Detection of IgM antibodies to Schistosoma mansoni gut-associated antigens for the study of the dynamics of schistosomiasis transmission in an endemic area with low worm burden

Development and evaluation of an indirect ELISA using a multiepitope antigen for the diagnosis of intestinal schistosomiasis

The laboratory diagnosis of intestinal schistosomiasis, carried out by detecting parasite eggs in feces, has low sensitivity when applied to individuals with low parasitic load. Serological tests can be more sensitive for the diagnosis of the disease. Therefore, the objective of this work was to develop and evaluate an ELISA-based immunoenzymatic assay, using a Schistosoma mansoni multiepitope antigen (ELISA IgG anti-SmME). For this, the amino acid sequences of S. mansoni cathepsin B and asparaginyl endopeptidase were submitted to the prediction of B cell epitopes and, together with peptide sequences obtained from earlier works, were used in the construction of a minigene. The multiepitope protein was expressed in Escherichia coli and the performance of the ELISA IgG anti-SmME for schistosomiasis was evaluated using serum samples from 107 individuals either egg positive or negative. In addition, 11 samples from individuals with other helminth infections were included. The ELISA IgG anti-SmME showed a sensitivity of 81.1% and a specificity of 46.1%. Further analysis revealed a 77.2% sensitivity in diagnosis of individuals with egg counts of ≤12 epg (eggs per gram feces) and 87.5% for individuals with 13–99 epg. It is worth mentioning that, to our knowledge, this was the first study using a multiepitope recombinant antigen in an ELISA for diagnosis of intestinal schistosomiasis, which demonstrated promising results in the diagnosis of individuals with low parasitic loads.

Serological approaches for the diagnosis of schistosomiasis - A review

Schistosomiasis is a common disease in endemic areas of Sub-Saharan Africa, South America and Asia. It is rare in Europe, mainly imported from endemic countries due to travelling or human migration. Available methods for the diagnosis of schistosomiasis comprise microscopic, molecular and serological approaches, with the latter detecting antigens or antibodies associated with Schistosoma spp. infection. The serological approach is a valuable screening tool in low-endemicity settings and for travel medicine, though the interpretation of any diagnostic results requires knowledge of test characteristics and a patient's history. Specific antibody detection by most currently used assays is only possible in a relatively late stage of infection and does not allow for the differentiation of acute from previous infections for therapeutic control or the discrimination between persisting infection and re-infection. Throughout the last decades, new target antigens have been identified, and assays with improved performance and suitability for use in the field have been developed. For numerous assays, large-scale studies are still required to reliably characterise assay characteristics alone and in association with other available methods for the diagnosis of schistosomiasis. Apart from S. mansoni, S. haematobium and S. japonicum, for which most available tests were developed, other species of Schistosoma that occur less frequently need to be taken into account. This narrative review describes and critically discusses the results of published studies on the evaluation of serological assays that detect antibodies against different Schistosoma species of humans. It provides insights into the diagnostic performance and an overview of available assays and their suitability for large-scale use or individual diagnosis, and thus sets the scene for serological diagnosis of schistosomiasis and the interpretation of results.

Schistosomiasis Prevalence and Intensity of Infection in Latin America and the Caribbean Countries, 1942-2014: A Systematic Review in the Context of a Regional Elimination Goal

Background

In 2012 the World Health Assembly adopted resolution WHA65.21 on elimination of schistosomiasis, calling for increased investment in schistosomiasis control and support for countries to initiate elimination programs. This study aims to analyze prevalence and intensity of Schistosoma mansoni infection in children in Latin America and the Caribbean countries and territories (LAC), at the second administrative level or lower.

Methodology

A systematic review of schistosomiasis prevalence and intensity of infection was conducted by searching at PubMed, LILACS and EMBASE. Experts on the topic were informally consulted and institutional web pages were reviewed (PAHO/WHO, Ministries of Health). Only SCH infection among children was registered because it can be a ‘proxi-indicator’ of recent transmission by the time the study is conducted.

Principal Findings

One hundred thirty two full-text articles met the inclusion criteria and provided 1,242 prevalence and 199 intensity of infection data points. Most of them were from Brazil (69.7%). Only Brazil published studies after 2001, showing several 'hot spots' with high prevalence. Brazil, Venezuela, Suriname and Saint Lucia need to update the epidemiological status of schistosomiasis to re-design their national programs and target the elimination of Schistosoma mansoni transmission by 2020. In Antigua and Barbuda, Dominican Republic, Guadeloupe, Martinique, Montserrat and Puerto Rico schistosomiasis transmission may be interrupted. However the compilation of an elimination dossier and follow-up surveys, per WHO recommendations, are needed to verify that status. Hence, the burden of subtle SCH chronic infection may be still present and even high in countries that may have eliminated transmission. Heterogeneity in the methodologies used for monitoring and evaluating the progress of the schistosomiasis programs was found, making cross-national and chronological comparisons difficult.

Conclusions

There is a need for updating the schistosomiasis status in the historically endemic countries and territories in LAC to address the required public health interventions for control and elimination programs or to verify the elimination of transmission of Schistosoma mansoni. Improved reporting and standardization of the monitoring and evaluation methodologies used are recommended, while using available WHO guidelines. Meeting a regional elimination goal will require additional and improved epidemiological data by age group and sex.

Schistosomiasis (Schistosoma spp) is an intestinal parasitic infection that causes anaemia, stunted growth, impaired cognition, and decreased physical fitness among other pathological effects. Currently, the control of schistosomiasis relies principally on mass drug administration of praziquantel. In addition, the implementation of further interventions such as snail (intermediate host) control, improving access to safe water and sanitation are required to achieve elimination of transmission in humans. An updated epidemiological situation will help countries to design tailor-made interventions enabling a step-up in prevention and control measures with the goal of elimination of transmission of this disease by 2020. In the region of the Americas, Schistosoma mansoni is the only species present that infect humans. This systematic review shows that in this region there is a need for re-mapping the schistosomiasis epidemiological situation in certain areas and countries in order to implement and optimize the best public health interventions needed to interrupt transmission or verify elimination of transmission. The methodology for monitoring and evaluating schistosomiasis control programs are well defined by current WHO guidelines. However, further investigations and guidelines on suitable tools for monitoring and evaluating schistosomiasis elimination programs and criteria and procedures for validating the elimination are required, and are currently being undertaken by WHO.

Comparative Study of the Accuracy of Different Techniques for the Laboratory Diagnosis of Schistosomiasis Mansoni in Areas of Low Endemicity in Barra Mansa City, Rio de Janeiro State, Brazil

Schistosomiasis constitutes a major public health problem, with an estimated 200 million people infected worldwide. Many areas of Brazil show low endemicity of schistosomiasis, and the current standard parasitological techniques are not sufficiently sensitive to detect the low-level helminth infections common in areas of low endemicity (ALEs). This study compared the Kato-Katz (KK); Hoffman, Pons, and Janer (HH); enzyme-linked immunosorbent assay- (ELISA-) IgG and ELISA-IgM; indirect immunofluorescence technique (IFT-IgM); and qPCR techniques for schistosomiasis detection in serum and fecal samples, using the circumoval precipitin test (COPT) as reference. An epidemiological survey was conducted in a randomized sample of residents from five neighborhoods of Barra Mansa, RJ, with 610 fecal and 612 serum samples. ELISA-IgM (21.4%) showed the highest positivity and HH and KK techniques were the least sensitive (0.8%). All techniques except qPCR-serum showed high accuracy (82–95.5%), differed significantly from COPT in positivity (P < 0.05), and showed poor agreement with COPT. Medium agreement was seen with ELISA-IgG (Kappa = 0.377) and IFA (Kappa = 0.347). Parasitological techniques showed much lower positivity rates than those by other techniques. We suggest the possibility of using a combination of laboratory tools for the diagnosis of schistosomiasis in ALEs.

Utilização de método sorológico como ferramenta diagnóstica para implementação da vigilância e controle da esquistossomose no Município de Holambra, São Paulo, Brasil

O presente estudo teve como objetivo avaliar a incorporação da reação de imunofluorescência indireta para pesquisa de anticorpos IgM (RIF-IgM) como método diagnóstico no programa de controle da esquistossomose do Município de Holambra, Estado de São Paulo, Brasil. O município foi selecionado para este estudo considerando-se a notificação dos primeiros casos de esquistossomose a partir de 1993 e a necessidade do município de implementar o programa com técnicas diagnósticas mais sensíveis, tendo em vista ser caracteristicamente área de baixa endemicidade. Duzentos e dois indivíduos foram submetidos à RIF-IgM, dos quais 48 apresentaram-se positivos, sendo 28 destes submetidos à técnica de Kato-Katz, examinando-se três amostras de fezes. Ovos de Schistosoma mansoni foram encontrados em 14, com carga parasitária variando de 2,7 a 224,0 ovos por grama de fezes. Os resultados indicam a potencialidade da RIF-IgM como método de triagem, para posterior confirmação exaustiva por método parasitológico, em áreas de baixa endemicidade.

Immunoassays as an auxiliary tool for the serodiagnosis of Schistosoma mansoni infection in individuals with low intensity of egg elimination

In an attempt to improve the screening of Schistosoma mansoni-infected individuals from a low-transmission area, we established a protocol that includes three independent coproscopy examinations and two serological assays. Three stool samples were examined using the Kato-Katz and free sedimentation methods and serum samples were tested by IgG-ELISA and IgM-immunofluorescence. Two hundred and sixty-nine individuals participated in the survey: 132 individuals (49%) showed positive serological test results. Of these, 16 (6%) had positive results in stool examination in the first sample batch. However, there were also cases with positive serological test results in spite of negative Kato-Katz stool examinations. Additional stool samples were obtained from these subjects and in this way an additional 11 egg-excretors were found. Our findings suggest that a screening method that combines antibody isotype detection and repeated parasitological stool examinations could increase the chances of detecting S. mansoni-infected patients.

Efficacy of an enzyme-linked immunosorbent assay as a diagnostic tool for schistosomiasis mansoni in individuals with low worm burden

IgM-ELISA is an immunoenzymatic method useful for detection of IgM antibodies against a fraction of Schistosoma mansoni adult worm antigen (AWA) that is soluble in trichloroacetic acid (AWA-TCA). This method was applied to three groups of individuals with different clinical and epidemiological characteristics, and the results compared with those obtained by other diagnostic methods: immunofluorescence test for detection of IgM antibodies (IgM-IFT) or IgG antibodies (IgG-IFT), ELISA for detection of IgG antibodies (IgG-ELISA), and two parasitological methods, Kato-Katz and miracidium hatching. The IgM-ELISA presented a sensitivity of 98%, when the parasitologic fecal examination was defined as reference diagnostic method, and a specificity of 98 and 97.3%, respectively for the group of clinically healthy individuals and other helminth carriers. A comparative analysis between the results of IgM-ELISA and those obtained by other serologic tests showed a good degree of agreement, with Kappa indices ranging from 0.95 to 0.98. The diagnostic efficacy of 97.8%, as determined with schistosomiasis patients with low parasitic burden, suggests the excellent performance of the IgM-ELISA and its usefulness for the diagnosis of schistosomiasis when applied in low endemic areas.

Schistosomiasis mansoni: follow-up of control program based on parasitologic and serologic methods in a Brazilian community of low endemicity

A field survey on schistosomiasis was carried out in 1998, in the municipality of Pedro de Toledo, a low endemic area in the state of São Paulo, Brazil. According to the parasitologic Kato-Katz method, the prevalence rate was 1.6%, with an infection intensity of 40.9 eggs per gram of stool. By the immunofluorescence test (IFT) for detection of IgG and IgM antibodies in the serum, IgG-IFT and IgM-IFT, respectively, prevalence indices of 33.2% and 33.5% were observed. To assess the impact of the schistosomiasis control program in the area, parasitologic and serologic data obtained in 1998, analyzed according to the age, sex, and residence zone, were compared to previous data obtained in a epidemiologic study carried out in 1980, when prevalence indices were of 22.8% and 55.5%, respectively by Kato-Katz and IgG-IFT. A significant fall of the prevalence was observed, indicating that the control measures were effective. Nonetheless, residual transmission was observed, demonstrating the need for a joint effort to include new approaches for better understanding the real situation and improving the control of the disease in low endemic areas.

Schistosomiasis mansoni in Bananal (State of São Paulo, Brazil): III. Seroepidemiological studies in the Palha District

The Palha district, municipality of Bananal, State of São Paulo, Brazil, had 10.3% cases of Schistosoma mansoni diagnosed from 1994 to 2000 by coproscopy: about three times the municipality average. The immunofluorescent antibody test was used to assess gut-associated IgM antibody titers of samples from 452 inhabitants. It disclosed 129 (28.5%) positive cases. Subjects were classified according to age, sex, birthplace, and period of residence. Titers varied from 8 to 4,096 (geometric mean: 170.2). Seropositives were aged from 6 to 69 years (average: 24.5), 75% of them aged 34 or less, predominantly males (78 or 60.5%). Of all subjects, 65.7% were born and had been living in Bananal since; 24.2% came from neighboring municipalities and are residing in Bananal from two months to 89 years (average: 22.7 years). Further Kato-Katz coproscopy from 97 seropositives (geometric mean titer, 619) revealed S. mansoni eggs in 11 subjects (11.3%). Serology was deemed useful in screening subjects to be further investigated by coproscopy, considering that blood collection had better acceptance than supplying fecal samples. Higher than average serological titers may indicate new cases in endemic areas. Longitudinal studies associated with epidemiological investigation, including titer evolution are advised, as isolated data are difficult to interpret.

[IgM-ELISA for diagnosis of schistosomiasis mansoni in low endemic areas]

An immunoenzymatic method for the detection of IgM antibodies (IgM-ELISA) against a fraction of Schistosoma mansoni adult worm antigen, soluble in trichloroacetic acid (TCA-soluble fraction), was evaluated for epidemiological purposes in low endemic areas for schistosomiasis. Blood samples on filter paper were collected from a population living in the municipality of Pedro de Toledo, São Paulo State, and submitted to IgM-ELISA. The results were compared to those obtained by the IgM-immunofluorescence test (IgM-IFT) and the Kato-Katz parasitological method. Positive rates of 36.8%, 33.5%, and 1.6% were obtained respectively by the IgM-ELISA, IgM-IFT, and Kato-Katz methods. The geometric mean obtained by the parasitological method was 40.9 eggs per gram of feces (epg). The nearly perfect agreement observed between the two serological tests (Kappa index of 0,89) indicates good diagnostic performance by the evaluated test. IgM-ELISA is a potentially useful method for diagnosis of schistosomiasis in individuals with low worm burden.

IgM-immunofluorescence test as a diagnostic tool for epidemiologic studies of Schistosomiasis in low endemic areas

The high sensitivity and the ability to diagnose schistosomiasis in a very early phase after infection have indicated the detection of IgM antibodies to Schistosoma mansoni gut antigens by the immunofluorescence test (IgM-IFT) as a useful serological test for epidemiological studies in low endemic areas. When applied in a follow-up study for two years, higher rates of seroconversion from IFT negative to positive were observed during the summer months, suggesting seasonal transmission of schistosomiasis in the rural area of the municipality of Itariri (São Paulo, Brazil). In each survey, blood samples from about 600 schoolchildren were collected on filter paper and submitted to IgM-IFT. When the blood samples were classified for the IgM antibody levels, according to the intensity of fluorescent reaction observed at fluorescence microscopy, and correlated to the egg counts in the Kato-Katz positive patients, no association was observed. This observation might suggest that the intensity of fluorescence observed in the IgM-IFT, as an indicator of IgM antibody levels, could not be an useful seroepidemiological marker for classifying areas of low endemicity according to degrees of infection.