Schistosomal hepatic fibrosis and the interferon gamma receptor: a linkage analysis using single-nucleotide polymorphic markers

Identification of Genomic Regions Implicated in Susceptibility to Schistosoma mansoni Infection in a Murine Backcross Genetic Model

Only a small number of infected people are highly susceptible to schistosomiasis, showing high levels of infection or severe liver fibrosis. The susceptibility to schistosome infection is influenced by genetic background. To assess the genetic basis of susceptibility and identify the chromosomal regions involved, a backcross strategy was employed to generate high variation in schistosomiasis susceptibility. This strategy involved crossing the resistant C57BL/6J mouse strain with the susceptible CBA/2J strain. The resulting F1 females (C57BL/6J × CBA/2J) were then backcrossed with CBA/2J males to generate the backcross (BX) cohort. The BX mice exhibited a range of phenotypes, with disease severity varying from mild to severe disease, lacking a fully resistant group. We observed four levels of infection intensity using cluster and principal component analyses and K-means based on parasitological, pathological, and immunological trait measurements. The mice were genotyped with 961 informative SNPs, leading to the identification of 19 new quantitative trait loci (QTL) associated with parasite burden, liver lesions, white blood cell populations, and antibody responses. Two QTLs located on chromosomes 15 and 18 were linked to the number of granulomas, liver lesions, and IgM levels. The corresponding syntenic human regions are located in chromosomes 8 and 18. None of the significant QTLs had been reported previously.

Frequency distribution of cytokine and associated transcription factor single nucleotide polymorphisms in Zimbabweans: Impact on schistosome infection and cytokine levels

Cytokines mediate T-helper (TH) responses that are crucial for determining the course of infection and disease. The expression of cytokines is regulated by transcription factors (TFs). Here we present the frequencies of single nucleotide polymorphisms (SNPs) in cytokine and TF genes in a Zimbabwean population, and further relate SNPs to susceptibility to schistosomiasis and cytokine levels. Individuals (N = 850) were genotyped for SNPs across the cytokines IL4, IL10, IL13, IL33, and IFNG, and their TFs STAT4, STAT5A/B, STAT6, GATA3, FOXP3, and TBX21 to determine allele frequencies. Circulatory levels of systemic and parasite-specific IL-4, IL-5, IL-10, IL-13, and IFNγ were quantified via enzyme-linked immunosorbent assay. Schistosoma haematobium infection was determined by enumerating parasite eggs excreted in urine by microscopy. SNP allele frequencies were related to infection status by case-control analysis and logistic regression, and egg burdens and systemic and parasite-specific cytokine levels by analysis of variance and linear regression. Novel findings were i) IL4 rs2070874*T’s association with protection from schistosomiasis, as carriage of ≥1 allele gave an odds ratio of infection of 0.597 (95% CIs, 0.421–0.848, p = 0.0021) and IFNG rs2069727*G’s association with susceptibility to schistosomiasis as carriage of ≥1 allele gave an odds ratio of infection of 1.692 (1.229–2.33, p = 0.0013). Neither IL4 rs2070874*T nor IFNG rs2069727*G were significantly associated with cytokine levels. This study found TH2-upregulating SNPs were more frequent among the Zimbabwean sample compared to African and European populations, highlighting the value of immunogenetic studies of African populations in the context of infectious diseases and other conditions, including allergic and atopic disease. In addition, the identification of novel infection-associated alleles in both TH1- and TH2-associated genes highlights the role of both in regulating and controlling responses to Schistosoma.

The Genetics of Human Schistosomiasis Infection Intensity and Liver Disease: A Review

Schistosomiasis remains the fourth most prevalent parasitic disease affecting over 200 million people worldwide. Control efforts have focussed on the disruption of the life cycle targeting the parasite, vector and human host. Parasite burdens are highly skewed, and the majority of eggs are shed into the environment by a minority of the infected population. Most morbidity results from hepatic fibrosis leading to portal hypertension and is not well-correlated with worm burden. Genetics as well as environmental factors may play a role in these skewed distributions and understanding the genetic risk factors for intensity of infection and morbidity may help improve control measures. In this review, we focus on how genetic factors may influence parasite load, hepatic fibrosis and portal hypertension. We found 28 studies on the genetics of human infection and 20 studies on the genetics of pathology in humans. S. mansoni and S. haematobium infection intensity have been showed to be controlled by a major quantitative trait locus SM1, on chromosome 5q31-q33 containing several genes involved in the Th2 immune response, and three other loci of smaller effect on chromosomes 1, 6, and 7. The most common pathology associated with schistosomiasis is hepatic and portal vein fibroses and the SM2 quantitative trait locus on chromosome six has been linked to intensity of fibrosis. Although there has been an emphasis on Th2 cytokines in candidate gene studies, we found that four of the five QTL regions contain Th17 pathway genes that have been included in schistosomiasis studies: IL17B and IL12B in SM1, IL17A and IL17F in 6p21-q2, IL6R in 1p21-q23 and IL22RA2 in SM2. The Th17 pathway is known to be involved in response to schistosome infection and hepatic fibrosis but variants in this pathway have not been tested for any effect on the regulation of these phenotypes. These should be priorities for future studies.

Genetic algorithms identify individuals with high risk of severe liver disease caused by schistosomes

Schistosomes induce severe hepatic disease, which is fatal in 2-10% of cases, mortality being higher in cases of co-infection with HBV or HCV. Hepatic disease occurs as a consequence of the chronic inflammation caused by schistosome eggs trapped in liver sinusoids. In certain individuals, the repair process leads to a massive accumulation of fibrosis in the periportal spaces. We and others have shown that genetic variants play a crucial role in disease progression from mild to severe fibrosis and explain why hepatic fibrosis progresses rapidly in certain subjects only. We will review here published findings concerning the strategies that have been used in the analysis of hepatic fibrosis in schistosome-infected individuals, the genetic variants that have associated with fibrosis, and variants in new pathways crucial for fibrosis progression. Together, these studies show that the development of fibrosis is under the tight genetic control of various common variants with moderate effects. This polygenic control has made it possible to develop models that identify schistosome-infected individual at risk of severe hepatic disease. We discuss the performances and limitations of these models.

Genetic variants in IFNG and IFNGR1 and tuberculosis susceptibility

BACKGROUND

Tuberculosis (TB) is the type of chronic infectious disease which majorly caused by Mycobacterium tuberculosis (M. TB). Emerging data suggest that interferon gamma (IFNG) and its receptor IFNGR1 may be involved in the risk of TB.

METHODS

A total of 636 TB patients and 608 healthy controls were selected. The association between single nucleotide polymorphisms (SNPs) and TB was estimated by logistic analyses adjusting for age, gender and smoking status. SNPs genotyping was done by using the improved multiplex ligase detection reaction (iMLDR).

RESULTS

The IFNG rs1861494 allele C was related to an increased risk for TB (OR = 1.25, 95%CI: 1.06-1.48; P = 0.009). Compared with TT genotype, CT (OR = 1.28, 95%CI: 1.01-1.63; P = 0.040) and CC (OR = 1.51, 95%CI: 1.04-2.19; P = 0.031) were also risk factors for TB. In the subgroup analysis, the association was stronger among participants < 25 years (OR = 2.40, 95%CI: 1.70-3.38; P < 0.001) and male groups (OR = 1.31, 95%CI: 1.03-1.66; P = 0.030). In addition, IFNG rs1861494 was associated with anti-TB treatment outcome (OR = 0.70, 95%CI: 0.52-0.94; P = 0.017). We also detected that IFNGR1 rs2234711 influenced the IFNG production.

CONCLUSION

IFNG rs1861494 polymorphism was associated with TB, particularly in the younger and male subgroups.

Diagnosing schistosomiasis-induced liver morbidity: implications for global control

BACKGROUND

Subclinical morbidity due to schistosomiasis was evaluated in 565 patients, and the enhanced liver fibrosis (ELF) test was assessed for the first time as a potential screening tool for disease.

METHODS

The prevalence and intensity of infection were determined by Kato-Katz thick smear stool examination at baseline and 2 years after curative treatment. The degree of hepatic fibrosis was assessed by ultrasound. Non-invasive serum biomarkers of hepatic fibrosis were also evaluated.

RESULTS

The baseline human prevalence and infection intensity were found to be moderately high at 34% and 123 eggs per gram, respectively. However, hepatic parenchymal fibrosis occurred in 50% of subjects, with grade II fibrosis in 19% and grade III in 6%. The ELF score and higher serum levels of tissue inhibitor of metalloproteinase 1 (TIMP-1) and hyaluronic acid (HA) correlated with the grade of liver fibrosis.

CONCLUSIONS

The findings of this study demonstrated that praziquantel treatment had a short-term impact on both the prevalence and intensity of infection, but less of an impact on established morbidity. Higher TIMP-1 and HA serum levels, and an ELF cut-off score of 8 were found to be correlated with the grade of liver fibrosis; these values may, therefore, assist physicians in identifying individuals at greater risk of disease.

An IL-13 promoter polymorphism associated with liver fibrosis in patients with Schistosoma japonicum

The aim of this study was to determine whether two polymorphisms in the gene encoding IL13 previously associated with Schistosoma hematobium (S. hematobium) and S. mansoni infection are associated with S. japonicum infection. Single nucleotide polymorphisms (SNPs) rs1800925 (IL13/-1112C>T) and rs20541 (IL13R130Q) were genotyped in 947 unrelated individuals (307 chronically infected, 339 late-stage with liver fibrosis, 301 uninfected controls) from a schistosomiasis-endemic area of Hubei province in China. Regression models were used to evaluate allelic and haplotypic associations with chronic and late-stage schistosomiasis adjusted for non-genetic covariates. Expression of IL-13 was measured in S. japonicun-infected liver fibrosis tissue and normal liver tissue from uninfected controls by immunohistochemistry (IHC). The role of rs1800925 in IL-13 transcription was further determined by Luciferase report assay using the recombinant PGL4.17-rs180092 plasmid. We found SNP rs1800925T was associated with late-stage schistosomiasis caused by S. japonicum but not chronic schistosomiasis (OR = 1.39, 95%CI = 1.02-1.91, p = 0.03) and uninfected controls (OR = 1.49, 95%CI = 1.03-2.13, p = 0.03). Moreover, the haplotype rs1800925T-rs20541C increased the risk of disease progression to late-stage schistosomiasis (OR = 1.46, p = 0.035), whereas haplotype rs1800925C-rs20541A showed a protective role against development of late-stage schistosomiasis (F = 0.188, OR = 0.61, p = 0.002). Furthermore, S. japonicum-induced fibrotic liver tissue had higher IL13 expression than normal liver tissue. Plasmid PGL4.17-rs1800925T showed a stronger relative luciferase activity than Plasmid PGL4.17-rs1800925C in 293FT, QSG-7701 and HL-7702 cell lines. In conclusion, the functional IL13 polymorphism, rs1800925T, previously associated with risk of schistosomiasis, also contributes to risk of late-stage schistosomiasis caused by S. japonicum.

Host genetics and parasitic infections

Parasites still impose a high death and disability burden on human populations, and are therefore likely to act as selective factors for genetic adaptations. Genetic epidemiological investigation of parasitic diseases is aimed at disentangling the mechanisms underlying immunity and pathogenesis by looking for associations or linkages between loci and susceptibility phenotypes. Until recently, most studies used a candidate gene approach and were relatively underpowered, with few attempts at replicating findings in different populations. However, in the last 5 years, genome-wide and/or multicentre studies have been conducted for severe malaria, visceral leishmaniasis, and cardiac Chagas disease, providing some novel important insights. Furthermore, studies of helminth infections have repeatedly shown the involvement of common loci in regulating susceptibility to distinct diseases such as schistosomiasis, ascariasis, trichuriasis, and onchocherciasis. As more studies are conducted, evidence is increasing that at least some of the identified susceptibility loci are shared not only among parasitic diseases but also with immunological disorders such as allergy or autoimmune disease, suggesting that parasites may have played a role in driving the evolution of the immune system.

The WHO ultrasonography protocol for assessing hepatic morbidity due to Schistosoma mansoni. Acceptance and evolution over 12 years

The aim of this study is to review the worldwide acceptance of the World Health Organization (WHO) ultrasound protocol for assessing hepatosplenic morbidity due to Schistosoma mansoni since its publication in 2000. A PubMed literature research using the keywords "schistosomiasis and ultrasound," "schistosomiasis and ultrasonography," and "S. mansoni and ultrasound" from 2001 to 2012 was performed. Case reports, reviews, reports on abnormalities due to parasites other than S. mansoni, organ involvement other than the human liver, and reports where ultrasound method was not described were excluded. Six studies were retrieved from other Brazilian sources. Sixty studies on 37,424 patients from 15 countries were analyzed. The WHO protocol was applied with increasing frequency from 43.75% in the years 2001 to 2004 to 84.61% in 2009 to 2012. Results obtained using the pictorial image pattern approach of the protocol are reported in 38/41 studies, whereas measurements of portal branch walls were applied in 19/41 and results reported in 2/41 studies only. The practical usefulness of the pictorial approach of the WHO protocol is confirmed by its wide acceptance. This approach alone proved satisfactory in terms of reproducibility, assessment of evolution of pathology, and comparability between different settings. The measurements of portal branches, also part of the protocol, may be omitted without losing relevant information since results obtained by these measurements are nonspecific. This would save resources by reducing the time required for each examination. It is also more feasible for examiners who are not specialized in medical imaging. As with all protocols, incipient liver fibrosis is difficult to distinguish from normal ultrasound findings of the liver. The ability of this protocol to predict complications in severe cases should be further evaluated in a higher number of patients.

Genetic polymorphisms of IFNG and IFNGR1 in association with the risk of pulmonary tuberculosis

OBJECTIVE

Genetic host factors play an important role in controlling individual's susceptibility to the pathogen. This study aims to explore the single and joint effect of genetic polymorphisms of interferon-gamma (IFNG) and its receptor (IFNGR1) in association with the pulmonary tuberculosis in a Chinese Han population.

METHODS

This population-based case control study consisted of 1434 pulmonary tuberculosis patients and 1412 healthy controls. Six tag SNPs in IFNG/IFNGR1 were genotyped using TaqMan allelic discrimination technology. The logistic regression model was carried out to analyze the associations between the genotypes and haplotypes and the risk of tuberculosis by calculating the odds ratio (OR) and 95% confidence interval (CI).

RESULTS

After the Bonferroni correction for multiple comparisons, three SNPs (rs2234711, rs1327475 and rs7749390) in IFNGR1 gene were observed to be significantly associated with the altered risks of tuberculosis. For the SNP rs2234711, individuals carrying C allele (vs. T) showed a decreased risk, with the adjusted OR(95% CI) of 0.82(0.76-0.91). The additive model revealed that each additional allele contributed about 14% decreased risk (OR: 0.86, 95% CI: 0.77-0.95). Moreover, we observed a strong linkage disequilibrium between rs2234711 and rs3799488. Compared with the common rs2234711C-rs3799488C haplotype, the haplotype rs2234711T-rs3799488C contributed to a significant increase in the risk of tuberculosis (adjusted OR: 1.24, 95% CI: 1.09-1.41).

CONCLUSIONS

Our results suggest that genetic polymorphisms in IFNGR1 gene are involved in the risk of tuberculosis in the Chinese population. Future studies should include a comprehensive sequencing analysis to identify the specific causative sequence variants underlying the observed associations.

Interaction Between the Neglected Tropical Disease Human Schistosomiasis and HCV Infection in Egypt: a Puzzling Relationship

Egypt has the highest prevalence of chronic hepatitis C virus (HCV) infection and seropositivity worldwide, and it has been proposed that this enhanced susceptibility to HCV is related to coinfection with schistosomiasis. Although currently, there are no studies regarding the actual prevalence of both human schistosomiasis and schistosomiasis/HCV coinfection evidences strongly support that eliminating human schistosomiasis from Egypt is necessary to reduce both HCV prevalence and liver pathology. The present review highlights the significant impact of the neglected tropical disease human schistosomiasis on both susceptibility of Egyptians to HCV coinfection, severity of the resulting liver pathology, and poor response to antiviral therapy. The immune evasion mechanisms exerted by the HCV-NS3/4A protease domain, and the possible impact of immune evasion mechanisms exerted by proteases of larval, worm and egg stages of the parasite Schistosoma on human susceptibility to HCV infection are discussed. In addition, schistosome immune evasion mechanisms may include immunosuppression that in turn prevents clearance of HCV viremia and leads to relapsing HCV infection and severe liver pathology. I propose the generation of a replicon system from the most prevailing genotype (HCV-4a) in Egypt and establishing its replication on hepatoplastoma or immune cells in presence of bilharzial antigens. Finally, the use of a humanized small animal model that can acquire both HCV and S. mansoni infections will be important to further understand in real time the impact of coinfection on both the immune system and liver pathology.

A unique DNA methylation signature defines a population of IFN-γ/IL-4 double-positive T cells during helminth infection

Th1 and Th2 cell fates are traditionally viewed as mutually exclusive, but recent work suggests that these lineages may be more plastic than previously thought. When isolating splenic CD4(+) T cells from mice infected with the parasitic helminth Schistosoma mansoni, we observed a defined population of IFN-γ/IL-4 double-positive cells. These IFN-γ(+) IL-4(+) cells showed differences in DNA methylation at the Ifng and Il4 loci when compared with IFN-γ(+) IL-4(-) (Th1) and IFN-γ(-) IL-4(+) (Th2) cells, demonstrating that they represent a distinct effector cell population. IFN-γ(+) IL-4(+) cells also displayed a discrete DNA methylation pattern at a CpG island within the body of the Gata3 gene, which encodes the master regulator of Th2 identity. DNA methylation at this region correlated with decreased Gata3 levels, suggesting a possible role in controlling Gata3 expression. These data provide important insight into the molecular mechanisms behind the co-existence of Th1 and Th2 characteristics.

Fibroscan of chronic HCV patients coinfected with schistosomiasis

BACKGROUND AND STUDY AIMS

Both hepatitis C virus (HCV) and schistosomiasis are highly endemic in Egypt and coinfection is frequently encountered. Such coinfection is responsible for leading to a more severe liver disease. Hence, the aim of the study was to assess the fibroscan in chronic HCV patients coinfected with Schistosoma.

PATIENTS AND METHODS

This study included 231 chronic HCV patients. Routine pre-treatment work-up was done including anti-schistosomal antibodies. Liver stiffness measurements using fibroscan and reference needle-liver biopsy were done. Patients were categorised into two groups: HCV patients with positive schistosomal serology and HCV patients with negative schistosomal serology.

RESULTS

Anti-schistosomal antibody was positive in 29% of the studied population. Positive schistosomal serology status was significantly associated with the disagreement between the results of liver biopsy (Metavir) and the fibroscan results (p value=0.02), which was more obvious in F2 and F3 fibrosis stages. The sensitivity of fibroscan for the detection of the F2 stage decreased from 64% among negative schistosomal serology patients to 30.8% among positive schistosomal serology patients, and for the F3 stage it decreased from 43.8% to 21.4%, respectively. Multivariate logistic regression showed that fibrosis stages (F0-F1 and F4) were the most independent factors that were associated with the agreement between fibroscan and liver biopsy (odds ratio (OR) 3.4, 7.12 and p value <0.001, <0.001, respectively).

CONCLUSION

Although the sensitivity of fibroscan for the detection of fibrosis stages (F2 and F3) was impaired in patients with positive schistosomal serology, fibrosis stages (F0-F1 and F4) were the most independent factors associated with the agreement between fibroscan and liver biopsy.

Coinfection with hepatitis C virus and schistosomiasis: Fibrosis and treatment response

AIM: To assess whether schistosomiasis coinfection with chronic hepatitis C virus (HCV) influences hepatic fibrosis and pegylated-interferon/ribavirin (PEG-IFN/RIB) therapy response.

METHODS: This study was designed as a retrospective analysis of 3596 chronic HCV patients enrolled in the Egyptian National Program for HCV treatment with PEG-IFN/RIB. All patients underwent liver biopsy and anti-schistosomal antibodies testing prior to HCV treatment. The serology results were used to categorize the patients into group A (positive schistosomal serology) or group B (negative schistosomal serology). Patients in group A were given oral antischistosomal treatment (praziquantel, single dose) at four weeks prior to PEG-IFN/RIB. All patients received a 48-wk course of PEG-IFN (PEG-IFNα2a or PEG-IFNα2b)/RIB therapy. Clinical and laboratory follow-up examinations were carried out for 24 wk after cessation of therapy (to week 72). Correlations of positive schistosomal serology with fibrosis and treatment response were assessed by multiple regression analysis.

RESULTS: Schistosomal antibody was positive in 27.3% of patients (15.9% females and 84.1% males). The patients in group A were older (P = 0.008) and had a higher proportion of males (P = 0.002) than the patients in group B. There was no significant association between fibrosis stage and positive schistosomal serology (P = 0.703). Early virological response was achieved in significantly more patients in group B than in group A (89.4% vs 86.5%, P = 0.015). However, significantly more patients in group A experienced breakthrough at week 24 than patients in group B (36.3% vs 32.3%, P = 0.024). End of treatment response was achieved in more patients in group B than in group A (62.0% vs 59.1%) but the difference did not reach statistical significance (P = 0.108). Sustained virological response occurred in significantly more patients in group B than in group A (37.6% vs 27.7%, P = 0.000). Multivariate logistic regression analysis of patient data at treatment weeks 48 and 72 showed that positive schistosomal serology was associated with failure of response to treatment at week 48 (OR = 1.3, P = 0.02) and at week 72 (OR = 1.7, P < 0.01).

CONCLUSION: Positive schistosomal serology has no effect on fibrosis staging but is significantly associated with failure of response to HCV treatment despite antischistosomal therapy.

Genetic analysis of human predisposition to hepatosplenic disease caused by schistosomes reveals the crucial role of connective tissue growth factor in rapid progression to severe hepatic fibrosis

Schistosome worms inhabit mammalian mesenteric veins. Their eggs cause chronic inflammation, which progresses to periportal fibrosis in 5 to 30% of cases, increasing portal blood pressure and leading to esophageal varices. Episodes of bleeding cause hepatic necrosis and may ultimately lead to hepatic failure and the death of the patient. Schistosome infections can also cause pulmonary hypertension and heart failure. The mechanisms of fibrogenesis and fibrolysis are beginning to be unraveled, but it remains unclear why disease occurs only in certain subjects, as also observed for other types of chronic liver inflammation, as in hepatitis C or B. We summarize here the results that showed that fibrosis progression is determined by a genetic locus on chromosome 6. The CCN2 gene at this locus, encodes CTGF that is a crucial regulator of fibrosis. Two groups of CCN2 polymorphisms independently modulate the progression of hepatic fibrosis. These results were obtained in an Asian population, but were extended to humans living in Africa and South America and are presently tested in liver fibrosis of other etiological origins.

A research agenda for helminth diseases of humans: basic research and enabling technologies to support control and elimination of helminthiases

Successful and sustainable intervention against human helminthiases depends on optimal utilisation of available control measures and development of new tools and strategies, as well as an understanding of the evolutionary implications of prolonged intervention on parasite populations and those of their hosts and vectors. This will depend largely on updated knowledge of relevant and fundamental parasite biology. There is a need, therefore, to exploit and apply new knowledge and techniques in order to make significant and novel gains in combating helminthiases and supporting the sustainability of current and successful mass drug administration (MDA) programmes. Among the fields of basic research that are likely to yield improved control tools, the Disease Reference Group on Helminth Infections (DRG4) has identified four broad areas that stand out as central to the development of the next generation of helminth control measures: 1) parasite genetics, genomics, and functional genomics; 2) parasite immunology; 3) (vertebrate) host–parasite interactions and immunopathology; and 4) (invertebrate) host–parasite interactions and transmission biology. The DRG4 was established in 2009 by the Special Programme for Research and Training in Tropical Diseases (TDR). The Group was given the mandate to undertake a comprehensive review of recent advances in helminthiases research in order to identify notable gaps and highlight priority areas. This paper summarises recent advances and discusses challenges in the investigation of the fundamental biology of those helminth parasites under the DRG4 Group's remit according to the identified priorities, and presents a research and development agenda for basic parasite research and enabling technologies that will help support control and elimination efforts against human helminthiases.

Hepatosplenic morbidity due to Schistosoma mansoni in schoolchildren on Ukerewe Island, Tanzania

The study was conducted to assess infection intensity and morbidity due to Schistosoma mansoni in schoolchildren on Ukerewe Island in Lake Victoria, Tanzania, East Africa. Three hundred and sixty pupils who have never been treated previously were enrolled (180 males/180 females, age 6-17 years [median 10 years]) in three different schools of the island. Double stool samples were collected from each pupil and egg excretion was classified according to WHO recommendations. Ultrasound investigations were performed in accordance with the WHO Niamey-Belo-Horizonte protocol. Male (112/180, 62.2%) and female (104/180; 57.7%) pupils were infected (difference, not significant [n.s.]). In the positive 216 cases, egg excretion varied from 1 to 2,440 eggs per gramme stool (epg) [median 165 epg]. There were 69/216 (31.9%) who had a low grade, 105/216 (53.2%) had a moderate and 42/216 (14.8%) had a heavy infection. There was no significant difference between male and female sex nor with regard to age groups. There were 354/360 children who underwent sonography: 321 (90.7%) had splenomegaly, 316 (89.3%) showed a left lobe and 109 (30.9%) had a right lobe hepatomegaly. Overt signs of portal fibrosis (PF) were present in 19 children (5.4%) out of whom 11 presented with echogenic thickening of peripheral portal and 8 with thickening of central portal branches. Non-specific portal wall changes were seen in 6 children (1.7%). Association of PF to quantitative egg excretion was not seen (median in PF, 172 epg vs. median in non PF, 168 epg; difference, n.s.). Portal vein dilatation was seen in 101/354 (28.5%) cases. In Ukerewe, the prevalence of S. mansoni infection and infection intensity in children is high, yet overt hepatic morbidity is low as compared to other endemic foci. Non-specific ultrasonographic abnormalities including hepatosplenomegaly and portal vein dilatation were seen frequently but the fraction attributable to schistosomiasis is difficult to assess.

Regulation of neutrophils by interferon-γ limits lung inflammation during tuberculosis infection

IFN-γ functions to suppress neutrophil accumulation in the lungs of mice infected with M. tuberculosis, in part by suppressing IL-17 production from CD4⁺ T cells.

Resistance to Mycobacterium tuberculosis requires the host to restrict bacterial replication while preventing an over-exuberant inflammatory response. Interferon (IFN) γ is crucial for activating macrophages and also regulates tissue inflammation. We dissociate these two functions and show that IFN-γ^−/− memory CD4⁺ T cells retain their antimicrobial activity but are unable to suppress inflammation. IFN-γ inhibits CD4⁺ T cell production of IL-17, which regulates neutrophil recruitment. In addition, IFN-γ directly inhibits pathogenic neutrophil accumulation in the infected lung and impairs neutrophil survival. Regulation of neutrophils is important because their accumulation is detrimental to the host. We suggest that neutrophilia during tuberculosis indicates failed Th1 immunity or loss of IFN-γ responsiveness. These results establish an important antiinflammatory role for IFN-γ in host protection against tuberculosis.

Modeling the effect of chronic schistosomiasis on childhood development and the potential for catch-up growth with different drug treatment strategies promoted for control of endemic schistosomiasis

In areas endemic for schistosomiasis having limited healthcare, targeted drug treatment of school-age children is recommended for control of Schistosoma-associated morbidity. However, optimal timing, number, and frequency of treatments are not established. Because longitudinal studies of long-term impact of treatment are few, for current policy considerations we performed quantitative simulation (based on calibrated modeling of Schistosoma-associated disease formation) to project the impact of different school-age treatment regimens. Using published efficacy data from targeted programs, combined with age-specific risk for growth retardation and reinfection, we examined the likely impact of different strategies for morbidity prevention. Results suggest the need for early, repeated treatment through primary school years to optimally prevent the disabling sequelae of stunting and undernutrition. Dynamics of infection/reinfection during childhood and adolescence, combined with early treatment effects against reversible infection-associated morbidities, create a need for aggressive retreatment of preadolescents to achieve optimal suppression of morbidity where drug-based control is used.

Association of HLA and post-schistosomal hepatic disorder: a systematic review and meta-analysis

Several human genetic variants, HLA antigens and alleles are reportedly linked to post-schistosomal hepatic disorder (PSHD), but the results from these reports are highly inconclusive. In order to estimate overall associations between human genetic variants, HLA antigens, HLA alleles and PSHD, we systematically reviewed and performed a meta-analysis of relevant studies in both post-schistosomal hepatic disorder and post-schistosomal non-hepatic disorder patients. PubMed, Scopus, Google Scholar, The HuGE Published Literature database, Cochrane Library, and manual search of reference lists of articles published before July 2009 were used to retrieve relevant studies. Two reviewers independently selected articles and extracted data on study characteristics and data regarding the association between genetic variants, HLA antigens, HLA alleles and PSHD in the form of 2×2 tables. A meta-analysis using fixed-effects or random-effects models to pooled odds ratios (OR) with corresponding 95% confidence intervals were calculated only if more than one study had investigated particular variation. We found 17 articles that met our eligibility criteria. Schistosoma mansoni and Schistosoma japonicum were reported as the species causing PSHD. Since human genetic variants were only investigated in one study, these markers were not assessed by meta-analysis. Thus, only HLA-genes (a total of 66 HLA markers) were conducted in the meta-analysis. Our meta-analysis showed that human leucocyte antigens HLA-DQB1*0201 (OR=2.64, P=0.018), DQB1*0303 (OR=1.93, P=0.008), and DRB1*0901 (OR=2.14, P=0.002) alleles and HLA-A1 (OR=5.10, P=0.001), A2 (OR=2.17, P=0.005), B5 (OR=4.63, P=0.001), B8 (OR=2.99, P=0.02), and B12 (OR=5.49, P=0.005) serotypes enhanced susceptibility to PSHD, whereas HLA-DQA1*0501 (OR=0.29, P≤0.001) and DQB1*0301 (OR=0.58, P=0.007) were protective factors against the disease. We further suggested that the DRB1*0901-DQB1*0201, DRB1*0901-DQB1*0303 and A1-B8 haplotypes enhanced susceptibility to PSHD, whereas DQA1*0501-DQB1*0301 linkage decreased the risk of PSHD. The result improved our understanding of the association between the HLA loci and PSHD with regard to pathogenic or protective T-cells and provided novel evidence that HLA alleles may influence disease severity.

Genetic studies of the etiology of asthma

Asthma is a heterogeneous disease for which a strong genetic basis is firmly established. Although the generally accepted definition includes three domains of symptoms (variable airway obstruction, airway hyper-responsiveness, and airway inflammation), there is general agreement that, rather than being a single disease entity, asthma consists of related, overlapping syndromes. A considerable proportion of asthma is IgE-mediated, but the observation that not all individuals with asthma are atopic adds to the heterogeneity. Although a genetic basis for asthma is undeniable, elucidation of polymorphisms that are "causal" is greatly hampered by variability in the clinical phenotype, which is likely due to the multiple molecular mechanisms underlying the complex pathological processes involved in disease development and progression. One objective of this review is to consider progress that has been made to date in gene discovery in the field of asthma, with a focus on the evolution of molecular genetic methods that have led to the discoveries thus far, and with a particular focus on the major advances owed to the published genome-wide association studies (GWAS) on asthma to date. A second objective is to consider a Darwinian approach toward understanding the genetic underpinnings of asthma, including evidence supporting a modified Hygiene Hypothesis, which suggests that there are co-associations between asthma risk polymorphisms and polymorphisms associated with another IgE-mediated disease, schistosomiasis. The overall conclusion is that the huge research efforts and expense committed to asthma genetics have changed the perception about disease etiology in general and the functional relevance of the asthma genes identified thus far in particular.

Schistosomiasis in the People's Republic of China: the era of the Three Gorges Dam

The potential impact of the Three Gorges Dam (TGD) on schistosomiasis transmission in China has invoked considerable global concern. The TGD will result in changes in the water level and silt deposition downstream, favoring the reproduction of Oncomelania snails. Combined with blockages of the Yangtze River's tributaries, these changes will increase the schistosomiasis transmission season within the marshlands along the middle and lower reaches of the Yangtze River. The changing schistosome transmission dynamics necessitate a comprehensive strategy to control schistosomiasis. This review discusses aspects of the epidemiology and transmission of Schistosoma japonicum in China and considers the pathology, clinical outcomes, diagnosis, treatment, immunobiology, and genetics of schistosomiasis japonica together with an overview of current progress in vaccine development, all of which will have an impact on future control efforts. The use of synchronous praziquantel (PZQ) chemotherapy for humans and domestic animals is only temporarily effective, as schistosome reinfection occurs rapidly. Drug delivery requires a substantial infrastructure to regularly cover all parts of an area of endemicity. This makes chemotherapy expensive and, as compliance is often low, a less than satisfactory control option. There is increasing disquiet about the possibility that PZQ-resistant schistosomes will develop. Consequently, as mathematical modeling predicts, vaccine strategies represent an essential component in the future control of schistosomiasis in China. With the inclusion of focal mollusciciding, improvements in sanitation, and health education into the control scenario, China's target of reducing the level of schistosome infection to less than 1% by 2015 may be achievable.

Variants of CTGF are associated with hepatic fibrosis in Chinese, Sudanese, and Brazilians infected with schistosomes

Abnormal fibrosis occurs during chronic hepatic inflammations and is the principal cause of death in hepatitis C virus and schistosome infections. Hepatic fibrosis (HF) may develop either slowly or rapidly in schistosome-infected subjects. This depends, in part, on a major genetic control exerted by genes of chromosome 6q23. A gene (connective tissue growth factor [CTGF]) is located in that region that encodes a strongly fibrogenic molecule. We show that the single nucleotide polymorphism (SNP) rs9402373 that lies close to CTGF is associated with severe HF (P = 2 x 10(-6); odds ratio [OR] = 2.01; confidence interval of OR [CI] = 1.51-2.7) in two Chinese samples, in Sudanese, and in Brazilians infected with either Schistosoma japonicum or S. mansoni. Furthermore, SNP rs12526196, also located close to CTGF, is independently associated with severe fibrosis (P = 6 x 10(-4); OR = 1.94; CI = 1.32-2.82) in the Chinese and Sudanese subjects. Both variants affect nuclear factor binding and may alter gene transcription or transcript stability. The identified variants may be valuable markers for the prediction of disease progression, and identify a critical step in the development of HF that could be a target for chemotherapy.

Conquering 'snail fever': schistosomiasis and its control in China

Schistosomiasis japonica is a serious parasitic disease and a major health risk for more than 60 million people living in the tropical and subtropical zones of south China. The disease is a zoonosis and its cause, the parasitic trematode Schistosoma japonicum, has a range of mammalian reservoirs, making control efforts difficult. Current control programs are heavily based on community chemotherapy with a single dose of the highly effective drug praziquantel. However, vaccines (for use in bovines and in humans) in combination with other control strategies are needed to eliminate the disease. In this review, we provide an overview of the transmission, clinical features, pathogenesis, diagnosis, treatment, genetics and susceptibility, epidemiology, and prospects for control of schistosomiasis japonica in China. The threat posed by the Three Gorges Dam may undermine control efforts because it will change the local ecology and associated schistosomiasis transmission risks over the next decade and beyond.

Immunopathogenesis of human schistosomiasis

Schistosomiasis continues to be a significant cause of parasitic morbidity and mortality worldwide. This review considers the basic features of the pathology and clinical outcomes of hepatointestinal and genitourinary schistosomiasis, presents an overview of the numerous studies on animal models that have clarified many of the immunopathological features, and provides insight into our current understanding of the immunopathogenesis and genetic control of human schistosomiasis. In murine schistosomiasis, pathology is induced by a CD4(+) Th2 driven granulomatous response directed against schistosome eggs lodged in the host liver. The Th2 cytokines IL-4 and IL-13 drive this response, whereas IL-10, IL13Ralpha2, IFN-gamma and a subset of regulatory T-cells act to limit schistosome induced pathology. A variety of cell types including hepatic stellate cells, alternatively activated macrophages and regulatory T-cells have also been implicated in the pathogenesis of schistosomiasis. Current knowledge suggests the immunopathogenic mechanisms underlying human schistosomiasis are likely to be similar. The review also considers the future development of anti-pathology schistosome vaccines. As fibrosis is an important feature of many other diseases such as Crohn's disease and sarcoidosis, a comprehensive understanding of the cellular and molecular mechanisms involved in schistosomiasis may also ultimately contribute to the development an effective disease intervention strategy for other granulofibrotic diseases.

Recent advances in primary immunodeficiencies: identification of novel genetic defects and unanticipated phenotypes

Primary immunodeficiencies (PIDs) have traditionally been defined according to their immunologic phenotype. Far from being concluded, the search for human genes that, when mutated, cause PID is actively being pursued. During the last year, four novel genetic defects that cause severe combined immunodeficiency and severe congenital neutropenia have been identified. At the same time, the immunologic definition of primary immunodeficiencies has been expanded by the recognition that genetic defects affecting innate immunity may result in selective predisposition to certain infections, such as mycobacterial disease, herpes simplex encephalitis, and invasive pneumococcal infections. Studies of genetically determined susceptibility to infections have recently shown that immunologic defects may also account for novel infectious phenotypes, such as malaria or leprosy. Finally, a growing body of evidence indicates that primary immunodeficiencies may present with a noninfectious clinical phenotype that may be restricted to single organs, as in the case of atypical hemolytic uremic syndrome or pulmonary alveolar proteinosis. Overall, these achievements highlight the importance of human models, which often differ from the corresponding animal models.

Influence of the HLA-DQB1*0201 allele on the immune response in a Schistosoma mansoni infection

We previously reported the association of the major histocompatibility complex class II HLA-DQB1*0201 allele with hepatosplenic schistosomiasis. The aim of this study was to evaluate the cytokine responses of peripheral blood mononuclear cells (PBMCs) and the serum levels of immunoglobulin isotypes. The study population was selected from a schistosomiasis endemic area. No significant differences in cytokine profiles were detected in PBMCs stimulated with Schistosoma mansoni soluble egg antigen (SEA), regardless of the subjects DQB1*0201 genotype or infection status. However, previously infected DQB1*0201 positive individuals had significantly lower levels of IgG4 compared to DQB1*0201 negative individuals (P<0.05).

Genetic epidemiology of human schistosomiasis in Brazil

Human schistosomiasis presents the classic, complex disease phenotype, with marked variation in the intensity of infection, the immune response to infection, and the development of schistosome-related pathology. Determining the role of host genetics in schistosomiasis is complicated by the numerous parasite and environmental factors involved in transmission. However, as a result of the increased availability of sequence data, novel statistical methods, and new methods of study design, the last decade has seen significant advances in identifying the role of host genetics in schistosome infection around the world. Many of these advances have taken place in Brazil. Epidemiological studies in Brazil have shown that the intensity of infection (worm burden) is a heritable phenotype (41%). Human genome scans have identified a locus responsible for controlling Schistosoma mansoni infection intensity on chromosome 5q31-q33. There is also evidence for genetic control of pathology due to S. mansoni, with linkage reported to a region containing the gene for the interferon-gamma receptor 1 subunit. Numerous association studies have also provided evidence for major histocompatibility complex control of pathology in schistosomiasis. Recent candidate gene studies suggest a role of other immune response genes in controlling helminth infection and pathology. We chronicle the many advances made in understanding the role of host genetics in S. mansoni infection that have taken place in Brazil by phenotype studied: infection intensity, immune response, and disease development. Results from Brazilian studies are compared with studies of S. mansoni and other schistosome species elsewhere in the world.

Regulatory role of interleukin-10 and interferon-gamma in severe hepatic central and peripheral fibrosis in humans infected with Schistosoma japonicum

BACKGROUND

Schistosoma japonicum is the most pathogenic agent of hepatosplenic schistosomiasis. It causes fibrosis of the central (CentF) and peripheral (PerF) portal areas. We investigated whether CentF and PerF in Chinese fishermen infected with S. japonicum were associated with an abnormal production of cytokines and chemokines that, in experimental models, have been implicated in the regulation of fibrosis.

METHODS

Cytokines were measured by enzyme-linked immunosorbent assay in cultures of peripheral blood mononuclear cells from 127 patients, after stimulation with S. japonicum egg antigens. Data were analyzed by logistic regression that included age, sex, number of treatment episodes, alcohol use, and exposure as covariates.

RESULTS

CentF was associated with low levels of interleukin (IL)-10 (P= .0004), regulated on activation normally T cell expressed and secreted (P= .0004), and macrophage inflammatory protein-1alpha (P= .007). In a multivariate analysis, only IL-10 was associated with CentF (odds ratio [OR], 10.8; 95% confidence interval [CI], 3.2-38; P= .0004). Splenomegaly was also associated with low IL-10 production and, independently, with CentF. In multivariate analysis, PerF was associated with low production of interferon (IFN)-gamma (OR, 8.2; 95% CI, 2-33; P= .0035) but not with production of IL-10.

CONCLUSIONS

IL-10 is associated with protection against central fibrosis, because of its anti-inflammatory and antifibrosis effects. IFN-gamma is associated with protection against PerF, which depends more on egg load and egg-associated toxicity.

Genetic studies of African populations: an overview on disease susceptibility and response to vaccines and therapeutics

Africa is the ultimate source of modern humans and as such harbors more genetic variation than any other continent. For this reason, studies of the patterns of genetic variation in African populations are crucial to understanding how genes affect phenotypic variation, including disease predisposition. In addition, the patterns of extant genetic variation in Africa are important for understanding how genetic variation affects infectious diseases that are a major problem in Africa, such as malaria, tuberculosis, schistosomiasis, and HIV/AIDS. Therefore, elucidating the role that genetic susceptibility to infectious diseases plays is critical to improving the health of people in Africa. It is also of note that recent and ongoing social and cultural changes in sub-Saharan Africa have increased the prevalence of non-communicable diseases that will also require genetic analyses to improve disease prevention and treatment. In this review we give special attention to many of the past and ongoing studies, emphasizing those in Sub-Saharan Africans that address the role of genetic variation in human disease.

Human genetics of infectious diseases: a unified theory

Since the early 1950s, the dominant paradigm in the human genetics of infectious diseases postulates that rare monogenic immunodeficiencies confer vulnerability to multiple infectious diseases (one gene, multiple infections), whereas common infections are associated with the polygenic inheritance of multiple susceptibility genes (one infection, multiple genes). Recent studies, since 1996 in particular, have challenged this view. A newly recognised group of primary immunodeficiencies predisposing the individual to a principal or single type of infection is emerging. In parallel, several common infections have been shown to reflect the inheritance of one major susceptibility gene, at least in some populations. This novel causal relationship (one gene, one infection) blurs the distinction between patient-based Mendelian genetics and population-based complex genetics, and provides a unified conceptual frame for exploring the molecular genetic basis of infectious diseases in humans.

Mendelian and complex genetics of susceptibility and resistance to parasitic infections

Uncovering the complex genetic basis of susceptibility and resistance to parasitic infectious diseases is an enormous challenge. It probably involves many different host genes, interacting with multiple parasite genetic and environmental factors. Several genes of interest have been identified by family and association studies in humans and by using mouse models, but more robust epidemiological studies and functional data are needed to authenticate these findings. With new technologies and statistical tools for whole-genome association analysis, the next few years are likely to see acceleration in the rate of gene discovery, which has the potential to greatly assist drug and vaccine development.

Genetic epidemiology of health disparities in allergy and clinical immunology

The striking racial and ethnic disparities in disease prevalence for common disorders, such as allergic asthma, cannot be explained entirely by environmental, social, cultural, or economic factors, and genetic factors should not be ignored. Unfortunately, genetic studies in underserved minorities are hampered by disagreements over the biologic construct of race and logistic issues, including admixture of different races and ethnicities. Current observations suggest that the frequency of high-risk variants in candidate genes can differ between African Americans, Puerto Ricans, and Mexican Americans, and this might contribute to the differences in disease prevalence. Maintenance of certain allelic variants in the population over time might reflect selective pressures in previous generations. For example, significant associations between markers in certain candidate genes (eg, STAT6, ADRB2, and IFNGR1) for traits such as high total IgE levels observed in resistance to extracellular parasitic disease in one population and atopic asthma in another supports the common disease/common variant model for disease. Herein is a discussion of how genetic variants might explain, at least in part, the marked disparities observed in risk to allergic asthma.