensity transmission focus in Bandeirantes, Paraná, southern Brazil

“…The difficulty of diagnosing schistosomiasis in areas of low-intensity transmission, such as Esteio, has prompted several efforts to improve the sensitivity of egg detection in stool samples, such as using the Percoll and saline density gradient methods (Eberl et al 2002, Coelho et al 2009) or polymerase chain reaction analyses of stool samples (Gomes et al 2010, in addition to the examination of slides using the KK method or combinations of different methods (Siqueira et al 2011).…”