Helminth-Tuberculosis Co-infection: An Immunologic Perspective

Intestinal Helminth Infections and Their Association with QuantiFERON-TB Gold Plus Test Performance in an Endemic Setting, Northwest Ethiopia

Background

Timely detection and treatment of latent TB infection (LTBI) is part of WHO's strategy against tuberculosis (TB). Helminth infections can modulate immune responses, potentially impacting the performance of interferon-gamma release assays (IGRAs) such as the QuantiFERON-TB Gold Plus (QFT-Plus). This study evaluated the association between helminth infections and QFT-Plus results among participants from a TB-endemic region.

Methods

A cross-sectional study was conducted from October 2022 to March 2023 in Bahir Dar, Ethiopia. Stool samples of 314 potential participants were examined for helminths using wet mount and Kato-Katz techniques. LTBI was assessed by QFT-Plus from a total of 100 gender-matched helminth-positive and -negative participants. The association between helminth infection status, egg count, and QFT-Plus positivity was analyzed, and p values <0.05 were considered significant.

Results

Overall, 53 of 314 screened participants were infected with helminths (16.9%), with A. lumbricoides (47.2%) and hookworm (30.2%) as most prevalent species. The overall QFT-Plus positivity rate was 30.0%, with similar rates observed between helminth-positive and helminth-negative participants. Although QFT-Plus positivity was slightly lower in hookworm carriers (25%) compared to those with A. lumbricoides (32%), a higher-than-median hookworm egg burden was significantly associated with reduced QFT-Plus positivity (P = 0.029). QFT-Plus positivity was significantly higher among male participants than females (P = 0.032).

Conclusion

While overall helminth infection status did not significantly affect QFT-Plus positivity, higher hookworm burden was associated with reduced QFT-Plus reactivity. These findings suggest that the type of helminth and infection intensity, rather than its mere presence, may influence IGRA performance. Further studies with larger sample sizes are warranted to understand the species-specific effect of helminth infection on immune modulation of the host.

Intestinal Parasitic Infections May Be Overlooked Drivers of the Tuberculosis Pandemic

The burden of tuberculosis (TB) is disproportionate in tropical and subtropical regions, where parasitic coinfections are common. Given the significant geographical overlap between TB and intestinal parasitic infections, it is important to consider the implications of intestinal parasitic infections for the TB pandemic. Intestinal parasitic infections have been theorized to increase vulnerability to TB by altering the inflammatory milieu, inducing undernutrition that blunts the immune response, and affecting drug pharmacokinetics. In this perspective, we provide a background of the epidemiological and immunological evidence that links parasitic infections to increased risk of TB progression and worse treatment outcomes. We also identify gaps in our knowledge and call for increased research on TB-parasitic coinfections to ensure action on a potentially widespread TB comorbidity.

Exposure to bovine livestock and latent tuberculosis infection in children: Investigating the zoonotic tuberculosis potential in a large urban and peri-urban area of Cameroon

Bovine tuberculosis (bTB), a neglected zoonotic disease, is endemic in cattle in many Sub-saharan African countries, yet its contribution to tuberculosis (TB) burden is understudied. Rapid urbanisation and increase in demand for animal proteins, including dairy products, increases the risk of spill over. This study compared the latent tuberculosis infection (LTBI) risk in children, a proxy-measure for recent TB infection, in children living in high cattle density areas to children from the general population in Cameroon. Cross-sectional study in the Centre Region of Cameroon in 2021, recruiting 160 children aged 2-15 years, stratified by exposure to livestock, people treated for pulmonary TB (PTB) and the general community. Veinous blood was tested for LTBI using QuantiFERON-TB Gold-Plus. Prevalence were calculated and the association to exposure and other risk factors investigated using logistic regression models. The crude LTBI prevalence were 8.2% in the general population, 7.3% in those exposed to cattle and 61% in pulmonary TB household contacts. After adjusting for confounding and sampling design, exposure to cattle and exposure to pulmonary TB were associated with higher risk of LTBI than the general population (respectively odds ratio (OR): 3.56, 95%CI: 0.34 to 37.03; and OR: 10.36, 95%CI: 3.13 to 34.21). Children frequently consuming cow milk had higher risk of LTBI (OR: 3.35; 95%CI 0.18 to 60.94). Despite limited statistical power, this study suggests that children exposed to cattle in a setting endemic for bTB had higher risk of LTBI, providing indirect evidence that Mycobacterium bovis may contribute to TB burden.

The amalgam of naive CD4+ T cell transcriptional states is reconfigured by helminth infection to dampen the amplitude of the immune response

Naive CD4+ T cells in specific pathogen-free (SPF) mice are characterized by transcriptional heterogeneity and subpopulations distinguished by the expression of quiescence, the extracellular matrix (ECM) and cytoskeleton, type I interferon (IFN-I) response, memory-like, and T cell receptor (TCR) activation genes. We demonstrate that this constitutive heterogeneity, including the presence of the IFN-I response cluster, is commensal independent insofar as being identical in germ-free and SPF mice. By contrast, Nippostrongylus brasiliensis infection altered this constitutive heterogeneity. Naive T cell-intrinsic transcriptional changes acquired during helminth infection correlated with and accounted for decreased immunization response to an unrelated antigen. These compositional and functional changes were dependent variables of helminth infection, as they disappeared at the established time point of its clearance in mice. Collectively, our results indicate that the naive T cell pool is subject to dynamic transcriptional changes in response to certain environmental cues, which in turn permutes the magnitude of the immune response.

Immunological and Haematological Relevance of Helminths and Mycobacterium tuberculosis Complex Coinfection among Newly Diagnosed Pulmonary Tuberculosis Patients from Bobo-Dioulasso, Burkina Faso

The effect of helminthiasis on host immunity is a neglected area of research, particularly in tuberculosis (TB) infection. This study aimed to evaluate the effect of helminthiasis on immunological and haematological parameters in newly diagnosed TB patients in Bobo-Dioulasso. After all biological analyses, we formed three subpopulations: group 1 (n = 82), as control, were participants without helminthic or Mycobacterium tuberculosis complex infection (Mtb-/Helm-), group 2 (n = 73) were TB patients without helminthic infection (Mtb+/Helm-), and group 3 (n = 22) were TB patients with helminthic infection (Mtb+/Helm+). The proportion of helminth coinfection was 23.16% (22/95) in TB patients, and Schistosoma mansoni infection was found in 77.3% (17/22) cases of helminthiasis observed in this study. A low CD4 T cell count and a low CD4:CD8 ratio were significantly associated with concomitant infection with helminths and the Mtb complex (Mtb+/Helm+) compared to the other groups (p < 0.05). However, there was no statistically significant difference in the CD8 median among the three participating groups (p > 0.05). Lymphopenia, monocytosis, thrombocytosis, and hypochromic microcytic anaemia were the haematological defects observed in the Mtb+/Helm+ and Mtb+/Helm- patients. Exploring these types of immune-haematological biomarkers would be a valuable aid in diagnosing and a better follow-up and monitoring of the tuberculosis-helminthiasis coinfection.

Enhanced Glycosylation Caused by Overexpression of Rv1002c in a Recombinant BCG Promotes Immune Response and Protects against Mycobacterium tuberculosis Infection

Tuberculosis (TB) is a major global health threat despite its virtual elimination in developed countries. Issues such as drug accessibility, emergence of multidrug-resistant strains, and limitations of the current BCG vaccine highlight the urgent need for more effective TB control measures. This study constructed BCG strains overexpressing Rv1002c and found that the rBCG-Rv1002c strain secreted more glycosylated proteins, significantly enhancing macrophage activation and immune protection against Mycobacterium tuberculosis (M. tb). These results indicate that Rv1002c overexpression promotes elevated levels of O-glycosylation in BCG bacteriophages, enhancing their phagocytic and antigenic presentation functions. Moreover, rBCG-Rv1002c significantly upregulated immune regulatory molecules on the macrophage surface, activated the NF-κB pathway, and facilitated the release of large amounts of NO and H2O2, thereby enhancing bacterial control. In mice, rBCG-Rv1002c immunization induced greater innate and adaptive immune responses, including increased production of multifunctional and long-term memory T cells. Furthermore, rBCG-Rv1002c-immunized mice exhibited reduced lung bacterial load and histological damage upon M. tb infection. This result shows that it has the potential to be an excellent candidate for a preventive vaccine against TB.

Seroepidemiological study on coinfection of toxoplasmosis and active tuberculosis in Northern Iran: a case control study

Coinfection of tuberculosis (TB) and human parasitic infections is common in developing countries. There is little information about the prevalence of Toxoplasma gondii (T. gondii) infection among TB patients in Iran. In this case-control study, anti-toxoplasma antibodies were measured by ELISA method in 100 patients with active tuberculosis and 100 healthy individuals who were matched in terms of sex, age, and place of residence. Anti-T. gondii IgG antibodies were diagnosed in 62% of TB patients (95% CI 53-71%) and 70% of control subjects (95% CI 62-78%). Anti-T. gondii IgM antibodies were found in 1% of both TB patients and control group. The seroprevalence of T. gondii infection was not significantly different between TB patients and healthy individuals (P > 0.05). None of the assessed sociodemographic and behavioral factors was recognized as a risk factor for toxoplasmosis in TB infected patients. Moreover, the level of anti-T. gondii IgG antibodies concentration in TB patients was significantly higher than in control subjects and revealed skewness towards humoral immune response in TB patients. Coinfection of toxoplasmosis and tuberculosis was prevalent but T. gondii infection was independent of active TB in this co-endemic area.

The impact of within-host coinfection interactions on between-host parasite transmission dynamics varies with spatial scale

Within-host interactions among coinfecting parasites can have major consequences for individual infection risk and disease severity. However, the impact of these within-host interactions on between-host parasite transmission, and the spatial scales over which they occur, remain unknown. We developed and apply a novel spatially explicit analysis to parasite infection data from a wild wood mouse (Apodemus sylvaticus) population. We previously demonstrated a strong within-host negative interaction between two wood mouse gastrointestinal parasites, the nematode Heligmosomoides polygyrus and the coccidian Eimeria hungaryensis, using drug-treatment experiments. Here, we show this negative within-host interaction can significantly alter the between-host transmission dynamics of E. hungaryensis, but only within spatially restricted neighbourhoods around each host. However, for the closely related species E. apionodes, which experiments show does not interact strongly with H. polygyrus, we did not find any effect on transmission over any spatial scale. Our results demonstrate that the effects of within-host coinfection interactions can ripple out beyond each host to alter the transmission dynamics of the parasites, but only over local scales that likely reflect the spatial dimension of transmission. Hence there may be knock-on consequences of drug treatments impacting the transmission of non-target parasites, altering infection risks even for non-treated individuals in the wider neighbourhood.

Epigenetic changes induced by parasitic worms and their excretory-secretory products

Parasitic worms are pathogens of major medical and veterinary importance. They have evolved highly effective and sophisticated strategies of immune system manipulation, typically involving actively excreted/secreted (E-S) products. These molecules dampen and regulate the host immune responses that would otherwise result in parasite expulsion, thereby enabling the worms to survive in the host for many years, and they can also help prevent the potentially serious tissue damage that the worms can induce. Reflecting these E-S product-associated anti-inflammatory activities, there is also increasing evidence that parasitic worms and their products may serendipitously protect against allergic and autoimmune conditions and in addition, comorbidities of ageing that are associated with inflammatory responses, like type 2 diabetes and obesity. Research in this area has to date generally focused on identifying the cellular and effector targets of immunomodulation induced by the worm E-S products. However, increasing evidence that they can induce stably imprinted phenotypes of haematopoietic and stromal cells which promote their long-lasting survival has recently ignited interest in the ability of the molecules to epigenetically rewire cells to 'resolve and repair' phenotypes. Here, we review and discuss these new data in the context of their potential for exploitation in identifying novel gene signatures for the development of advanced and safe therapeutics for chronic inflammatory diseases.

Combination with Annual Deworming Treatments Does Not Enhance the Effects of PCV2 Vaccination on the Development of TB in Wild Boar Populations

Vaccination against PCV2 has been proven to be an effective measure to reduce the severity of TB in wild boar. The combination of this measure with strategies focused on treating other key concomitant pathogens, such as nematodes, could be a useful strategy. This study assesses whether a combination of deworming treatments and PCV2 vaccination may reduce the prevalence and severity of TB in wild boar. The study was conducted on five game estates in mid-western Spain where four groups of wild boar were produced: control, vaccinated, dewormed and vaccinated-dewormed. Wild boars from all groups were hunted between 2017 and 2020, and all of them received a TB diagnosis based on pathological and microbiological tests. Generalised linear models were used to explore the effect of deworming and PCV2 vaccination on TB prevalence and severity. PCV2-vaccinated animals showed lower probabilities of suffering severe TB lesions. However, no differences regarding TB severity were found between dewormed and non-dewormed wild boar. PCV2 vaccination reduces TB severity in wild boar. However, annual deworming does not produce a long-term parasitological reduction that can influence the development of TB in wild boar, nor does it improve the effect of PCV2 vaccination on TB.

Intestinal helminth co-infection and associated factors among pulmonary tuberculosis patients in Africa and Asia: a systematic review and meta-analysis

INTRODUCTION

Tuberculosis (TB) and intestinal helminths have huge public health importance, and they are geographically overlapped. Data about the burden of intestinal helminth and TB co-infection in these areas are fragmented. In this systematic review and meta-analysis we compile the current literatures and generate pooled prevalence. We also identity factors associated with intestinal helminth co-infection among TB patients.

METHODS

Original articles published in English language up to March 23, 2022 were systematically searched from electronic database (PubMed/Medline, Scopus, Science Direct, Google Scholars and HINARI). The search was done using medical subject heading terms and keywords. Identified articles were exported into the EndNote library. The identified articles were screened using PRISMA flow diagram. Then the methodological quality of included articles was evaluated and rated using the modified version of Newcastle-Ottawa Scale. Data were extracted using Microsoft Excel. Sensitivity analysis and Egger regression test were used for the assessment of heterogeneity and publication bias. Finally the results are presented with a meta-analysis of pooled estimates, forest plots, and tables. The quantitative data were analyzed using Stata version 14.

RESULTS

From a total of 5457 searched articles, 22 eligible articles were included in the review. The pooled prevalence of helminth co-infection among TB cases was 29.69% (95%CI: 21.10, 38.29). TB patients were found to more frequently harbor one or more intestinal helminths than TB negative individuals (OR = 1.72 (95%CI: 1.20, 2.48)). Among the reported helminths, Schistosoma mansoni and Strongyloides stercoralis had the highest pooled prevalence among TB cases. However, unlike other individual helminths, only Strongyloides stercoralis (OR = 2.67 (95% CI, 1.20-6.76)) had significant association with TB cases compared to TB negatives. BMI was significantly associated with intestinal helminth co-infection among TB patients (OR = 2.75 (95%CI: 1.19, 6.38)).

CONCLUSIONS

Patients with TB have been shown to harbor co-infection with one or more intestinal helminths with considerable proportions when compared with TB-negative individuals. The higher prevalence of helminth infection in TB cases might indicate that co-infection promotes active TB disease. Thus, routine intestinal helminth screening and assessment of their nutritional status is suggested for TB patients.

Prevalence and Clinical Relevance of Schistosoma mansoni Co-Infection with Mycobacterium tuberculosis: A Systematic Literature Review

Tuberculosis disease stands for the second leading cause of death worldwide after COVID-19, most active tuberculosis cases result from the reactivation of latent TB infection through impairment of immune response. Several factors are known to sustain that process. Schistosoma mansoni, a parasite of the helminth genus that possesses switching power from an immune profile type Th1 to Th2 that favors reactivation of latent TB bacteria. The aim of the study was to assess the prevalence of the co-infection between the two endemic infections. Systematic literature was contacted at the University Clinical Research Center at the University of Sciences, Techniques, and Technologies of Bamako in Mali. Original articles were included, and full texts were reviewed to assess the prevalence and better understand the immunological changes that occur during the co-infection. In total, 3530 original articles were retrieved through database search, 53 were included in the qualitative analysis, and data from 10 were included in the meta-analysis. Prevalence of the co-infection ranged from 4% to 34% in the literature. Most of the articles reported that immunity against infection with helminth parasite and more specifically Schistosoma mansoni infection enhances latent TB reactivation through Th1/Th2. In sum, the impact of Schistosoma mansoni co-infection with Mycobacterium tuberculosis is under-investigated. Understanding the role of this endemic tropical parasite as a contributing factor to TB epidemiology and burden could help integrate its elimination as one of the strategies to achieve the END-TB objectives by the year 2035.

Helminth species-specific effects on IFN-γ producing T cells during active and latent tuberculosis

BACKGROUND

Interferon-γ (IFN-γ) is a key cytokine inducing protective immune responses during tuberculosis (TB) infection. Helminth-induced immune responses may affect IFN-γ production by T cells, although its connection with disease severity and immune recovery during treatment is unexplored. We investigated the species-specific effect of helminths on the IFN-γ production by T cells in relation to disease severity during active and latent TB infection (LTBI).

METHODS

In this study, 69 active pulmonary TB patients (PTB), 28 with LTBI and 66 healthy controls were included. Active TB was diagnosed using GenXpert MTB/RIF while QuantiFERON test (QFT) was used for the screening of healthy community controls (CCs) and for the diagnosis of LTBI. Helminth infection was identified by routine diagnosis whereas clinical disease severity was evaluated by the TB score. Intracellular IFN-γ production of T cells in stimulated peripheral blood mononuclear cells (PBMCs) was analyzed by flow cytometry using TB antigens (PPD), the polyclonal T cell activator staphylococcal enterotoxin B (SEB), or medium as unstimulated control.

RESULTS

Helminth infected CCs and LTBI subjects showed a significant reduction of IFN-γ+ CD4+ T cells by PPD-stimulation compared to non-helminth infected control groups. The significant reduction in the frequency of IFN-γ+ T cells in both latent and active PTB patients following SEB stimulation was mostly attributed to Schistosoma mansoni infection, whereas Ascaris lumbricoides, Schistosoma mansoni, and hookworm infection contributed equally in CCs. Following anti-helminthic and anti-TB treatment for 2 months, the frequency of IFN-γ+ CD4 T cells in helminth coinfected PTB was restored to levels of helminth negative PTB before treatment. Helminth coinfected PTB patients with an intermediate and severe clinical course had reduced capacity for production of IFN-γ+ T cells compared to the corresponding non-helminth infected PTB.

CONCLUSION

We found a reduction in IFN-γ producing T cells by helminth coinfection which was restored following anti-helminthic treatment. This reduction was helminth species-dependent in an exploratory sub-analysis and correlated to increased disease severity.

IL-4 and helminth infection downregulate MINCLE-dependent macrophage response to mycobacteria and Th17 adjuvanticity

The myeloid C-type lectin receptor (CLR) MINCLE senses the mycobacterial cell wall component trehalose-6,6'-dimycolate (TDM). Recently, we found that IL-4 downregulates MINCLE expression in macrophages. IL-4 is a hallmark cytokine in helminth infections, which appear to increase the risk for mycobacterial infection and active tuberculosis. Here, we investigated functional consequences of IL-4 and helminth infection on MINCLE-driven macrophage activation and Th1/Th17 adjuvanticity. IL-4 inhibited MINCLE and cytokine induction after macrophage infection with Mycobacterium bovis bacille Calmette-Guerin (BCG). Infection of mice with BCG upregulated MINCLE on myeloid cells, which was inhibited by IL-4 plasmid injection and by infection with the nematode Nippostrongylus brasiliensis in monocytes. To determine the impact of helminth infection on MINCLE-dependent immune responses, we vaccinated mice with a recombinant protein together with the MINCLE ligand trehalose-6,6-dibehenate (TDB) as adjuvant. Concurrent infection with N. brasiliensis or with Schistosoma mansoni promoted T cell-derived IL-4 production and suppressed Th1/Th17 differentiation in the spleen. In contrast, helminth infection did not reduce Th1/Th17 induction by TDB in draining peripheral lymph nodes, where IL-4 levels were unaltered. Upon use of the TLR4-dependent adjuvant G3D6A, N. brasiliensis infection impaired selectively the induction of splenic antigen-specific Th1 but not of Th17 cells. Inhibition of MINCLE-dependent Th1/Th17 responses in mice infected with N. brasiliensis was dependent on IL-4/IL-13. Thus, helminth infection attenuated the Th17 response to MINCLE-dependent immunization in an organ- and adjuvant-specific manner via the Th2 cytokines IL-4/IL-13. Taken together, our results demonstrate downregulation of MINCLE expression on monocytes and macrophages by IL-4 as a possible mechanism of thwarted Th17 vaccination responses by underlying helminth infection.

Gastrointestinal helminths increase Bordetella bronchiseptica shedding and host variation in supershedding

Co-infected hosts, individuals that carry more than one infectious agent at any one time, have been suggested to facilitate pathogen transmission, including the emergence of supershedding events. However, how the host immune response mediates the interactions between co-infecting pathogens and how these affect the dynamics of shedding remains largely unclear. We used laboratory experiments and a modeling approach to examine temporal changes in the shedding of the respiratory bacterium Bordetella bronchiseptica in rabbits with one or two gastrointestinal helminth species. Experimental data showed that rabbits co-infected with one or both helminths shed significantly more B. bronchiseptica, by direct contact with an agar petri dish, than rabbits with bacteria alone. Co-infected hosts generated supershedding events of higher intensity and more frequently than hosts with no helminths. To explain this variation in shedding an infection-immune model was developed and fitted to rabbits of each group. Simulations suggested that differences in the magnitude and duration of shedding could be explained by the effect of the two helminths on the relative contribution of neutrophils and specific IgA and IgG to B. bronchiseptica neutralization in the respiratory tract. However, the interactions between infection and immune response at the scale of analysis that we used could not capture the rapid variation in the intensity of shedding of every rabbit. We suggest that fast and local changes at the level of respiratory tissue probably played a more important role. This study indicates that co-infected hosts are important source of variation in shedding, and provides a quantitative explanation into the role of helminths to the dynamics of respiratory bacterial infections.

Immunological Interactions between Intestinal Helminth Infections and Tuberculosis

Helminth infections are among the neglected tropical diseases affecting billions of people globally, predominantly in developing countries. Helminths’ effects are augmented by coincident tuberculosis disease, which infects a third of the world’s population. The role of helminth infections on the pathogenesis and pathology of active tuberculosis (T.B.) remains controversial. Parasite-induced suppression of the efficacy of Bacille Calmette-Guerin (BCG) has been widely reported in helminth-endemic areas worldwide. T.B. immune response is predominantly proinflammatory T-helper type 1 (Th1)-dependent. On the other hand, helminth infections induce an opposing anti-inflammatory Th2 and Th3 immune-regulatory response. This review summarizes the literature focusing on host immune response profiles during single-helminth, T.B. and dual infections. It also aims to necessitate investigations into the complexity of immunity in helminth/T.B. coinfected patients since the research data are limited and contradictory. Helminths overlap geographically with T.B., particularly in Sub-Saharan Africa. Each disease elicits a response which may skew the immune responses. However, these effects are helminth species-dependent, where some parasites have no impact on the immune responses to concurrent T.B. The implications for the complex immunological interactions that occur during coinfection are highlighted to inform government treatment policies and encourage the development of high-efficacy T.B. vaccines in areas where helminths are prevalent.

Superinfection with SARS-CoV-2 Has Deleterious Effects on Mycobacterium bovis BCG Immunity and Promotes Dissemination of Mycobacterium tuberculosis

An estimated one-third of the world's population is infected with Mycobacterium tuberculosis, with the majority being vaccinated with Mycobacterium bovis BCG. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains a threat, and we must understand how SARS-CoV-2 can modulate both BCG immunity and tuberculosis pathogenesis. Interestingly, neither BCG vaccination nor tuberculosis infection resulted in differences in clinical outcomes associated with SARS-CoV-2 in transgenic mice. Surprisingly, earlier M. tuberculosis infection resulted in lower SARS-CoV-2 viral loads, mediated by the heightened immune microenvironment of the murine lungs, unlike vaccination with BCG, which had no impact. In contrast, M. tuberculosis-infected tissues had increased bacterial loads and decreased histiocytic inflammation in the lungs following SARS-CoV-2 superinfection. SARS-CoV-2 modulated BCG-induced type 17 responses while decreasing type 1 and increasing type 2 cytokines in M. tuberculosis-infected mice. These findings challenge initial findings of BCG's positive impact on SARS-CoV-2 infection and suggest potential ramifications for M. tuberculosis reactivation upon SARS-CoV-2 superinfection. IMPORTANCE Prior to SARS-CoV-2, M. tuberculosis was the leading infectious disease killer, with an estimated one-third of the world's population infected and 1.7 million deaths a year. Here, we show that SARS-CoV-2 superinfection caused increased bacterial dissemination in M. tuberculosis-infected mice along with immune and pathological changes. SARS-CoV-2 also impacted the immunity of BCG-vaccinated mice, resulting in decreased interleukin-17 (IL-17) levels, while offering no protective effect against SARS-CoV-2. These results demonstrate that SARS-CoV-2 may have a deleterious effect on the ongoing M. tuberculosis pandemic and potentially limit BCG's efficacy.

Expansion of Opportunistic Enteric Fungal Pathogens and Occurrence of Gut Inflammation in Human Liver Echinococcosis

Increasing evidence shows that the gut fungal mycobiota is implicated in human disease. However, its relationship with chronic helminth infections, which cause immunosuppression and affect over 1 billion people worldwide, remains unexplored. In this study, we investigated the gut mycobiome and its associations with gut homeostasis in a severe helminth disease worldwide: liver echinococcosis. Fecal samples from 63 patients and 42 healthy controls were collected to characterize the fungal signatures using ITS1 sequencing, QIIME pipeline, and machine learning analysis. The levels of fecal calprotectin and serological anti-Saccharomyces cerevisiae antibodies (ASCA) in these subjects were experimentally measured. We found that fungal microbiota was significantly skewed in disease, with an overrepresentation of Aspergillus, Candida, Geotrichum, Kazachstania, and Penicillium and a decrease of Fusarium. Machine learning analysis revealed that the altered fungal features could efficiently predict infection with high sensitivity and specificity (area under the curve [AUC] = 0.93). The dysbiosis was characterized by expansions of multiple opportunistic pathogens (Aspergillus spp. and Candida spp.). Clinical association analysis revealed that host immunity might link to the expansions of the invasive fungi. Accompanying the opportunistic pathogen expansion, the levels of fungi-associated fecal calprotectin and serological ASCA in the patients were elevated, suggesting that gut inflammation and microbiota translocation occurred in this generally assumed extraintestinal disease. This study highlights enteric fungal pathogen expansions and increased levels of markers for fungi-associated mucosal inflammation and intestinal permeability as hallmarks of liver echinococcosis. IMPORTANCE Helminth infection affects over 1 billion people worldwide. However, its relationship with the gut mycobiome remains unknown. Among the most prevalent helminth diseases, human hydatid disease (echinococcosis) is highlighted as one of the most important (second/third for alveolar/cystic echinococcosis) foodborne parasitic diseases at the global level. Herein, we investigated the mycobiome and gut homeostasis (i.e., inflammation and permeability) in human echinococcosis. Our results revealed that fungal dysbiosis with an expansion of opportunistic pathogens and increased levels of fecal calprotectin and serum ASCA are hallmarks of human liver echinococcosis. Host immunity is associated with enteric fungal expansions. These findings suggest that an extraintestinal helminth infection is able to alter gut fungal microbiota and impair gut homeostasis, which resembles concomitant gut symptoms in inflammatory gut-related diseases (e.g., AIDS). In clinical practice, physicians need to take cautious medical consideration of gut health for nonintestinal helminth diseases.

Strongyloidiasis stercoralis coinfection is associated with altered iron status biomarkers in tuberculous lymphadenitis

Soil-transmitted helminth [mainly Strongyloidiasis stercoralis (Ss)] and tuberculous lymphadenitis (TBL) coinfection in humans is a significant public health problem. We have previously shown that TBL+Ss+ coinfection significantly alters diverse cytokine, matrix metalloproteinase, and tissue inhibitors of metalloproteinase profiles. However, no data is available to understand the influence of Ss coinfection in TBL disease with respect to iron status biomarkers. Hence, we have studied the effect of Ss coinfection on the circulating levels of iron status (ferritin, transferrin [TF], apotransferrin [ApoT], hepcidin, hemopexin) biomarkers in TBL disease. Our results show that TBL+Ss+ and/or TBL+Ss- individuals are associated with significantly altered biochemical and hematological (red blood cell (RBC) counts, hemoglobin (Hb), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) were decreased, and platelets were increased) parameters compared to TBL-Ss+ individuals. Our results also show that TBL+Ss+ coinfection is associated with diminished circulating levels of ferritin, ApoT, hepcidin, and hemopexin compared to TBL+Ss- individuals. TBL+Ss+ and TBL+Ss- groups are associated with altered iron status biomarkers (decreased ferritin [TBL+Ss+ alone] and increased TF, ApoT, hepcidin and hemopexin [TBL+Ss- alone]) compared to TBL-Ss+ group. The heat map expression profile and principal component analysis (PCA) analysis of iron status biomarkers were significantly altered in TBL+Ss+ compared to TBL+Ss- and/or TBL-Ss+ individuals. A significant correlation (positive/negative) was obtained among the biochemical and hematological parameters (white blood cells (WBC)/ferritin, TF, and hepcidin, mean corpuscular hemoglobin concentration (MCHC)/ferritin and hemopexin) with iron status biomarkers. Finally, receiver operating characteristic (ROC) analysis revealed that hemopexin was significantly associated with greater specificity and sensitivity in discriminating TBL+Ss+ and TBL+Ss- coinfected individuals. Thus, our data conclude that Ss coinfection is associated with altered iron status biomarkers indicating that coinfection might alter the host-Mtb interface and could influence the disease pathogenesis.

Clonorchis sinensis infection modulates key cytokines for essential immune response impacted by sex

Infection with helminths can modulate the host immune response, which ultimately shape morbidity and mortality of the associated diseases. We studied key cytokines for essential immune response in sera from 229 southeastern China individuals infected with Clonorchis sinensis and 60 individuals without C. sinensis infection, and measured serum specific IgG and IgE against worms in these people. Individuals infected with C. sinensis had significantly higher antigen-specific IgG and IgE levels, which were positively correlated with egg counts in feces. However, less enhancement of IgE antibody was observed in females when compared to males with similar infection levels. C. sinensis infection caused diminished Th1 cytokines (IL-1β, IL-2, IL-12p70, IFN-γ and TNF-α), Th2 cytokine (IL-4), as well as Th17 cytokine (IL-17A) in sera, which showed decreasing trend by infection intensity. Notably, these phenotypes were more significant in females than those in males. Although C. sinensis infection is associated with the development of hepatobiliary diseases, there was no significant correlation between the dampened cytokine profiles and the hepatobiliary morbidities. Our study indicates C. sinensis infection is strongly related to the immune suppression in human. Sex differences shape the immune milieus of clonorchiasis. This study provides a better understanding of how worms affect immune responses and cause a long-term immune alternation in humans with C. sinensis infection.

Immunometabolism of Immune Cells in Mucosal Environment Drives Effector Responses against Mycobacterium tuberculosis

Tuberculosis remains a major threat to global public health, with more than 1.5 million deaths recorded in 2020. Improved interventions against tuberculosis are urgently needed, but there are still gaps in our knowledge of the host-pathogen interaction that need to be filled, especially at the site of infection. With a long history of infection in humans, Mycobacterium tuberculosis (Mtb) has evolved to be able to exploit the microenvironment of the infection site to survive and grow. The immune cells are not only reliant on immune signalling to mount an effective response to Mtb invasion but can also be orchestrated by their metabolic state. Cellular metabolism was often overlooked in the past but growing evidence of its importance in the functions of immune cells suggests that it can no longer be ignored. This review aims to gain a better understanding of mucosal immunometabolism of resident effector cells, such as alveolar macrophages and mucosal-associated invariant T cells (MAIT cells), in response to Mtb infection and how Mtb manipulates them for its survival and growth, which could address our knowledge gaps while opening up new questions, and potentially be applied for future vaccination and therapeutic strategies.

Viral coinfection promotes tuberculosis immunopathogenesis by type I IFN signaling-dependent impediment of Th1 cell pulmonary influx

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is often exacerbated upon coinfection, but the underlying immunological mechanisms remain unclear. Here, to elucidate these mechanisms, we use an Mtb and lymphocytic choriomeningitis virus coinfection model. Viral coinfection significantly suppresses Mtb-specific IFN-γ production, with elevated bacterial loads and hyperinflammation in the lungs. Type I IFN signaling blockade rescues the Mtb-specific IFN-γ response and ameliorates lung immunopathology. Single-cell sequencing, tissue immunofluorescence staining, and adoptive transfer experiments indicate that viral infection-induced type I IFN signaling could inhibit CXCL9/10 production in myeloid cells, ultimately impairing pulmonary migration of Mtb-specific CD4⁺ T cells. Thus, our study suggests that augmented and sustained type I IFNs by virus coinfection prior to the pulmonary localization of Mtb-specific Th1 cells exacerbates TB immunopathogenesis by impeding the Mtb-specific Th1 cell influx. Our study highlights a negative function of viral coinfection-induced type I IFN responses in delaying Mtb-specific Th1 responses in the lung.

Viral coinfection alongside mycobacterium tuberculosis (Mtb) infection may lead to immune complications or interference with immune responses. Here the authors show that in mice infected with Mtb and LCMV virus the specific T_H1 response to MTb is reduced through a type I IFN response to the infecting virus.

An Annotated Inventory of Tanzanian Medicinal Plants Traditionally Used for the Treatment of Respiratory Bacterial Infections

This review comprehensively covers and analyzes scientific information on plants used in Tanzanian traditional medicine against respiratory diseases. It covers ethnobotanical and ethnopharmacological information extracted from SciFinder, Google Scholar, and Reaxys as well as the literature collected at the Institute of Traditional Medicine in Dar-es-Salaam. Crude extracts and fractions of 133 plant species have literature reports on antimicrobial bioassays. Of these, 16 plant species had a minimum inhibitory activity of MIC ≤ 50 µg/mL. Structurally diverse compounds were reported for 49 plant species, of which 7 had constituents with MIC ≤ 5 µg/mL against various bacteria: Bryophyllum pinnatum (Lam.) Oken, Warburgia ugandensis Sprague, Diospyros mespiliformis Hochst. ex DC., Cassia abbreviata Oliv., Entada abyssinica A. Rich., Strychnos spinosa Lam., and Milicia excelsa (Welw.) C.C. Berg. The low number of antimicrobial active extracts and compounds suggests that antibacterial and antimycobacterial drug discovery needs to have a fresh look at ethnobotanical information, diverting from too reductionist an approach and better taking into account that the descriptions of symptoms and concepts of underlying diseases are different in traditional African and modern Western medicine. Nevertheless, some structurally diverse compounds found in anti-infective plants are highlighted in this review as worthy of detailed study and chemical modification.

The association of Schistosoma and geohelminth infections with β-cell function and insulin resistance among HIV-infected and HIV-uninfected adults: A cross-sectional study in Tanzania

Objectives

Data on the role of helminths on diabetes in Africa are limited. We investigated whether Schistosoma and geohelminth infections are associated with β-cell function and insulin resistance among adults.

Methods

A cross-sectional study was conducted among adults during 2016–2017. Demography, Schistosoma and geohelminth infections, HIV and insulin data were collected. Insulin during an oral glucose tolerance test (fasting, 30, and 120-min), overall insulin secretion index, insulinogenic index, HOMA-β, and HOMA-IR were main outcome measures for β-cell function and insulin resistance, respectively. Generalized estimating equations and generalized linear models assessed the association of Schistosoma and geohelminth infections with outcome measures separately by HIV status. Outcomes were presented as marginal means with 95% CI.

Results

Data were obtained for 1718 participants. Schistosoma infection was associated with higher 30-min insulin (24.2 mU/L, 95% CI: 6.9, 41.6) and overall insulin secretion index (13.3 pmol/L/mmol/L; 3.7, 22.9) among HIV-uninfected participants but with lower fasting insulin (-0.9 mU/L; -1.6, -0.2), 120-min insulin (-12.0 mU/L; -18.9, -5.1), and HOMA-IR (-0.3 mmol/L; -0.6, -0.05) among HIV-infected participants not yet on antiretroviral therapy (ART). Among HIV-infected participants not on ART, geohelminth infection was associated with lower fasting insulin (-0.9 mU/L; -1.6, -0.2), 120-min insulin (-9.1 mU/L; -17.3, -1.0), HOMA-β (-8.9 mU/L)/(mmol/L; -15.3, -2.6) and overall insulin release index (-5.1 pmol/L/mmol/L; -10.3, 0.02), although this was marginally significant. There was no association among those on ART.

Conclusions

Schistosoma infection was associated with higher β-cell function among HIV-uninfected participants whereas Schistosoma and geohelminth infections were associated with reduced β-cell function among HIV-infected participants not on ART.

Deletion of BCG_2432c from the Bacillus Calmette-Guérin vaccine enhances autophagy-mediated immunity against tuberculosis

BACKGROUND

Mycobacterium bovis bacillus Calmette-Guérin (BCG) is an attenuated live vaccine that provides insufficient protection against tuberculosis (TB), the underlying mechanisms for which remain unknown. Assuming that the BCG vaccine inherits immune evasive strategies from virulent parent M. bovis strains, we aimed to identify the associated genes and assess their effects on the vaccine efficacy.

METHODS

Three genes, BCG_3174, BCG_1782, and BCG_2432c, associated with immune evasion were first identified via bioinformatics analysis and then confirmed in the genome of M. bovis and 12 commercial BCG vaccine substrains using Polymerase Chain Reaction (PCR) and DNA sequencing. These genes were disrupted to develop mutant strains, and their effects on autophagy and their protective efficacy were further compared with the BCG vaccine in vitro and in vivo.

RESULTS

Of the three identified genes, only the disruption of BCG_2432c, namely ΔBCG_2432c, conferred stronger protection against intranasal TB in vaccinated mice, when compared with the BCG vaccine. ΔBCG_2432c showed a stronger ability to trigger intracellular ROS-mediated complete autophagic flux in infected THP-1 cells that resulted in higher antigen presentation. The improved protection could be attributed to early and increased IFN-γ⁺ CD4⁺ T_EM and IL-2⁺ CD4⁺ T_CM cells in the spleens and lungs of ΔBCG_2432c-vaccinated mice.

CONCLUSIONS

The insufficient efficacy of the BCG vaccine is attributable to the important autophagy-inhibition gene BCG_2432c that blocks the autophagosome-lysosome pathway of antigen presentation. ΔBCG_2432c provides a promising platform to either replace the current BCG vaccine or develop vaccines that are more effective against TB.

In Vitro Potential of the Acetone Leaf Extract and Fractions of Psychotria capensis (Eckl.) Vatke (Rubiaceae) to Combat Co-Infection of Tuberculosis and Helminthiasis

Tuberculosis (TB) is a disease of global importance that affects millions of people. Approximately a quarter of the world’s population is currently infected with M. tuberculosis, and about 10% of those infected will develop into active disease, particularly immune compromised individuals. Helminthiasis is of global health importance, affecting over 2 billion people mostly in resource-poor countries. Co-infection with tuberculosis (TB) and helminths (worms) is an emerging global public health concern with both affecting about one-third of the global population. Chronic infection with helminths can result in impaired immune responses to TB as well as enhancing failure to TB therapy and BCG vaccination. Antimycobacterial and anthelmintic activities of the acetone extract and fractions of Psychotria capensis were evaluated, including their in vitro safety. In addition, the anti-inflammatory and immunomodulatory effect of the fractions and crude extract of P. capensis were assessed. Antimycobacterial activity of the extract and fractions was tested against four non-tuberculous mycobacteria (Mycobacterium smegmatis, M. fortuitum, M. aurum, M. bovis BCG) and pathogenic M. tuberculosis H37Rv while the Egg Hatch Assay (EHA) was used for the anthelmintic test on eggs of Haemonchus contortus. Cytotoxicity was determined against Vero kidney cells while in vitro immune modulation via cytokine production was determined on activated macrophages. The minimum inhibitory concentration (MIC) values of the Psychotria capensis acetone extract and fractions ranged from 39 to 1,250 μg/ml with the crude extract and hexane fraction having the best MIC values (both 39 μg/ml). In the EHA, the inhibitory concentration (IC₅₀) ranged from 160 to 630 μg/ml with the hexane fraction having the best activity. The hexane and chloroform fractions were relatively non-toxic with LC₅₀ values of 290 and 248 μg/ml respectively, while the acetone crude extract (64 μg/ml) and n-butanol fraction (71 μg/ml) were moderately toxic. The SI values (LC₅₀/MIC) ranged from 0.1 to 7.4 with the hexane fraction having the highest value against M. smegmatis (7.4). The hexane fraction had the best dual anthelmintic and antimycobacterial activity. This fraction had the best NO inhibitory activity and was the least cytotoxic, indicating that its activity was not due to general metabolic toxicity, with 96.54% cell viability. Pro-inflammatory cytokines such as IL-12p70 were upregulated while IL-10 expression was inhibited by the extracts. Compounds were detected using GC-MS analysis, and in both the crude acetone extract and the hexane fraction was the diterpene neophytadiene, which has anti-inflammatory and antimicrobial activity. Finding alternative or complementary approaches to dealing with TB infections by, amongst other things, reducing the incidence of helminth infestations may lessen the burden of TB, contributing to slowing the spread of multi-drug resistance.

Intestinal helminth infection transforms the CD4+ T cell composition of the skin

Intestinal helminth parasites can alter immune responses to vaccines, other infections, allergens and autoantigens, implying effects on host immune responses in distal barrier tissues. We herein show that the skin of C57BL/6 mice infected with the strictly intestinal nematode Heligmosomoides polygyrus contain higher numbers of CD4⁺ T cells compared to the skin of uninfected controls. Accumulated CD4⁺ T cells were H. polygyrus-specific T_H2 cells that skewed the skin CD4⁺ T cell composition towards a higher T_H2/T_H1 ratio which persisted after worm expulsion. Accumulation of T_H2 cells in the skin was associated with increased expression of the skin-homing chemokine receptors CCR4 and CCR10 on CD4⁺ T cells in the blood and mesenteric lymph nodes draining the infected intestine and was abolished by FTY720 treatment during infection, indicating gut-to-skin trafficking of cells. Remarkably, skin T_H2 accumulation was associated with impaired capacity to initiate IFN-γ recall responses and develop skin-resident memory cells to mycobacterial antigens, both during infection and months after deworming therapy. In conclusion, we show that infection by a strictly intestinal helminth has long-term effects on immune cell composition and local immune responses to unrelated antigens in the skin, revealing a novel process for T cell colonisation and worm-mediated immunosuppression in this organ.

SARS-CoV-2 and helminth co-infections, and environmental pollution exposure: An epidemiological and immunological perspective

Soil-transmitted helminths infect billions of people globally, particularly those residing in low- and middle-income regions with poor environmental sanitation and high levels of air and water pollution. Helminths display potent immunomodulatory activity by activating T helper type 2 (Th2) anti-inflammatory and Th3 regulatory immune responses. The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the virus that causes Coronavirus disease 2019 (COVID-19), can exacerbate Th1/Th17 pro-inflammatory cytokine production in humans, leading to a cytokine storm. Air pollutants (particulate matter, oxygen radicals, hydrocarbons and volatile organic compounds) and water pollutants (metals and organic chemicals) can also intensify Th1/Th17 immune response and could exacerbate SARS-CoV-2 related respiratory distress and failure. The present review focused on the epidemiology of SARS-CoV-2, helminths and fine particulate matter 2.5 µm or less in diameter (PM2.5) air pollution exposure in helminth endemic regions, the possible immunomodulatory activity of helminths against SARS-CoV-2 hyper-inflammatory immune response, and whether air and water pollutants can further exacerbate SARS-CoV-2 related cytokine storm and in the process hinder helminths immunomodulatory functionality. Helminth Th2/Th3 immune response is associated with reductions in lung inflammation and damage, and decreased expression levels of angiotensin-converting enzyme 2 (ACE2) receptors (SARS-CoV-2 uses the ACE2 receptors to infect cells and associated with extensive lung damage). However, air pollutants are associated with overexpression of ACE2 receptors in the epithelial cell surface of the respiratory tract and exhaustion of Th2 immune response. Helminth-induced immunosuppression activity reduces vaccination efficacy, and diminishes vital Th1 cytokine production immune responses that are crucial for combating early stage infections. This could be reversed by continuous air pollution exposure which is known to intensify Th1 pro-inflammatory cytokine production to a point where the immunosuppressive activities of helminths could be hindered. Again, suppressed activities of helminths can also be disadvantageous against SARS-CoV-2 inflammatory response. This "yin and yang" approach seems complex and requires more understanding. Further studies are warranted in a cohort of SARS-CoV-2 infected individuals residing in helminths and air pollution endemic regions to offer more insights, and to impact mass periodic deworming programmes and environmental health policies.

Eosinophils are part of the granulocyte response in tuberculosis and promote host resistance in mice

Host resistance to Mycobacterium tuberculosis (Mtb) infection requires the activities of multiple leukocyte subsets, yet the roles of the different innate effector cells during tuberculosis are incompletely understood. Here we uncover an unexpected association between eosinophils and Mtb infection. In humans, eosinophils are decreased in the blood but enriched in resected human tuberculosis lung lesions and autopsy granulomas. An influx of eosinophils is also evident in infected zebrafish, mice, and nonhuman primate granulomas, where they are functionally activated and degranulate. Importantly, using complementary genetic models of eosinophil deficiency, we demonstrate that in mice, eosinophils are required for optimal pulmonary bacterial control and host survival after Mtb infection. Collectively, our findings uncover an unexpected recruitment of eosinophils to the infected lung tissue and a protective role for these cells in the control of Mtb infection in mice.

Effect of Helicobacter pylori and Helminth Coinfection on the Immune Response to Mycobacterium tuberculosis

Tuberculosis remains one of the main causes of morbidity and mortality worldwide despite decades of efforts to eradicate the disease. Although the immune response controls the infection in most infected individuals (90%), the ability of the bacterium to persist throughout the host's life leads to a risk of reactivation. Underlying conditions including human immunodeficiency virus (HIV) infection, organ transplantation, and immunosuppressive therapies are considered risk factors for progression to active disease. However, many individuals infected with Mycobacterium tuberculosis may develop clinical disease in the absence of underlying immunosuppression. It is also possible that unknown conditions may drive the progression to disease. The human microbiota can be an important modulator of the immune system; it can not only trigger inflammatory disorders, but also drive the response to other infectious diseases. In developing countries, chronic mucosal infections with Helicobacter pylori and helminths may be particularly important, as these infections frequently coexist throughout the host's life. However, little is known about the interactions of these pathogens with the immune system and their effects on M. tuberculosis clinical disease, if any. In this review, we discuss the potential effects of H. pylori and helminth co-infections on the immune response to M. tuberculosis. This may contribute to our understanding of host-pathogen interactions and in designing new strategies for the prevention and control of tuberculosis.

Concomitant experimental coinfection by Plasmodium berghei NK65-NY and Ascaris suum downregulates the Ascaris-specific immune response and potentiates Ascaris-associated lung pathology

Background

Ascariasis and malaria are highly prevalent parasitic diseases in tropical regions and often have overlapping endemic areas, contributing to high morbidity and mortality rates in areas with poor sanitary conditions. Several studies have previously aimed to correlate the effects of Ascaris-Plasmodium coinfections but have obtained contradictory and inconclusive results. Therefore, the present study aimed to investigate parasitological and immunopathological aspects of the lung during murine experimental concomitant coinfection by Plasmodium berghei and Ascaris suum during larvae ascariasis.

Methods

C57BL/6J mice were inoculated with 1 × 10⁴P. berghei strain NK65-NY-infected red blood cells (iRBCs) intraperitoneally and/or 2500 embryonated eggs of A. suum by oral gavage. P. berghei parasitaemia, morbidity and the survival rate were assessed. On the seventh day postinfection (dpi), A. suum lung burden analysis; bronchoalveolar lavage (BAL); histopathology; NAG, MPO and EPO activity measurements; haematological analysis; and respiratory mechanics analysis were performed. The concentrations of interleukin (IL)-1β, IL-12/IL-23p40, IL-6, IL-4, IL-33, IL-13, IL-5, IL-10, IL-17A, IFN-γ, TNF and TGF-β were assayed by sandwich ELISA.

Results

Animals coinfected with P. berghei and A. suum show decreased production of type 1, 2, and 17 and regulatory cytokines; low leukocyte recruitment in the tissue; increased cellularity in the circulation; and low levels of NAG, MPO and EPO activity that lead to an increase in larvae migration, as shown by the decrease in larvae recovered in the lung parenchyma and increase in larvae recovered in the airway. This situation leads to severe airway haemorrhage and, consequently, an impairment respiratory function that leads to high morbidity and early mortality.

Conclusions

This study demonstrates that the Ascaris-Plasmodium interaction is harmful to the host and suggests that this coinfection may potentiate Ascaris-associated pathology by dampening the Ascaris-specific immune response, resulting in the early death of affected animals.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03824-w.

Natural resistance to worms exacerbates bovine tuberculosis severity independently of worm coinfection

Pathogen interactions arising during coinfection can exacerbate disease severity, for example when the immune response mounted against one pathogen negatively affects defense of another. It is also possible that host immune responses to a pathogen, shaped by historical evolutionary interactions between host and pathogen, may modify host immune defenses in ways that have repercussions for other pathogens. In this case, negative interactions between two pathogens could emerge even in the absence of concurrent infection. Parasitic worms and tuberculosis (TB) are involved in one of the most geographically extensive of pathogen interactions, and during coinfection worms can exacerbate TB disease outcomes. Here, we show that in a wild mammal natural resistance to worms affects bovine tuberculosis (BTB) severity independently of active worm infection. We found that worm-resistant individuals were more likely to die of BTB than were nonresistant individuals, and their disease progressed more quickly. Anthelmintic treatment moderated, but did not eliminate, the resistance effect, and the effects of resistance and treatment were opposite and additive, with untreated, resistant individuals experiencing the highest mortality. Furthermore, resistance and anthelmintic treatment had nonoverlapping effects on BTB pathology. The effects of resistance manifested in the lungs (the primary site of BTB infection), while the effects of treatment manifested almost entirely in the lymph nodes (the site of disseminated disease), suggesting that resistance and active worm infection affect BTB progression via distinct mechanisms. Our findings reveal that interactions between pathogens can occur as a consequence of processes arising on very different timescales.

Whole Blood Mycobacterial Growth Assays for Assessing Human Tuberculosis Susceptibility: A Systematic Review and Meta-Analysis

Background

Whole blood mycobacterial growth assays (WBMGA) quantify mycobacterial growth in fresh blood samples and may have potential for assessing tuberculosis vaccines and identifying individuals at risk of tuberculosis. We evaluated the evidence for the underlying assumption that in vitro WBMGA results can predict in vivo tuberculosis susceptibility.

Methods

A systematic search was done for studies assessing associations between WBMGA results and tuberculosis susceptibility. Meta-analyses were performed for eligible studies by calculating population-weighted averages.

Results

No studies directly assessed whether WBMGA results predicted tuberculosis susceptibility. 15 studies assessed associations between WBMGA results and proven correlates of tuberculosis susceptibility, which we divided in two categories. Firstly, WBMGA associations with factors believed to reduce tuberculosis susceptibility were statistically significant in all eight studies of: BCG vaccination; vitamin D supplementation; altitude; and HIV-negativity/therapy. Secondly, WBMGA associations with probable correlates of tuberculosis susceptibility were statistically significant in three studies of tuberculosis disease, in a parasitism study and in two of the five studies of latent tuberculosis infection. Meta-analyses for associations between WBMGA results and BCG vaccination, tuberculosis infection, tuberculosis disease and HIV infection revealed consistent effects. There was considerable methodological heterogeneity.

Conclusions

The study results generally showed significant associations between WBMGA results and correlates of tuberculosis susceptibility. However, no study directly assessed whether WBMGA results predicted actual susceptibility to tuberculosis infection or disease. We recommend optimization and standardization of WBMGA methodology and prospective studies to determine whether WBMGA predict susceptibility to tuberculosis disease.

Coinfection and infection duration shape how pathogens affect the African buffalo gut microbiota

Changes in the gut microbiota during pathogen infection are often predicted to influence disease outcomes. However, studies exploring whether pathogens induce microbiota shifts have yielded inconsistent results. This suggests that variation in infection, rather than the presence of infection alone, might shape pathogen-microbiota relationships. For example, most hosts are coinfected with multiple pathogens simultaneously, and hosts vary in how long they are infected, which may amplify or diminish microbial shifts expected in response to a focal pathogen. We used a longitudinal anthelmintic treatment study of free-ranging African buffalo (Syncerus caffer) to examine whether (i) coinfection with bovine tuberculosis (Mycobacterium bovis, TB) and gastrointestinal nematodes, and (ii) the duration of TB infection, modified effects of single pathogens on the gut microbiota. By accounting for the interaction between TB and nematodes, we found that coinfection affected changes in microbial abundance associated with single infections. Furthermore, the duration of TB infection predicted more microbiota variation than the presence of TB. Importantly, coinfection and infection duration had nearly as much influence on microbial patterns as demographic and environmental factors commonly examined in microbiota research. These findings demonstrate that acknowledging infection heterogeneities may be crucial to understanding relationships between pathogens and the gut microbiota.

Immunological underpinnings of Ascaris infection, reinfection and co-infection and their associated co-morbidities

Human ascariasis is the most common and prevalent neglected tropical disease and is estimated that ~819 million people are infected around the globe, accounting for 0.861 million years of disability-adjusted life years in 2017. Even with the existence of highly effective drugs, the constant presence of infective parasite eggs in the environment contribute to a high reinfection rate after treatment. Due to its high prevalence and broad geographic distribution Ascaris infection is associated with a variety of co-morbidities and co-infections. Here, we provide data from both experimental models and humans studies that illustrate how complex is the interaction of Ascaris with the host immune system, especially, in the context of reinfections, co-infections and associated co-morbidities.

Tuberculosis endotypes to guide stratified host-directed therapy

There is hope that host-directed therapy (HDT) for Tuberculosis (TB) can either shorten treatment duration, help cure drug resistant disease or limit the immunopathology. Many candidate HDT drugs have been proposed, however solid evidence only exists for a few select patient groups. The clinical presentation of TB is variable, with differences in severity, tissue pathology, and bacillary burden. TB clinical phenotypes likely determine the potential benefit of HDT. Underlying TB clinical phenotypes, there are TB "endotypes," defined as distinct molecular profiles, with specific metabolic, epigenetic, transcriptional, and immune phenotypes. TB endotypes can be characterized by either immunodeficiency or pathologic excessive inflammation. Additional factors, like comorbidities (HIV, diabetes, helminth infection), structural lung disease or Mycobacterial virulence also drive TB endotypes. Precise disease phenotyping, combined with in-depth immunologic and molecular profiling and multimodal omics integration, can identify TB endotypes, guide endotype-specific HDT, and improve TB outcomes, similar to advances in cancer medicine.

Strongyloides stercoralis Coinfection Is Associated With Greater Disease Severity, Higher Bacterial Burden, and Elevated Plasma Matrix Metalloproteinases in Pulmonary Tuberculosis

BACKGROUND

Helminths and tuberculosis (TB) largely overlap at the population level. Whether helminth infections influence disease severity and bacterial burdens in TB is not well understood.

METHODS

This study was conducted to examine the disease severity in a cohort of pulmonary TB (PTB) individuals with (Ss+) or without (Ss-) seropositivity for Strongyloides stercoralis infection.

RESULTS

Ss+ was associated with increased risk of cavitation (odds ratio [OR], 4.54; 95% confidence interval [CI], 2.33-9.04; P < .0001) and bilateral lung involvement (OR, 5.97; 95% CI, 3.03-12.09; P < .0001) in PTB individuals. Ss+ was also associated with higher bacterial burdens (OR, 7.57; 95% CI, 4.18-14.05; P < .0001) in PTB individuals. After multivariate analysis adjusting for covariates, Ss+ was still associated with greater risk of cavitation (adjusted OR [aOR], 3.99; 95% CI, 1.73-9.19; P = .0014), bilateral lung involvement (aOR, 4.09; 95% CI, 1.78-9.41; P = .0011), and higher bacterial burden (aOR, 9.32; 95% CI, 6.30-13.96; P < .0001). Finally, Ss+ was also associated with higher plasma levels of matrix metalloproteinases ([MMP]-1, -2, -7, -8, and -9) in PTB individuals.

CONCLUSIONS

Therefore, our data demonstrate that coexistent Ss infection is associated with greater disease severity and higher bacterial burden in PTB. Our data also demonstrate enhanced plasma levels of MMPs in coinfected individuals, suggesting a plausible biological mechanism for these effects.

Immunological Considerations for Schistosoma Vaccine Development: Transitioning to Endemic Settings

Despite mass drug administration programmes with praziquantel, the prevalence of schistosomiasis remains high. A vaccine is urgently needed to control transmission of this debilitating disease. As some promising schistosomiasis vaccine candidates are moving through pre-clinical and clinical testing, we review the immunological challenges that these vaccine candidates may encounter in transitioning through the clinical trial phases in endemic settings. Prior exposure of the target population to schistosomes and other infections may impact vaccine response and efficacy and therefore requires considerable attention. Schistosomes are known for their potential to induce T-reg/IL-10 mediated immune suppression in populations which are chronically infected. Moreover, endemicity of schistosomiasis is focal whereby target and trial populations may exhibit several degrees of prior exposure as well as in utero exposure which may increase heterogeneity of vaccine responses. The age dependent distribution of exposure and development of acquired immunity, and general differences in the baseline immunological profile, adds to the complexity of selecting suitable trial populations. Similarly, prior or concurrent infections with other parasitic helminths, viral and bacterial infections, may alter immunological responses. Consequently, treatment of co-infections may benefit the immunogenicity of vaccines and may be considered despite logistical challenges. On the other hand, viral infections leave a life-long immunological imprint on the human host. Screening for serostatus may be needed to facilitate interpretation of vaccine responses. Co-delivery of schistosome vaccines with PZQ is attractive from a perspective of implementation but may complicate the immunogenicity of schistosomiasis vaccines. Several studies have reported PZQ treatment to induce both transient and long-term immuno-modulatory effects as a result of tegument destruction, worm killing and subsequent exposure of worm antigens to the host immune system. These in turn may augment or antagonize vaccine immunogenicity. Understanding the complex immunological interactions between vaccine, co-infections or prior exposure is essential in early stages of clinical development to facilitate phase 3 clinical trial design and implementation policies. Besides well-designed studies in different target populations using schistosome candidate vaccines or other vaccines as models, controlled human infections could also help identify markers of immune protection in populations with different disease and immunological backgrounds.

Helminth species specific expansion and increased TNF-alpha production of non-classical monocytes during active tuberculosis

Both Mycobacterium tuberculosis infection and helminths may affect innate immune mechanisms such as differential effects on monocytes towards the non-classical and intermediate subsets that favor bacterial persistence. Our aim, was to investigate helminth species specific effects on the frequency and functional activity of monocyte subsets in patients with active tuberculosis and healthy subjects. HIV-negative patients with active pulmonary tuberculosis (PTB) and community controls (CCs) in Gondar, Ethiopia were screened for helminth infection by stool microscopy. Flow cytometric analysis of peripheral blood mononuclear cells (PBMCs) and ex vivo stimulation with purified protein derivative (PPD) and helminth antigens were used to characterize the distribution of monocyte subsets and their function. A total of 74 PTB patients and 57 CCs with and without helminth infection were included. Non-classical monocytes were increased in PTB patients with Ascaris and hookworm infection but not in Schistosoma-infected patients. Ascaris had the strongest effect in increasing the frequency of non-classical monocytes in both PTB patients and CCs, whereas PTB without helminth infection did not affect the frequency of monocyte subsets. There was a helminth specific increase in the frequency of TNF-α producing non-classical monocytes in hookworm infected PTB patients, both with and without PPD-stimulation. Low-to-intermediate TB disease severity associated with increased frequency of non-classical monocytes only for helminth-positive PTB patients, and the frequency of TNF-α producing monocytes were significantly higher in intermediate and non-classical monocytes of helminth positive PTB patients with an intermediate disease score. Helminth infection affected the frequency of monocyte subsets and function both in TB patients and controls which was helminth species dependent in TB patients. The clinical role of this potential immunomodulatory effect needs further study and may affect the response and protection to tuberculosis in areas where helminth infections are endemic.

Embracing nature's complexity: Immunoparasitology in the wild

A wealth of research is dedicated to understanding how resistance against parasites is conferred and how parasite-driven pathology is regulated. This research is in part driven by the hope to better treatments for parasitic diseases of humans and livestock, and in part by immunologists who use parasitic infections as biomedical tools to evoke physiological immune responses. Much of the current mechanistic knowledge has been discovered in laboratory studies using model organisms, especially the laboratory mouse. However, wildlife are also hosts to a range of parasites. Through the study of host-parasite interactions in these non-laboratory systems we can gain a deeper understanding of parasite immunology in a more natural, complex environment. With a focus on helminth parasites, we here explore the insights gained into parasite-induced immune responses through (for immunologists) non-conventional experimental systems, and how current core findings from laboratory studies are reflected in these more natural conditions. The quality of the immune response is undoubtedly a central player in susceptibility versus resistance, as many laboratory studies have shown. Yet, in the wild, parasite infections tend to be chronic diseases. Whilst reading our review, we encourage the reader to consider the following questions which may (only) be answered by studying naturally occurring parasites in the wild: a) what type of immune responses are mounted against parasites in different hosts in the wild, and how do they vary within an individual over time, between individuals of the same species and between species? b) can we use wild or semi-wild study systems to understand the evolutionary drivers for tolerance versus resistance towards a parasite? c) what determines the ability of the host to cope with an infection and is there a link with the type of immune response mounted? d) can we modulate environmental factors to manipulate a wild animal's immune response to parasitic infections, with translation potential for humans, wildlife, and livestock? and e) in context of this special issue, what lessons for Type 2 immunity can we glean from studying animals in their natural environments? Further, we aim to integrate some of the knowledge gained in semi-wild and wild settings with knowledge gained from traditional laboratory-based research, and to raise awareness for the opportunities (and challenges) that come with integrating a multitude of naturally-occurring variables into immunoparasitological research.

Schistosoma mansoni Infection Is Associated With a Higher Probability of Tuberculosis Disease in HIV-Infected Adults in Kenya

BACKGROUND

Helminth infections can modulate immunity to Mycobacterium tuberculosis (Mtb). However, the effect of helminths, including Schistosoma mansoni (SM), on Mtb infection outcomes is less clear. Furthermore, HIV is a known risk factor for tuberculosis (TB) disease and has been implicated in SM pathogenesis. Therefore, it is important to evaluate whether HIV modifies the association between SM and Mtb infection.

SETTING

HIV-infected and HIV-uninfected adults were enrolled in Kisumu County, Kenya, between 2014 and 2017 and categorized into 3 groups based on Mtb infection status: Mtb-uninfected healthy controls, latent TB infection (LTBI), and active TB disease. Participants were subsequently evaluated for infection with SM.

METHODS

We used targeted minimum loss estimation and super learning to estimate a covariate-adjusted association between SM and Mtb infection outcomes, defined as the probability of being Mtb-uninfected healthy controls, LTBI, or TB. HIV status was evaluated as an effect modifier of this association.

RESULTS

SM was not associated with differences in baseline demographic or clinical features of participants in this study, nor with additional parasitic infections. Covariate-adjusted analyses indicated that infection with SM was associated with a 4% higher estimated proportion of active TB cases in HIV-uninfected individuals and a 14% higher estimated proportion of active TB cases in HIV-infected individuals. There were no differences in estimated proportions of LTBI cases.

CONCLUSIONS

We provide evidence that SM infection is associated with a higher probability of active TB disease, particularly in HIV-infected individuals.

Adults from Kisumu, Kenya have robust γδ T cell responses to Schistosoma mansoni, which are modulated by tuberculosis

Schistosoma mansoni (SM) is a parasitic helminth that infects over 200 million people and causes severe morbidity. It undergoes a multi-stage life cycle in human hosts and as such stimulates a stage-specific immune response. The human T cell response to SM is complex and varies throughout the life cycle of SM. Relative to the wealth of information regarding the immune response to SM eggs, little is known about the immune response to the adult worm. In addition, while a great deal of research has uncovered mechanisms by which co-infection with helminths modulates immunity to other pathogens, there is a paucity of data on the effect of pathogens on immunity to helminths. As such, we sought to characterize the breadth of the T cell response to SM and determine whether co-infection with Mycobacterium tuberculosis (Mtb) modifies SM-specific T cell responses in a cohort of HIV-uninfected adults in Kisumu, Kenya. SM-infected individuals were categorized into three groups by Mtb infection status: active TB (TB), Interferon-γ Release Assay positive (IGRA+), and Interferon-γ Release Assay negative (IGRA-). U.S. adults that were seronegative for SM antibodies served as naïve controls. We utilized flow cytometry to characterize the T cell repertoire to SM egg and worm antigens. We found that T cells had significantly higher proliferation and cytokine production in response to worm antigen than to egg antigen. The T cell response to SM was dominated by γδ T cells that produced TNFα and IFNγ. Furthermore, we found that in individuals infected with Mtb, γδ T cells proliferated less in response to SM worm antigens and had higher IL-4 production compared to naïve controls. Together these data demonstrate that γδ T cells respond robustly to SM worm antigens and that Mtb infection modifies the γδ T cell response to SM.

Schistosomiasis, a disease caused by parasitic helminths including Schistosoma mansoni (SM), affects hundreds of millions of people globally. SM undergoes a complex life cycle within humans resulting in adult worm pairs that release eggs into the circulatory system. The human immune response to SM, especially to adult worms, is not well characterized. In addition, the impact of co-infections, which are common in SM endemic regions, on the immune response to SM is unknown. In this study, we first sought to characterize the T cell response to different stages of the SM life cycle. We next evaluated whether T cell responses to SM were altered in the setting of co-infection with Mycobacterium tuberculosis, the bacteria that causes tuberculosis. We determined that human T cell responses to SM adult worm antigen are more robust than to SM egg antigen. This response is dominated by a non-classical T cell subset of γδ T cells producing IFNγ and TNFα. Lastly, we found that the ability of γδ T cells to proliferate in response to SM worm was lower in individuals with tuberculosis compared to naïve controls. This study provides novel insights into the immune response to SM and how tuberculosis may impair SM immunity.

A rare case of coexisting tuberculosis with hydatid disease from North India with review of literature

Coexisting tuberculosis (TB) and hydatid disease in an immunocompetent individual is an extremely rare occurrence. Given the similarities in the clinical manifestations and morbidities of both, specific diagnosis in individuals coinfected with these is difficult. We, hereby present a case of a 17-year-old adolescent man diagnosed to be a coinfection of pulmonary TB with pulmonary and cardiac hydatid disease, with the review of cases having a similar presentation. The coexistence of these infections should be considered in endemic areas. Management can only be done by a multidisciplinary approach including surgical, microbiological, histopathological and radiological facilities. Complete surgical excision of the cyst is the treatment of choice and medical therapy for both aetiologies should be appropriate to achieve cure.

Intestinal parasites and HIV in Ethiopian tuberclosis patients: A systematic review and meta-analysis

BACKGROUND

The distribution of intestinal parasites among patients with tuberculosis in Ethiopia is not well understood.

OBJECTIVE

This systematic review and meta-analysis was designed to determine the pooled national prevalence of intestinal parasites and its association with HIV among patients with tuberculosis in Ethiopia.

METHODS

Original articles were searched in PubMed, Google Scholar, EMBASE, World Health Organization's HINARI portal, and supplemented by the hand searching of cross-references. Data were extracted using a standard data extraction checklist. Random-effects model was used to estimate the pooled prevalence of intestinal parasites and odds ratio of the association. The I 2 statistic was utilized to quantify statistical heterogeneity across studies. Funnel plot asymmetry and Egger regression tests were used to check for publication bias. The analysis was done by STATA version 14 for Windows.

RESULTS

Of 725 identified studies, 12 articles were eligible for inclusion in the final analysis. The pooled national prevalence of intestinal parasites among patients with tuberculosis in Ethiopia was 36.1% (95% CI, 22.1-50.1; I 2 = 98.7%). Subgroup analysis based on study design indicated that the prevalence of intestinal parasite among case-control studies was 41.69% (95% CI, 28.6-54.8; I 2 = 95.1%). The odds of intestinal parasites among patients with tuberculosis-HIV coinfection was not significantly different compared with patients with tuberculosis without HIV/AIDS (odds ratio = 0.99; 95% CI, 0.7-4.7; P = 0.96).

CONCLUSIONS

In Ethiopia, at least 1 out of 3 patients with tuberculosis have an intestinal parasite. These findings suggest a need of more attention on increasing screening tuberculosis patients for intestinal parasites and deworming interventions. (Curr Ther Res Clin Exp. 2020; 81:XXX-XXX).

Frequency, associated factors and clinical symptoms of intestinal parasites among tuberculosis and non-tuberculosis groups in Iran: a comparative cross-sectional study

BACKGROUND

Co-infection of human tuberculosis (TB) and intestinal parasites infections (IPIs) is a public health problem, especially in low- and middle-income countries. There is no data on this issue in Iran. Therefore, we investigated the prevalence of IPIs among patients with TB in Iran.

METHODS

Stool samples were collected from 161 patients with TB and 181 healthy people (non-TB group). Standard parasitological methods including direct slide smear, formalin-ether concentration, trichrome, modified Ziehl-Neelsen and chromotrope 2R staining techniques were used for detection of intestinal protozoa and helminths. Nested-PCR and sequence analysis were used to identify the genotypes of Cryptosporidium and human-infecting species of microsporidia. Data analysis was performed using SPSS version 16.

RESULTS

The frequency of IPIs in the non-TB group (16.5%) was slightly lower than in patients with TB (21.1%), although statistical significance was not observed (OR, 0.74; 95% CI, 0.43-1.27; P= 0.28). Blastocystis (11.8%) was the most common parasite detected in patients with TB. Infection with multiple parasites in the non-TB group (2.2%) was significantly lower than in patients with TB (7.5%) (OR, 0.28; 95% CI, 0.08-0.88; P=0.02). The ova of Taenia spp., Ascaris lumbricoides and Hyamenolepis nana were identified in three patients with TB (1.9%), while only one person (0.5%) in the non-TB group was infected with Enterobius vermicularis. The results of genotyping revealed two C. parvum subtype families (IIa and IId) and three E. bieneusi genotypes (Ebcar4, IH and jLD-1).

CONCLUSION

Our results showed a higher prevalence of IPIs in patients with TB in comparison with non-TB subjects. Moreover, our findings suggest a proper health education program for good personal hygiene habits, and also preventative measures to avoid the acquisition of IPIs in patients with TB.

Intestinal parasites co-infection among tuberculosis patients in Ethiopia: a systematic review and meta-analysis

Background

Tuberculosis and intestinal parasites are mostly affecting poor people. They are in a vicious since one is the risk factor for the other. However, the comprehensive report on the burden and co-incidence of intestinal parasites and tuberculosis in Ethiopia is scant. This systematic review and meta-analysis aimed to provide abridge conclusive evidence on the intestinal parasite-tuberculosis co-infection in Ethiopia.

Methods

A total of 414 articles published in English were searched from both electronic databases (CINAHL, DOAJ, Embase, Emcare, Medline, ProQuest, and PubMed, Science Direct, and Web of Science) and other sources. The qualities of the included studies were assessed using the Joanna Briggs Institute Critical Appraisal tools and the publication bias was measured using the funnel plot and Eggers regression test. Comprehensive meta-analysis (CMA) Version 3.3.07 and Review Manager software were used to estimate pooled prevalence and associations of intestinal parasites and tuberculosis infection.

Results

Eleven articles with a total of 3158 tuberculosis patients included in the analysis based on the eligibility criteria. The estimated pooled prevalence of intestinal parasites co-infection was 33% (95% CI: 23.3, 44.3) using the random-effects model. The most common intestinal parasites were Ascaris lumbricoides 10.5% (95% CI: 6.0, 17.5), Hookworm 9.5% (95% CI: 6.10, 14.4), Giardia lamblia 5.7% (95% CI: 2.90, 10.9) and Strongyloides sterocoralis 5.6% (95% CI: 3.3, 9.5). The odds of intestinal parasites infection was higher among tuberculosis patients compared to tuberculosis free individuals (OR = 1.76; 95% CI: 1.17, 2.63). A significant difference was observed among TB patients for infection with intestinal helminths (OR = 2.01; 95% CI: 1.07, 3.80) but not for intestinal protozoans when compared with their counterparts. The odds of multiple parasitic infections was higher among tuberculosis patients (OR = 2.59, 95% CI: 1.90, 3.55) compared to tuberculosis free individuals. However, intestinal parasites co-infection was not associated with HIV status among tuberculosis patients (OR = 0.97; 95% CI: 0.71, 1.32).

Conclusion

One-third of tuberculosis patients are co-infected with one or more intestinal parasites, and they are more likely to be infected with intestinal helminths and multiple intestinal parasitic infections compared to TB free individuals. We recommend routine screening of tuberculosis patients for intestinal parasites. The effect of mass deworming on tuberculosis incidence would be important to be considered in future researches.

Trial registration

Registered on PROSPERO with reference number ID: CRD42019135350.

Immunity to Soil-Transmitted Helminths: Evidence From the Field and Laboratory Models

Infection with soil-transmitted helminths (STH) remains a major burden on global health and agriculture. Our understanding of the immunological mechanisms that govern whether an individual is resistant or susceptible to infection is derived primarily from model infections in rodents. Typically, experimental infections employ an artificially high, single bolus of parasites that leads to rapid expulsion of the primary infection and robust immunity to subsequent challenges. However, immunity in natura is generated slowly, and is only partially effective, with individuals in endemic areas retaining low-level infections throughout their lives. Therefore, there is a gap between traditional model STH systems and observations in the field. Here, we review the immune response to traditional model STH infections in the laboratory. We compare these data to studies of natural infection in humans and rodents in endemic areas, highlighting crucial differences between experimental and natural infection. We then detail the literature to date on the use of "trickle" infections to experimentally model the kinetics of natural infection.