Leah Machen
Kirsten Rogers
Parasites and Pestilence Proposal
Mapping the Key to Prevention
Spotlighting the link between Dam Construction and Schistosomiasis Outbreak
Introduction:
Since 1970, there has been an upsurge in dam construction in Nigeria that has been
strongly correlated to schistosomiasis outbreak in endemic states. Although there are several
ways to combat the increased incidence of schistosomiasis associated with water development
projects including the administration of praziquantel to residents of endemic areas, molluscides
for intermediate host snail control, or the introduction of a competitor species to reduce the snail
population, a preventative intervention must also be implemented to promote the awareness of
the adverse health effects caused by water development projects so that appropriate action can be
taken.
Specific Aims:
This project will investigate the correlation between dam construction and
schistosomiasis prevalence in Nigeria with the goal of constructing a color-coded nation-wide
map. The map consists of bulleted locations of all dams within the country along with colorcoded indicators of schistosomiasis prevalence. This map will serve as a tool designed to
provide the information needed to establish a positive correlation between dam and reservoir
construction and schistosomiasis outbreak. Demonstration of a significant positive correlation
will promote the consideration of the potential adverse health effects caused by water
development. The purpose of the map is to deter further dam and reservoir construction in areas
with endemic schistosomiasis, promote pre-construction examination of schistosomiasis
prevalence, promote the instillation of snail (schistosoma reservoirs) abundance monitoring
systems in areas with dams, and to make schistosomiasis control a key factor in the planning and
building of dams.
Background:
Schistosomiasis, also known as Bilharzia or Snail fever, is a parasitic disease caused by
trematode flatworms of the genus Schistosoma. It is a major source of morbidity affecting over
200 million people worldwide and it is endemic to 76 developing countries throughout the
tropics. The prevalence of schistosomiasis demonstrated in Figure 1 is changing dramatically due
to control programs in Asia and the Americas that have eliminated or drastically reduced
transmission however; similar success has yet to be achieved in sub-Saharan Africa as its
prevalence of schistosomiasis is increasing. i
Three species of schistosomiasis, S. haematobium (Africa), S. japonicum (Japan,
Southeast Asia, Western Pacific) and S. mansoni (Africa, Southwest Asia, Brazil, Caribbean) are
responsible for the majority of schistosomiasis infection while the other two species, S.
intercalatum and S. mekongi parasitize humans to a much lesser extent. Humans are the most
important reservoir for S. haematobium and S. mansoni and are infected when exposed to
contaminated freshwater (e.g., when wading, swimming, or bathing). ii The life cycles of the
human schistosomes, as seen in Figure 2, are generally similar. Eggs are released into the
environment from the urine or stool of infected individuals. Once the eggs reach water, they
hatch to release free-swimming miracidium. The miracidium then infect the intermediate host, a
freshwater snail, by penetrating its foot. The host snails of the important human schistosomes are
those of the genera Biomphalaria (S. mansoni), Bulinus (S. haematobium) and Onchomelania
(S. japonicum) as seen in Figure 3. After infection, asexual proliferation occurs in the snail and
thousands of new larval parasites known as cercariae emerge. When humans are in contaminated
freshwater, cercariae attach to, explore, and ultimately penetrate the skin. The cercariae morphs
into a migrating schistosomulum and travels to the lungs. In the lungs, the schistosomlum
undergoes developmental changes, which allow it to migrate to the liver where it feeds on redblood cells, grows into an adult worm and finds a partner. After finding its mate, the pair unites
and copulation begins. Pairs of male and female worms relocate to the rectal veins, in the case of
S. mansoni and S. japonicum, and in the case of S. haematobium, the worms migrate to the
perivesical venous plexus of the bladder, kidneys and ureters. S. mansoni and S. japonicum eggs
pass through blood vessel and intestinal wall to be passed out the body’s feces. S. haematobium
eggs pass through the ureteral or bladder wall and exit the body in the urine. Worm pairs can
dwell in the body for an average of four and a half years, but may persist up to 20 years. The
pathology associated with schistosomiasis is caused by the cellular infiltration resulting from
antigens secreted by trapped eggs. These antigens elicit a vigorous bodily immune response
creating illness, rather than the worms themselves. Acute clinical manifestations of
schistosomiasis include abdominal pain, fever, cough, diarrhea and hepatosplenomegaly
(FIGURE 4) while individuals with persistent infections may suffer from severe symptoms such
as cystitis and ureteritis, pulmonary and portal hypertension and bladder cancer.iii
Currently, there is neither a vaccine nor is there chemoprohylaxis for schistosomiasis
available. The most effective treatment for schistosomiasis is prescription Praziquantel, which
treats all three forms of the disease. Drug treatment is effective at killing parasites already in the
body, however it does not prevent new infections. For this reason, repeated treatments are often
necessary and prevention of transmission is of the utmost importance.
The most significant part of the schistosomiasis lifecycle for this project is the
availability of suitable snail hosts in bodies of freshwater that are accessible to humans. Dams
themselves do not cause schistosomiasis, but rather promote schistosomiasis transmission by
dramatically altering the surrounding snail ecology and environment. The resulting ecological
changes significantly extend the range of the snail habitats thereby promoting the proliferation of
both snail reservoirs and cercariae parasites.iv Conditions supporting snail development are
beaches located in the areas higher than 175 m but lower than the flooded water level, which are
created upon dam construction. Predictive studies have demonstrated that beaches that form after
the dam construction caused by the decrease in velocity of water flow and the sedimentation of
silts make suitable habitats for snail reservoirs of schistosomiasis. Experimentation has shown
that the vegetation, soil and physical and chemical characteristics of beaches in areas where
reservoirs have been constructed are like those that are currently endemic to schistosomiasis.v
Furthermore, ditches that surround migratory settlements created after damn construction are
ideal breeding grounds for snails. vi
Dam construction in Nigeria raises particular concern, as it is a country endemic to
schistosomiasis. In response to the Sahelian drought in the 1970s, there was an increase in dam
construction in Nigeria. Of 325 formal dams now registered in Nigeria, over 226 were
constructed since 1970. More than 200 of these dams were built in the 10 most endemic
schistosomiasis states and the rest in the other 26 less endemic states.vii Due to this upsurge of
dam construction in Nigeria since 1970, schistosomiasis outbreak has been recorded in many
areas. There have been multiple studies on the increase in schistosomiasis prevalence near water
development projects in Nigeria. A study done by the University of Ilorin, Nigeria verified that
intestinal helminthes infections among school-aged children were recovered at an overall
prevalence of 78.3% of 309 children examined in the Eko-ende and Ore areas near the Erinle
Dam Reservoir in Osun State, Nigeria and Schistosoma mansoni was one of the three most
prevalent infections. viii A subsequent study by Oladejo et al. conveyed that the mean
Schistosoma haematobium infection rate in school children in the rural areas of Oba-ile and Ilie
was 46%. This study also showed that, Bulinus globosus, the snail reservoir, was present in
abundance and continually throughout the year.ix These studies indicate the prevalence of more
than one type of schistosoma infection within Nigeria, as well as the abundance of the snail
reservoir species within close proximity to dam sites. A study conducted among school children
living near the Bakalori Dam in Nigeria found that 52.1% of the subjects were positive for the
test of urinary schistosomiasis (S. haematobium), and concluded that the prevalence of
schistosomiasis was high and demanded intervention.x
Not only has the burden of schistosomiasis in Nigeria been verified by numerous
studies, but it has been confirmed that viable snail species are in highest concentrations in areas
surrounding dams. A study done by the department of zoology at the University of Ibadan found
that the Owena river damn in Idanre was the richest (of all surrounding areas) in molluscan
fauna, including the intermediate species B. globosus and Biomphalaria Pfeiffer, which were
continuously shedding cercariae.xi
The impact of schistosomiasis outbreak due to dam construction is undeniable.
Many of these studies call for an intervention of some kind within the study region, but due to
the number of dams and corresponding the schistosomiasis prevalence within the country of
Nigeria, a national campaign cannot be effectively designed without a tool that effectively
compiles and organizes the data.
Methodology
Since this project attempts to create a map of schistosomiasis prevalence in relation to
dam locations of the entire country of Nigeria, the most efficient way for this to be accomplished
is by a state-by-state breakdown, starting with the most endemic states. The project will be
designed as a two-part study where first, Global Information Systems (GIS) and Global
Positioning Systems (GPS) will be used to identify the exact location of the dams within the state
and study villages within close proximity to the dam, and second data will be collected to
determine schistosomiasis prevalence in the study villages. Global Information Systems and
Global Positioning Systems have become increasingly affordable and used to improve
epidemiological research to better understand how ecological variation affects the distribution of
intermediate hosts of schistosomiasis. A study was done in China regarding the distribution of
Oncomelania hupensis (the intermediate host snail of Schistosoma japonicum) using GPS
coordinates to map the 11 villages in which the researchers performed cross sectional surveys.xii
Studies have shown that the use of GPS and GIS technologies for mapping epidemiological data
promotes intersectoral collaboration for disease control, allows better analysis of spatial
distribution of parasite infection in relation to environmental factors, and aids in the design of
optimal drug or health measure delivery systems. Studies have also supported the use of GIS
technology to serve as tools for spatial distribution data collection and potential use as tools for
parasite control.xiii, xiv GIS and GPS imaging allow epidemiological data to be mapped with great
accuracy, providing better data to make a strong case for the positive correlation between dams
in Nigeria and increased schistsomiasis prevalence in local areas. In this study, the GIS and GPS
will be used to ensure the accuracy of the map produced, by using satellite data to confirm exact
coordinates of dam locations and the proximity of villages with schistosomiasis. By solidifying
the accuracy of the map and the exact locations with endemic schistosomiasis in relation to the
location of the dam, not only can the most effective intervention strategy be developed, but also a
more accurate picture of the exact effect of the dam on the prevalence of schistosomiasis
including a precise measure of at risk proximity can be constructed.
For the data collection aspect of the study, data will be obtained in the form of previously
conducted post-dam construction studies measuring schistosomiasis prevalence in specific
locations. If no data exists for the identified site then urine filtration tests and Kato-Katz smears
to identify schistosome eggs will be performed in primary school-aged children (5-14 years) to
determine prevalence. This method of determining prevalence will be used in order to assess the
actual prevalence of schistosoma infection in the populations as opposed to using a predictive
model of infection based on environmental and climate indicators. Researchers have used
primary school age children participants to determine the prevalence of schistosomiasis in
communities since children ages 5-14 years have the highest prevalence of any age group of
infection in Nigeria. xv,xvi Although the dams specifically effect the population of infectious
snails in the water, and measuring the density of infectious snails in the water would give a more
precise view of the impact of the dam (and would control for human water contact habits), this
study aims to specifically show the effect of the increased infectious snail population (caused by
the dam) on the surrounding human population. This method also controls for the fact that there
is not a significant amount of data measuring the density of infectious snails in the water pre-dam
construction, which would weaken the positive correlation that this study aims to establish. Once
all previous data is collected and necessary additional studies are conducted, all of the data can
be compiled into a map with all dam locations flagged with corresponding color-coded
schistosomiasis prevalence.
Significance
A map of all of the dam locations in Nigeria with color coded indicators of
schistosomiasis prevalence corresponding to dam location would be an invaluable tool for
developing a nation-wide intervention program to reduce the prevalence of schistosomiasis. In
areas that may have low prevalence and incidence of schistosomiasis, a drug treatment
intervention could be planned, as opposed to areas that have high endemicity and are in close
proximity to dams, where molluscides or elimination of host species may be a more appropriate
intervention. More importantly, academic literature on schistosomiasis in Nigeria is lacking
comprehensive data showing the effect of dams/reservoirs on schistosomiasis prevalence in local
communities. The map will be used as a way to indicate the cumulative effect of dam
construction on schistosomiasis prevalence. Since many sites lack pre-dam construction data of
schistosomiasis prevalence, the color-coded map will provide evidence of the high correlation
between the presence of dams and schistosomiasis endemicity. The map will be used as a tool to
aid the national government (and private sectors) to consider the adverse health effects of water
development projects before undertaking dam construction and will eventually lead to a shift
toward improved dam engineering strategies and alternative energy and water sources. With a
tool that can effectively show the direct correlation between dam development and
schistosomiasis outbreak, not only can undertaking water development projects be reconsidered,
but also locations for dam projects can be more strategically placed to reduce the prevalence of
schistosomiasis and its associated morbidity. Fewer dams constructed in endemic states of
Nigeria will directly prevent the over-abundance of intermediate host snail species that release
cercariae into water used for recreation, bathing, washing, and drinking by local residents, thus
there will be a decrease in schistosomiasis incidence. Furthermore, even if the Nigerian
government (or dam constructing entity) decides to proceed with dam construction despite
evidence of the potential for a schistosomiasis outbreak, they can still test the prevalence of
schistosomiasis infection before the project is underway, providing more opportunities for
researchers to indicate causation instead of simply correlation. Furthermore, if the government is
aware of the associated health risk of dam construction, the post-dam snail abundance can be
continuously monitored, which would better assist an intervention using molluscides to control
snail population before it reached a point of abundance that would be too difficult to control.
Most importantly, schistosomiasis prevalence is second only to malaria and is endemic to
Nigeriaxvii, and due to the recent (since 1970) upsurge of dam construction, Nigeria is the
optimal place for this mapping project to occur. Because droughts are common in Nigeria, dam
construction will not be coming to an end anytime soon, which is why this map is essential for
future control and prevention of schistosomiasis.
Conclusion:
The burden of schistosomiasis weighs heavily on the citizens of Nigeria, which is why it
is imperative that not only intervention, but also prevention becomes an integral role of a
national campaign to reduce the morbidity caused by schistosomiasis. Using GPS/GIS
technology and data on schistosomiasis prevalence from previous and newly conducted studies,
this project will produce an accurate and specific mapping of schistosomiasis prevalence of
communities in close proximity to dam locations. The proposed color-coded map of dams and
schistosomiasis prevalence will undoubtedly serve as a key tool in the prevention of
schistosomiasis outbreak nationwide.
APPENDIX
FIGURE 1
Geographic distribution of schistosomiasis.
Source: Center for Disease Control. Prevention of Specific Infectious Disease: Schistosomiasis.
http://wwwn.cdc.gov/travel/yellowBookCh4-Schistosomiasis.aspx Date Accessed: May 15,
2008.
FIGURE 2
Schistosomiasis Life Cycle
Source: Ross G, Bartley PB and Sleigh AC, Olds GR, Li Y, Willliams GM,McCanus DP.
Schistosomiasis, N Engl J Med 2002;346:1212–1220.
FIGURE
3
Source: Masden et al. “Bilharzia in Lake Malawi, What are the facts?” NSF/NIH joint project in
Ecology of Infectious Disease (DEB-0224958).
FIGURE 4
source: Oneil. “An individual in chronic stages of Schistosomiasis” .University science. Irish
Universities Promoting Science.
<<http://www.universityscience.ie/pages/scientists/sci_sandraoneill.php>
i
Chitsulo L, Engels D, Montresor A, Savioli L. The global status of schistosomiasis and its
control. Acta Trop 2000;77:41-51.
ii
WHO Expert Committee. Prevention and control of schistosomiasis and soil-transmitted
helminthiasis. World Health Organ Tech Rep Ser. 2002;912:1-57.
iii
Ross G, Bartley PB and Sleigh AC, Olds GR, Li Y, Willliams GM,McCanus DP.
Schistosomiasis, N Engl J Med 2002;346:1212–1220.
iv
Li, Y, Raso G, Zhao Y, He HK, Ellis M, and McManus DP. Predicted impact of large water
management projects on schistosomiasis transmission and control in the Dongting Lake Region,
China. Emerg. Infect. Dis. 2007;13:973-979.
v
Scientific leading Team of Chinese Academy of Science. Studying on environment of Three
Gorge Project. Proceedings of Ecological and Environmental Impact of Three Gorge Project and
Strategies. Science Press, 1987. pp. 277–923.
vi
Zheng J, Gu XG, Xu YL, et al. Relationship between the transmission of schistosomiasis
japonica and the construction of the Three Gorge Reservoir. Acta Trop 2002; 82:147–56.
vii
Oladejo SO, Ofoezie IE. “Unabated Schistosomiasis Transmission in Erinle River dam, Osun
Sate, Nigeria: evidence of environmental effects of development projects.” Trop Med Int Health.
June;11 2006;6:843-50.
viii
Ugbomoiko US, Ofoezie IE. “Multiple infection diagnosis of intestinal helminthiasis in the
assessment of health and effect of development projects in Nigeria.” J.Helminthol. 2007 Sep;
227-31. Epub 2007 June 21.
ix
Ibid., at 7
x
Umar AS, Parakoyi DB. “The prevalence and Intensity of Urinary Schistosomiasis Among
School Children Living in Bakalori Dam, Nigeria.” Niger Postgrad Med J. 2005 Sep; 12(3):16872
xi
Odaibo AB, Adewunmi CO, Olorunmola FO, Adewoyin FB, Olofintoye LK, Adetula Mo,
Awe CO, Akinyemi F.”Afr. J Med Med Sci. 2004 Sep; 33(3): 219-24.
xii
Yang K. Wang Xh, Yan GJ, Wu XH, Qi YL, Li HJ, Zhou Xn. “An integrated approach to
identify distribution of Concomelania hupensis, the intermediate host of schistosoma japonicum,
in a mountainous region in china.” Int J Parasitol. 2008 Jan 24.
Brooker, S., Michael E. “The potential of geographical information systems and remote
sensing in the epidemiology and control of human helminth infections” Adv. Parasitol.
2000;47:245-88
xiv
N.R. Bergquist. “Vector-borne parasitic diseases: new trends in data collection and risk
assessment” Elsevier Science B.V. 2001.
xv
Olaseha IO, Sridhar MK. “Participatory action research: community diagnosis and
intervention in controlling urinary schistosomiasis in an urban community in Ibadan, Nigera.” Int
Q Community Health Educ. 2005-2006; 24(2): 153-160.
xvi
Umar AS, Parakoyi DB. “The prevalence and Intensity of Urinary Schistosomiasis Among
xiii
School Children Living in Bakalori Dam, Nigeria.” Niger Postgrad Med J. 2005 sep; 12(3):16872
xvii
Ibid., at 13