L. van Lieshout

Are poor responses to praziquantel for the treatment of Schistosoma mansoni infections in Senegal due to resistance? An overview of the evidence

This paper summarizes and concludes in‐depth field investigations on suspected resistance of Schistosoma mansoni to praziquantel in northern Senegal. Praziquantel at 40 mg/kg usually cures 70–90% of S. mansoni infections. In an initial trial in an epidemic S. mansoni focus in northern Senegal, only 18% of the cases became parasitologically negative 12 weeks after treatment, although the reduction in mean egg counts was within normal ranges (86%). Among other hypotheses to explain the observed low cure rate in this focus, the possibility of drug resistance or tolerance had to be considered. Subsequent field trials with a shorter follow‐up period (6–8 weeks) yielded cure rates of 31–36%. Increasing the dose to 2 × 30 mg/kg did not significantly improve cure rates, whereas treatment with oxamniquine at 20 mg/kg resulted in a normal cure rate of 79%. The efficacy of praziquantel in this focus could be related to age and pre‐treatment intensity but not to other host factors, including immune profiles and water contact patterns. Treatment with praziquantel of individuals from the area residing temporarily in an urban region with no transmission, and re‐treatment after 3 weeks of non‐cured individuals within the area resulted in normal cure rates (78–88%). The application of an epidemiological model taking into account the relation between egg counts and actual worm numbers indicated that the low cure rates in this Senegalese focus could be explained by assuming a 90% worm reduction after treatment with praziquantel; in average endemic situations, such a drug efficacy would result in normal cure rates. Laboratory studies by others on the presence or absence of praziquantel resistance in Senegalese schistosome strains have so far been inconclusive. We conclude that there is no convincing evidence for praziquantel‐resistant S. mansoni in Senegal, and that the low cure rates can be attributed to high initial worm loads and intense transmission in this area.

Immunodiagnosis of schistosomiasis by determination of the circulating antigens CAA and CCA, in particular in individuals with recent or light infections

In the present paper, we evaluate determination of circulating anodic (CAA) and cathodic (CCA) antigen for the diagnosis of an active Schistosoma infection in humans, in comparison to the diagnostic performance of parasitological examination and the demonstration of specific antibodies. Illustrated by three different studies, which all deal with the diagnosis of either recent or low intensity infections, we further discuss our experiences with these diagnostic methods. For the diagnosis of recent infections, specific antibody determination showed to be very sensitive, particularly in individuals originating from non-endemic areas. For the assessment of cure and for the diagnosis of active infections in endemic areas, the methods of choice are parasitological examination and CAA or CCA determination. Depending on infection levels of the target population and on logistic conditions, CAA and CCA determination may either replace parasitological examination or, in the case of light infections, may be used as a complementary diagnostic tool.

Determining the prevalence of Oesophagostomum bifurcum and Necator americanus infections using specific PCR amplification of DNA from faecal samples

Until recently infection of humans with Oesophagostomum bifurcum was regarded as a rare zoonosis. But in northern Togo and Ghana its prevalence is 50% or more in certain villages. Diagnosis is hampered by the fact that the eggs of O. bifurcum are morphologically identical to those of the hookworm Necator americanus. Stools have to be cultured for 7 days to allow eggs to hatch to the characteristic third‐stage (L3) larvae. We evaluated the applicability of specific polymerase chain reactions (PCRs) to amplify DNA from faecal samples as an alternative method for the differential diagnosis of the two infections. Oesophagostomum bifurcum‐PCR was positive in 57 of 61 faecal samples known to contain O. bifurcum L3 larvae in coproculture. Necator americanus PCR was positive in 137 of 146 faecal samples known to contain N. americanus L3 larvae in coproculture. PCR also detected 26 additional O. bifurcum cases in 72 samples from O. bifurcum endemic villages in which no O. bifurcum larvae were found and 45 N. americanus cases in 78 samples in which no N. americanus larvae were found in coproculture. No O. bifurcum DNA was detected in 91 stool samples from individuals from two non‐endemic villages. These results prove the usefulness of specific PCR assays as epidemiological tools to estimate the prevalence of O. bifurcum and N. americanus infections in human populations.

New diagnostic tools in schistosomiasis

Schistosomiasis is a water-based parasitic disease that affects over 250 million people. Control efforts have long been in vain, which is one reason why schistosomiasis is considered a neglected tropical disease. However, since the new millennium, interventions against schistosomiasis are escalating. The initial impetus stems from a 2001 World Health Assembly resolution, urging member states to scale-up deworming of school-aged children with the anthelminthic drug praziquantel. Because praziquantel is safe, efficacious and inexpensive when delivered through the school platform, diagnosis before drug intervention was deemed unnecessary and not cost-effective. Hence, there was little interest in research and development of novel diagnostic tools. With the recent publication of the World Health Organization (WHO) Roadmap to overcome the impact of neglected tropical diseases in 2020, we have entered a new era. Elimination of schistosomiasis has become the buzzword and this has important ramifications for diagnostic tools. Indeed, measuring progress towards the WHO Roadmap and whether local elimination has been achieved requires highly accurate diagnostic assays. Here, we introduce target product profiles for diagnostic tools that are required for different stages of a schistosomiasis control programme. We provide an update of the latest developments in schistosomiasis diagnosis, including microscopic techniques, rapid diagnostic tests for antigen detection, polymerase chain reaction (PCR) assays and proxy markers for morbidity assessments. Particular emphasis is placed on challenges and solutions for new technologies to enter clinical practice.

Immunodiagnosis of schistosomiasis mansoni in a low endemic area in Surinam by determination of the circulating antigens CAA and CCA

We evaluated the applicability of circulating antigen detection in serum and urine for the diagnosis of Schistosoma infections in a low endemic area. In total 389 individuals from Saramacca (Surinam) participated in the survey. Stool samples were examined using the Kato method, while circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) were determined by highly specific monoclonal antibody-based ELISAs. Also schistosome specific IgM antibodies were measured by the indirect immunofluorescence assay, but the diagnostic performance of this test was found to be poor in this population. S. mansoni eggs were found in 29% of the examined cases, while CAA and CCA could be demonstrated in 23% and 17% of the serum samples and in 3% and 28% of the urine samples, respectively. Forty three percent of the study population was positive in at least one of these diagnostic assays, indicating that each individual test misses a substantial part of the subjects with an active infection. In most positive cases, intensities of infection were very low. As 204 individuals participated in all screening assays, diagnostic performance of each test was evaluated in this sub-population. The highest sensitivities were achieved with the urine-CCA assay and the parasitological examination, detecting 59 and 58 out of the 107 cases with an active infection, respectively. The serum-CAA assay detected 47 positive cases. Our results demonstrate that determination of circulating antigens, especially CCA in urine and CAA in serum, provides information additional to the parasitological examination, for the assessment of prevalence and intensity of Schistosoma infection in low endemic areas.

Detection of Clonorchis sinensis in stool samples using real-time PCR

Abstract Human clonorchiasis, caused by infection with the trematode Clonorchis sinensis, is a common health problem in East Asia. In an attempt to develop a new, sensitive method for the diagnosis of the disease, the use of a real-time PCR (targeting the internal-transcribed-spacer-2 sequence of the parasite) to detect C. sinensis-specific DNA in faecal samples has recently been evaluated. The PCR-based assay, which included an internal control to detect any inhibition of the amplification by faecal constituents in the sample, was performed on stool samples and on DNA controls representing a wide range of intestinal microorganisms. The assay appeared very specific, only showing positivity with C. sinensis and Opisthorchis felineus. The sensitivity of the assay was explored by testing 170 preselected samples of human faeces, from an endemic area of South Korea, which had known (microscopically-determined) densities of C. sinensis eggs. The sensitivity of the assay was 100% for the 74 samples that each had > 100 eggs/g and 91.4% for the other 70 samples found egg-positive by microcopy (i.e. those that had ≤ 100 eggs/g). Three of the 26 samples that appeared egg-negative by microscopy were found PCR-positive. Encouragingly, the PCR cycle-threshold values, which reflect parasite-specific DNA loads, showed significant correlation with the egg counts. The real-time PCR used in this study therefore appears to be a powerful tool for both the detection and quantification of C. sinensis infections.

Monitoring the efficacy of different doses of praziquantel by quantification of circulating antigens in serum and urine of schistosomiasis patients

We evaluated the quantitation of two schistosome circulating antigens in serum and urine as a tool for the assessment of the efficacy of praziquantel dosage regimens (40 versus 60 mg/kgbw). In addition we compared the efficacy of two different brands of praziquantel (Biltricide and Distocide), given at the same dosage (40 mg/kgbw). Thirty five Egyptian hospitalized schistosomiasis mansoni patients participated in this study. Thirteen patients (Group 1) received 60 mg/kgbw Biltricide, administered in 3 oral doses of 20 mg in one day; 22 individuals (Group 2) were treated with 40 mg/kgbw (12 Biltricide, 10 Distocide), given in one oral dose. Circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) were quantitated by monoclonal antibody-based ELISAs before, and 1, 3 and 6 weeks after chemotherapy. Before treatment, all patients were positive for at least one of the circulating antigen assays. Three to six weeks after treatment significantly more patients were found to be negative in Group 1 compared to Group 2 (X2 = 7.13, P = 0.008, n = 35). Also the levels of CCA and CAA in serum and of CCA in urine were found to be significantly higher in Group 2 (Mann-Whitney U < 85, P < 0.05, n = 35). These results were confirmed by parasitological data. No differences were found between treatment with Biltricide or Distocide.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemiology of HIV and Schistosoma mansoni infections among sugar-estate residents in Ethiopia

Few studies have examined the interaction between schistosomiasis and infection with human immunodeficiency virus (HIV). The overlap between the two infections, and the effect of HIV infection on the egg output and worm load of individuals co-infected with Schistosoma mansoni, were therefore investigated in a sugar estate in central Ethiopia. The 1239 subjects were selected by stratified sampling of residents aged 15-54 years. The intensities of infection with S. mansoni were measured as egg output in stools (all subjects) and as the concentration of circulating cathodic antigen (CCA) in urine (a proxy for worm load, measured in 287 subjects). Schistosome infection was detected in 358 subjects [adjusted prevalence (AP) = 31.4%] and HIV infection in 52 (AP = 3.1%). The two infections clustered into different populations of the estate: the schistosome infections were predominantly found in the camps, and primarily affected young people (aged < 20 years) and those working in the field, whereas the HIV epidemic was found in the main village, primarily affecting those aged > 20 years and those who had recently arrived on the estate. Schistosome infection was detected in 348 of the 1187 HIV-negatives (AP = 31.6%) and 10 of the 52 HIV-positives (AP = 25.1%; P > 0.05). Schistosoma mansoni egg output was significantly lower in the HIV-positives than in the HIV-negatives (Mann-Whitney test; P = 0.03; ratio of geometric means = 0.74), and remained so after controlling for potential confounders (gender, age, and residence). However, CCA concentrations (i.e. worm loads) were found to be similar for these two groups, after controlling for potential confounders (age, gender, residence, and duration of residence).

A simple technique to pretreat urine and serum samples for quantitation of schistosome circulating anodic and cathodic antigen

For the detection of the circulating schistosome antigens CAA (circulating anodic antigen) and CCA (circulating cathodic antigen) in serum and urine samples of Schistosoma infected individuals, pretreatment of samples with trichloroacetic acid (TCA) is a standard procedure. In the present study several methods were evaluated in order to develop a more simple and rapid technique than the--especially for pretreatment of urine samples--laborious TCA technique. Optimal results were obtained with a method in which serum or urine samples were pretreated by a heat-incubation step (70 degrees C, 30 min) in an alkaline buffer (pH 9.6). In a comparison of the new technique with the TCA pretreatment, serum and urine samples of S. mansoni infected individuals from Zaire (n = 80) and of uninfected controls from The Netherlands (n = 208) were pretreated and assayed for CAA and CCA. Both pretreatment techniques showed similar sensitivities and specificities for CAA and CCA in serum, and CCA in urine. However, for the determination of CAA in urine the new technique performed significantly better, resulting in an increase of the sensitivity from 32 to 70% (titre determination).

The contribution made by Schistosoma infection to non-traumatic disorders of the spinal cord in Malawi

Abstract In Malawi, although schistosomal myelopathy has been reported in visitors from overseas who have swum in Lake Malawi, the incidence of this disorder in local residents has never been investigated. Consecutive patients with non-traumatic disorders of the spinal cord were therefore recruited in a hospital and a rehabilitation centre in Blantyre. Of the 33 patients investigated, 16 were presumed to be cases of schistosomal myelopathy as they had the markers of past or current schistosomiasis and apparently no other conditions that could explain their clinical features. There was microscopical and/or immunodiagnostic evidence indicating that eight of these presumptive cases had active schistosomiasis. All 16 presumptive cases had symptoms that were similar to those of 177 presumptive or proven cases of neuroschistosomiasis described in the scientific literature. Following antihelminthic treatment, eight of the presumptive cases showed marked improvement. Schistosomal myelopathy seems to occur relatively frequently in Malawi. Early treatment with praziquantel is strongly recommended for all patients with unexplained myelopathy and a history of exposure to schistosome cercariae.