Environmental Engineering Reference
In-Depth Information
a city is related to municipal drinking water. Of course, drinking water must
not be ruled out as a source of infection when more than expected cases of
giardiasis are recognized in a community, but the possibility that the cases
are associated with a daycare center outbreak, drinking untreated stream
water, or international travel should also be entertained.
To understand the finer aspects of
Giardia
transmission and strategies for
control, the drinking water practitioner must become familiar with several
aspects of the parasite's biology. Two forms of the parasite exist: a
trophozo-
ite
and a
cyst
, both of which are much larger than bacteria (see
Figure 6.4
).
Trophozoites live in the upper small intestine where they attach to the intes-
tinal wall by means of a disc-shaped suction pad on their ventral surface.
Cyst
Excystation in duodenum
(Infective stage)
External
environment
Human
Multiplication by
longitudinal
binary fission
Figure 6.4
Life cycle of
Giardia lamblia
.
