Transactions of the Royal Society of Tropical Medicine and Hygiene (2007) 101, 155—160

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Human fascioliasis infection: gender differenceswithin school-age children from endemic areasof the Nile Delta, Egypt

Filippo Curtalea,∗, Yehia Abdel Wahab Hassaneinb,Paolo Barduagnia, Mohamed Mostafa Yousefb,Aly El Wakeelc, Zuhair Hallajd, Santiago Mas-Comae

a Directorate General for Development Cooperation (DGCS), Ministry of Foreign Affaires, Rome, Italyb Endemic Diseases Control Department, Ministry of Health and Population, Cairo, Egyptc Behera Regional Health Directorate, Ministry of Health and Population, Damanhour, Egyptd Department of Communicable Diseases, Eastern Mediterranean Regional Office, World Health Organization, Cairo, Egypte Department of Parasitology, Faculty of Pharmacy, University of Valencia, Valencia, Spain

Received 24 December 2005; received in revised form 14 May 2006; accepted 15 May 2006Available online 4 August 2006

KEYWORDSFascioliasis;Fasciola;Schistosoma mansoni;Transmission;Risk factors;Egypt

Summary Several studies have reported a higher prevalence of infection for human fascio-liasis among girls than among boys. To investigate this aspect further a sufficiently large dataset was assembled comprising of 21 477 subjects with 932 positive cases. Subjects were pri-mary school children covered by a control programme implemented by the Egyptian Ministry ofHealth and Population in the Nile Delta from 1988 to 2002. Stool analyses were performed bythe Kato—Katz thick smear technique for a quantitative diagnosis on the intensity of infection.Both prevalence and intensity of infection, indirectly measured as mean number of eggs pergram of faeces, were significantly higher among girls than boys. The higher level of infectionin girls was consistent across different years and in different survey areas. Co-infection withSchistosoma mansoni was present and associated with fascioliasis, but schistosomiasis was sig-nificantly more prevalent among boys. In Egypt rural girls are often involved in household and

farm work and are exposed more than boys to infected foci. The lower school attendance forgirls in rural areas appears to be an important factor increasing risk of infection. The precisemode of transmission and behavioural risk factors for human infection need to be investigatedfurther to identify those related© 2006 Royal Society of Tropicareserved.

∗ Corresponding author. Present address: Agenzia di Sanita Pubblica deTel.: +39 06 83060375; fax: +39 06 83060405.

E-mail address: curtale@asplazio.it (F. Curtale).

0035-9203/$ — see front matter © 2006 Royal Society of Tropical Medicindoi:10.1016/j.trstmh.2006.05.006

to gender.

l Medicine and Hygiene. Published by Elsevier Ltd. All rights

l Lazio, Via di Santa Costanza 53, 00198 Rome, Italy.

e and Hygiene. Published by Elsevier Ltd. All rights reserved.

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. Introduction

uman infection with Fasciola spp. can often induce severeathology (Chen and Mott, 1990). In the past, human fas-ioliasis has been considered a rare disease, concerningust sporadic cases (Haswell-Elkins and Elkins, 1996), but inecent years the number of human cases affected by Fasciolapp. has increased drastically (Mas-Coma et al., 1999). Theres evidence that this parasite is able to adapt to differentefinitive hosts, including humans, initiating the spread ofisease into new transmission foci (Mas-Coma et al., 2005).

The Nile Delta, where the first human cases wereetected in 1928, is considered to be one of the mostndemic areas in the world for human fascioliasis (Curtale etl., 1998; El Shazly et al., 1991; Farag et al., 1979). In 1995,HO estimated an overall prevalence of 3% in Egypt, with at

east 830 000 people infected and 27.7 million people beingt risk of infection (WHO, 1995a). Although the actual figureay be lower, due to the control intervention implementedy the Egyptian Ministry of Health and Population since 1998Curtale et al., 2005), human fascioliasis is still consideredserious public health problem in Egypt.As for other helminth infections, the most affected pop-

lation group appears to be school children (Esteban etl., 1998). A field study recently conducted in Behera, theargest and most populated Governorate of the Nile Delta,as confirmed a peak prevalence and intensity of human fas-ioliasis infection among children, between 9 and 11 yearsf age (Curtale et al., 2003a).

In terms of infection prevalence and intensity, genderifferences have also been reported in different endemicreas. In Egypt, higher prevalence and intensity of infec-ion were found among girls compared with boys (Faragt al., 1979). In Andean countries, prevalence did not dif-er between the sexes, but females excreted more eggshan males (Esteban et al., 1999). A recent study in Egyptetected a significant difference in prevalence, but not forntensity of infection (Esteban et al., 2003). Most of the stud-es conducted until now have failed to detect significantifferences in intensity of infections, which is consideredo be a more reliable indicator of infection risk and, as forther intestinal helminth infections, to be a useful predictorf later morbidity (Montresor et al., 1998).

In Egypt, a low number of positive cases are usuallyetected in a survey population, which may account for fail-ng to detect significant differences by gender for intensityf infection. To investigate this further it is necessary totilize sufficiently large data sets. In this paper we anal-se data collected during a screening of fascioliasis in therimary schools of endemic districts in Behera (Curtale etl., 2005), where, from 1998 until 2002, just over 20 000hildren were screened and 932 cases of human fascioliasisere identified and treated. This sample size was consid-red sufficient to test the hypothesis that girls are more atisk of being infected with Fasciola spp. than boys.

. Materials and methods

.1. Study area and subjects

he faecal sample collection took place from 1998 to 2002n the primary schools of six endemic districts in Behera

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overnorate, identified during former assessments. Thechools surveyed were those covered by a national selec-ive chemotherapy control programme described elsewhereCurtale et al., 2005) and were different every year.

Faecal samples were collected from class five children,or the pre-screening activities (years 1998 and 2001), androm all primary school children for the screening activitiesyears 2000 and 2002). The pre-screening consisted in thedentification of endemic villages/foci, through the screen-ng by a single Kato—Katz stool examination of 100 class fivechool children (10—12 years of age), attending a primarychool randomly selected in each village of the endemic dis-ricts. Then, in villages where a school had reported four orore positive cases, all children attending every primary

chool (6—12 years of age) in that village were screened. Inowns and large settlements with more than 100 000 inhabi-ants, such as Delengat town, a pre-screening was conductedor all the schools in the urban area, treating each school inhat area as a different village.

All children excreting ova of Fasciola spp. or any otherntestinal helminth, either during pre-screening or screen-ng, were treated with appropriate anthelminthics. A singleose of triclabendazole (10 mg/kg body weight) was usedor treatment of fascioliasis (WHO, 1998), and the recom-ended WHO treatment guidelines were followed for all

ther parasites detected (WHO, 1995b).

.2. Faecal analysis

he Kato—Katz thick-smear technique (WHO, 1994) was uti-ized for diagnosis of human fascioliasis, which is consideredore appropriate than sedimentation techniques for large-

cale screenings and surveys (Ebrahim et al., 1997). Theumber of eggs per slide is considered a reliable indicator oform load and was used as an indirect method to assess the

ntensity of infection (Shehab et al., 1999). One slide wasrepared and read for each individual faecal sample, uti-izing a template of 41.7 mg. The number of eggs per slideas converted to eggs per gram of faeces (epg) applying aultiplication factor of 24. No attempt was made to differ-

ntiate between F. hepatica and F. gigantica, both presentn Egypt. In this paper, they will be referred to as Fasciolapp.

.3. Data management

creening data were entered using EpiInfo software (CDC,tlanta, GA, USA), edited, and then analysed using SSPS,elease 10.0, software program (SPSS Inc., Chicago, IL, USA).o minimize the effect of confounding factors, and to assessonsistency of the results over time and in different areas,ata were analysed by year. Differences in prevalence ofnfection by gender were statistically tested using the �2

est and odds ratios. Prevalence data on infection withchistosoma mansoni, the most prevalent helminth in therea, including association with Fasciola spp. infection and

ender differences, were also calculated on the same sam-le to analyse any possible role of co-infection in genderias.

Differences on intensity of infection were calculatedcross all samples, including negative slides, and presented

Gender differences in human fascioliasis infection 157

Table 1 Primary school surveys, conducted from 1998 to 2002, in six districts of the Nile Delta, Egypt endemic for humanfascioliasis

Year Assessment Total population (n) Cases (n) Males (%) Females (%)

1998 Pre-screening 4585 171 2494 (54) 2091 (46)2000 Screening 10 739 528 5925 (55) 4814 (45)2001 Pre-screening 2020 42 1112 (55) 908 (45)2002 Screening 4133 191 2307 (56) 1826 (44)

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Total 21 477

by arithmetic and geometric means. Geometric meanswere calculated after individual egg counts were convertedaccording to the log (n + 1) transformation (Stephenson,1987). Differences in intensity of infection were tested byindependent t test on log-transformed data only, to satisfyassumption on equality of variance.

3. Results

A total of 21 477 primary school children were screenedduring four rounds of stool collections and analysis of pro-gramme implementation, with 932 cases of human fas-cioliasis detected. Males represented 55% of the sample(n = 11838), females 45% (n = 9639). Total population, type of

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Table 2 Prevalence of human fascioliasis infections among schooEgypt

Year of survey Total (n) Positive cases (n)

Males Females Males Females

1998 2494 2091 79 922000 5925 4814 255 2732001 1112 908 18 242002 2307 1826 86 105

Total 11 838 9639 428 494

NS: not significant.a Pearson �2.b Odds ratios for females.

Table 3 Prevalence of Schistosoma mansoni, double infections ain Behera Governorate, Nile Delta, Egypt

Year of survey Total no. subjectsa Positive cases (n)

S. mansoni Fasciola

1998 4585 (46) 667 1712000 10 739 (117) 1548 5282001 2020 (6) 80 422002 4133 (26) 305 191

Total 21 477 (195) 2392 932a Number of double infections in brackets.b Correlation coefficient (r).c Significance (two-tailed).

932 11 838 (55) 9639 (45)

ssessment and number of human fascioliasis cases detectedach year are presented in Table 1.

.1. Prevalence of infection by gender

revalence of infection and odds ratios (OR) were consis-ently higher among female than male subjects. A significantifference emerged every year, with the exception of 2001,hen, despite the fact that boys presented 40% lower preva-

ence of infections than girls, the limited number of subjectscreened did not make it possible to find a statistical signif-cance for the difference. As summarized in Table 2, differ-nces reported by gender appeared to be significant whenhe number of cases detected during the survey was higher

l-age children by gender, in Behera Governorate, Nile Delta,

Prevalence P-valuea ORb

Males (95% CI) Females (95% CI)

3.2% (2.5—3.9) 4.4% (3.6—5.4) <0.05 1.414.3% (3.8—4.9) 5.7% (5.0—6.4) <0.001 1.341.6% (1.0—2.6) 2.6% (1.7—4.0) NS 1.653.7% (3.0—4.6) 5.8% (4.8—6.9) <0.01 1.58

3.6% (3.3—4.0) 5.1% (4.7—5.6) <0.001 1.44

nd association with Fasciola spp. among school-age children

Prevalence rb P-valuec

S. mansoni (95% CI) Fasciola (95% CI)

14.5% (13.5—15.6) 3.7% (3.2—4.3) 0.07 <0.00114.4% (13.7—15.1) 4.9% (4.5—5.3) 0.05 <0.0014.0% (3.2—4.9) 2.1% (1.5—2.8) 0.08 <0.017.4% (6.6—8.2) 4.6% (4.0—5.3) 0.05 <0.01

11.1% (10.7—11.6) 4.3% (4.1—4.6) — —

158 F. Curtale et al.

Table 4 Prevalence of Schistosoma mansoni infections among school-age children by gender, in Behera Governorate, Nile Delta,Egypt

Year of survey Total (n) Positive cases (n) Prevalence P-valuea ORb

Males Females Males Females Males (95% CI) Females (95% CI)

1998 2494 2091 459 208 18.4% (16.9—20.0) 9.9% (8.7—11.3) <0.001 2.042000 5925 4814 1005 543 17.0% (16.0—17.9) 11.3% (10.4—12.2) <0.001 1.612001 1112 908 57 23 5.1% (3.9—6.6) 2.5% (1.7—3.8) <0.01 2.082002 2307 1826 192 113 8.3% (7.2—9.5) 6.2% (5.2—7.4) <0.01 1.38

Total 11 838 9639 1713 887 14.5% (13.8—15.1) 9.2% (8.6—9.8) <0.001 1.67

a Pearson �2.b Odds ratios for males.

Table 5 Intensity of human fascioliasis infection among school children by gender, expressed by arithmetic (ARI) and geometric(GEO) means, in Behera Governorate, Nile Delta, Egypt

1998 2000 2001 2002

ARI mean ± SEMales 4.56 ± 0.90 7.51 ± 0.83 2.12 ± 0.75 5.07 ± 0.80Females 8.26 ± 1.55 10.39 ± 1.16 4.41 ± 1.82 10.08 ± 1.88

GEO mean (95% CI)Males 1.15 (1.11—1.19) 1.22 (1.19—1.25) 1.07 (1.04—1.11) 1.18 (1.14—1.23)Females 1.23 (1.18—1.28) 1.30 (1.26—1.34) 1.12 (1.07—1.18) 1.30 (1.24—1.37)

t 2.51 3.22 1.59 3.14P-valuea <0.05 <0.001 NS <0.01

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han 150. A cumulative analysis of all the samples gives anR = 1.44 with a remarkable high �2 = 29.47 (P < 0.001), illus-rative of strong gender bias.

.2. Co-infection with Schistosoma mansoni

n the total sample, infection with S. mansoni was presentn 11.1% of school children (n = 2392) and it was more preva-ent than fascioliasis, which had an overall prevalence of.3%. Fewer than 1% of subjects (n = 195) were infected withoth parasites. A significant positive association was presentetween the two infections (Table 3). At the same time,nalysis of data by gender showed that boys were signifi-antly more infected with S. mansoni than girls (Table 4),ith an OR = 1.67 and high value of �2 = 138.58 (P < 0.001).

.3. Intensity of infection by gender

imilar results emerged from the analysis of differences inntensity of infection by gender. Both arithmetic and geo-

etric means of epg were higher among female than male

ubjects. The difference, tested by t test, was significant forach year, except for 2001, as for the results on prevalence.esults for intensity of infection by gender are summarizedn Table 5.

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. Discussion

rimary school girls appeared to be significantly morenfected with Fasciola spp. than boys. Both prevalence andntensity of infection, indirectly measured as mean num-er of epg, were significantly higher among females thanales. The higher level of infection among girls was con-

istent across different years and in different survey areas.his evidence, rather than being a conclusion, is a start-

ng point for future research and draws attention to ourresent limited knowledge on this parasite’s transmissionode. In light of these data, the traditional way of trans-ission for fascioliasis, mainly through the ingestion of raw

quatic vegetables (watercress), or the occasional suckingf grass, on which larval parasites are encysted (Haswell-lkins and Elkins, 1996) cannot be now considered the mainoute of infection. In recent studies, other foods, such aslfalfa juice in Peru (Marcos et al., 2006) and raw pumpkineeds in Egypt (Curtale et al., 2003b), have been associ-ted with the human infection, and our common knowledgen the modality of infection for this parasite needs to be

evised.

Gender differences are not usually observed in parasiticiseases transmitted through food, especially in a countryuch as Egypt, where traditionally all household membershare the same food. However, unlike boys, young girls are

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Gender differences in human fascioliasis infection

often involved in the preparation of household meals, beingexposed to the management of different kinds of fresh veg-etables, which are eaten raw in salad and have been foundto carry attached encysted metacercarie (El Sayed et al.,1997).

The significant positive association between human fasci-oliasis and S. mansoni infection, formerly observed in Egypt(Curtale et al., 1998; Esteban et al., 2003), was substan-tiated by the results of the present study, suggesting that,even using a different intermediate host, both infectionsshare a common mode of infection. The identification offloating metacercarie, which can infect humans by drink-ing or swimming in contaminated water, also supports thepossibility that canal water represents the main route ofinfection (Bargues et al., 1996). Still, schistosomiasis is usu-ally more prevalent among boys (El-Khoby et al., 2000), aswas confirmed by analysis of the present data sets. Boyshave more frequent and unrestricted access to canal waterthan girls, although these contacts are concentrated in thesummer season and are for a short time in the infectedwater. Conversely, in Egypt, young girls are often involved inwashing clothes and kitchen utensils directly in the canal,with a longer and regular daily contact with canal water,where intermediate hosts and infecting metacercarie arepresent. Although the two infections were associated, thehigher prevalence of schistosomiasis among boys comparedwith girls does not support a possible role of co-infection indetermining the gender imbalance. The significant positiveassociation between Fasciola spp. and S. mansoni infections,with an opposite gender bias, needs further study and inter-pretation.

A case—control study conducted in the same area hasidentified a number of risk factors related to human fasci-oliasis infection (Curtale et al., 2003b). The factors statis-tically associated with the infection could not be directlyrelated with gender, but rather to dietary habits (raw seedseaten daily) and household characteristics (producing veg-etables, bringing animals to the canal). It should be takeninto account that young girls in Egypt are often employedfor agricultural work in irrigated plantations, such as ricefields, and for the care of domestic animals.

In general, due to cultural, hygienic and behaviouralhabits, girls may be more frequently in contact with trans-mission foci and for a longer time than boys. Furthermore,the Egypt Demographic and Health Survey 2000 has esti-mated that 25% of girls in rural areas had either neverattended school or dropped out, compared with 14% ofboys (El Zanaty and Way, 2001). One of the reasons thatkeeps girls out of school is that they are required to helpin the household for domestic and agricultural work, whichmay cause temporary absence from school, depending onseasonal work in agriculture (rice plantation, harvest, ani-mal washing) and special occasions in the household life(weddings, guests, religious festivals). In the same sur-vey, 10% of rural mothers reported as a reason for absen-teeism of their children the answer ‘child needed at home’,with a percentage for girls more than double than for

boys.

Differences in school attendance rate between boys andgirls were confirmed by the present study (55 vs. 45%), whichcollected a representative random sample of primary schoolchildren. This finding supports the conclusion that girls may

C

159

pend more time in contact with transmission foci, whileheir male siblings are at school.

Besides absenteeism and drop out, there is a proportionf school-age girls who have never attended school, in ruralreas close to 20% of the total school-age girl population (Elanaty and Way, 2001). These girls were not seen during thechool screenings, and it is reasonable to assume that theyay be affected by an even higher prevalence and intensity

f infection for human fascioliasis than that detected in thetudy population.

In conclusion, the mode of transmission and behaviourst risk for human infection in Egypt need to be investigatedurther, with controlled studies implemented in endemicreas, to identify specific risk factors related to gender.his will help to better target control interventions towardhe subjects most in need and, in a country with rele-ant differences in school attendance by gender, facilitatehe promotion of strategies that can correct this additionalurden.

ole of funding sourcehe funding source financially supported the data collec-ion for this study, but had no role in the study design,nalysis and interpretation of results, in the writing of theanuscript, or in the decision to submit the paper for pub-

ication.

onflicts of interest statementhe author have no conflicts of interest concerning the workeported in this paper.

cknowledgements

he data and results presented in this paper were collectedithin the framework of the bilateral co-operation project:trengthening Rural Health Services in Behera, Dakhaliand Qena Governorates (AID n.3703), between the Primaryealth Care Department, Ministry of Health and Population,gypt, and the Directorate General for Development Cooper-tion (DGCS), Ministry of Foreign Affaires, Italy. The authorsould like to thank the two anonymous referees who con-

ributed to the final version of the manuscript.

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