Page 70 - parasitology for medical and clinical laboratoryprofessionals

50 CHAPTER 3 MICROSCOPIC DIAGNOSTIC

Source: Centers for Disease Control and Prevention (CDC) General FEATURE

Flagellate
Classification
Giardia lamblia
Organism
Specimen Required Stool specimen

cysts, with cyst

stage being the most
diagnostic
FIGURE 3-9 Giardia lamblia trophozoites on a wet Stage Trophozoites and
mount; can be found in the small intestine of an Size Trophozoite—9–21 3
infected host 5–15 μm; Cysts—
8–17 3 7–10 μm
presented in this section. One other important anatomi- Shape Pear-shaped tropho-
cal feature of G. lamblia is an adhesive disc which is dif- zoites; oval and
ficult to visualize as an organelle (small organ) on the somewhat elongated
ventral side of the organism. cysts
Sometimes identification of G. lamblia is necessary Motility Characteristic “falling
by obtaining a biopsy of the small intestine or from the leaf” motility on wet
examination of duodenal fluid. Another method requires mount
the patient to swallow a gelatin capsule attached by a Nucleus(i) 2 for trophozoites
nylon string, the end of which is taped to the patient’s and up to 4 for cysts
cheek. After 4 to 8 hours the capsule is withdrawn and Cytoplasm Unremarkable
the bile-stained mucous on the end of the string where Other Features 4 pairs of refractile
the capsule is attached is microscopically examined flagella
by either a wet mount (Figure 3-9) or by permanent
staining. A wet mount is merely a drop of water or saline
in which the specimen is mixed, after which a cover slip Giardia lamblia
is placed over the mixture and the specimen is examined Trophozoite Cyst
microscopically.

Treatment and Prevention

Children in daycare centers and in those from rural areas
who drink water from streams and contaminated wells are
frequently afforded the greatest opportunity for infection
along with male homosexual contacts. Domestic cats are
also a source of giardiasis where close contact enables
the transmission of the organism to humans. A sanitary
lifestyle for both the body and for food eaten as well as
a safe water source would prevent most of the infections Delmar/Cengage Learning
contracted worldwide. The common practice of using
human waste as fertilizer, found in several parts of the
world, is probably the most causative factor in the trans-
mission of this disease.