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Am. J. Trop. Med. Hyg., 76(5), 2007, pp. 943-949
Copyright © 2007 by The American Society of Tropical Medicine and Hygiene

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REDUCED SERUM CONCENTRATIONS OF RETINOL AND {alpha}-TOCOPHEROL AND HIGH CONCENTRATIONS OF HYDROPEROXIDES ARE ASSOCIATED WITH COMMUNITY LEVELS OF S. MANSONI INFECTION AND SCHISTOSOMAL PERIPORTAL FIBROSIS IN ETHIOPIAN SCHOOL CHILDREN

NEGA BERHE*, BENTE L. HALVORSEN, THOMAS E. GUNDERSEN, BJØRN MYRVANG, SVEIN G. GUNDERSEN, AND RUNE BLOMHOFF
Aklilu Lemma Institute of Pathobiology, Addis Ababa University, Addis Ababa, Ethiopia; Institute for International Health, University of Oslo, Oslo, Norway; Ullevål University Hospital, Department of Infectious Diseases, Centre for Imported and Tropical Diseases, Oslo, Norway; Sorlandet Hospital HF/Agder University College, Kristiansand, Norway; Institute for Basic Medical Sciences, Department of Nutrition, University of Oslo, Oslo, Norway


ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 STUDY SUBJECTS, MATERIALS, AND...
 RESULTS
 DISCUSSION
 REFERENCES
 
To study the relationship between micronutrient malnutrition and schistosomiasis mansoni, a cross-sectional study was undertaken involving 421 schoolchildren (mean age 12.6 years; 333 from schistosomiasis mansoni–endemic villages (Workemado and Sille) and 88 non-endemic controls from Sheno). Prevalence of schistosomiasis mansoni infection in Workemado and Sille was comparable (90.6% versus 95%, respectively), and prevalence of PPF in Workemado was significantly higher than in Sille (7.0% versus 0.6%, P < 0.001). Compared with non-endemic controls, serum retinol concentrations were significantly lower and hydroperoxides were significantly higher in subjects from schistosomiasis mansoni–endemic areas. Furthermore, serum {alpha}-tocopherol concentrations in subjects from an area with high prevalence of PPF were significantly reduced while the concentrations in subjects from an area with low prevalence of PPF were comparable to the levels found in non-endemic healthy controls. In conclusion, micronutrient malnutrition and oxidative stress are associated with Schistosoma mansoni infection and levels of schistosomal PPF.


INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
STUDY SUBJECTS, MATERIALS, AND...
 RESULTS
 DISCUSSION
 REFERENCES
 
Worldwide, schistosomiasis currently affects an estimated 200 million people,1 85% of whom are in sub-Saharan Africa.2 Micronutrient deficiency is estimated to affect about one-third of Sub-Saharan Africa’s people affecting minds, bodies, energies, and economic prospects of nations.3 Micro-nutrient deficiencies often occur in association with protein-energy malnutrition and, as part of a "vicious cycle" with infection, in which one exacerbates and increases vulnerability to the other.

Morbidity and mortality associated with schistosomiasis mansoni are mainly the result of Symmers periportal fibrosis (PPF) of the liver, which afflicts only a smaller proportion among subjects with infection. Disparities between community prevalence of infection and levels of PPF are often observed in various endemic areas. Although the reasons for these differences are not entirely clear, duration and intensity of infection,4–6 sex,6 and host genetics7,8 are some of the factors considered to influence the development of PPF. Furthermore, experimental animal studies show that extent to which the host can down-modulate the T-helper 2 dominated granulomatous immune response directed against Schistosoma mansoni eggs seem to be crucial in the development of schistosomal PPF, and IL-13 has been shown to be most prominent profibrotic cytokines involved.9–11 When it comes to humans, some cytokine-based studies involving peripheral blood mononuclear cells seem to be inline with the overall findings of experimental animal studies,12–14 although some have reported differing results.15

Oxidative stress may contribute to the development of fibrosis in the liver either through direct stimulation or by promoting the production of profibrotic cytokines.16–18 Furthermore, oxidative stress may also promote polarization of T-cell differentiation toward T helper 2 phenotype.19 Using experimental models of the disease, it has been shown that the granulomatous inflammatory response to S. mansoni eggs entrapped in the liver induces hepatic oxidative stress, with production of reactive oxygen species (ROS) and reduced anti-oxidant status of the organ.20–23 The ultimate result of ROS generation is killing of the parasite eggs; however, the process is potentially harmful for the host as production of ROS may initiate a fibrogenesis cascade in the liver or modulate tissue and cellular events responsible for progression of liver fibrosis. Thus, the pathophysiologic effect of ROS production associated with inflammatory response depend on a balance between opposing mechanisms that can either terminate the oxidative process or lead to increased generation of potentially harmful oxidants.17,18 The latter condition may promote the development of liver fibrosis, particularly in subjects with suboptimal antioxidant micronutrients status.

Earlier community based studies have reported association of S. mansoni infection with micronutrient malnutrition.24,25 Furthermore, in two recent studies from the Sudan involving 35 (mean age 34 years) and 50 individuals (mean age 26 years) from endemic regions, serum markers of fibrosis (hyaluronic acid) and oxidative stress (lipid peroxides and protein carbonyls) were shown to be high in subjects with schistosomal PPF.26,27 However, the causal relationship between micronutrient malnutrition and S. mansoni infection and/or development of schistosomal periportal fibrosis is not entirely clear. To further elucidate on the role of micronutrients as possible determinants of morbidity, a community-based study was undertaken involving 421 school children (mean age 12.6 years) from three communities (333 from two S. mansoni–endemic villages and 88 students from an area non-endemic for malaria and schistosomiasis).


STUDY SUBJECTS, MATERIALS, AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 STUDY SUBJECTS, MATERIALS, AND...
RESULTS
 DISCUSSION
 REFERENCES
 
Study subjects, morbidity questionnaire, and parasitological examination. The study was conducted during the months of June 2003 and May 2004 involving school children from Workemado village (Kemisse administrative zone, {approx} 320 km north of Addis Ababa at an altitude of 1500 meters above sea level (m.a.s.l.)), Sille village (Northern Omo Administrative zone, situated about 520 km southwest of Addis Ababa, 1300 m.a.s.l.), and Sheno town (Northern Shoa administrative zone, situated 80 km north of Addis Ababa, 2825 m.a.s.l.). Both Workemado and Sille villages are endemic for malaria and schistosomiasis, and Sheno town is non-endemic for both diseases. The study subjects were children of rural peasant families or low-income farm laborers. All communities had fairly comparable socioeconomic status. However, Sille community has better access to fruits and vegetables, and, most notably, considerable amounts of cooked fresh leaves of Moringa stenopetala (locally called "halleku") are widely consumed during most part of the year.

Using random numbers generated from EPI-6 statistical module (WHO/CDC), {approx} 50% of elementary school children were taken at random from the list of students in Workemado and Sille communities. In addition, a random 50% of the students from junior high school classes of Sheno Secondary School, who had no travel history to schistosomiasis-endemic areas, and whose stool exams showed no ova or parasites, were recruited as non-endemic healthy controls. Stool specimens collected from each study subject were processed using 41.7 mg templates according to the modified Kato-Katz technique.28 For each study subject, quintet Kato-Katz thick smears were prepared to optimize detection of S. mansoni infection.29 Furthermore, for each participant, a pre-tested questionnaire on signs and symptoms of ill health was administered, in the local language, by trained local high-school graduates.

Clinical examination and ultrasonography. Body weight was measured to the nearest 0.1 kg, with light clothing on, and body height was measured to the nearest centimeter with the subject wearing no shoes. After a brief clinical examination, ultrasonographic study of the liver was done using Hitachi (Tokyo, Japan) EUB 405 portable ultrasound equipment fitted with a 3.5 MHz convex abdominal probe. Standard ultrasonographic liver scans were performed for all subjects; if the liver scan appeared normal, no further examination was undertaken. In subjects with image patterns suggestive of PPF, the liver picture was compared with standard images,30,31 and the corresponding image pattern score was recorded. In addition, assessment of periportal thickening was made by taking inner and outer portal branch wall thickness (PBWT) measurements of 2–3 second branching portal veins. The summation of the image pattern and PBWT scores gave the final periportal thickening/fibrosis (PPT/F) grading of each individual.30,31 In subjects with PPT/F, inner to inner diameter of the main portal vein was measured at the entry point to the liver.

Sera collection, processing, and laboratory measurements. During the dry season of the year, venous blood samples were collected from 421 study subjects using sterile needles and Vacutainer tubes (Becton-Dickinson Vacutainer SST tubes, cat. no. 367986, BD Diagnostics, Franklin Lake, NJ) and were kept in a dark room or in ice-box until clotting and sera separation. Sera were collected and temporarily stored in deep freezers (about –20°C) of the respective health institutions during two 2-week survey periods. At the end of each survey, the sera were transported cool in icepacks to Addis Ababa and stored at –20°C for less than 6 weeks, and finally transported to Norway, in dry ice, and stored at –80°C until use. In addition, thick and thin blood films were prepared for each study subject and were examined for hemoparasites.

C-reactive protein (CRP) assay was done using commercially available CRP-latex test from LiNEAR Chemicals, s.l. (Joaquim Costa No. 18, Montgat (Barcelona, Spain).

Assays for retinol and {alpha}-tocopherol were performed using high-performance liquid chromatography. One hundred microliters of human serum was diluted with 300 µL of 2-pro-panol containing internal standards retinyl acetate and tocol and BHT as an antioxidant. After thorough mixing (15 minutes) and centrifugation (10 min, 4000g at 10°C), an aliquot of 7 µL was injected from the supernatant into the HPLC system equipped with a HP1100 single-wavelength UV detector operated at 325 nm and a fluorescence detector operated at 295 nm (excitation) and 330 nm (emission) (Agilent Technologies, Palo Alta, CA). Retinol was separated from the matrix and internal standard on a 4.6 mm x 50 mm reversed-phase column using 10% water in methanol as the eluent. {alpha}-Tocopherol was analyzed in a separate run by elution with methanol. Two-point calibration curves were generated from analysis of serum calibrators with known concentrations of retinol and {alpha}-tocopherol.

Serum concentrations of hydroperoxides were measured in blood samples by the Diacron reactive oxygen metabolites (D-ROM) test (Diacron International s.r.l., Grosetto, Italy).32 Photometric measurements at 550 nm were performed using a Technicon RA 1000 system (Technicon Instruments Corporation, New York), and the test was carried out in kinetic mode. The results were expressed as Carratelli Units (Carr. U.) All of these assays were done at the Department of Nutrition of the University of Oslo and at AS Vitas (Oslo, Norway).

Statistical analysis. Statistical analysis was done using SPSS, version 10, statistical software (SPSS, Inc., Chicago, IL). Body-mass-index-for-age percentile distributions and Z scores were calculated using Epi-Nut module of EPI-Info 2000 statistical package (WHO-CDC 2000). Serum {alpha}-tocopherol concentrations < 11.6 µmol/L and retinol concentrations < 0.7 µmol/L were considered to be low.1,33 For each study subject, S. mansoni egg count per Kato-Katz thick smear slide was calculated, taking the average count of five Kato-Katz thick smear slides. Normality and equality of variances were assessed before employing parametric tests and S. mansoni egg counts per gram of stool (epg) were transformed to natural logarithms, using log(epg +1) to allow computing for subjects with zero counts. Mean intensities of S. mansoni epg expressed in text or tables are geometric means. One-way ANOVA was used for comparisons of mean serum retinol, {alpha}-tocopherol, and hydroperoxides by study group and by categories of S. mansoni egg excretion and also for comparisons of mean S. mansoni egg excretions by study group. Partial correlation analysis was used to assess the relationship between serum biomarkers and intensity of egg excretion after controlling for age and place of residence. Comparisons of proportions between groups were made using the {chi}2 test. Results were considered significant for P < 0.05.

Ethical considerations. The study was a component of a larger research project entitled "Control of schistosomiasis with local production and use of the Ethiopian soap-berry Endod," which had ethical clearance from Institutional and National Ethical Clearance committees of Ethiopia and from the Norwegian Board of Medical Research Ethics. All diagnostic and treatment procedures were carried out after obtaining informed consent from each subject or his/her guardians. Free treatment was offered to all subjects with schistosomiasis and/or other helminth infections. All subjects who were positive for S. mansoni were treated with a single dose of praziquantel at 40 mg/kg body weight. Subjects with Taenia spp. or Hymenolepis nana infections were treated with a 3-day course of albendazol 400 mg/day or with praziquantel if they had S. mansoni coinfection. Other helminth infections were treated with a single dose of albendazol 400 mg.


RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 STUDY SUBJECTS, MATERIALS, AND...
 RESULTS
DISCUSSION
 REFERENCES
 
Table 1Go shows demographic characteristics of study subjects. A total of 421 children (245 males and 176 females) with mean age of 12.6 ± 3.6 years were enrolled in the study. The age sex, body-mass-index-for-age, and proportion with S. mansoni infection in both Workemado and Sille schools were comparable, and prevalence of PPF was over 10-fold higher among students in Workemado compared with those in Sille. Mean intensity of S. mansoni infection and proportions of subjects with other helminth infections were significantly higher among Sille school children compared with those in Workemado. Mean body-mass-index-for-age of students in both Sille and Workemado were significantly lower than among students from Sheno (Table 1Go). Overall, 13 cases of schistosomal PPF (1/162 (0.6%) in Sille and 12/171 (7.0%) in Workemado) were detected. Among these, 5 subjects had image pattern C and 8 had image pattern D; one of these subjects had mild dilatation of main portal vein without visible portocaval collaterals and two subjects had palpably enlarged spleens (data not shown). None of the 88 non-endemic healthy controls from Sheno had S. mansoni infection or PPF. The percentages of students in Workemado, Sille, and Sheno with serum retinol concentrations below the lower reference value of 0.7 µmol/L were 69.6%, 74.7%, and 1.1%, respectively. Mean serum retinol concentrations were significantly lower in students from Workemado and Sille compared with healthy students from Sheno (Table 2Go).


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TABLE 1
Demographic and parasitological characteristics of 421 subjects from study sites in Ethiopia endemic and non-endemic to S. mansoni
 

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TABLE 2
Serum levels of retinol, {alpha}-tocopherol, and hydroperoxides in 421 subjects from study sites in Ethiopia endemic and non-endemic to S. mansoni
 
Mean serum concentrations of {alpha}-tocopherol were low in all three study populations. The percentages of students in Workemado (i.e., endemic, high PPF), Sille (i.e., endemic, low PPF), and Sheno (i.e., healthy controls) with serum {alpha}-tocopherol concentrations below the lower reference value of 11.6 µmol/L were 87.1%, 55.6%, and 65.9%, respectively. The mean serum {alpha}-tocopherol among students in Workemado was significantly lower than those in Sille or Sheno, whereas mean concentrations in the latter two groups were comparable (Table 2Go).

Concentrations of serum hydroperoxide, biomarker of oxidative stress, were significantly increased in students from both schools in endemic areas compared with controls. About 28.7% and 25.8% of the students from Workemado and Sille, respectively, had hydroperoxide concentrations above the upper reference value compared with only 3.4% of students from Sheno. Overall, only 15 subjects (3.6%) had serum CRP concentrations above 10 mg/L and serum hydroperoxide concentrations were elevated in 22% of subjects (Table 2Go).

There was an inverse relationship between intensity of S. mansoni infection and concentrations of serum retinol in S. mansoni-endemic villages (Table 3Go). This inverse correlation was still significant after controlling for age and place of residence (r2 = –0.2; P < 0.001). Furthermore, among study groups from the endemic area, serum retinol was significantly lower in subjects excreting S. mansoni eggs, infected individuals, compared with subjects not excreting eggs, non-infected individuals (Table 4Go). However, serum {alpha}-tocopherol, hydro-peroxides, and CRP were not related to S. mansoni infection status or intensity of egg excretion at individual subject level (Tables 3Go and 4Go).


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TABLE 3
Serum levels of retinol, {alpha}-tocopherol, and hydroperoxides in relation to categories of S. mansoni egg excretions among 333 study subjects from S. mansoni-endemic sites in Ethiopia
 

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TABLE 4
Serum retinol, {alpha}-tocopherol, CRP, and hydroperoxide levels among 333 primary school students from S. mansoni-endemic sites in Ethiopia
 
Neither serum concentration of retinol, {alpha}-tocopherol, hydroperoxides, nor CRP was related to presence of other helminth infections (Table 4Go). Blood films of all study subjects showed no malaria parasites (data not shown).


DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 STUDY SUBJECTS, MATERIALS, AND...
 RESULTS
 DISCUSSION
REFERENCES
 
The present study shows that serum retinol concentrations are markedly low in school children from S. mansoni-endemic areas, which was in sharp contrast to the normal concentrations found in school children from non-endemic area. In agreement with earlier reports,24,25 serum retinol concentrations were inversely related to intensity of S. mansoni infection. Furthermore, we observed an increased oxidative stress (i.e., increased serum hydroperoxides) in children in endemic areas, and a reduced antioxidant status (i.e., reduced serum {alpha}-tocopherol) in children from Workemado, with high prevalence of schistosomal PPF compared with children in Sille, with low prevalence of schistosomal PPF. Thus, whereas children in the endemic region with low PPF (i.e., Sille) had reduced vitamin A status and increased oxidative stress, the children in the endemic region with high PPF (i.e., Workemado) also had reduced antioxidant status.

Serum retinol may transiently be low due to reduced production of retinol binding protein, which is often observed as part of acute-phase response to infection.34–36 In subjects with such condition and with elevated CRP, an indicator of acute-phase response, serum retinol may fall by {approx} 25% of the original value and may not necessarily reflect actual vitamin A status.36 In our series, however, only a few subjects had elevated CRP, and serum retinol concentrations were quite low, even among well-nourished subjects with normal concentrations of CRP. Furthermore, neither the status nor intensity of any of the helminth infections was associated with serum concentrations of CRP, suggesting that the observed low concentrations are not due to confounding effects of acute-phase response to infection but rather are a reflection of the actual vitamin A status of individuals in our S. mansoni-endemic setting.

Other possible confounding factors that may influence serum micronutrient concentrations include presence of other endemic infections, such as malaria, and seasonal variation in food sources rich in micronutrients. Earlier studies have shown that serum micronutrients concentrations are low in subjects with acute malaria,37–39 and their concentrations improve after clearance of parasites.39,40 In our case, however, although malaria is endemic in our S. mansoni-endemic study sites, we do not expect it to affect our estimates of serum micronutrients because sera were collected during the non-malaria transmission season. Blood films of all subjects, examined at the time of sera collections, were also negative for malaria parasites. Because our sera collections were done during the same period of the year, we expect any seasonal variations of micronutrient-rich food sources to have a uniform effect on all study groups.

In agreement with previous reports,25,41,42 serum retinol, {alpha}-tocopherol, or hydroperoxide concentrations were not related to the presence of other intestinal helminth infections.

Obviously, based on cross-sectional study such as ours, it is not possible to make inferences regarding cause–effect relationships. Furthermore, with such chronic infection, current micronutrient status of individuals may not reflect their pre-infection status or the concentrations that prevailed during the development of schistosomal PPF. However, the finding of an inverse relationship between serum retinol and intensity of S. mansoni infection and the finding of high levels of PPF occurring with low antioxidant micronutrient concentrations suggest that micronutrients may have important roles in the differential morbidity patterns observed among communities who, otherwise, have comparable levels and intensities of S. mansoni infection. Recent reports showing high levels of markers of fibrosis and oxidative stress among subjects with PPF,26,27 together with the experimental evidence which showed that antioxidants prevent most of the schistosomal liver changes,22 support our argument and call for a prospective study to see if supplemental antioxidant micronutrients in anti-schistosomal chemotherapy could prevent the development of and/or promote reversibility of schistosomal PPF.

Inadequacy of a single nutrient is most likely associated with deficiencies of other micronutrients. Controlling vitamin and mineral deficiencies, through food/crop fortification, diversification, and/or modification,3,43–46 is among the most cost-effective strategies for improving human welfare. As stated above, in the Sille community, which has a very low prevalence of schistosomal PPF despite a high prevalence and intensity of S. mansoni infection, considerable amounts of cooked fresh leaves of the drought-resistant plant M. stenopetala ("halleku") are widely consumed during most of the year. Earlier studies have indicated that fresh and cooked leaves of M. stenopetala are rich in vitamins and minerals47 besides having other potential beneficial effects.48 Interestingly, we have recently also observed that M. stenopetala contains very high amounts of total antioxidants: fresh leaves contain 3.7 mmol antioxidants/100 g and dry leaves contain 11.9 mmol/100 g. (Halvorsen, Berhe, and Blomhoff, unpublished results). When a daily consumption of 100–200 g/person is assumed,47 leaves of M. stenopetala are probably the major dietary sources of total antioxidants in this population. More often than not, dietary antioxidants other than the well-known sources may contribute significantly to antioxidant defenses.49 Thus, further in-depth nutritional studies are needed to look into the potentials M. stenopetala as a cheap, locally available alternative source of micronutrients in semi-arid areas with a scarcity of vitamin-rich food sources.

Although these are long-term solutions, some deficiencies, such as vitamin A deficiency, may in the short term be tackled through targeted supplementation programs. Earlier studies in Ethiopia have shown that vitamin A deficiency is of major public-health importance among children under 6 years of age50,51 and may also be a public-health concern among school-age children as well.52,53 Current recommendations for vitamin A supplementation aim at the most vulnerable section of the population, i.e., children under 6 years of age and pregnant women. However, on the basis of our study and other recent studies,52,53 it appears that supplementation may also need to target primary-school children in selected high-risk communities, such as those with high prevalence and intensity of S. mansoni infection. Because a considerable quantity of vitamin A can be stored in the liver, large-dose capsules can be effective for up to 6 months,3 and such supplementations may conveniently be undertaken in conjunction with the currently recommended school-age targeted chemotherapy for control of schistosomiasis and other helminth infections.1

Because the number of subjects with PPF detected in our study sample was quite few (only 13 cases, and those had only mild or moderate PPF), we were not able to assess correlations between severity of PPF and serum levels of specific biomarkers; thus, our summary statistics were largely based on group-level comparisons. To address this important issue, a prospective case-control study involving a larger sample size needs to be undertaken. In summary, the present study shows that vitamin A deficiency and increased oxidative stress are widespread in school children from the S. mansoni-endemic areas and that reduced antioxidant status is additionally observed in children from an area with a high prevalence of schistosomal PPF. We suggest that further intervention-based study be initiated to see if micronutrient vitamins and anti-oxidants are causally related to schistosomiasis mansoni and schistosomal PPF.

Received August 20, 2006. Accepted for publication December 8, 2006.

Acknowledgments: We express our thanks to Endashaw Habte, Mulugeta Ginchile, and Abraham Redda for their excellent laboratory work; to Mr. Girmay Medhin and Dr. Leiv Sandvik for statistical advice; and to the staff of Kemisse Health Centre and Sille clinic for their unreserved assistance in our fieldwork. We also thank the administrative and technical staff of Aklilu Lemma Institute of Pathobiology for their encouragement and support.

Disclaimer: The authors have no conflict of interest. NB, RB, and SGG were responsible for the study concept and design. NB was responsible for the acquisition of clinical, parasitological, and ultrasonographic data. BLH and TEG were responsible for biochemical assays and interpretation. NB analyzed the data and prepared the manuscript. All authors had access to the data and also verified the data analysis. NB, RB, SGG, BM, BLH, and TEG contributed to critical revision of the manuscript for important intellectual content. The study was financially supported by Throne Holst Foundation, Norway; Centre for Imported and Tropical Diseases, Ullevål University Hospital, Norway. Dr. Nega Berhe is a recipient of a Ph.D. scholarship through the Norwegian Statens Lånekasse.

* Address correspondence to Nega Berhe, P.O. Box 25881, Code 1000, Aklilu Lemma Institute of Pathobiology, Addis Ababa University, Addis Ababa, Ethiopia. E-mail: nega_berhe{at}yahoo.com Back

Authors’ addresses: Nega Berhe, Aklilu Lemma Institute of Pathobiology, Addis Ababa University, PO Box 1176, Addis Ababa, Ethiopia, Telephone: +251-11-2763091, Fax: +251-11-2755296, E-mail: nega_berhe{at}yahoo.com. Bente L. Halvorsen, Thomas E. Gundersen, and Rune Blomhoff, Institute for Basic Medical Sciences, Department of Nutrition, University of Oslo, P.O. Box 1046, N-0316 Oslo, Norway, Telephone: +47 22851395, Fax: +47 22851396, E-mails: b.l.halvorsen{at}medisin.uio.no, teg{at}vitas.no, and rune.blomhoff{at}medisin.uio.no. Bjørn Myrvang, Ullevål University Hospital, Department of Infectious Diseases, Centre for Imported and Tropical Diseases, N-0407 Oslo, Norway, Telephone: +47 22119097, Fax: +47 23016020, E-mail: Bjorn.Myrvang{at}ulleval.no. Svein G. Gundersen, Sorlandet Hospital HF/Agder University College, Box 416, 4604 Kristiansand, Norway, Telephone: +47 38074474, Fax: +47 38074173, E-mail: s.g.gundersen{at}sshf.no.

Reprint requests: Dr. Nega Berhe, Aklilu Lemma Institute of Pathobiology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia, Telephone: +251-11-2763091, Fax: +251-11-2755296, E-mail: nega_berhe{at}yahoo.com.


REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 STUDY SUBJECTS, MATERIALS, AND...
 RESULTS
 DISCUSSION
 REFERENCES
 

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N. Berhe, B. Myrvang, and S. G. Gundersen
Intensity of Schistosoma Mansoni, Hepatitis B, Age, and Sex Predict Levels of Hepatic Periportal Thickening/Fibrosis (PPT/F): A Large-Scale Community-Based Study in Ethiopia
Am J Trop Med Hyg, December 1, 2007; 77(6): 1079 - 1086.
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