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184 CHAPTER 8

present. Local inflammation occurs when the worms
attach to the intestinal mucosa, and eosinophilia MICROSCOPIC DIAGNOSTIC
is common as an allergic response to the invasion of this FEATURE
parasite.

General Classification—Egg of Liver Fluke
Life Cycle
Organism Fasciolopsis buski
All trematodes have a similar lifestyle but differ as Specimen Required Feces
to the intermediate hosts utilized and the stage of Stage Ovum (egg) most
development reached by eggs as they are passed in commonly; indistin-
the feces. The primary reservoir for the intestinal fluke guishable from
is the pig. Dogs may also harbor the parasite, which F. hepatica
bolsters the position by some investigators that there Size 130 μm × 60–90 μm
is a close correlation between human parasites and (average length
those found in domesticated animals. Following the slightly exceeds
passing of unembryonated eggs in the stool, micacidia F. hepatica)
develop in the water within approximately a month. Shape Ellipsoid
As is characteristic of flukes, the snail acts as the first Shell Transparent
intermediate host and is penetrated by the miracidia. Other Features Ovum unembryonated
Cercariae are then produced from these miracidia when passed in
and are released from the snail where they encyst on feces
freshwater vegetation, a life form that is considered the
F. buski
second intermediate host. Water chestnuts and bamboo
shoots are the primary second intermediate hosts, where Operculum
the cercariae develop into metacercariae. These forms
encyst in the vegetation and, after being ingested into the
intestinal tract, the metacercariae excyst (hatch from the
cyst). Further development, self-fertilization, occurs in
the intestine to the adult form. The eggs are evacuated in Delmar/Cengage Learning
the feces, where they again go through development into
cercariae and infect snails. The life span of the worm is
somewhat short, existing for a period of approximately
6 months.

Disease Transmission Treatment and Prevention

Ingestion of uncooked or poorly cooked and encysted Treatment with praziquantel or niclosamide is most
vegetation containing metacercariae provides transmis- common for F. buski. Prevention entails proper human
sion for the organism. Animals that feed on raw vegeta- waste disposal and control of snail populations. Eating
tion also may become infected. raw vegetation from watery areas is discouraged.

Laboratory Diagnosis HETEROPHYES HETEROPHYES

F. buski infection is diagnosed by examination of fecal Heterophyes heterophyes and Metagonimus yokogawai are
samples for both ova and parasites. Eggs are quite char- presented together as so many similarities exist between
acteristic and are often passed in the feces, but may be the two parasites. The two parasites are easily confused
confused with the eggs of Fasciola hepatica, due to simi- but a distinguishing factor is that they are found in differ-
larities in both size and shape. ent geographic locations of the world. H. heterophyes, an