Serological responses among individuals in areas where both schistosomiasis and malaria are endemic: cross-reactivity between Schistosoma mansoni and Plasmodium falciparum

Humoral antimalaria immune response in Nigerian children exposed to helminth and malaria parasites

Background

Malaria and helminthic parasites are endemic in tropical countries, and co-infections might influence host-parasite interactions. In this community-based cross-sectional study, the effect that the presence of soil-transmitted helminths (STH) (Hookworm, Hymenolepis nana) and Schistosoma haematobium infections could have on the immunoglobulin (Ig) candidate protein of the malaria vaccine GMZ2 levels was evaluated.

Methods

Blood, stool, and urine samples were collected from 5-15-year-old children to diagnose P. falciparum (Pf), STH, and Schistosoma haematobium, respectively. Identification and quantification of the parasite load of STH and S. haematobium were achieved by light microscopy. A polymerase chain reaction was carried out to detect submicroscopic infections of P. falciparum. Plasma levels of GMZ2 specific IgG and its subclasses were quantified by ELISA.

Results

The median level of total IgG in individuals with co-infection with Pf/H. nana was significantly lower in the mono-infected group with Pf (p = 0.0121) or study participants without infection (p=0.0217). Similarly, the median level of IgG1 was statistically lower in Pf/H. nana group compared to Pf-group (p=0.0137). Equally, the Pf/H. nana infected individuals posted a lower level of IgG1 compared to Pf-group (p=0.0137) and IgG4 compared to the Pf-group (p=0.0144). Spearman rank correlation analyses indicated positive relationships between the densities of H. nana (ρ=0.25, p=0.015) and S. haematobium (ρ=0.36, p<0.0001).

Conclusions

Hookworm and H. nana infections are associated with reduced GMZ2 specific IgG levels. This study shows the possible manipulation of immune responses by helminths for their survival and transmission, which may have serious implications for vaccine development and deployment in helminth-endemic regions.

Circulating IL-6, IL-10, and TNF-alpha and IL-10/IL-6 and IL-10/TNF-alpha ratio profiles of polyparasitized individuals in rural and urban areas of gabon

Malaria, blood-borne filarial worms and intestinal parasites are all endemic in Gabon. This geographical co-distribution leads to polyparasitism and, consequently, the possibility of immune-mediated interactions among different parasite species. Intestinal protozoa and helminths could modulate antimalarial immunity, for example, thereby potentially increasing or reducing susceptibility to malaria. The aim of the study was to compare the cytokine levels and cytokine ratios according to parasitic profiles of the population to determine the potential role of co-endemic parasites in the malaria susceptibility of populations. Blood and stool samples were collected during cross-sectional surveys in five provinces of Gabon. Parasitological diagnosis was performed to detect plasmodial parasites, Loa loa, Mansonella perstans, intestinal helminths (STHs) and protozoan parasites. Nested PCR was used to detect submicroscopic plasmodial infection in individuals with negative blood smears. A cytometric bead array was used to quantify interleukin (IL)-6, IL-10 and tumour necrosis factor (TNF)-α in the plasma of subjects with different parasitological profiles. Median IL-6 and IL-10 levels and the median IL-10/TNF-α ratio were all significantly higher among individuals with Plasmodium (P.) falciparum infection than among other participants (p<0.0001). The median TNF-α level and IL-10/IL-6 ratio were higher in subjects with STHs (p = 0.09) and P. falciparum-intestinal protozoa co-infection (p = 0.04), respectively. IL-6 (r = -0.37; P<0.01) and IL-10 (r = -0.37; P<0.01) levels and the IL-10/TNF-α ratio (r = -0.36; P<0.01) correlated negatively with age. Among children under five years old, the IL-10/TNF-α and IL-10/IL-6 ratios were higher in those with intestinal protozoan infections than in uninfected children. The IL-10/TNF-α ratio was also higher in children aged 5–15 years and in adults harbouring blood-borne filariae than in their control counterparts, whereas the IL-10/IL-6 ratio was lower in those aged 5–15 years with filariae and intestinal parasites but higher in adults with intestinal parasitic infections. Asymptomatic malaria is associated with a strong polarization towards a regulatory immune response, presenting high circulating levels of IL-10. P. falciparum/intestinal protozoa co-infections were associated with an enhanced IL-10 response. Immunity against malaria could differ according to age and carriage of other parasites. Helminths and intestinal protozoa can play a role in the high susceptibility to malaria currently observed in some areas of Gabon, but further investigations are necessary.

The current epidemiological transition of malaria observed in Gabon included, for example, a shift in the at-risk population from children aged less than 5 years old to older children aged 5–15 years. Another consequence was the increasing number of cases of infection among adults. In view of these findings, it is important to explain this phenomenon of epidemiological modification of malaria in Gabon. Intestinal parasites and blood filariasis are endemic in Gabon. These parasites are described to alter the malaria immune response and can be implicated in the susceptibility of individuals to malaria. In Gabon, malaria presents a heterogeneous repartition. Thus, in the present study, we investigated the role of co-endemic parasitosis in the alteration of the malarial immune response by comparing Th1 (IL-6 and TNF-α) and Th2/Treg (IL-10) cytokine production between mono- and co-parasitized individuals in many localities with different epidemiological patterns of malaria. Microscopic analyses and rapid antigenic tests were performed for malaria diagnosis. The nested PCR technique was used to demonstrate the submicroscopic parasitaemia of Plasmodium sp. Then, once groups with different parasitological profiles were constituted, IL-6, IL-10 and TNF-α levels were measured in the plasma of individuals. Th2/Th1 ratios, which can indicate the level of susceptibility of individuals to malaria, were calculated. We observed that there was no interaction between Plasmodium sp. and co-endemic parasites in the present study. However, the high Th2/Th1 cytokine ratio among patients with intestinal protozoa seems to suggest that these intestinal parasites could also play a role in susceptibility to malaria as they do for helminths.

Serology- and Blood-PCR-Based Screening for Schistosomiasis in Pregnant Women in Madagascar-A Cross-Sectional Study and Test Comparison Approach

This work was conducted as a cross sectional study to define the disease burden of schistosomiasis in pregnant Madagascan women and to evaluate serological and molecular diagnostic assays. A total of 1154 residual EDTA blood samples from pregnant Madagascan women were assessed. The nucleic acid extractions were subjected to in-house real-time PCRs specifically targeting S. mansoni complex, S. haematobium complex, and African Schistosoma spp. on genus level, while the EDTA plasma samples were analyzed using Schistosoma-specific IgG and IgM commercial ELISA and immunofluorescence assays. The analyses indicated an overall prevalence of schistosomiasis in Madagascan pregnant women of 40.4%, with only minor regional differences and differences between serology- and blood PCR-based surveillance. The S. mansoni specific real-time PCR showed superior sensitivity of 74% (specificity 80%) compared with the genus-specific real-time PCR (sensitivity 13%, specificity 100%) in blood. The laborious immunofluorescence (sensitivity IgM 49%, IgG 87%, specificity IgM 85%, IgG 96%) scored only slightly better than the automatable ELISA (sensitivity IgM 38%, IgG 88%, specificity IgM 78%, IgG 91%). Infections with S. mansoni were detected only. The high prevalence of schistosomiasis recorded here among pregnant women in Madagascar calls for actions in order to reduce the disease burden.

Schistosoma haematobium infection modulates Plasmodium falciparum parasite density and antimalarial antibody responses

AIMS

Schistosomiasis and malaria are endemic in sub-Saharan Africa where Schistosoma haematobium (Sh) and Plasmodium falciparum (Pf) coinfections are thus frequent. We explored the effect of Sh infection on antibody responses directed to Pf merozoite antigens and on malaria susceptibility in Beninese children.

METHODS AND RESULTS

A total of 268 children were followed during a malaria transmission season. Detection of Pf infection was performed by microscopy and rapid diagnostic tests. Sh infection was determined in urine by microscopy. Antimalarial antibody, cytokine and HLA-G concentrations were quantified by ELISA. The expression of HLA-G receptors by immune cells was assessed by flow cytometry. Children infected by Sh had higher concentrations of IgG1 directed to MSP3 and GLURP_R0 , IgG2 directed to GLURP_R0 and IgG3 directed to MSP3, GLURP_R0 and GLURP_R2 and have lower Pf densities than those uninfected by Sh. No difference in cytokine and HLA-G concentrations was observed between Sh egg carriers and non-carriers.

CONCLUSION

Schistosoma haematobium modulates host immune responses directed to Pf antigens. The absence of immune downregulation usually observed during helminth infections is surprising in our study. We hypothesize that the stage of Sh development could partly explain the immune pathways leading to increased antibody levels that favour better control of Pf parasitemia.

Infection against infection: parasite antagonism against parasites, viruses and bacteria

Background

Infectious diseases encompass a large spectrum of diseases that threaten human health, and coinfection is of particular importance because pathogen species can interact within the host. Currently, the antagonistic relationship between different pathogens during concurrent coinfections is defined as one in which one pathogen either manages to inhibit the invasion, development and reproduction of the other pathogen or biologically modulates the vector density. In this review, we provide an overview of the phenomenon and mechanisms of antagonism of coinfecting pathogens involving parasites.

Main body

This review summarizes the antagonistic interaction between parasites and parasites, parasites and viruses, and parasites and bacteria. At present, relatively clear mechanisms explaining polyparasitism include apparent competition, exploitation competition, interference competition, biological control of intermediate hosts or vectors and suppressive effect on transmission. In particular, immunomodulation, including the suppression of dendritic cell (DC) responses, activation of basophils and mononuclear macrophages and adjuvant effects of the complement system, is described in detail.

Conclusions

In this review, we summarize antagonistic concurrent infections involving parasites and provide a functional framework for in-depth studies of the underlying mechanisms of coinfection with different microorganisms, which will hasten the development of promising antimicrobial alternatives, such as novel antibacterial vaccines or biological methods of controlling infectious diseases, thus relieving the overwhelming burden of ever-increasing antimicrobial resistance.

Electronic supplementary material

The online version of this article (10.1186/s40249-019-0560-6) contains supplementary material, which is available to authorized users.

To B or Not to B: Understanding B Cell Responses in the Development of Malaria Infection

Malaria is a widespread disease caused mainly by the Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) protozoan parasites. Depending on the parasite responsible for the infection, high morbidity and mortality can be triggered. To escape the host immune responses, Plasmodium parasites disturb the functionality of B cell subsets among other cell types. However, some antibodies elicited during a malaria infection have the potential to block pathogen invasion and dissemination into the host. Thus, the question remains, why is protection not developed and maintained after the primary parasite exposure? In this review, we discuss different aspects of B cell responses against Plasmodium antigens during malaria infection. Since most studies have focused on the quantification of serum antibody titers, those B cell responses have not been fully characterized. However, to secrete antibodies, a complex cellular response is set up, including not only the activation and differentiation of B cells into antibody-secreting cells, but also the participation of other cell subsets in the germinal center reactions. Therefore, a better understanding of how B cell subsets are stimulated during malaria infection will provide essential insights toward the design of potent interventions.

Physiological, but not fitness, effects of two interacting haemoparasitic infections in a wild rodent

In contrast to the conditions in most laboratory studies, wild animals are routinely challenged by multiple infections simultaneously, and these infections can interact in complex ways. This means that the impact of a parasite on its host's physiology and fitness cannot be fully assessed in isolation, and requires consideration of the interactions with other co-infections. Here we examine the impact of two common blood parasites in the field vole (Microtus agrestis): Babesia microti and Bartonella spp., both of which have zoonotic potential. We collected longitudinal and cross-sectional data from four populations of individually tagged wild field voles. This included data on biometrics, life history, ectoparasite counts, presence/absence of microparasites, immune markers and, for a subset of voles, more detailed physiological and immunological measurements. This allowed us to monitor infections over time and to estimate components of survival and fecundity. We confirm, as reported previously, that B. microti has a preventative effect on infection with Bartonella spp., but that the reverse is not true. We observed gross splenomegaly following B. microti infection, and an increase in IL-10 production together with some weight loss following Bartonella spp. infection. However, these animals appeared otherwise healthy and we detected no impact of infection on survival or fecundity due to the two haemoparasite taxa. This is particularly remarkable in the case of B. microti which induces apparently drastic long-term changes to spleen sizes, but without major adverse effects. Our work sheds light on the ecologies of these important zoonotic agents, and more generally on the influence that interactions among multiple parasites have on their hosts in the wild.

The impact of Tetracapsuloides bryosalmonae and Myxobolus cerebralis co-infections on pathology in rainbow trout

Background

Myxozoan parasites pose emerging health issues for wild and farmed salmonid fish. Rainbow trout (Oncorhynchus mykiss) is a particularly susceptible species to Tetracapsuloides bryosalmonae (Malacosporea), the etiological agent of Proliferative Kidney Disease (PKD), and to Myxobolus cerebralis (Myxosporea), the etiological agent of Whirling Disease (WD). The objective of this study was to investigate the impact of myxozoan co-infections on the pathogenesis of PKD and WD in the rainbow trout.

Methods

Two groups of rainbow trout (96 fish each) were primarily infected with T. bryosalmonae and triactinomyxons of M. cerebralis; after 30 days half of the fish in each group were co-infected with these parasites vice versa and remaining half was continued as single infection. Mortalities and clinical signs were recorded at different time points. Histopathology and immunohistochemistry were performed to assess the extent of each infection and estimate the parasite burden between groups.

Results

Fish firstly infected with M. cerebralis and co-infected with T. bryosalmonae exhibited exacerbated pathological changes of both parasitic diseases and elicited a higher mortality rate. A higher kidney swelling index (grade 4) appeared together with more severe cartilage destruction and displacement, when compared to the pathological changes in fish upon single infections with T. bryosalmonae or M. cerebralis. Conversely, fish firstly infected with T. bryosalmonae and co-infected with M. cerebralis also exhibited typical pathological changes of both parasitic diseases, but with a lower mortality rate, similar as caused by the single T. bryosalmonae or M. cerebralis infection. WD clinical signs were milder, without skeletal deformities, while kidney swelling index was similar to single infection with T. bryosalmonae (grade 2 to 3).

Conclusions

In this study, a co-infection with myxozoan parasites was for the first time successfully achieved in the laboratory under controlled conditions. The impact of co-infections in concurrent myxozoan infections mainly depends on the primary pathogen infecting the host, which could alter the outcomes of the secondary pathogen infection. The primary M. cerebralis infection followed by T. bryosalmonae had a much more serious impact and elicited a synergistic interaction. Contrasting results were instead seen in rainbow trout primarily infected with T. bryosalmonae and then co-infected with M. cerebralis.

Blood parasites of penguins: a critical review

Blood parasites are considered some of the most significant pathogens for the conservation of penguins, due to the considerable morbidity and mortality they have been shown to produce in captive and wild populations of these birds. Parasites known to occur in the blood of penguins include haemosporidian protozoans (Plasmodium, Leucocytozoon, Haemoproteus), piroplamid protozoans (Babesia), kinetoplastid protozoans (Trypanosoma), spirochete bacteria (Borrelia) and nematode microfilariae. This review provides a critical and comprehensive assessment of the current knowledge on these parasites, providing an overview of their biology, host and geographic distribution, epidemiology, pathology and implications for public health and conservation.

Anti-Schistosoma IgG responses in Schistosoma haematobium single and concomitant infection with malaria parasites

Areas prone to schistosomiasis are also at risk of malaria transmission. The interaction between the causal agents of the two diseases could modulate immune responses tailored toward protecting or aggravating morbidity dynamics and impair Schistosoma diagnostic precision. This study aimed at assessing the effect of Plasmodium spp. in concomitant infection with Schistosoma haematobium in modulation of anti-Schistosoma IgG antibodies. The school-based cross-sectional study recruited a total of 322 children screened for S. haematobium and Plasmodium spp. Levels of IgG against S. haematobium-soluble egg antigen (SEA) in single S. haematobium/malaria parasites infection and co-infection of the two parasites in schoolchildren were determined. Data were analyzed using χ(2), Fisher's exact test, and Tukey's multiple comparison test analyses. The prevalence of single infection by S. haematobium, Plasmodium spp., and concurrent infection due to the two pathogens was 27.7, 41.0, and 9.3%, respectively (p < 0.0001). Anti-Schistosoma IgG production during co-infection of the two pathogens (1.950 ± 0.742 AU) was significantly higher than the value recorded for single malaria parasites' infection (1.402 ± 0.670 AU) (p < 0.01) but not in S. haematobium infection (1.591 ± 0.604 AU) (p > 0.05). The anti-Schistosoma IgG production in co-infection status was however dependent on the intensity of Plasmodium spp. with individuals having high intensity of malaria parasites recording lower anti-Schistosoma IgG. This study has implication for diagnosis of schistosomiasis where anti-Schistosoma IgG is used as an indicator of infection. Efforts should be made to control the two infections simultaneously in order not to undermine the efforts targeted toward the control of one.

Increased exposure to Plasmodium chabaudi antigens sustains cross-reactivity and avidity of antibodies binding Nippostrongylus brasiliensis: dissecting cross-phylum cross-reactivity in a rodent model

Mounting an antibody response capable of discriminating amongst and appropriately targeting different parasites is crucial in host defence. However, cross-reactive antibodies that recognize (bind to) multiple parasite species are well documented. We aimed to determine if a higher inoculating dose of one species, and thus exposure to larger amounts of antigen over a longer period of time, would fine-tune responses to that species and reduce cross-reactivity. Using the Plasmodium chabaudi chabaudi (Pcc)–Nippostrongylus brasiliensis (Nb) co-infection model in BALB/c mice, in which we previously documented cross-reactive antibodies, we manipulated the inoculating dose of Pcc across 4 orders of magnitude. We investigated antigen-specific and cross-reactive antibody responses against crude and defined recombinant antigens by enzyme linked immunosorbent assay, Western blot and antibody depletion assays. Contrary to our hypothesis that increasing exposure to Pcc would reduce cross-reactivity to Nb, we found evidence for increased avidity of a subpopulation of antibodies that recognized shared antigens. Western blot indicated proteins of apparent monomer molecular mass 28 and 98 kDa in both Nb and Pcc antigen preparations and also an Nb protein of similar size to recombinant Pcc antigen, merozoite surface protein-119. The implications of antibodies binding antigen from such phylogenetically distinct parasites are discussed.

IFNγ and IL-12 Restrict Th2 Responses during Helminth/Plasmodium Co-Infection and Promote IFNγ from Th2 Cells

Parasitic helminths establish chronic infections in mammalian hosts. Helminth/Plasmodium co-infections occur frequently in endemic areas. However, it is unclear whether Plasmodium infections compromise anti-helminth immunity, contributing to the chronicity of infection. Immunity to Plasmodium or helminths requires divergent CD4⁺ T cell-driven responses, dominated by IFNγ or IL-4, respectively. Recent literature has indicated that Th cells, including Th2 cells, have phenotypic plasticity with the ability to produce non-lineage associated cytokines. Whether such plasticity occurs during co-infection is unclear. In this study, we observed reduced anti-helminth Th2 cell responses and compromised anti-helminth immunity during Heligmosomoides polygyrus and Plasmodium chabaudi co-infection. Using newly established triple cytokine reporter mice (Il4^gfpIfng^yfpIl17a^FP635), we demonstrated that Il4^gfp+ Th2 cells purified from in vitro cultures or isolated ex vivo from helminth-infected mice up-regulated IFNγ following adoptive transfer into Rag1^–/– mice infected with P. chabaudi. Functionally, Th2 cells that up-regulated IFNγ were transcriptionally re-wired and protected recipient mice from high parasitemia. Mechanistically, TCR stimulation and responsiveness to IL-12 and IFNγ, but not type I IFN, was required for optimal IFNγ production by Th2 cells. Finally, blockade of IL-12 and IFNγ during co-infection partially preserved anti-helminth Th2 responses. In summary, this study demonstrates that Th2 cells retain substantial plasticity with the ability to produce IFNγ during Plasmodium infection. Consequently, co-infection with Plasmodium spp. may contribute to the chronicity of helminth infection by reducing anti-helminth Th2 cells and converting them into IFNγ-secreting cells.

Approximately a third of the world’s population is burdened with chronic intestinal parasitic helminth infections, causing significant morbidities. Identifying the factors that contribute to the chronicity of infection is therefore essential. Co-infection with other pathogens, which is extremely common in helminth endemic areas, may contribute to the chronicity of helminth infections. In this study, we used a mouse model to test whether the immune responses to an intestinal helminth were impaired following malaria co-infection. These two pathogens induce very different immune responses, which, until recently, were thought to be opposing and non-interchangeable. This study identified that the immune cells required for anti-helminth responses are capable of changing their phenotype and providing protection against malaria. By identifying and blocking the factors that drive this change in phenotype, we can preserve anti-helminth immune responses during co-infection. Our studies provide fresh insight into how immune responses are altered during helminth and malaria co-infection.

Impact of Schistosoma mansoni on malaria transmission in Sub-Saharan Africa

Background

Sub-Saharan Africa harbors the majority of the global burden of malaria and schistosomiasis infections. The co-endemicity of these two tropical diseases has prompted investigation into the mechanisms of coinfection, particularly the competing immunological responses associated with each disease. Epidemiological studies have shown that infection with Schistosoma mansoni is associated with a greater malaria incidence among school-age children.

Methodology

We developed a co-epidemic model of malaria and S. mansoni transmission dynamics which takes into account key epidemiological interaction between the two diseases in terms of elevated malaria incidence among individuals with S. mansoni high egg output. The model was parameterized for S. mansoni high-risk endemic communities, using epidemiological and clinical data of the interaction between S. mansoni and malaria among children in sub-Saharan Africa. We evaluated the potential impact of the S. mansoni–malaria interaction and mass treatment of schistosomiasis on malaria prevalence in co-endemic communities.

Principal Findings

Our results suggest that in the absence of mass drug administration of praziquantel, the interaction between S. mansoni and malaria may reduce the effectiveness of malaria treatment for curtailing malaria transmission, in S. mansoni high-risk endemic communities. However, when malaria treatment is used in combination with praziquantel, mass praziquantel administration may increase the effectiveness of malaria control intervention strategy for reducing malaria prevalence in malaria- S. mansoni co-endemic communities.

Conclusions/Significance

Schistosomiasis treatment and control programmes in regions where S. mansoni and malaria are highly prevalent may have indirect benefits on reducing malaria transmission as a result of disease interactions. In particular, mass praziquantel administration may not only have the direct benefit of reducing schistosomiasis infection, it may also reduce malaria transmission and disease burden.

Malaria and Schistosoma mansoni are co-endemic in many regions of sub-Saharan Africa. Evidence from clinical and epidemiological studies support the hypothesis that concurrent infection with S. mansoni is associated with greater malaria incidence among school-age children. We use mathematical modeling to evaluate the epidemiological impact of S. mansoni infection on malaria transmission in sub-Saharan Africa. Using epidemiological data on the increased risk of malaria incidence in S. mansoni endemic communities from Senegal, we developed a co-epidemic model of malaria and S. mansoni transmission dynamics to address key epidemiological interactions between the two diseases. Parameterizing our model for S. mansoni high-risk endemic communities, we show that the interaction between S. mansoni and malaria may reduce the effectiveness of malaria treatment for curtailing malaria transmission. Moreover, we show that in addition to reducing schistosomiasis health burden, mass praziquantel administration will generate indirect benefit in terms of reducing malaria transmission and disease burden in S. mansoni–malaria co-endemic communities. Our findings indicate the possible benefit of scaling up schistosomiasis control efforts in sub-Saharan Africa, and especially in areas were S. mansoni and malaria are highly prevalent.

Malaria and helminth co-infections in school and preschool children: a cross-sectional study in Magu district, north-western Tanzania

BACKGROUND

Malaria, schistosomiasis and soil transmitted helminth infections (STH) are important parasitic infections in Sub-Saharan Africa where a significant proportion of people are exposed to co-infections of more than one parasite. In Tanzania, these infections are a major public health problem particularly in school and pre-school children. The current study investigated malaria and helminth co-infections and anaemia in school and pre-school children in Magu district, Tanzania.

METHODOLOGY

School and pre-school children were enrolled in a cross-sectional study. Stool samples were examined for Schistosoma mansoni and STH infections using Kato Katz technique. Urine samples were examined for Schistosoma haematobium using the urine filtration method. Blood samples were examined for malaria parasites and haemoglobin concentrations using the Giemsa stain and Haemoque methods, respectively.

PRINCIPAL FINDINGS

Out of 1,546 children examined, 1,079 (69.8%) were infected with one or more parasites. Malaria-helminth co-infections were observed in 276 children (60% of all children with P. falciparum infection). Malaria parasites were significantly more prevalent in hookworm infected children than in hookworm free children (p = 0.046). However, this association was non-significant on multivariate logistic regression analysis (OR = 1.320, p = 0.064). Malaria parasite density decreased with increasing infection intensity of S. mansoni and with increasing number of co-infecting helminth species. Anaemia prevalence was 34.4% and was significantly associated with malaria infection, S. haematobium infection and with multiple parasite infections. Whereas S. mansoni infection was a significant predictor of malaria parasite density, P. falciparum and S. haematobium infections were significant predictors of anaemia.

CONCLUSIONS/SIGNIFICANCE

These findings suggest that multiple parasite infections are common in school and pre-school children in Magu district. Concurrent P. falciparum, S. mansoni and S. haematobium infections increase the risk of lower Hb levels and anaemia, which in turn calls for integrated disease control interventions. The associations between malaria and helminth infections detected in this study need further investigation.

Coinfection with Plasmodium falciparum and Schistosoma haematobium: additional evidence of the protective effect of Schistosomiasis on malaria in Senegalese children

Parasitic infections are associated with high morbidity and mortality in developing countries. Several studies focused on the influence of helminth infections on malaria but the nature of the biological interaction is under debate. Our objective was to undertake a study to explore the influence of the measure of excreted egg load caused by Schistosoma haematobium on Plasmodium falciparum parasite densities. Ten measures of malaria parasite density and two measures of schistosomiasis egg urinary excretion over a 2-year follow-up period on 178 Senegalese children were considered. A linear mixed-effect model was developed to take data dependence into account. This work showed that children with a light S. haematobium infection (1-9 eggs/mL of urine) presented lower P. falciparum parasite densities than children not infected by S. haematobium (P < 0.04). Possible changes caused by parasite coinfections should be considered in the anti-helminth treatment of children and in malaria vaccination development.

Advances in our understanding of the epidemiology of Plasmodium and schistosome infection: informing coinfection studies

PURPOSE OF REVIEW

Schistosomes and Plasmodium parasites have complex patterns of transmission, leading to differing dynamics of host-parasite interactions across study sites and a bias of studying differing age groups in monoinfection studies. Combined, these infections lead to difficulties in conducting and interpreting human coinfection studies.

RECENT FINDINGS

Interactions between the two parasites may affect morbidity associated with either infection; both by influencing mechanisms directly associated with the development of those morbidities and by influencing mechanisms associated with resistance or susceptibility to the other infection. However, conflicting results are reported due to inherent difficulties in studying coinfections. More studies with stringent designs are required to clarify interactions between the two parasites. Recent monoinfection studies indicate that further coinfection studies may need to have a wider age range than previously studied. These studies also need to harness new techniques, both for data collection and analysis that are being developed for modern epidemiological studies. These techniques will allow an essential multidisciplinary approach to be taken.

SUMMARY

Coinfection with Plasmodium and schistosome infection has implications for the health of children of all ages in sub-Saharan Africa. It is important to gain further understanding of the interactions between the two parasites in all age groups.

IgG Antibody responses in mice coinfected with Toxocara canis and other helminths or protozoan parasites

The immune response expressed by IgG antibodies in BALB/c mice experimentally infected with Toxocara canis, was studied with the aim of verifying the possible in vivo cross-reactivity between antigens of T. canis and other parasites (Ascaris suum, Taenia crassiceps, Schistosoma mansoni, Strongyloides venezuelensis and Toxoplasma gondii). Experiments included three groups of mice: one infected only by T. canis, another with one of the other species of parasites and a third concomitantly infected with T. canis and the other species in question. Animals were bled by orbital plexus at 23, 38 and 70 days post infection (p.i.). Sera were analyzed for anti-Toxocara antibodies by ELISA and Immunoblotting, using excretion-secretion antigens (ES), obtained from culture of third-stage larvae of T. canis. For all experiments a control group comprised by ten non-infected mice was used. Only in the case of A. suum infection, in these experimental conditions, the occurrence of cross-reactivity with T. canis was observed. However, in the case of co-infection of T. canis - S. mansoni, T. canis - S. venezuelensis and T. canis - T. crassiceps the production of anti-Toxocara antibodies was found at levels significantly lower than those found in mice infected with T. canis only. Co-infection with S. mansoni or S. venezuelensis showed lower mortality rates compared to what occurred in the animals with single infections. Results obtained in mice infected with T. canis and T. gondii showed significant differences between the mean levels of the optical densities of animals infected with T. canis and concomitantly infected with the protozoan only in the 23rd day p.i.

Terminal galactosylation of glycoconjugates in Plasmodium falciparum asexual blood stages and Trypanosoma brucei bloodstream trypomastigotes

There is definitive biochemical evidence for the presence of terminal α-galactosyl residues (α-gal) in the N-linked oligosaccharides and glycophosphatidylinositol anchors (GPI anchors) of the variant surface glycoprotein of Trypanosoma brucei bloodstream trypomastigotes. Indirect evidence also exists for α-gal in Plasmodium falciparum asexual blood stage glycoproteins and glycolipids. The occurrence of α-gal in glycoproteins and glycolipids of T. brucei bloodstream trypomastigotes and P. falciparum late asexual blood stages was investigated by the binding of α-gal-specific Bandeirea simplicifolia B4 lectin 1 (BSB4), incorporation of [(3)H]galactose from UDP-[(3)H]galactose into glycoproteins and glycolipids in microsomes in vitro, and bioinformatic searches for galactosyl-transferase coding sequences. The findings confirm the presence of α-gal in a spectrum of T. brucei bloodstream trypomastigote glycoproteins and glycolipids and indicate its relative absence from P. falciparum asexual blood stage glycoconjugates.

Exposure, infection, systemic cytokine levels and antibody responses in young children concurrently exposed to schistosomiasis and malaria

Despite the overlapping distribution of Schistosoma haematobium and Plasmodium falciparum infections, few studies have investigated early immune responses to both parasites in young children resident in areas co-endemic for the parasites. This study measures infection levels of both parasites and relates them to exposure and immune responses in young children. Levels of IgM, IgE, IgG4 directed against schistosome cercariae, egg and adult worm and IgM, IgG directed against P. falciparum schizonts and the merozoite surface proteins 1 and 2 together with the cytokines IFN-γ, IL-4, IL-5, IL-10 and TNF-α were measured by ELISA in 95 Zimbabwean children aged 1–5 years. Schistosome infection prevalence was 14·7% and that of Plasmodium infection was 0% in the children. 43. 4% of the children showed immunological evidence of exposure to schistosome parasites and 13% showed immunological evidence of exposure to Plasmodium parasites. Schistosome–specific responses, indicative of exposure to parasite antigens, were positively associated with cercariae-specific IgE responses, while Plasmodium-specific responses, indicative of exposure to parasite antigens, were negatively associated with responses associated with protective immunity against Plasmodium. There was no significant association between schistosome-specific and Plasmodium-specific responses. Systemic cytokine levels rose with age as well as with schistosome infection and exposure. Overall the results show that (1) significantly more children are exposed to schistosome and Plasmodium infection than those currently infected and; (2) the development of protective acquired immunity commences in early childhood, although its effects on infection levels and pathology may take many years to become apparent.

Impact of schistosome infection on Plasmodium falciparum Malariometric indices and immune correlates in school age children in Burma Valley, Zimbabwe

A group of children aged 6-17 years was recruited and followed up for 12 months to study the impact of schistosome infection on malaria parasite prevalence, density, distribution and anemia. Levels of cytokines, malaria specific antibodies in plasma and parasite growth inhibition capacities were assessed. Baseline results suggested an increased prevalence of malaria parasites in children co-infected with schistosomiasis (31%) compared to children infected with malaria only (25%) (p = 0.064). Moreover, children co-infected with schistosomes and malaria had higher sexual stage geometric mean malaria parasite density (189 gametocytes/µl) than children infected with malaria only (73/µl gametocytes) (p = 0.043). In addition, a larger percentage of co-infected children (57%) had gametocytes as observed by microscopy compared to the malaria only infected children (36%) (p = 0.06). There was no difference between the two groups in terms of the prevalence of anemia, which was approximately 64% in both groups (p = 0.9). Plasma from malaria-infected children exhibited higher malaria antibody activity compared to the controls (p = 0.001) but was not different between malaria and schistosome plus malaria infected groups (p = 0.44) and malaria parasite growth inhibition activity at baseline was higher in the malaria-only infected group of children than in the co-infected group though not reaching statistical significance (p = 0.5). Higher prevalence and higher mean gametocyte density in the peripheral blood may have implications in malaria transmission dynamics during co-infection with helminths.

Using serological measures to monitor changes in malaria transmission in Vanuatu

Background

With renewed interest in malaria elimination, island environments present unique opportunities to achieve this goal. However, as transmission decreases, monitoring and evaluation programmes need increasingly sensitive tools to assess Plasmodium falciparum and Plasmodium vivax exposure. In 2009, to assess the role of serological markers in evaluating malaria transmission, a cross-sectional seroprevalence study was carried out in Tanna and Aneityum, two of the southernmost islands of the Vanuatu archipelago, areas where malaria transmission has been variably reduced over the past few decades.

Methods

Malaria transmission was assessed using serological markers for exposure to P. falciparum and P. vivax. Filter blood spot papers were collected from 1,249 people from Tanna, and 517 people from Aneityum to assess the prevalence of antibodies to two P. falciparum antigens (MSP-1₁₉ and AMA-1) and two P. vivax antigens (MSP-1₁₉ and AMA-1). Age-specific prevalence was modelled using a simple catalytic conversion model based on maximum likelihood to generate a community seroconversion rate (SCR).

Results

Overall seropositivity in Tanna was 9.4%, 12.4% and 16.6% to P. falciparum MSP-1₁₉, AMA-1 and Schizont Extract respectively and 12.6% and 15.0% to P. vivax MSP-1₁₉ and AMA-1 respectively. Serological results distinguished between areas of differential dominance of either P. vivax or P. falciparum and analysis of age-stratified results showed a step in seroprevalence occurring approximately 30 years ago on both islands, indicative of a change in transmission intensity at this time. Results from Aneityum suggest that several children may have been exposed to malaria since the 2002 P. vivax epidemic.

Conclusion

Seroepidemiology can provide key information on malaria transmission for control programmes, when parasite rates are low. As Vanuatu moves closer to malaria elimination, monitoring changes in transmission intensity and identification of residual malaria foci is paramount in order to concentrate intervention efforts.

Serologic markers for detecting malaria in areas of low endemicity, Somalia, 2008

Areas in which malaria is not highly endemic are suitable for malaria elimination, but assessing transmission is difficult because of lack of sensitivity of commonly used methods. We evaluated serologic markers for detecting variation in malaria exposure in Somalia. Plasmodium falciparum or P. vivax was not detected by microscopy in cross-sectional surveys of samples from persons during the dry (0/1,178) and wet (0/1,128) seasons. Antibody responses against P. falciparum or P. vivax were detected in 17.9% (179/1,001) and 19.3% (202/1,044) of persons tested. Reactivity against P. falciparum was significantly different between 3 villages (p<0.001); clusters of seroreactivity were present. Distance to the nearest seasonal river was negatively associated with P. falciparum (p = 0.028) and P. vivax seroreactivity (p = 0.016). Serologic markers are a promising tool for detecting spatial variation in malaria exposure and evaluating malaria control efforts in areas where transmission has decreased to levels below the detection limit of microscopy.

Association of schistosomiasis with false-positive HIV test results in an African adolescent population

This study was designed to investigate the factors associated with the high rate of false-positive test results observed with the 4th-generation Murex HIV Ag/Ab Combination EIA (enzyme immunoassay) within an adolescent and young-adult cohort in northwest Tanzania. (4th-generation assays by definition detect both HIV antigen and antibody.) The clinical and sociodemographic factors associated with false-positive HIV results were analyzed for 6,940 Tanzanian adolescents and young adults. A subsample of 284 Murex assay-negative and 240 false-positive serum samples were analyzed for immunological factors, including IgG antibodies to malaria and schistosoma parasites, heterophile antibodies, and rheumatoid factor (RF) titers. Conditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). False-positive HIV test results were associated with evidence of other infections. False positivity was strongly associated with increasing levels of Schistosoma haematobium worm IgG1, with adolescents with optical densities in the top quartile being at the highest risk (adjusted OR=40.7, 95% CI=8.5 to 194.2 compared with the risk for those in the bottom quartile). False positivity was also significantly associated with increasing S. mansoni egg IgG1 titers and RF titers of >or=80 (adjusted OR=8.2, 95% CI=2.8 to 24.3). There was a significant negative association between Murex assay false positivity and the levels of S. mansoni worm IgG1 and IgG2 and Plasmodium falciparum IgG1 and IgG4. In Africa, endemic infections may affect the specificities of immunoassays for HIV infection. Caution should be used when the results of 4th-generation HIV test results are interpreted for African adolescent populations.

Antibody isotype analysis of malaria-nematode co-infection: problems and solutions associated with cross-reactivity

BACKGROUND

Antibody isotype responses can be useful as indicators of immune bias during infection. In studies of parasite co-infection however, interpretation of immune bias is complicated by the occurrence of cross-reactive antibodies. To confidently attribute shifts in immune bias to the presence of a co-infecting parasite, we suggest practical approaches to account for antibody cross-reactivity. The potential for cross-reactive antibodies to influence disease outcome is also discussed.

RESULTS

Utilising two murine models of malaria-helminth co-infection we analysed antibody responses of mice singly- or co-infected with Plasmodium chabaudi chabaudi and Nippostrongylus brasiliensis or Litomosoides sigmodontis. We observed cross-reactive antibody responses that recognised antigens from both pathogens irrespective of whether crude parasite antigen preparations or purified recombinant proteins were used in ELISA. These responses were not apparent in control mice. The relative strength of cross-reactive versus antigen-specific responses was determined by calculating antibody titre. In addition, we analysed antibody binding to periodate-treated antigens, to distinguish responses targeted to protein versus carbohydrate moieties. Periodate treatment affected both antigen-specific and cross-reactive responses. For example, malaria-induced cross-reactive IgG1 responses were found to target the carbohydrate component of the helminth antigen, as they were not detected following periodate treatment. Interestingly, periodate treatment of recombinant malaria antigen Merozoite Surface Protein-119 (MSP-119) resulted in increased detection of antigen-specific IgG2a responses in malaria-infected mice. This suggests that glycosylation may have been masking protein epitopes and that periodate-treated MSP-119 may more closely reflect the natural non-glycosylated antigen seen during infection.

CONCLUSIONS

In order to utilize antibody isotypes as a measure of immune bias during co-infection studies, it is important to dissect antigen-specific from cross-reactive antibody responses. Calculating antibody titre, rather than using a single dilution of serum, as a measure of the relative strength of the response, largely accomplished this. Elimination of the carbohydrate moiety of an antigen that can often be the target of cross-reactive antibodies also proved useful.

Metabolic alterations in the hamster co-infected with Schistosoma japonicum and Necator americanus

Co-infection with hookworm and schistosomes is a common phenomenon in sub-Saharan Africa, as well as in parts of South America and southeast Asia. As a first step towards understanding the metabolic response of a hookworm-schistosome co-infection in humans, we investigated the metabolic consequences of co-infection in an animal model, using a nuclear magnetic resonance (NMR)-based metabolic profiling technique, combined with multivariate statistical analysis. Urine and serum samples were obtained from hamsters experimentally infected with 250 Necator americanus infective L(3) and 100 Schistosoma japonicum cercariae simultaneously. In the co-infection model, similar worm burdens were observed as reported for single infection models, whereas metabolic profiles of co-infection represented a combination of the altered metabolite profiles induced by single infections with these two parasites. Consistent differences in metabolic profiles between the co-infected and non-infected control hamsters were observed from 4 weeks p.i. onwards. The predominant metabolic alterations in co-infected hamsters consisted of depletion of amino acids, tricarboxylic acid cycle intermediates (e.g. citrate and succinate) and glucose. Moreover, alterations of a series of gut microbial-related metabolites, such as decreased levels of hippurate, 3-hydroxyphenylpropionic acid, 4-hydroxyphenylpropionic acid and trimethylamine-N-oxide, and increased concentrations of 4-cresol glucuronide and phenylacetylglycine were associated with co-infection. Our results provide a first step towards understanding the metabolic response of an animal host to multiple parasitic infections.

Reduced protective effect of Plasmodium berghei immunization by concurrent Schistosoma mansoni infection

Studies on concomitant schistosomiasis and human and experimental malaria have shown a variation in the immunospecific response, as well as an increase in the severity of both parasitoses. In the present study, a murine co-infection model was used to determine the effects of a co-infection with Schistosoma mansoni and Plasmodium berghei on the protective immunity acquired by repeated malarial infections and subsequent curative treatment with chloroquine. Our results have demonstrated that, compared to an infection with P. berghei only, the co-infection increases the malarial parasitaemia and decreases the survival rate. Indeed, mice that were immunized by infection and treatment with drug displayed no mortality whereas co-infected mice showed a reduced protective efficacy of immunization against P. berghei (mortality > 60%). Interestingly, this high mortality rate was not associated with high levels of parasitaemia. Our findings support the idea of a suppressive effect of a Schistosoma co-infection on the anti-malarial protection by immunization. This result reveals a possible drawback of the development of anti-malarial vaccines, especially considering the wide endemic areas for both parasitoses.

Why do adaptive immune responses cross-react?

Antigen specificity of adaptive immune responses is often in the host's best interests, but with important and as yet unpredictable exceptions. For example, antibodies that bind to multiple flaviviral or malarial species can provide hosts with simultaneous protection against many parasite genotypes. Vaccinology often aims to harness such imprecision, because cross-reactive antibodies might provide broad-spectrum protection in the face of antigenic variation by parasites. However, the causes of cross-reactivity among immune responses are not always known, and here, we explore potential proximate and evolutionary explanations for cross-reactivity. We particularly consider whether cross-reactivity is the result of constraints on the ability of the immune system to process information about the world of antigens, or whether an intermediate level of cross-reactivity may instead represent an evolutionary optimum. We conclude with a series of open questions for future interdisciplinary research, including the suggestion that the evolutionary ecology of information processing might benefit from close examination of immunological data.

Effect of treating Schistosoma haematobium infection on Plasmodium falciparum-specific antibody responses

BACKGROUND

The overlapping geographical and socio-economic distribution of malaria and helminth infection has led to several studies investigating the immunological and pathological interactions of these parasites. This study focuses on the effect of treating schistosome infections on natural human immune responses directed against plasmodia merozoite surface proteins MSP-1 (DPKMWR, MSP1(19)), and MSP-2 (CH150 and Dd2) which are potential vaccine candidates as well as crude malaria (schizont) and schistosome (whole worm homogenate) proteins.

METHODS

IgG1 and IgG3 antibody responses directed against Schistosoma haematobium crude adult worm antigen (WWH) and Plasmodium falciparum antigens (merozoite surface proteins 1/2 and schizont extract), were measured by enzyme linked immunosorbent assay (ELISA) in 117 Zimbabweans (6-18 years old) exposed to S. haematobium and P. falciparum infection. These responses were measured before and after anti-helminth treatment with praziquantel to determine the effects of treatment on anti-plasmodial/schistosome responses.

RESULTS

There were no significant associations between antibody responses (IgG1/IgG3) directed against P. falciparum and schistosomes before treatment. Six weeks after schistosome treatment there were significant changes in levels of IgG1 directed against schistosome crude antigens, plasmodia crude antigens, MSP-1(19), MSP-2 (Dd2), and in IgG3 directed against MSP-1(19). However, only changes in anti-schistosome IgG1 were attributable to the anti-helminth treatment.

CONCLUSION

There was no association between anti-P. falciparum and S. haematobium antibody responses in this population and anti-helminth treatment affected only anti-schistosome responses and not responses against plasmodia crude antigens or MSP-1 and -2 vaccine candidates.

Validez de los estudios de asociación entre geohelmintos e incidencia de malaria: ¿Debería impactar las políticas de salud?

INTRODUCCIÓN: La distribución mundial de las geohelmintiasis y la malaria se encuentra ampliamente sobrepuesta. Algunos estudios sugieren una asociación entre las infecciones por geohelmintos y la incidencia de malaria. OBJETIVOS: Identificar la evidencia epidemiológica disponible y evaluar la validez de estos estudios. METODOLOGÍA: Una revisión sistemática fue realizada en bases de datos especializadas. Los estudios identificados fueron analizados críticamente y ordenados según clasificación de la U.S. Preventive Services Task Force. Se identificaron las principales limitaciones metodológicas de cada estudio. RESULTADOS: Se encontraron seis estudios publicados sobre el tema. Solo dos estudios tienen un alto nivel de evidencia (nivel I), tres de nivel II-2, y uno de nivel III-3. Existen importantes limitaciones metodológicas para aclarar la asociación entre geohelmintos e incidencia de malaria. CONCLUSIONES: Es apresurado discutir las potenciales implicaciones en salud pública de estos hallazgos dada la escasez de estudios y la validez limitada de la evidencia existente. Futuros estudios con nuevas consideraciones metodológicas podrían mejorar el conocimiento acerca de esta asociación. Sin embargo, es más importante realizar acciones sobre los determinantes estructurales para controlar y prevenir la ocurrencia de ambas enfermedades.

Hepatosplenomegaly in Kenyan schoolchildren: exacerbation by concurrent chronic exposure to malaria and Schistosoma mansoni infection

OBJECTIVES

Chronic exposure to malaria exacerbates Schistosoma mansoni-associated hepatosplenomegaly in school-aged children. However, residual hepatosplenomegaly after treatment of S. mansoni with concurrent mollusciciding suggests malaria could be an underlying cause of hepatosplenomegaly. We investigated the role of chronic malaria in childhood hepatosplenomegaly in the presence and absence of concurrent S. mansoni infection.

METHODS

Cross-sectional study of children in an study area where transmission of S. mansoni, but not malaria, is restricted to the eastern end. Clinical and ultrasound examinations were conducted, and parasitological and serological tests used to determine S. mansoni infection intensities and comparative exposure levels to malaria.

RESULTS

Chronic exposure to malaria, as determined by Pfs-IgG3 levels, was associated with hepatosplenomegaly even in the absence of S. mansoni infection. Children infected with S. mansoni mostly had light to moderate infection intensities but greater enlargement of the liver and spleen than children who did not have schistosomiasis, and for the left liver lobe this was S. mansoni infection intensity dependent.

CONCLUSIONS

Children chronically exposed to malaria but without S. mansoni infection can have hepatosplenomegaly, which even light S. mansoni infections can exacerbate in an intensity-dependent manner. Thus, concurrent chronic exposure to S. mansoni and Plasmodium falciparum can have an additive or synergistic effect on childhood morbidity.

Anti-malaria humoral responses in children exposed to Plasmodium falciparum and Schistosoma haematobium

Antibody responses directed against the Plasmodium falciparum antigens, total extract, anti-merozoite surface protein-3 (MSP3b) and glutamate-rich protein (Glurp-R0) were studied in 42 children exposed to both Schistosoma haematobium and P. falciparum infections. The association between levels of the anti-malaria IgG subclasses and IgM with host age, sex, schistosome infection intensity and schistosome specific antibodies was studied before chemotherapeutic treatment of schistosome infections. This showed a significant negative association between schistosome infection intensity and levels of IgG1, IgG3, and IgG4 directed against malaria total extract antigen, and a positive association between levels of anti-schistosome soluble egg antigen IgG2, IgG3, and IgG4 and levels of the same subclasses directed against malaria total extract antigens. The effect of treating schistosome infections with praziquantel on malaria specific responses was also studied. This treatment resulted in increases in significant IgG4 levels against MSP3b and IgM against Glurp R0. Treatment also resulted in a significant decrease in IgG4 levels against Glurp R0. Host age, sex or pre-treatment infection intensity was not associated with the magnitude of change in the two IgG4 responses while males showed a significantly higher increase in levels of IgM. The results suggest cross reactivity between schistosome and malaria antigens in this population.

Avian malaria (Plasmodium spp) in yellow-eyed penguins: investigating the cause of high seroprevalence but low observed infection

AIM

To investigate the cause of a high seroprevalence of antibodies to Plasmodium spp known to cause avian malaria, but extremely low levels of observed infection, in yellow-eyed penguins, Megadyptes antipodes.

METHODS

A polymerase chain reaction (PCR) test specific for malarial parasites was applied to DNA extracted from blood samples collected from 143 yellow-eyed penguins from an area where seroprevalence for malarial antibodies was known to be high but no parasites were observed in blood smears.

RESULTS

None of the samples tested positive for malarial parasite DNA using the PCR test. Assuming a sensitivity of 90% for this test, this means that prevalence of infection was 95% likely to be <2.3% in this population during this sampling period.

CONCLUSIONS

Serological studies of a population of adult yellow-eyed penguins indicated a high level of exposure to avian malaria parasites, but a correspondingly high level of infection was not observed and no evidence of malarial parasite DNA was found in the current study. Discrepancies between these findings and historical records of Plasmodium spp found in blood smears and post mortem may be explained either by inaccuracy of the serological test used, or by infection occurring in juveniles which is subsequently cleared in surviving adults.

Age-adjusted Plasmodium falciparum antibody levels in school-aged children are a stable marker of microgeographical variations in exposure to Plasmodium infection

Background

Amongst school-aged children living in malaria endemic areas, chronic morbidity and exacerbation of morbidity associated with other infections are often not coincident with the presence or levels of Plasmodium parasitaemia, but may result from long-term exposure to the parasite. Studies of hepatosplenomegaly associated with Schistosoma mansoni infection and exposure to Plasmodium infection indicate that differences that occur over 1–2 km in levels of Plasmodium transmission are related to the degree of exacerbation of hepatosplenomegaly and that Plasmodium falciparum schizont antigen (Pfs)-IgG3 levels may be a marker for the differing levels of exposure.

Methods

To investigate the validity of Pfs-IgG3 measurements as a tool to assess these comparative exposure levels on a microgeographical scale, cross-sectional community surveys were conducted over a 10 × 6 km study site in Makueni District, Kenya, during low and high malaria transmission seasons. During both high and low malaria transmission seasons, thick blood smears were examined microscopically and circulating Pfs-IgG3 levels measured from dried blood spot elute. GIS techniques were used to map prevalence of parasitaemia and Pfs-IgG3 levels.

Results

Microgeographical variations in prevalence of parasitaemia were observed during the high but not the low transmission season. Pfs-IgG3 levels were stable between high and low transmission seasons, but increased with age throughout childhood before reaching a plateau in adults. Adjusting Pfs-IgG3 levels of school-aged children for age prior to mapping resulted in spatial patterns that reflected the microgeographical variations observed for high season prevalence of parasitaemia, however, Pfs-IgG3 levels of adults did not. The distances over which age-adjusted Pfs-IgG3 of school-aged children fluctuated were comparable with those distances over which chronic morbidity has previous been shown to vary.

Conclusion

Age-adjusted Pfs-IgG3 levels of school-aged children are stable and when mapped can provide a tool sensitive enough to detect microgeographical variations in malaria exposure, that would be useful for studying the aetiology of morbidities associated with long-term exposure and co-infections.

Increased human IgE induced by killing Schistosoma mansoni in vivo is associated with pretreatment Th2 cytokine responsiveness to worm antigens

In schistosomiasis endemic areas, children are very susceptible to postchemotherapy reinfection, whereas adults are relatively resistant. Different studies have reported that schistosome-specific IL-4 and IL-5 responses, or posttreatment worm-IgE levels, correlate with subsequent low reinfection. Chemotherapy kills i.v. worms providing an in vivo Ag challenge. We measured anti-worm (soluble worm Ag (SWA) and recombinant tegumental Ag (rSm22.6)) and anti-egg (soluble egg Ag) Ab levels in 177 Ugandans (aged 7-50) in a high Schistosoma mansoni transmission area, both before and 7 wk posttreatment, and analyzed these data in relation to whole blood in vitro cytokine responses at the same time points. Soluble egg Ag-Ig levels were unaffected by treatment but worm-IgG1 and -IgG4 increased, whereas worm-IgE increased in many but not all individuals. An increase in worm-IgE was mainly seen in >15-year-olds and, unlike in children, was inversely correlated to pretreatment infection intensities, suggesting this response was associated both with resistance to pretreatment infection, as well as posttreatment reinfection. The increases in SWA-IgE and rSm22.6-IgE positively correlated with pretreatment Th2 cytokines, but not IFN-gamma, induced by SWA. These relationships remained significant after allowing for the confounding effects of pretreatment infection intensity, age, and pretreatment IgE levels, indicating a link between SWA-specific Th2 cytokine responsiveness and subsequent increases in worm-IgE. An exceptionally strong relationship between IL-5 and posttreatment worm-IgE levels in < 15-year-olds suggested that the failure of younger children to respond to in vivo Ag stimulation with increased levels of IgE, is related to their lack of pretreatment SWA Th2 cytokine responsiveness.

Schistosomiasis and malaria: another piece of the crossreactivity puzzle

The recent discovery that individuals living in endemic areas have antibodies in their sera that are crossreactive for both helminth and malaria parasites raises important questions both of the interpretation of existing immunoepidemiological data and of the basic biology of the host and the parasites. One such shared antigen (SmLRR) has now been cloned and has, therefore, opened up an intriguing and exciting field of research for immunologists and parasitologists.

Identification of a novel antigen of Schistosoma mansoni shared with Plasmodium falciparum and evaluation of different cross-reactive antibody subclasses induced by human schistosomiasis and malaria

Plasmodium falciparum and Schistosoma mansoni are often found in human coinfections, and cross-reactive antibodies to different components of the two parasites have been detected. In this work, we identified a cross-reactive S. mansoni gene product, referred to as SmLRR, that seems to belong to the leucine-rich repeat protein family. Comparative analysis of SmLRR revealed 57% similarity with a putative gene product encoded in the P. falciparum genome. Antibodies to SmLRR were found in experimental infections and in both S. mansoni- and P. falciparum-infected individuals. Correlative analysis of human anti-SmLRR responses in Kenya and Uganda suggested that malaria and schistosomiasis drive the immunoglobulin G3 (IgG3) and IgG4 isotypes, respectively, against SmLRR, suggesting that there is differential regulation of cross-reactive isotypes depending on the infection. In addition, the levels of anti-SmLRR IgG4, but not the levels of IgG3, correlated positively with the intensity of S. mansoni infection.

Applied and basic research on the epidemiology, morbidity, and immunology of schistosomiasis in fishing communities on Lake Albert, Uganda

We report multidisciplinary studies on schistosomiasis which have been ongoing in the fishing communities of Piida, Booma, Bugoigo and Walakuba, on Lake Albert, Uganda, since 1996. Schistosomiasis is the major health problem in this area, with high infection intensities and prevalence. In addition to generating basic data on the epidemiology, morbidity and immunology of human schistosomiasis, this research programme is providing important descriptive and methodological information, and has contributed to the increase in operational capacity within Uganda in recent years. Such information and operational capacity are needed to facilitate much needed schistosomiasis control programmes, such as the Schistosomiasis Control Initiative that was launched in Uganda in 2003.

An historical and genomic view of schistosome conjugal biology with emphasis on sex-specific gene expression

The genetic programmes associated with the sexual biology of dioecious schistosomes remain a critically important but significantly understudied area of parasitology. Throughout the last four decades, progress has been slow in describing the gross antigenic and proteomic differences linked to sexually mature schistosomes and in characterizing some of the sex-associated transcripts and regulatory mechanisms induced during developmental maturation. These investigations have been severely hindered by the lack of complete EST/genomic information, as well as corresponding post- and functional-genomic tools for studying these pathogenic parasites. As near complete transcriptomes forSchistosoma japonicumandS. mansonihave recently been reported, and both DNA microarrays and post-transcriptional gene silencing have been applied to schistosomes, the tools and techniques for the high-throughput identification and characterization of transcripts involved in conjugal biology are now readily available. Here, an historical review is presented that summarizes some of the most significant findings associated with schistosome sex and sexual maturation during the last several decades. Following this discussion is a current overview of some modern day genomic approaches used to study schistosomes, which illustrates how major advances in the field of conjugal biology will be achieved.

Cytokine profile associated with human chronic schistosomiasis mansoni

This study objective was to evaluate the cytokines associated with early events of hepatic fibrosis in schistosomiasis mansoni. Hepatic fibrosis was classified by ultrasonography in 94 patients. Immunological evaluation was performed by measurement of secreted cytokines (interleukin IL-5, IL-10, IL-13, interferon-gamma, tumor necrosis factor-alpha and transforming growth factors-beta) in peripherl blood mononuclear cells stimulated by Schistosoma mansoni antigens. Significantly, higher levels of IL-5, IL-10 and IL-13 were found in supernatants of SEA-stimulated PBMC from subjects with degree III hepatic fibrosis as compared to patients with degree I or II fibrosis, Significant increases in IL-5 and IL-13 levels were also observed in some of the subjects who remained untreated for one year following initial assessment and developed more serious fibrosis during this period. The data suggests a role for type 2 cytokines in early stages of hepatic fibrosis in human schistosomiasis mansoni.

Immunopathogenesis of schistosomiasis

In schistosomiasis mansoni, the chronic egg-induced granulomatous response in the liver and intestines may eventually cause extensive tissue scarring and development of portal hypertension. Indeed, much of the morbidity and mortality associated with this disease is directly attributable to the deposition of connective tissue elements in affected tissues. Elucidating the mechanisms that regulate the severity of schistosomiasis has been a major research objective over the past several years. Research conducted with DNA microarrays as well as investigations with a variety of gene knock-out mice have been particularly helpful in achieving this goal. A notable accomplishment in the past few years was the identification of interleukin-13 (IL-13) and the IL-13 receptor complex as central regulators of disease progression in schistosomiasis. Liver fibrogenesis is severely decreased in infected IL-13-deficient mice as well as in wildtype animals treated with IL-13 antagonists. In contrast, IL-13 effector function increases dramatically in IL-13 receptor alpha2 (IL-13Ralpha2)-deficient mice. These mice develop severe hepatic fibrosis, fail to downregulate granuloma formation in the chronic phase of S. mansoni infection, and succumb to the disease at an accelerated rate; thus, identifying the 'decoy' IL-13 receptor as a critical life sustaining 'off' switch for tissue damaging egg-induced inflammation.

Exposure to malaria affects the regression of hepatosplenomegaly after treatment for Schistosoma mansoni infection in Kenyan children

BACKGROUND

Schistosoma mansoni and malaria infections are often endemic in the same communities in sub-Saharan Africa, and both have pathological effects on the liver and the spleen. Hepatosplenomegaly associated with S. mansoni is exacerbated in children with relatively high exposure to malaria. Treatment with praziquantel reduces the degree of hepatosplenomegaly, but the condition does not completely resolve in some cases. The present analysis focused on the possibility that exposure to malaria infection may have limited the resolution of hepatosplenomegaly in a cohort of Kenyan schoolchildren.

METHODS

Ninety-six children aged 6-16, from one community in Makueni district, Kenya, were treated with praziquantel. At baseline, all children had hepatomegaly and most had splenomegaly. The source of S. mansoni infection, a river, was molluscicided regularly over the following three years to limit S. mansoni re-infection, whereas malaria exposure was uninterrupted. Hepatic and splenic enlargement was assessed annually outside the malaria transmission season.

RESULTS

Children living in an area of relatively high exposure to both infections presented with the largest spleens before treatment and at each follow-up. Spleens of firm consistency were associated with proximity to the river. The regression of hepatomegaly was also affected by location, being minimal in an area with relatively low S. mansoni exposure but high exposure to malaria, and maximal in an area with relatively low exposure to both infections.

CONCLUSIONS

The outcome of treating cases of hepatosplenomegaly with praziquantel in this cohort of Kenyan children depended strongly on their level of exposure to malaria infection. Furthermore, a residual burden of hepatosplenic morbidity was observed, which was possibly attributable to the level of exposure to malaria. The results suggest that exposure to malaria infection may be a significant factor affecting the outcome of praziquantel treatment to reduce the level of hepatosplenic morbidity.

Association of type 2 cytokines with hepatic fibrosis in human Schistosoma mansoni infection

The objective of this study was to evaluate the role of cytokines in hepatic fibrosis in the prehepatosplenic and early hepatosplenic stages of schistosomiasis mansoni. Hepatic fibrosis was classified by ultrasonography of 94 patients. Immunological evaluation was performed by the measurement of secreted cytokines (interleukin-5 [IL-5], IL-10, IL-13, gamma interferon, tumor necrosis factor alpha, and transforming growth factor beta) in peripheral blood mononuclear cells (PBMC) stimulated by Schistosoma mansoni antigens. Significantly, higher levels of IL-5, IL-10, and IL-13 were found in supernatants of soluble egg antigen-stimulated PBMC from subjects with degree III hepatic fibrosis compared to patients with degree I or II fibrosis. Significant increases in IL-5 and IL-13 levels were also observed in some of the subjects who remained untreated for 1 year following initial assessment and developed more serious fibrosis during this period. The data suggest a role for type 2 cytokines in hepatic fibrosis in human schistosomiasis mansoni.

Micro-geographical variation in exposure to Schistosoma mansoni and malaria, and exacerbation of splenomegaly in Kenyan school-aged children

BACKGROUND

Schistosoma mansoni and Plasmodium falciparum are common infections of school aged children in Kenya. They both cause enlargement of the spleen, but their relative contribution to the condition of splenomegaly remains unknown in areas where both infections are endemic. Here, we have investigated whether relatively high exposure to both infections has a clinically measurable effect on this condition.

METHODS

96 children aged 6-16 years living along a ten kilometre stretch and within 4 km south of a river that is a source of both S. mansoni and malaria infections were examined clinically for splenomegaly along the mid clavicular line (MCL) and mid axillary line (MAL). The survey was conducted outside the malaria transmission season. The consistency of the organ was recorded as soft, firm or hard. Mapping of the locations of houses and the course of the river was undertaken. Egg counts were mapped at the household level, as were IgG3 responses to Plasmodium falciparum schizont antigen (anti-Pfs IgG3), in order to identify areas with relatively high exposure to both infections, either infection or neither infection. ANOVA was used to test for differences in egg counts, IgG3 levels and the magnitude of spleen enlargement between these areas.

RESULTS

4 contiguous sectors were identified, one where anti-Pfs IgG3 responses and S. mansoni egg counts were both high, one where only anti-Pfs IgG3 responses were high, one where only egg counts were high, and one where both anti-Pfs IgG3 responses and egg counts were low. Spleen MAL and MCL values were significantly higher amongst children from the sector with highest IgG3 levels and highest egg counts but similar amongst children from elsewhere. Both egg counts and anti-Pfs IgG3 responses were significantly higher in children with MAL values > or =4 cm. Hardening of spleens was associated with proximity of domicile to the river.

CONCLUSIONS

Micro-geographical variation in exposure to S. mansoni and malaria infections can be exploited to investigate the chronic impact of these two infections. These results provide firm evidence that relatively high exposure to both infections exacerbates splenomegaly even outside the malaria transmission season. Major implications include assessing the burden of infection in school age-children.