Risk factors:
(1) eating uncooked and unwashed watercress or freshwater aquatic vegetation growing in water contaminated with animal feces
(2) living around herbivores (sheep, goats, cattle, horses, camels, other)
(3) presence of abundant snails
(4) drinking contaminated water (with metacercaria floating free on the water surface)
(5) using contaminated utensils
Aquatic vegetation may include (Haswell-Elkins and Elkins, page 1465):
(1) water caltrop
(2) water hyacinth
(3) water chestnut
(4) water bamboo
(5) lotus roots
(6) wild rice shoots
The metacercaria are on the surface of the plants and not in the edible centers. They are ingested when the outer surface is torn between the teeth and lips.
Preventive measures:
(1) draining standing water from pastures
(2) treating infected animals
(3) control of snail populations
(4) cooking watercress and aquatic vegetation prior to eating
(5) strict control on commercial production of water plants
