Overview of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 30

Human acquire infection through
consumption of contaminated
water or food, or by fecal-oral
route or by hands or fomites.

Cyst

i

Contamination of water, food, or
hands/fomites with infective cysts.

Trophozoites are also passed
in stool but they do not
survive in the
environment.

Trophozoite

= Infective stage
= Diagnostic stage

i

i
d

d

d

Cyst

Intestinal phase Excystation occurs as the

parasites transit towards
the colon. Cysts are resistant
forms and are responsible
for transmission.

Excystation occurs in the small
intestine. Two trophozoites are
released from each cysts.

Cyst

Trophozoite

The trophozoites multiply by longitudinal
binary fission. They remain in the lumen of
the proximal small bowel where they can be
free or attached to the mucosa by a ventral
sucking disk.

Figure 2.9 Giardia cysts and trophozoites life cycle. Source: http://www.dpd.cdc.gov/
dpdx/HTML/Giardiasis.htm . (For color version of this figure, the reader is referred to the
online version of this topic.)