In some localities throughout the world (see map at end of book), bodies of
fresh water such as lakes, rivers, streams, swamps, ponds, irrigation ditches, and
flooded rice fields may harbor the larvae or cercariae (young forms) of
various blood-worms or flukes. Human infestation with these flukes is known
by the terms schistosomiasis or bilharziasis. The only type found in the Western
Hemisphere (Caribbean Islands and South America) is the variety which produces
intestinal lesions and dysentery and is known as intestinal bilharziasis. In
certain regions of Africa these flukes produce a condition known as urinary
bilharziasis, though the intestinal form also is present. Heavy areas of infection are
found in Egypt and in some of the oases of the North African desert. In parts of
the Far East, notably Japan and China, an intestinal variety is known as oriental
bilharziasis. The geographical distribution of these diseases is shown on the
map referred to above.
The cercariae or young forms of these flukes are harbored by certain
species of fresh-water snails. When the parasites leave the snail host and are
discharged into the water, the survival time of the cercariae is less
than 48 hours unless another suitable victim is found. These cercariae may
enter the body through the unbroken skin of swimmers, bathers, or persons wading in such
waters, or through contaminated drinking water that has not been boiled or
sufficiently treated with chlorine. If water for bathing is stored in a clean container
and is free of snails, it will become entirely safe for use in 48 to 72 hours. This
will not insure water satisfactory for drinking purposes.
One should be extremely cautious in wading, bathing, or swimming in fresh-water
ponds, streams, lakes, or rivers which have not been examined and found to be
safe by Army medical officers or others competent to judge. Salt-water bathing
and swimming, except at beaches near the mouths of fresh-water streams or near
city sewage outlets are safe and do not constitute health hazards.
*Prepared in the Office of the Surgeon General.