Page 154 - Medical Parasitology_ A Textbook ( PDFDrive )

Intestinal Flukes 147

The operculated eggs are similar to those of Fasciola hepatica. Eggs are laid in
the lumen of the intestine.

Life Cycle (Fig. 12.9)
(1) Unembryonated eggs are passed in faeces of humans or pigs. (2) The eggs
embryonate in water. (3) Miracidia hatch and penetrate freshwater snail. (4) In the
snail, the miracidia develop to the cercarial stage. (5–6) The snail releases free
swimming cercariae. The cercariae develop into metacercariae on water plants and
are ingested by humans or pigs causing infection. (7–8) The metacercariae excyst in
the duodenum and develop into adults in the small intestine.

Pathogenesis and Clinical Features
Adults that attach to the duodenal and jejunal mucosa cause inflammation and local
ulceration. In heavy infections, the adult worms may cause partial obstruction of the
bowel, malabsorption and protein-losing enteropathy. Clinical manifestations of
fasciolopsiasis are diarrhoea and abdominal pain.

Diagnosis
1. Microscopic examination
Detection of eggs in faeces. Adult worms are rarely found in faecal specimen.

Metacercariae
6
4a 4b 4c on water plant
Sporocysts Rediae Cercariae ingested by
5 Free-swimming humans or pigs,
causing infection
cercariae
i
in snail tissue

4 Snail

Excyst in
3 7 duodenum
Miracidia hatch, 7
penetrate snail
8

2 Embryonated eggs
in water d
8
i = Infective Stage Unembryonated eggs Adults in
d = Diagnostic Stage 1 passed in faeces small intestine
Fig. 12.9 Life cycle of Fasciolopsis buski (Reproduced from https://www.cdc.gov/dpdx/fascio-
lopsiasis/index.html)