Disentangling complex parasite interactions: Protection against cerebral malaria by one helminth species is jeopardized by co-infection with another

Network Analysis of Hosts and Vectors in the Multiple Transmissions of Flavivirus

Background: It is well established that infection patterns in nature can be driven by host, vector, and symbiont communities. One of the first stages in understanding how these complex systems have influenced the incidence of vector-borne diseases is to recognize what are the major vertebrate (i.e., hosts) and invertebrate (i.e., vectors) host species that propagate those microbes. Such identification opens the possibility to identify such essential species to develop targeted preventive efforts. Methods: The goal of this study, which relies on a compilation of a global database based on published literature, is to identify relevant host species in the global transmission of mosquito-borne flaviviruses, such as West Nile virus, St. Louis virus, Dengue virus, and Zika virus, which pose a concern to animal and public health. Results: The analysis of the resulting database involving 1174 vertebrate host species and 46 reported vector species allowed us to establish association networks between these species. Three host species (Mus musculus, Sapajus flavius, Sapajus libidinosus, etc.) have a much larger centrality values, suggesting that they play a key role in flavivirus community interactions. Conclusion: The methods used and the species detected as relevant in the network provide new knowledge and consistency that could aid health officials in rethinking prevention and control strategies with a focus on viral communities and their interactions. Other infectious diseases that harm animal and human health could benefit from such network techniques.

Helminth-host-environment interactions: Looking down from the tip of the iceberg

In 1978, the theory behind helminth parasites having the potential to regulate the abundance of their host populations was formalized based on the understanding that those helminth macroparasites that reduce survival or fecundity of the infected host population would be among the forces limiting unregulated host population growth. Now, 45 years later, a phenomenal breadth of factors that directly or indirectly affect the host-helminth interaction has emerged. Based largely on publications from the past 5 years, this review explores the host-helminth interaction from three lenses: the perspective of the helminth, the host, and the environment. What biotic and abiotic as well as social and intrinsic host factors affect helminths? What are the negative, and positive, implications for host populations and communities? What are the larger-scale implications of the host-helminth dynamic on the environment, and what evidence do we have that human-induced environmental change will modify this dynamic? The overwhelming message is that context is everything. Our understanding of second-, third-, and fourth-level interactions is extremely limited, and we are far from drawing generalizations about the myriad of microbe-helminth-host interactions.Yet the intricate, co-evolved balance and complexity of these interactions may provide a level of resilience in the face of global environmental change. Hopefully, this albeit limited compilation of recent research will spark new interdisciplinary studies, and application of the One Health approach to all helminth systems will generate new and testable conceptual frameworks that encompass our understanding of the host-helminth-environment triad.

Effects of Age, Gender and Soil-Transmitted Helminth Infection on Prevalence of Plasmodium Infection among Population Living in Bata District, Equatorial Guinea

Introduction: Malaria and soil-transmitted helminth (STH) co-infection is an important parasitic infection affecting populations in co-endemic countries including Equatorial Guinea. To date, the health impact of STH and malaria co-infection is inconclusive. The current study aimed to report the malaria and STH infection epidemiology in the continental region of Equatorial Guinea. Methods: We performed a cross-sectional study between October 2020 and January 2021 in the Bata district of Equatorial Guinea. Participants aged 1–9 years, 10–17 years and above 18 were recruited. Fresh venous blood was collected for malaria testing via mRDTs and light microscopy. Stool specimens were collected, and the Kato–Katz technique was used to detect the presence of Ascaris lumbricoides, Trichuris trichiura, hookworm spp. and intestinal Schistosoma eggs. Results: A total of 402 participants were included in this study. An amount of 44.3% of them lived in urban areas, and only 51.9% of them reported having bed nets. Malaria infections were detected in 34.8% of the participants, while 50% of malaria infections were reported in children aged 10–17 years. Females had a lower prevalence of malaria (28.8%) compared with males (41.7%). Children of 1–9 years carried more gametocytes compared with other age groups. An amount of 49.3% of the participants infected with T. trichiura had malaria parasites compared with those infected with A. lumbricoides (39.6%) or both (46.8%). Conclusions: The overlapping problem of STH and malaria is neglected in Bata. The current study forces the government and other stakeholders involved in the fight against malaria and STH to consider a combined control program strategy for both parasitic infections in Equatorial Guinea.

Potential Facilitation Between a Commensal and a Pathogenic Microbe in a Wildlife Disease

We assessed the potential for microbial interactions influencing a well-documented host-pathogen system. Mycoplasma agassizii is the known etiological agent of upper respiratory tract disease in Mojave desert tortoises (Gopherus agassizii), but disease in wild animals is extremely heterogeneous. For example, a much larger proportion of animals harbor M. agassizii than those that develop disease. With the availability of a new quantitative PCR assay for a microbe that had previously been implicated in disease, Pasteurella testudinis, we tested 389 previously collected samples of nasal microbes from tortoise populations across the Mojave desert. We showed that P. testudinis is a common commensal microbe. However, we did find that its presence was associated with higher levels of M. agassizii among the tortoises positive for this pathogen. The best predictor of P. testudinis prevalence in tortoise populations was average size of tortoises, suggesting that older populations have higher levels of P. testudinis. The prevalence of co-infection in populations was associated with the prevalence of URTD, providing additional evidence for an indirect interaction between the two microbes and inflammatory disease. We showed that URTD, like many chronic, polymicrobial diseases involving mucosal surfaces, shows patterns of a polymicrobial etiology.

Capturing complex interactions in disease ecology with simplicial sets

Network approaches have revolutionized the study of ecological interactions. Social, movement and ecological networks have all been integral to studying infectious disease ecology. However, conventional (dyadic) network approaches are limited in their ability to capture higher-order interactions. We present simplicial sets as a tool that addresses this limitation. First, we explain what simplicial sets are. Second, we explain why their use would be beneficial in different subject areas. Third, we detail where these areas are: social, transmission, movement/spatial and ecological networks and when using them would help most in each context. To demonstrate their application, we develop a novel approach to identify how pathogens persist within a host population. Fourth, we provide an overview of how to use simplicial sets, highlighting specific metrics, generative models and software. Finally, we synthesize key research questions simplicial sets will help us answer and draw attention to methodological developments that will facilitate this.

Plasmodium falciparum coinfection is associated with improved IgE and IgG3 response against hookworm antigens

Background

Plasmodium falciparum and Hookworm infections are prevalent in West Africa and they cause iron deficiency anemia and protein malnutrition in Children. Immune response of these parasites interact and their interactions could have repercussions on vaccine development and efficacy. The current goal of hookworm eradication lies on vaccination. We evaluated the effect of P. falciparum coinfection and albendazole treatment on naturally acquired antibody profile against hookworm L3 stage larvae antigen.

Methods

In a longitudinal study, 40 individuals infected with Necator americanus only, 63 participants infected with N. americanus and P. falciparum, and 36 nonendemic controls (NECs) were recruited. The study was done in the Kintampo North Metropolis of Ghana. Stool and blood samples were taken for laboratory analyses. Serum samples were obtained before hookworm treatment and 3 weeks after treatment.

Results

The malaria-hookworm (N. americanus and P. falciparum) coinfected subjects had significantly higher levels of IgE (β = 0.30, 95% CI = [0.12, 0.48], p = 0.023) and IgG3 (β = 0.15, 95% CI = [0.02, 0.52], p = 0.004) compared to those infected with hookworm only (N. americanus). The N. americanus groups had significantly higher levels of IgG3 (β = 0.39, 95% CI = [0.14-0.62], p = 0.002) compared to the control group. Similarly, N. americanus and P. falciparum coinfected participants had significantly higher levels of IgE (β = 0.35, 95% CI = [0.70-0.39], p = 0.002) and IgG3 (β = 0.54, 95% CI = [0.22-0.76], p = 0.002). Moreover, albendazole treatment led to a significant reduction in IgE, IgA, IgM, and IgG3 antibodies against hookworm L3 stage larvae (p < 0.05).

Conclusion

P. falciparum is associated with improved IgE and IgG response against hookworm L3 stage larvae. Treatment with single dose of albendazole led to reduction in naturally acquired immune response against hookworm infection. Thus, P. falciparum infection may have a boosting effect on hookworm vaccine effectiveness.

Possible Interactions between Malaria, Helminthiases and the Gut Microbiota: A Short Review

Malaria, caused by the Plasmodium species, is an infectious disease responsible for more than 600 thousand deaths and more than 200 million morbidity cases annually. With above 90% of those deaths and cases, sub-Saharan Africa is affected disproportionately. Malaria clinical manifestations range from asymptomatic to simple, mild, and severe disease. External factors such as the gut microbiota and helminthiases have been shown to affect malaria clinical manifestations. However, little is known about whether the gut microbiota has the potential to influence malaria clinical manifestations in humans. Similarly, many previous studies have shown divergent results on the effects of helminths on malaria clinical manifestations. To date, a few studies, mainly murine, have shown the gut microbiota’s capacity to modulate malaria’s prospective risk of infection, transmission, and severity. This short review seeks to summarize recent literature about possible interactions between malaria, helminthiases, and the gut microbiota. The knowledge from this exercise will inform innovation possibilities for future tools, technologies, approaches, and policies around the prevention and management of malaria in endemic countries.

Microbial (co)infections: Powerful immune influencers

It is well established that by modulating various immune functions, host infection may alter the course of concomitant inflammatory diseases, of both infectious and autoimmune etiologies. Beyond the major impact of commensal microbiota on the immune status, host exposure to viral, bacterial, and/or parasitic microorganisms also dramatically influences inflammatory diseases in the host, in a beneficial or harmful manner. Moreover, by modifying pathogen control and host tolerance to tissue damage, a coinfection can profoundly affect the development of a concomitant infectious disease. Here, we review the diverse mechanisms that underlie the impact of (co)infections on inflammatory disorders. We discuss epidemiological studies in the context of the hygiene hypothesis and shed light on the sometimes dual impact of germ exposure on human susceptibility to inflammatory disease. We then summarize the immunomodulatory mechanisms at play, which can involve pleiotropic effects of immune players and discuss the possibility to harness pathogen-derived compounds to the host benefit.

Plasmodium falciparum and Helminth Coinfections Increase IgE and Parasite-Specific IgG Responses

Coinfection with Plasmodium falciparum and helminths may impact the immune response to these parasites because they induce different immune profiles. We studied the effects of coinfections on the antibody profile in a cohort of 715 Mozambican children and adults using the Luminex technology with a panel of 16 antigens from P. falciparum and 11 antigens from helminths (Ascaris lumbricoides, hookworm, Trichuris trichiura, Strongyloides stercoralis, and Schistosoma spp.) and measured antigen-specific IgG and total IgE responses. We compared the antibody profile between groups defined by P. falciparum and helminth previous exposure (based on serology) and/or current infection (determined by microscopy and/or qPCR). In multivariable regression models adjusted by demographic, socioeconomic, water, and sanitation variables, individuals exposed/infected with P. falciparum and helminths had significantly higher total IgE and antigen-specific IgG levels, magnitude (sum of all levels) and breadth of response to both types of parasites compared to individuals exposed/infected with only one type of parasite (P ≤ 0.05). There was a positive association between exposure/infection with P. falciparum and exposure/infection with helminths or the number of helminth species, and vice versa (P ≤ 0.001). In addition, children coexposed/coinfected tended (P = 0.062) to have higher P. falciparum parasitemia than those single exposed/infected. Our results suggest that an increase in the antibody responses in coexposed/coinfected individuals may reflect higher exposure and be due to a more permissive immune environment to infection in the host. IMPORTANCE Coinfection with Plasmodium falciparum and helminths may impact the immune response to these parasites because they induce different immune profiles. We compared the antibody profile between groups of Mozambican individuals defined by P. falciparum and helminth previous exposure and/or current infection. Our results show a significant increase in antibody responses in individuals coexposed/coinfected with P. falciparum and helminths in comparison with individuals exposed/infected with only one of these parasites, and suggest that this increase is due to a more permissive immune environment to infection in the host. Importantly, this study takes previous exposure into account, which is particularly relevant in endemic areas where continuous infections imprint and shape the immune system. Deciphering the implications of coinfections deserves attention because accounting for the real interactions that occur in nature could improve the design of integrated disease control strategies.

Asymptomatic Malaria and Helminths Coinfection and Its Association with Anemia among Primary School Children in Gedeo Zone, Southern Ethiopia: A Cross-Sectional Study

Background

Asymptomatic malaria and helminths coinfection occurs mainly in the tropics and subtropics where poverty and sanitary practice favor its high prevalence. In the tropics, where malaria is endemic, helminths also thrive resulting in coinfection. This study aimed to access the prevalence of asymptomatic malaria and helminths coinfection and its contribution for anemia in primary school children of Gedeo Zone, Southern Ethiopia. Methodology. This was a cross-sectional study conducted among 413 primary school children from February to April 2020. Finger-prick blood samples were used to determine asymptomatic malaria and hemoglobin concentrations. Stool samples were collected and processed through formalin-ether concentration techniques to detect the presence of intestinal helminths. Data were double entered into Epi Data version 3.1 software and exported to SPSS version 20 for analysis. Pearson's chi-square and correlation analysis were performed as part of the statistical analyses.

Result

A total of 413 primary school children aged 6 to 16 years (mean age ± SD: 10.7 ± 2.64years) were enrolled in the study. 159 (38.5%) of school children were infected with at least one of the parasitic diseases. The overall prevalence of asymptomatic malaria and intestinal helminths was 46 (11.1%) and 113 (27.3%) respectively. Asymptomatic malaria and helminths coinfection was 29 (7%). Total of 39.1% of asymptomatic malaria-infected school children were anemic, which is statistically significant (P < 0.05). 15.9% of helminths-infected school children were anemic, not statistically significant (P > 0.05). The prevalence of anemia was 12 (41.3%) among coinfected students, which is statistically significant (P < 0.005).

Conclusion

Asymptomatic malaria and helminths coinfection affects the health status of considerable number of primary school children in the study area. Therefore, simultaneous combat against the two parasitic infections is crucial to improve health of the school children.

Indirect interactions among co-infecting parasites and a microbial mutualist impact disease progression

Interactions among parasites and other microbes within hosts can impact disease progression, yet study of such interactions has been mostly limited to pairwise combinations of microbes. Given the diversity of microbes within hosts, indirect interactions among more than two microbial species may also impact disease. To test this hypothesis, we performed inoculation experiments that investigated interactions among two fungal parasites, Rhizoctonia solani and Colletotrichum cereale, and a systemic fungal endophyte, Epichloë coenophiala, within the grass, tall fescue (Lolium arundinaceum). Both direct and indirect interactions impacted disease progression. While the endophyte did not directly influence R. solani disease progression or C. cereale symptom development, the endophyte modified the interaction between the two parasites. The magnitude of the facilitative effect of C. cereale on the growth of R. solani tended to be greater when the endophyte was present. Moreover, this interaction modification strongly affected leaf mortality. For plants lacking the endophyte, parasite co-inoculation did not increase leaf mortality compared to single-parasite inoculations. By contrast, for endophyte-infected plants, parasite co-inoculation increased leaf mortality compared to inoculation with R. solani or C. cereale alone by 1.9 or 4.9 times, respectively. Together, these results show that disease progression can be strongly impacted by indirect interactions among microbial symbionts.

An Ecologically Framed Comparison of The Potential for Zoonotic Transmission of Non-Human and Human-Infecting Species of Malaria Parasite

The threats, both real and perceived, surrounding the development of new and emerging infectious diseases of humans are of critical concern to public health and well-being. Among these risks is the potential for zoonotic transmission to humans of species of the malaria parasite, Plasmodium, that have been considered historically to infect exclusively non-human hosts. Recently observed shifts in the mode, transmission, and presentation of malaria among several species studied are evidenced by shared vectors, atypical symptoms, and novel host-seeking behavior. Collectively, these changes indicate the presence of environmental and ecological pressures that are likely to influence the dynamics of these parasite life cycles and physiological make-up. These may be further affected and amplified by such factors as increased urban development and accelerated rate of climate change. In particular, the extended host-seeking behavior of what were once considered non-human malaria species indicates the specialist niche of human malaria parasites is not a limiting factor that drives the success of blood-borne parasites. While zoonotic transmission of non-human malaria parasites is generally considered to not be possible for the vast majority of Plasmodium species, failure to consider the feasibility of its occurrence may lead to the emergence of a potentially life-threatening blood-borne disease of humans. Here, we argue that recent trends in behavior among what were hitherto considered to be non-human malaria parasites to infect humans call for a cross-disciplinary, ecologically-focused approach to understanding the complexities of the vertebrate host/mosquito vector/malaria parasite triangular relationship. This highlights a pressing need to conduct a multi-species investigation for which we recommend the construction of a database to determine ecological differences among all known Plasmodium species, vectors, and hosts. Closing this knowledge gap may help to inform alternative means of malaria prevention and control.

Encapsulation of Anguillicola crassus reduces the abundance of adult parasite stages in the European eel (Anguilla anguilla)

Encapsulation of the parasitic nematode Anguillicola crassus Kuwahara, Niimi & Hagaki is commonly observed in its native host, the Japanese eel (Anguilla japonica Temminck & Schlegel). Encapsulation has also been described in a novel host, the European eel (A. anguilla L.), and there is evidence that encapsulation frequency has increased since the introduction of A. crassus. We examined whether encapsulation of A. crassus provides an advantage to its novel host in Lake Müggelsee, NE Germany. We provide the first evidence that encapsulation was associated with reduced abundance of adult A. crassus. This pattern was consistent in samples taken 3 months apart. There was no influence of infection on the expression of the two metabolic genes studied, but the number of capsules was negatively correlated with the expression of two mhc II genes of the adaptive immune response, suggesting a reduced activation. Interestingly, eels that encapsulated A. crassus had higher abundances of two native parasites compared with non-encapsulating eels. We propose that the response of A. anguilla to infection by A. crassus may interfere with its reaction to other co-occurring parasites.

Malaria Parasitemia in Febrile Patients Mono- and Coinfected with Soil-Transmitted Helminthiasis Attending Sanja Hospital, Northwest Ethiopia

Background

Malaria is a life-threatening disease associated with high morbidity and mortality. Helminths are among the most widespread infectious agents prevalent in tropical and subtropical regions of the developing world. Malaria and soil-transmitted helminthiasis (STHs) are coendemic and major public health problems in Ethiopia. The effects of helminth coinfection on malaria parasitemia remained poorly understood. Therefore, the objective of this study was to assess malaria parasitemia among malaria-monoinfected and malaria-soil-transmitted helminthiasis-coinfected febrile patients attending Sanja Hospital, Northwest Ethiopia.

Methods

A cross-sectional study with parallel groups was conducted to assess malaria parasitemia among malaria-monoinfected and malaria-soil-transmitted helminthiasis-coinfected febrile patients in Sanja Hospital from January to March 2019. Double population proportion formula was used for sample size calculation, and convenient sampling technique was used to select 134 study participants. Data were entered and analyzed by using the Statistical Package for Social Sciences (SPSS) version 20. Descriptive statistics, independent t-test, and one-way analysis of variance (ANOVA) were performed. A P value of <0.05 was considered as statistically significant.

Results

From 134 malaria-positive study participants, 67 were malaria-monoinfected and 67 were malaria-STHs-coinfected patients. Out of 67 malaria STHs-coinfected patients, 54 (80.6%) were infected with hookworm followed by Ascaris lumbricoides 11 (16.4%) and Strongyloides stercoralis 2 (3%). The mean Plasmodium parasite density was significantly higher in malaria-STHs-coinfected patients than in patients infected with only Plasmodium parasite density was significantly higher in malaria-STHs-coinfected patients than in patients infected with only P value of <0.05 was considered as statistically significant. Plasmodium parasite density was significantly higher in malaria-STHs-coinfected patients than in patients infected with only F = 6.953, P value of <0.05 was considered as statistically significant.

Conclusions

Infections with STHs, especially hookworm, were positively associated with Plasmodium parasite density. The current study finding also revealed that increased worm burden of hookworm as expressed by egg intensity had significantly increased Plasmodium parasite density.Plasmodium parasite density was significantly higher in malaria-STHs-coinfected patients than in patients infected with only Plasmodium parasite density was significantly higher in malaria-STHs-coinfected patients than in patients infected with only.

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.

Associations between soil-transmitted helminthiasis and viral, bacterial, and protozoal enteroinfections: a cross-sectional study in rural Laos

Background

Humans are susceptible to over 1400 pathogens. Co-infection by multiple pathogens is common, and can result in a range of neutral, facilitative, or antagonistic interactions within the host. Soil-transmitted helminths (STH) are powerful immunomodulators, but evidence of the effect of STH infection on the direction and magnitude of concurrent enteric microparasite infections is mixed.

Methods

We collected fecal samples from 891 randomly selected children and adults in rural Laos. Samples were analyzed for 5 STH species, 6 viruses, 9 bacteria, and 5 protozoa using a quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay. We utilized logistic regression, controlling for demographics and household water, sanitation, and hygiene access, to examine the effect of STH infection on concurrent viral, bacterial, and protozoal infection.

Results

We found that STH infection was associated with lower odds of concurrent viral infection [odds ratio (OR): 0.48, 95% confidence interval (CI): 0.28–0.83], but higher odds of concurrent bacterial infections (OR: 1.81, 95% CI: 1.06–3.07) and concurrent protozoal infections (OR: 1.50, 95% CI: 0.95–2.37). Trends were consistent across STH species.

Conclusions

The impact of STH on odds of concurrent microparasite co-infection may differ by microparasite taxa, whereby STH infection was negatively associated with viral infections but positively associated with bacterial and protozoal infections. Results suggest that efforts to reduce STH through preventive chemotherapy could have a spillover effect on microparasite infections, though the extent of this impact requires additional study. The associations between STH and concurrent microparasite infection may reflect a reverse effect due to the cross-sectional study design. Additional research is needed to elucidate the exact mechanism of the immunomodulatory effects of STH on concurrent enteric microparasite infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3471-2) contains supplementary material, which is available to authorized users.

Antagonistic effects of Plasmodium-helminth co-infections on malaria pathology in different population groups in Côte d'Ivoire

Introduction

Plasmodium spp. and helminths are co-endemic in many parts of the tropics; hence, co-infection is a common phenomenon. Interactions between Plasmodium and helminth infections may alter the host’s immune response and susceptibility and thus impact on morbidity. There is little information on the direction and magnitude of such interactions and results are conflicting. This study aimed at shedding new light on the potential interactions of Plasmodium and helminth co-infections on anemia and splenomegaly in different population groups in Côte d’Ivoire.

Methodology

Parasitologic and clinical data were obtained from four cross-sectional community-based studies and a national school-based survey conducted between 2011 and 2013 in Côte d’Ivoire. Six scenarios of co-infection pairs defined as Plasmodium infection or high parasitemia, combined with one of three common helminth infections (i.e., Schistosoma mansoni, S. haematobium, and hookworm) served for analysis. Adjusted logistic regression models were built for each scenario and interaction measures on additive scale calculated according to Rothman et al., while an interaction term in the model served as multiplicative scale measure.

Principal findings

All identified significant interactions were of antagonistic nature but varied in magnitude and species combination. In study participants aged 5–18 years from community-based studies, Plasmodium-hookworm co-infection showed an antagonistic interaction on additive scale on splenomegaly, while Plasmodium-Schistosoma co-infection scenarios showed protective effects on multiplicative scale for anemia and splenomegaly in participants aged 5–16 years from a school-based study.

Conclusions/Significance

No exacerbation from co-infection with Plasmodium and helminths was observed, neither in participants aged 5–18 years nor in adults from the community-based studies. Future studies should unravel underlying mechanisms of the observed interactions, as this knowledge might help shaping control efforts against these diseases of poverty.

Malaria (due to infection with Plasmodium spp.) and parasitic worms (for example soil-transmitted helminths and Schistosoma spp.) are common in the tropics. Hence, people are often co-infected, depending on various factors. Interactions between Plasmodium and helminth infections may alter immune response and susceptibility of the infected host, and thus impact on morbidity by either making it worse (synergism) or by reducing it (antagonism). Although these co-infections are common, little is known about the direction and magnitude of such interactions. To deepen the understanding of how co-infection could affect morbidity in infected people, we looked at clinical data (i.e., anemia and splenomegaly) in different population groups in Côte d’Ivoire. We did not observe any exacerbation from co-infection with Plasmodium and helminths; all identified significant interactions were of antagonistic nature but varied in magnitude and parasite combination. In the light of enhanced control efforts targeting helminthiases, a better understanding about potential effects on susceptibility to malaria in co-endemic areas should be gained and intervention strategies against the two type of diseases be planned in a more integrative manner.

The Influence of Parasite Infections on Host Immunity to Co-infection With Other Pathogens

Parasites have evolved a wide range of mechanisms that they use to evade or manipulate the host's immune response and establish infection. The majority of the in vivo studies that have investigated these host-parasite interactions have been undertaken in experimental animals, especially rodents, which were housed and maintained to a high microbiological status. However, in the field situation it is increasingly apparent that pathogen co-infections within the same host are a common occurrence. For example, chronic infection with pathogens including malarial parasites, soil-transmitted helminths, Mycobacterium tuberculosis and viruses such as HIV may affect a third of the human population of some developing countries. Increasing evidence shows that co-infection with these pathogens may alter susceptibility to other important pathogens, and/or influence vaccine efficacy through their effects on host immune responsiveness. Co-infection with certain pathogens may also hinder accurate disease diagnosis. This review summarizes our current understanding of how the host's immune response to infection with different types of parasites can influence susceptibility to infection with other pathogenic microorganisms. A greater understanding of how infectious disease susceptibility and pathogenesis can be influenced by parasite co-infections will enhance disease diagnosis and the design of novel vaccines or therapeutics to more effectively control the spread of infectious diseases.