GLOBAL POVERTY RESEARCH
Results from the third nationwide cluster sampling sur-
vey on the epidemiology of schistosomiasis in the People’s
Republic of China, conducted by the Ministry of Health in
2004, are presented. A stratifi ed cluster random sampling
technique was used, and 239 villages were selected in 7
provinces where Schistosoma japonicum remains endemic.
A total of 250,987 residents 6–65 years of age were includ-
ed in the survey. Estimated prevalence rates in the provinc-
es of Hunan, Hubei, Jiangxi, Anhui, Yunnan, Sichuan, and
Jiangsu were 4.2%, 3.8%, 3.1%, 2.2%, 1.7%, 0.9%, and
0.3%, respectively. The highest prevalence rates were in
the lake and marshland region (3.8%) and the lowest rates
were in the plain region with waterway networks (0.06%).
Extrapolation to all residents in schistosome-endemic areas
indicated 726,112 infections. This indicates a reduction of
16.1% compared with a nationwide survey conducted in
1995. However, human infection rates increased by 3.9% in
settings where transmission is ongoing.
People’s Republic of China despite a documented history
chistosomiasis, which is caused by Schistosoma japon-
icum, is one of the most serious parasitic diseases in the
>2,100 years. The fi rst reported clinical case in modern
China was made by an American physician in 1905 (1).
On the basis of limited hospital-based data and fragmentary
epidemiologic survey reports, schistosomiasis japonica in
1947 was endemic in 138 counties in China. The rural pop-
ulation at that time in those counties was ≈25.3 million,
which was the at-risk population. The estimated number of
people infected with S. japonicum was 5.3 million (2). Mao
estimated that 32.8 million Chinese were infected with S.
japonicum in the late 1940s (2). However, use of differ-
ent sources and province-specifi c prevalence data showed
higher estimates of the number of people infected and at-
risk populations (3,4).
Since 1949, after the founding of the People’s Repub-
lic of China, large-scale epidemiologic surveys were con-
ducted by Chinese health workers to identify schistosomia-
sis-endemic areas, prevalence and incidence of this disease,
and number of deaths caused by S. japonicum infections.
Results showed that schistosomiasis was endemic in 12
provinces, with an estimated 11.6 million people infected.
There were 1.2 million infected cattle and an area of 14,300
km2 was infested by the intermediate host snail, Oncome-
lania hupensis (5).
Over the past 50 years, the ongoing national control
program has made great progress in controlling this disease.
To date, 5 of 12 formerly S. japonicum–endemic provinces
and >60% of disease-endemic counties have reached the
national criteria of transmission interruption, and the num-
ber of human infections has been reduced by >90% (6–8).
However, in 2003, 110 counties had not yet reached the cri-
teria for transmission control, i.e., the overall prevalence in
disease-endemic villages of these counties was >1% (9,10).
The epidemiology of S. japonicum in China and achieve-
ments made in its control have been reviewed (11). New
data suggest that progress has stalled since the termination
Epidemiology of S chistosomiasis in
the People’s Republic of China, 2004
Xiao-Nong Zhou,* Jia-Gang Guo,* Xiao-Hua Wu,* Qing-Wu Jiang,† Jiang Zheng,* Hui Dang,*
Xian-Hong Wang,* Jing Xu,* Hong-Qing Zhu,* Guan-Ling Wu,‡ Yue-Sheng Li,§ Xing-Jian Xu,¶
Hong-Gen Chen,# Tian-Ping Wang,** Yin-Chang Zhu,†† Dong-Chuan Qiu,‡‡ Xing-Qi Dong,§§
Gen-Ming Zhao,† Shao-Ji Zhang,# Nai-Qing Zhao,† Gang Xia,¶¶ Li-Ying Wang,¶¶ Shi-Qing Zhang,**
Dan-Dan Lin,# Ming-Gang Chen,* and Yang Hao¶¶
*National Institute of Parasitic Diseases, Shanghai, People’s Re-
public of China; †Fudan University, Shanghai, People’s Republic of
China; ‡Nanjing Medical University, Nanjing, People’s Republic of
China; §Hunan Institute of Parasitic Diseases, Yueyang, People’s
Republic of China; ¶Hubei Institute of Parasitic Diseases, Wuhan,
People’s Republic of China; #Jiangxi Institute of Parasitic Diseases,
Nanchang, People’s Republic of China; **Anhui Institute of Parasit-
ic Diseases, Wuhu, People’s Republic of China; ††Jiangsu Institute
of Parasitic Diseases, Wuxi, People’s Republic of China; ‡‡Sich-
uan Institute of Parasitic Diseases, Chengdu, People’s Republic
of China; §§Yunnan Institute of Endemic Diseases, Dali, People’s
Republic of China; and ¶¶Ministry of Health, Beijing, People’s Re-
public of China
1470 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 10, October 2007
Epidemiology of Schistosomiasis in China, 2004
of the World Bank Loan Project (WBLP) for schistosomia-
sis control at the end of 2001 (7,9,12,13).
In 1989, the fi rst nationwide schistosomiasis sampling
survey was conducted by the Chinese Ministry of Health
to determine the prevalence of S. japonicum in all regions
of the country where transmission occurs (14–16). An es-
timated 1,638,103 people were infected (8,16). Six years
later, the second nationwide schistosomiasis survey was
completed. The number of people infected with S. japoni-
cum had been reduced by >40% to 865,084 (15). Neverthe-
less, there is considerable concern that schistosomiasis has
reemerged in some adjacent areas of hyperendemic regions
in the new millennium (9,17–19).
The third nationwide cluster sample survey was con-
ducted in 2004 to update epidemiologic data for schisto-
somiasis in China. The data generated can serve as bench-
marks for design of a new framework of a national control
program that includes mid-term and long-term goals and a
more fl exible strategy. The National Institute of Parasitic
Diseases (IPD) at the Chinese Center for Disease Control
and Prevention in Shanghai (10) was entrusted by the Min-
istry of Health to design, manage, and supervise this survey
in close collaboration with specialized provincial institu-
tions in the 7 provinces where S. japonicum was endemic.
Materials and Methods
Sampling Strategy and Study Population
The third nationwide schistosomiasis sampling survey
covered all 7 schistosome-endemic provinces (Anhui, Hu-
bei, Hunan, Jiangsu, Jiangxi, Sichuan, and Yunnan). The
sampling unit was the administrative village (i.e., basic lev-
el of administration, often comprising >1 natural village),
with only those villages selected where transmission was
A stratifi ed cluster random sampling technique with 3
strata was used for village selection. The 7 schistosome-en-
demic provinces represented the fi rst stratum. Within each
province, the second stratum was categorized by character-
istics of environmental ecosystems defi ned and widely used
by Chinese health workers, which includes 8 subtypes: 1)
fork beach, 2) islet without embankment, 3) islet with em-
bankment, 4) inner embankment in the lake and marshland
region, 5) plateau, 6) mountain, 7) hill in the hilly and moun-
tainous region, and 8) waterway networks in the plain region
(20). Within each ecosystem, estimated local prevalence of
S. japonicum, which was based on results of recent parasi-
tologic examinations, served as the third stratum and used
cut-off prevalences of 1%, 5%, and 10%. In each disease-
endemic province, ≈1% of administrative villages of the
same prevalence class and ecosystem type were randomly
selected. One administrative village was randomly selected
if the total number of villages was <100 (Figure 1).
All residents 6–65 years of age in selected villages
were invited to participate in the study. If the total number
of eligible persons was <1,000, residents from neighboring
villages with similar ecoepidemiologic characteristics were
recruited until >1,000 persons were included.
All participants were screened for S. japonicum–spe-
cifi c immunoglobulin G by using a standardized ELISA
(Shenzhen Kangbaide Biotech Co., Shenzhen, People’s
Republic of China). Seropositive persons were tested by
stool examination. One stool specimen was obtained from
each participant, and 3 Kato-Katz thick smear slides were
prepared and examined under a light microscope by expe-
rienced laboratory technicians (21). The number of S. ja-
ponicum eggs was counted on each slide, and the arithmetic
mean value was calculated for each person.
In a subsample of villages (n = 25), study participants
were interviewed regarding previous infection with S. ja-
ponicum and previous treatment history. Common symp-
toms, e.g., abdominal pain and diarrhea, were investigated
by using a recall period of 2 weeks. Liver and spleen en-
largement and the degree of hepatic fi brosis were assessed
with a portable ultrasound device. Assessment of illness
was performed on supine persons during baseline respi-
ration who had fasted. The fi brotic degree of liver paren-
chyma was graded between 0 and 3 according to criteria of
the World Health Organization–sponsored Cairo Working
In 11 villages selected at random from different eco-
systems and for different infection levels, seropositive
study participants provided 1 stool specimen and 3 Kato-
Katz thick smear slides were prepared. Miracidium hatch-
ing test after concentration of eggs with a nylon tissue bag
was used. Persons with positive results in the miracidium
hatching test or with eggs on the slides were identifi ed as
Figure 1. Design of the cluster sampling survey for schistosomiasis,
People’s Republic of China.
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 10, October 2007 1471
GLOBAL POVERTY RESEARCH
having S. japonicum infections and served as the standard
for the diagnosis (24–26). Comparisons of results of 2 diag-
nostic approaches enabled calculation of sensitivity of the
Data Management and Statistical Analysis
Samples of every new batch of ELISA kits used in the
survey were randomly selected and tested with standard
serum samples to determine their sensitivity and cross-
reactivity with antibodies against hepatitis B virus and
Paragonimus spp. Rates of false-negative results of se-
rologic tests (compared with the Kato-Katz method) and
Kato-Katz thick smears (compared with the hatching test)
All data were checked for internal consistency before
double entry into standardized databases at provincial in-
stitutes. Senior scientists from IPD validated data and es-
tablished a masterfi le from which coverage, compliance,
prevalence, and intensity of S. japonicum infection and to-
tal estimates of persons infected were calculated. Statistical
analyses were performed by using SAS version 8.0 (SAS In-
stitute Inc., Cary, NC, USA). The following formulas were
used to calculate the corrected human infection rate in the
village: infection rate p = (x/X)/(1 – Q) × (f/F)/(1 – R) and
rected human infection rate in a sampled village, S2
variance of p, x is the number of the seropositive persons,
X is the number of eligible persons screened by the sero-
logic test, f is the number of stool-positive persons by the
Kato-Katz technique, F is the number of persons tested by
the Kato-Katz technique, Q is the false-negative rate of the
serologic test, R is the false-negative rate of Kato-Katz thick
smears, and n is the total population in a sampled village.
The χ2 test was used to compare S. japonicum infection
rates between provinces, ecosystems, occupational groups,
sex and age. Ordinal logistic regression analysis was used
to investigate whether there was an association between se-
rologic results and the degree of liver fi brosis, stratifi ed by
p = p(1 – p)/(X – 1) (1 – X/n), where p is the cor-
p is the
A rigorous quality control system was implemented
throughout the study. Blood samples and Kato-Katz thick
smear slides from each survey were kept, and 5% of the
samples were randomly selected for re-evaluation in the
respective provincial institutes. Surveys were repeated in
villages where quality control showed a sensitivity <90%.
All original data were entered twice, and 10% of origi-
nal data were compared with submitted databases at IPD.
Data from sites where level of agreement was <95% were
Disease-Endemic Villages, Sampling Scheme,
Overall, 17,542 administrative villages with an esti-
mated population of 29,059,194 were classifi ed as endemic
for S. japonicum in 2004. Online Appendix Table 1 (avail-
able from www.cdc.gov/EID/content/13/10/1470-appT1.
htm) summarizes the number of villages and persons strati-
fi ed by different levels of endemicity. Prevalence of S. ja-
ponicum infection was <1% in >50% of villages (n = 9,243)
inhabited by >15 million persons. A total of 1,334 villages
(7.6%) were classifi ed as settings where infection prevalence
was >10%. Estimated population size in these settings was
The present survey was conducted in 239 villages and
included 291,167 persons 6–65 years of age. This corre-
sponds to 1.4% of all schistosome-endemic villages and
1.0% of the population living therein. Compliance to un-
dergo a serodiagnostic test and, among S. japonucum–posi-
tive persons, to submit a stool sample was high (86.2%).
Infection Rate and Estimated Number of
Overall, 30,680 (12.2%) of 250,987 participants were
positive for S. japonucum by ELISA. Of these persons,
94.2% submitted a stool specimen and 9.1% of these speci-
mens were egg positive. Estimated corrected S. japonicum
prevalence, when sensitivity of the Kato-Katz method in S.
japonicum–endemic villages was taken into account, was
2.5%. Prevalence varied considerably by province, from
0.3% (Jiangsu) to 4.2% (Hunan). Prevalence rates above
average were found in Hubei (3.8%) and Jianxi (3.1%)
Provinces, and prevalence rates in Anhui, Yunnan, and Si-
chuan Provinces were 2.2%, 1.7% and 0.9%, respectively.
Stratifi cation by ecosystem showed that the highest
corrected prevalence was found in the lake and marshland
region (3.8%). Overall prevalence in the hilly and moun-
tainous region was 1.1%. Human infection rates among
different subtypes of disease-endemic areas showed that
the highest rate (7.1%) was seen in the subtype mountain
regions, followed by subtypes islets with embankment
(4.3%), inner embankment (4.3%), fork beach (3.4%), and
islet without embankment (2.7%). Lower prevalence rates
were observed in subtypes hill (1.01%) and plateau (0.3%)
in the hilly and mountainous regions. A lower prevalence
rate of 0.06% was found in the plain region characterized
by waterway networks.
As shown in Figure 2, prevalence of S. japonicum in-
fection in male study participants (2.6%) was higher than
that in female participants (2.2%). There was a tendency
1472 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 10, October 2007
Epidemiology of Schistosomiasis in China, 2004
for prevalence to increase with age, with the highest prev-
alence found in men 40–49 years of age. Prevalence of
infection also varied with occupation. The prevalence in
fi shermen and boatmen was 3.3%, which was signifi cantly
higher than in other professional groups (p<0.001). How-
ever, no signifi cant association was found between infec-
tion prevalence and educational level (Table).
On the basis of survey results, total number of per-
sons infected with S. japonicum in China in 2004 was
estimated to be 726,112 (95% confi dence interval [CI]
714,497–737,728). More than 82% of infected persons
lived in lake and marshland regions (596,599, 95% CI
585,910–607,287), and most of the remaining persons re-
sided in hilly and mountainous regions (128,720, 95% CI
The geometric mean of infection intensity was 33 eggs
per gram (EPG) of feces among egg-positive persons and
0.4 EPG in the general population. Stratifi ed by province,
the highest geometric mean among egg-positive persons
was found in Jiangxi (56 EPG) and Hunan (0.70 EPG)
when the general population was considered. With regard
to ecosystem stratifi cation, the highest infection intensity in
egg-positive persons was in the plain region with waterway
networks (128 EPG), and the highest infection intensity in
the entire population was in the lake and marshland regions
Male study participants had a higher infection inten-
sity than females, both among egg-positive persons (34 vs.
30 EPG) and the general population (0.4 vs. 0.3 EPG). No
clear trend emerged when stratifi cation was conducted by
age, but intensity of infection was generally less variable
between age groups in male participants and decreased
somewhat with age in female participants. With regard to
occupation, fi sherman, boatmen, and preschool children
had the highest geometric mean infection intensity (0.9
EPG), followed by farmers and students (0.4 EPG). The
infection intensity generally decreased with higher educa-
tional level (Table).
Illness and Self-reported Symptoms
Results of S. japonicum–related illness, as assessed by
ultrasonography, and self-reported signs and symptoms, are
shown in online Appendix Table 2 (available from www.
persons were more likely to report diarrhea over the past 2
weeks than seronegative persons. Degree of liver fi brosis
was positively associated with a positive serologic result
and with residency in the lake and marshland region. Per-
sons living in the plain region with waterway networks had
lower levels of liver fi brosis. No association was found be-
tween serologic status and hepatomegaly or splenomegaly.
Results of the third nationwide cluster sampling sur-
vey on the epidemiologic status of schistosomiasis provide
a comprehensive update on the current extent and distribu-
tion of human S. japonicum infections in China. The epi-
Figure 2. Corrected Schistosoma japonicum infection prevalence
rates in humans stratifi ed by age and sex, 2004, People’s Republic
Table. ELISA and Kato-Katz thick smear results for Schistosoma japonicum infection prevalence and intensity, stratified by occupation
and education, People’s Republic of China*
rate, % examined
Preschool children 848 8.765
Students 61,4306.7 3,861
Farmers 184,32514.0 24,285
Fishermen and boatmen 1,150 25.0284
Primary school 119,01612.2 13,655
Junior high school 101,28311.4 10,917
Senior high school 11,61610.41,160
Additional education 1,993 7.1 136
*EPG, eggs per gram of feces.
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 10, October 2007 1473
GLOBAL POVERTY RESEARCH
demiology of schistosomiasis japonica in China is closely
related to local environmental conditions (20). Thus, schis-
tosome-endemic areas in China have traditionally been
classifi ed according to local environment and local preva-
lence of infection. The Ministry of Health created different
thresholds to classify areas into distinct stages of control.
For example, once infection prevalence of S. japonicum de-
creases to <5%, this disease-endemic setting is considered
to have reached infection control. Transmission control is
declared once local prevalence decreases to <1%. Trans-
mission interruption has been achieved if <2 of 1,000 stool
samples examined are egg positive and no new cases have
occurred for 5 years. Once this level has been achieved,
local elimination can be declared after another surveillance
period for 5 years without new infection (8,12,27,28).
The 2004 nationwide schistosomiasis survey, which
included a correction factor because of the low sensitivity
of the Kato-Katz technique, indicated an estimated 726,112
S. japonicum infections in humans with a small 95% CI.
This estimate is lower than other recent estimates of other
research groups (29–32). During the survey, the Kato-Katz
technique and the miracidium hatching test were used for
fecal examination. It is well known in China that the hatch-
ing test is more sensitive than the Kato-Katz technique be-
cause the volume of fecal material used for parasitologic
detection is several hundred times higher than that used
on Kato-Katz slides. However, because immature eggs of
schistosomes cannot hatch and egg excretion of S. japoni-
cum is not uniform, samples that showed no hatching may
show eggs in Kato-Katz slides. The hatching test and Kato-
Katz technique are mutually complementary and provide
higher sensitivity in parasitologic diagnosis of S. japoni-
cum infection. A combination of these 2 techniques was
used in 11 villages as the standard for diagnosis in calculat-
ing the false-negative rate of the Kato-Katz technique and
is believed to be the most sensitive method for individual
and community diagnosis in determining true prevalence
The WBLP for schistosomiasis control was started in
1992. It emphasized praziquantel-based control of illness,
and progress in disease control was made (12). However,
in subsequent years, data suggested that schistosomiasis
has reemerged (7,9). Several factors have been suggested
as underlying causes, such as unusually severe fl oods in
1998 (34), major ecologic transformations caused by wa-
ter resource development (35), potential effects of climate
change (36,37), market and health sector reforms (38), and
termination of the WBLP for schistosomiasis control and
insuffi cient attention to control efforts until 2001 (29).
Because of conceptual and technical differences, direct
comparison is not possible between the current survey and
the previous ones conducted in 1989 and 1995. In addition,
the current survey covered a wider geographic area because
it included all schistosome-endemic areas in which trans-
mission has not yet been interrupted. In previous surveys,
the focus was on comparatively smaller areas that had not
reached transmission control status, i.e., had a prevalence
Notwithstanding these differences, several conclusions
can be drawn, which in turn are relevant for future design,
implementation, and monitoring of schistosomiasis control
program in China. The main differences between the sec-
ond and third nationwide schistosomiasis surveys are sum-
marized in online Appendix Table 3 (available from www.
cdc.gov/EID/content/13/10/1470-appT3.htm). First, esti-
mated number of human cases decreased to 726,112 from
865,084 in the mid-1990s. Consideration of areas where
transmission was not controlled showed that the number
of infected persons decreased from 847,584 in the sec-
ond survey to 710,790 in the current survey; a decrease of
16.1%. Second, the number of villages in the areas where
transmission was still ongoing has been reduced by 40.3%
from 13,911 in 1995 to 8,299 in 2004. Third, the number
of people at risk in remaining disease-endemic villages was
13,937,235, a decrease from 22,209,662 in the mid-1990s
and a reduction of 37.3%. Finally, areas where schistoso-
miasis transmission control had not been achieved decreased
considerably (online Appendix Figure 1, available from
www.cdc.gov/EID/content/13/10/1470-appG1.htm, and on-
line Appendix Figure 2, available from www.cdc.gov/EID/
content/13/10/1470-appG2.htm). These fi ndings underscore
that the national schistosomiasis control program in China
has made further progress over the past decade. Conversely,
human prevalence rates in the areas where transmission con-
trol has not been achieved increased from 4.9% in 1995 to
5.1% in the present survey, an increase of 3.9%.
Estimated corrected S. japonicum prevalence in the
current survey averaged over all schistosome-endemic ar-
eas was 2.5%. Stratifi cation by province and ecosystem
showed spatial heterogeneities. Mean prevalence in vil-
lages with an infection rate >1% decreased in Hubei, Hu-
nan, and Yunnan Provinces. In Yunnan, the decrease was
most pronounced (–58.6%). Increased prevalences were
observed in Jiangsu and Sichuan; prevalence increased
from 0.03% to 2.9% in Jiangsu. A fairly constant preva-
lence was observed in Anhui. Highest corrected prevalence
was in the lake and marshland region of eastern and central
China, and a low prevalence was found in the mountainous
region of Yunnan and Sichuan Provinces. Highest preva-
lence among all ecosystems was in the mountain ecosystem
(7.1%) rather than in the lake and marshland region. This
fi nding probably resulted from decreasing control efforts
for schistosomiasis after the end of the WBLP. Corrected
prevalence in the plain region with waterway networks was
nearly zero. When compared with the previous nationwide
survey, prevalence increased by 20.6%–59.0% in fork
1474 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 10, October 2007
Epidemiology of Schistosomiasis in China, 2004
beach and mountain and hill ecosytems, but decreased by
8.9%–39.7% in other ecosystems.
Typical features of chronic S. japonicum infection in-
clude pathologic changes in the spleen and liver (39). Ill-
ness assessed by ultrasonography showed changes in ≈70%
of all seropositive persons in the plain region with waterway
networks, inner embankment, islet without embankment,
and hilly ecosystems. Lower rates were found in islets with
embankment, plateaus, and mountain ecosystems. In addi-
tion, 174 cases of advanced schistosomiasis were detected.
Most of these advanced cases were found in the lake and
marshland region but 22.4% were in the mountainous and
hilly region, a slightly higher percentage than the fraction
of the total number of estimated cases in this area.
Additional progress has been made in control of schis-
tosomiasis in China over the past decade. However, cur-
rently used control strategies and tools will not eliminate
schistosomiasis in certain areas if these strategies are used
at the same level of intensity. Applied research on schisto-
somiasis control is needed to develop new approaches to
further reduce infection in these hotspots of transmission.
Results of the third national schistosomiasis survey provide
a comprehensive overview of the current epidemiology of
the disease, which is crucial for the design of the next 5-
year plan on schistosomiasis control. This overview will
help create at the local level better control programs that in-
clude current epidemiologic and socioeconomic conditions
to increase their effi ciency, address remaining challenges,
and avoid reemergence of S. japonicum infection in areas
where it had been controlled (28,31). By consideration
of these challenges and potential risks for transmission
of schistosomiasis in China, such as ecosystem changes
caused by construction of the Three Gorges Dams on the
Yangtze River and effects of global warming (7,18,19,29),
the Chinese central government has given high priority to
control of schistosomiasis and new control goals have been
made (7,40). One goal is to achieve transmission interrup-
tion in the hilly and mountainous regions and the plain
regions with waterway networks by 2015. The same time
frame has been set for transmission control in the lake and
marshland region. To attain these goals, renewed efforts
are needed to further improve available tools and develop
additional control strategies; adapt programs to changing
demographic, ecologic, and socioeconomic issues; imple-
ment new strategies; and achieve schistosomiasis control
We thank the 7 provincial institutions and 117 counties in-
volved in the cluster sampling survey for their assistance.
Field activities were supported by the Ministry of Health and
Department of Health in the 7 provinces.
Dr Zhou is chairman of the national expert advisory com-
mittee on schistosomiasis at the Ministry of Health and research
scientist at the National Institute of Parasitic Disease in Shanghai.
His research interests include schistosomiasis control programs
and the epidemiology of S. japonicum.
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Address for correspondence: Xiao-Nong Zhou, National Institute of
Parasitic Diseases, Chinese Center for Disease Control and Prevention,
207 Rui Jin Er Rd, Shanghai 200025, People’s Republic of China; email:
1476 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 10, October 2007
[shis”-, skis” to-so-mi’ə-sis], from the Greek—skhistos (split) and soma (body)
Infection of the blood with a parasite of the genus Schistosoma. Originally thought a single organism with a split
body, the parasite was eventually recognized as having male and female forms. Three main species cause human
infection: S. haematobium, S. mansoni, and S. japonicum. Each species has its own range of host snails. The parasite
releases eggs containing larvae through feces or urine; if the eggs reach water, the larvae are released and may
penetrate a snail. A very large number of larvae are then produced inside the snail and released back into the water.
Infection is acquired through skin contact with contaminated water.
Schistosomiasis, which leads to chronic hepatic and intestinal fi brosis of the urinary tract, was fi rst identifi ed in Egypt
in 1851 by German pathologist Theodor Bilharz and is also called bilharzia. Approximately 160 million persons
throughout the world are infected, particularly in Africa, the Middle East, South America, and Southeast Asia.
Source: Institute of Tropical Medicine of Antwerp: www.itg.be