Schistosoma mansoni miracidia: revisiting motility and survival parameters for improved computational modelling.

Schistosoma mansoni is the main causative agent of intestinal schistosomiasis which affects millions of people worldwide. At the larval stage, miracidia are released into bodies of water where they utilize their motility to successfully infect their intermediate host, snails. Here, we revisit the motility and survival of S. mansoni miracidia throughout its life span. Briefly, miracidia motility was monitored at 30-min and 60-min intervals under the presence/absence of natural/artificial light. Based on a subjective evaluation of activity, body shape and transparency, 6 categories of miracidia activity were established from its fully active stage to its immobile larva stage. The estimated life span of miracidia was 5.8 and 3.5 h in the experiments with 60-min and 30-min observation intervals, respectively. Death was defined by an absence of cilia and body movement. When mobility was used as a proxy for infectivity, infective miracidia were detected at 2.5 and 4.5 h, respectively. The present miracidia motility and survival re-evaluation supports parameters optimization for computational modelling of schistosomiasis transmission dynamics. Target control interventions, especially at late stages next to transmission interruption, may greatly benefit from improved modelling studies.

Criteria for identification of Schistosoma mansoni eggs in faecal sediments prepared with the Helmintex method and stained by ninhydrin.

Helmintex is a sensitive method used for detecting Schistosoma mansoni eggs. Here, we describe the observed frequency of six proposed criteria associated with the identification of S. mansoni eggs prepared with the Helmintex method and stained with ninhydrin. The efficacy of these criteria in classifying S. mansoni eggs when applied in various combinations was also examined. Nine observers registered the presence or absence of 6 different criteria in 100 eggs using a microscope at 100x magnification. Ninhydrin purple, which was frequently observed, was the criterion associated with the lowest inter-observer variability. At least three criteria were associated with a significantly better performance in egg identification. In conclusion, ninhydrin staining and a combination of criteria are recommended for microscope examination of faecal sediments.

Use of Schistosoma mansoni soluble egg antigen (SEA) for antibody detection and diagnosis of schistosomiasis: The need for improved accuracy evaluations of diagnostic tools.

Many antigens for use in antibody-detection systems for schistosomiasis have been investigated over the past 40 years. In particular, soluble egg antigens (SEA) are still widely used in enzyme-linked immunosorbent assays (ELISAs) for detection of immunoglobulin classes and subclasses. Here, we conducted a literature review to examine accuracy evaluations of SEA-Immunoglobulin G (IgG)-ELISAs performed to detect Schistosoma mansoni infections and published between 1979 and 2019. S. mansoni is the main causative agent for intestinal schistosomiasis in many countries in Africa and Central and South America. After retrieving 214 relevant abstracts from the PubMed database, we selected 15 publications to undergo a full review. Sensitivity and specificity values varied from 71 to 99%, and from 6 to 100%, respectively. In addition, 11/15 studies did not state confidence intervals. Therefore, the findings from this review indicate that after four decades, we still do not have consistent evaluation estimates of SEA-IgG-ELISAs. Antigen mass per well and dilution of test sera in these articles varied from 0.018 µg to 1.5 µg, and from 1:50 to 1:500, respectively. Most of the reported accuracy evaluations used control sera which were selected based on parasitological examinations for egg detection, although ill-defined criteria were also noted. The number and composition of control serum panels was considered not adequate in approximately half of the studies. It is also noteworthy that among more than 30 diagnostic antigen preparations under development since the 1970s, most were not validated in the field and they failed to reach populations in need. Thus, attention to guidelines for standardization, estimations of accuracy, and reporting of results is needed to facilitate coordinated efforts aimed at schistosomiasis control and elimination.

Low specificity of point-of-care circulating cathodic antigen (POCCCA) diagnostic test in a non-endemic area for schistosomiasis mansoni in Brazil.

A point-of-care test for detecting schistosome circulating cathodic antigen in urine (POCCCA) has been proposed for mapping infection and defining prevalence thresholds for mass drug administration (MDA). However, there is increasing evidence that POCCCA may yield false-positive results, which requires rigorous specificity evaluation in non-endemic areas. POCCCA was applied in an area known to be free from infection and devoid of any condition for schistosomiasis transmission as part of a multicentre study to evaluate the performance of POCCCA in Brazil's low or potentially endemic settings. Besides POCCCA detection in urine, a search for eggs in stool was performed by Kato-Katz (KK) and Helmintex (HTX) methods. One-hundred-and-seventy-four participants returned urine samples, 140 of which delivered stool samples. All these were HTX-negative for Schistosoma mansoni, and all 118 tested with KK were negative for both S. mansoni and soil-transmitted helminths. POCCCA results from freshly collected urine yielded a specificity of 62.1% (95% CI: 53.6% - 70.2%), taking trace outcomes as positive according to the manufacturer's instructions. Retesting urine from the 140 HTX-negatives after one-year storage at -20 °C with two new POCCCA batches simultaneously yielded significantly different specificities (34.3%; 95%CI: 26.5% - 42.8% and 75.0%; 95% CI: 67.0% - 81.9%). These two batches had a weak agreement (Cohen's kappa: 0.56; 95%CI: 0.44-0.68) among the 174 urine samples retested. At present, POCCCA cannot be recommended either as a cut-off point for MDA or a reliable diagnostic tool for treatment of the infection carriers (selective chemotherapy) in low endemic areas and at final stages of transmission interruption. Manufacturers should be required to optimize production standardization and to assure quality and reproducibility of the test. Extended rigorous performance evaluations by different users from different regions are needed before POCCCA is widely recommended.

Study of diagnostic accuracy of Helmintex, Kato-Katz, and POC-CCA methods for diagnosing intestinal schistosomiasis in Candeal, a low intensity transmission area in northeastern Brazil.

Control initiatives have successfully reduced the prevalence and intensity of schistosomiasis transmission in several localities around the world. However, individuals that release low numbers of eggs in their feces may not be detected by classical methods that are limited by low sensitivity. Given that accurate estimates of prevalence are key to implementing planning control actions for the elimination of schistosomiasis, new diagnostic tools are needed to effectively monitor infections and confirm transmission interruption. The World Health Organization recommends the Kato-Katz (KK) thick smear as a parasitological test for epidemiological surveys, even though this method has been demonstrated to underestimate prevalence when egg burdens are low. The point-of-care immunodiagnostic for detecting schistosome cathodic circulating antigen (POC-CCA) method has been proposed as a more sensitive substitute for KK in prevalence estimations. An alternative diagnostic, the Helmintex (HTX) method, isolates eggs from fecal samples with the use of paramagnetic particles in a magnetic field. Here, a population-based study involving 461 individuals from Candeal, Sergipe State, Brazil, was conducted to evaluate these three methods comparatively by latent class analysis (LCA). The prevalence of schistosomiasis mansoni was determined to be 71% with POC-CCA, 40.% with HTX and 11% with KK. Most of the egg burdens of the individuals tested (70%) were < 1 epg, thereby revealing a dissociation between prevalence and intensity in this locality. Therefore, the present results confirm that the HTX method is a highly sensitive egg detection procedure and support its use as a reference method for diagnosing intestinal schistosomiasis and for comparative evaluation of other tests.

Criteria for identification of Schistosoma mansoni eggs in faecal sediments prepared with the Helmintex method and stained by ninhydrin

Helmintex is a sensitive method used for detecting Schistosoma mansoni eggs. Here, we describe the observed frequency of six proposed criteria associated with the identification of S. mansoni eggs prepared with the Helmintex method and stained with ninhydrin. The efficacy of these criteria in classifying S. mansoni eggs when applied in various combinations was also examined. Nine observers registered the presence or absence of 6 different criteria in 100 eggs using a microscope at 100x magnification. Ninhydrin purple, which was frequently observed, was the criterion associated with the lowest inter-observer variability. At least three criteria were associated with a significantly better performance in egg identification. In conclusion, ninhydrin staining and a combination of criteria are recommended for microscope examination of faecal sediments.