Bilharziasis (also called schistosomiasis) is one of the
most widespread human
diseases caused by parasites. This entry explains in general
terms what is
necessary for personal protection from bilharzia and for
ridding an area of the
disease. Further information from the references given is
with government or other programs is essential.
An estimated 150 to 250 million people suffer from the
disease. It is found in
much of Africa, the Tigris and Euphrates valleys, parts of
Israel, northern Syria,
Arabia, Iran, Iraq, parts of Puerto Rico, Venezuela, Dutch
Guiana, Brazil, Lesser
Antilles, Dominica, Taiwan and parts of China, the
Philippines, Japan, and a few
villages in southern Thailand.
A basic understanding of the life cycle of the parasites,
called schistosomes, and
the characteristics of each phase is the first step in
preventing the disease (see
The disease has been found, besides in humans, in baboons, monkeys,
water buffalo, horses, cattle, pigs, cats, and dogs. When
water is contaminated by
urine or feces from a victim of the disease, the eggs
contained in these hatch out
larvae that penetrate certain types of fresh-water snails.
In the snail host, the
larvae develop into cercariae, which work their way out of
the snail and become
free-swimming; this is the form that infects people. It can
survive in water for a
few days under favorable conditions.
The disease is contracted by contact with water containing
ways are bathing, drinking, washing teeth, washing pots and
through water, irrigating, and cultivating crops. Once the
parasite has contacted a
host, five minutes may be enough for it to penetrate the
It is important to note that bilharziasis cannot be passed
from human to human;
it depends on the snail intermediary. A victim must live in
or have visited an
area where the parasite is found.
SYMPTOMS AND DIAGNOSIS
At the spot where the parasite penetrates the host, a red
itching eruption lasting
several days usually develops. After the host is infected,
symptoms relate particularly
to the large bowel, the lower urinary tract, liver, spleen,
lungs, and the
central nervous system. The most characteristic symptoms are
bladder and colon
irritation, ulceration, and bleeding. Three to 12 weeks
after infection, a victim
will likely develop fever, malaise, abdominal pain, cough,
itchy skin, sweating,
chills, nausea, vomiting, and sometimes mental and neurological
developments may include frequent painful urination with
blood in the urine,
dysentery with blood and pus in the stool, loss of weight,
anemia, and enlargement
of the liver and spleen. Numerous complications are
Typically the acute phase subsides and host and parasite
live together over a
period of years, sometimes as long as 30, with the host
suffering a variety of
symptoms of intermittent and variable types. Bladder and
bowel troubles are the
most characteristic symptoms in this period.
The variety of vague and general symptoms is considerable
and may not be very
specific. Examination of urine and/or feces is very
important; special concentration
techniques may be necessary to reveal the eggs. Tissue tests
and skin tests
can be used by medically-trained personnel to identify the
The disease can be treated with drugs, but only well-trained
undertake to treat a victim. Supportive treatment, which
includes good diet,
nursing care, rest, and treatment of other ailments and
infections, is important.
The disease can be prevented by:
uncontaminated water-a properly built sealed well or an improved
sealed spring is
safe. (See section on "Water Resources.")
However, it is important to remember that all
water used must be safe.
Never bathe in or
touch water you wouldn't drink. Avoid suspected water. If
it is necessary
to use questionable water, boil it, or treat it with iodine or
chlorine. If you must
enter suspected waters, wear rubber gloves and wading
boots, and put
repellent on your skin; insect repellent (either diethyl
dimethyl phthalate), benzyl benzoate, cedar wood oil, or
effective protection for about eight hours if applied to the
contact with the water. In case of accidental contact, rub your
with a dry cloth. Once cercariae have penetrated the skin,
measures are possible.
kills cercariae slowly, but properly chlorinated water
almost always free of the larvae. Use 2 halazone tablets in a
liter (quart) of
clear water; 4 tablets if the water is cloudy. In a water
system, use 1
part per million chlorine. Iodine is even more lethal to
section on "Chlorination of Polluted Water."
Filtering-Cercariae are just big enough to be seen with the unaided eye,
can be filtered
from the water. However, dependence on filtration is
since improperly made or operated filters will not only allow
pass, but may even provide a place for the host snail to live. In
is a poor technique.
water at temperatures over 21C (70F) completely isolated
from snail hosts
for four days will allow the cercariae to die; at cooler
may live as long as six days. This is seldom a practical
Eliminating the snail intermediate host is at present the
most effective single
method of controlling bilharziasis. The following methods
o Use a sealed,
covered well or properly developed spring for a water supply.
Make sure it is
covered; this prevents access of organic matter that snails
eat, cuts out
light that would allow plants to grow for snail food, and
people from bathing in or contaminating the water.
o If surface water
must be used, put long-lasting (copper) screens on the
intake; draw lake
water far from vegetated shorelines, and preferably 2.4m
(8') deep; take
stream water from a fast moving spot.
o Be sure filters
and reservoir tanks are kept covered and dark and keep them
o Since snails
prefer the stagnant water of canals, irrigation ditches, and
dams, control has
been possible where the water level in ditches has been
varied, where it
has been turned off completely for periods, and where
canals have been
lined with cement or pipes have been used. Although the
initially expensive, it pays dividends not only in better health, but
also in less
o Poison the snails
with copper sulfate, copper chromate, or other copper
salts. Use a dose
of 15-30 parts per million by weight of copper and try to
copper-treated water over the snails for 24 hours. All or most of
vegetation should be stripped from the stream bed or pool before
Results for other than small controlled pools have been poor.
to treat streams, lakes, or other natural waters, study the
material and seek experienced help.
RIDDING AN AREA OF BILHARZIASIS
Education is a major step in a continuing campaign against
steps involved in improving your local waters so they will
not spread the disease
are as follows:
o Inform yourself.
Study this article, locate reference material cited below,
available health officials.
o Learn to identify
dangerous snails; for Africa, Professor Mozley's book is
very helpful. To
find the percentage of snails harboring schistosomes, collect
a large sample of
suspects (use rubber gloves, repellant, and snail scoop),
in test tubes or glass jars of water. Those shedding cercariae
detected, as the cercariae (0.5mm long and easily visible to
the naked eye)
are released in clouds. This test reveals only the snails
cercariae. Observe precautions at all times when collecting
o Find dangerous
snails locally, collect (again using rubber gloves, repellent,
and snail scoop)
and kill them. Mail empty shells to an expert to confirm
identification. Visit the expert if possible. Find out about government
or other programs
and participate in these.
o Make a personal
survey on foot (wearing boots) of local waters, using maps
and keeping exact
records to locate all dangerous snails. Local people can
often help here.
Aerial photographs are also helpful.
o Survey types and
intensity of bilharzia present in populace. Differences may
infection points. Keep special records for three- to six-year-olds,
who are the most
recently infected; these records will show most
incidence of new infections.
o Educate the
public as much as possible, and get them to participate in the
sanitation facilities, medical care, and improved nutrition are
critical, but improved
sanitary facilities are worthless if nobody uses them.
to live in villages away from infected waters, and to
culverts or bridges at places where paths cross streams. The
number of such
crossings should be reduced. Any improvement should cater
to local customs
or offer an attractive alternative.
supervise, participate in, and measure the effectiveness of
o Take continuing
steps to destroy the natural breeding places of snails,
sites where humans and snails congregate. For example, the
place where a
stream crosses a road is a focal point: people stop to drink
and bathe; they
cook and wash out pots, providing food for snails. The
embankments slow and impound the water, making ideal breeding
Finally, a favorite sheltered place to defecate is under a bridge.
Filling in places
where water stands, changing drainage patterns, and
food sources are possible techniques.
o Maintain a
continuing surveillance of focal spots and repeat poisoning
Mozley, Alan. The Snail Hosts of Bilharzia in Africa: Their
Destruction. London: H. K. Lewis & Co. Ltd.
Schistosomiasis, Bulletin No. 6. London: The Ross Institute,
The London School of
Hygiene and Tropical Medicine.
Mason V. Hargett, M.D., Hamilton, Montana
Dr. Guy Esposito
Dr. Thomas W. M. Cameron, Montreal, Canada
Craig, C. F. and Faust. Clinical Parasitology. Philadelphia:
Lea and Fibeger, 1964.
Hinman, E.H. World Eradication of Infectious Diseases.
Charles C. Thomas, 1966.
Markell, Edward K. and M. Voge. Medical Parasitology.
Philadelphia: W.B. Saunders
The Merck Manual of Diagnosis & Therapy. Rahway, New
Manson, Patrick. Tropical Diseases. Baltimore: William &
Wilkins Co., 1966.
In addition, up-to-date information can be obtained from the
Organization, Geneva, Switzerland.