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letters to nature NATURE |VOL 405 |8 JUNE 2000 |www.nature.com 681

Summary: letters to nature
NATURE |VOL 405 |8 JUNE 2000 |www.nature.com 681
Host±parasite system
Potamopyrgus antipodarum serves as the ®rst intermediate host to at least a dozen species
of digenetic trematodes. One of these trematode species, Microphallus sp., produces
encysted larvae (metacercariae) in the snail in 3±4 months under laboratory conditions.
The cysts `hatch' after ingestion by the ®nal host (waterfowl and wading birds), and the
resulting hermaphroditic worms produce cross-fertilized eggs within several days; these
eggs then pass into the environment. We have found that mice can serve as the ®nal host in
laboratory experiments. Snails become exposed to infection after the ingestion of these
eggs. An infection resulting from a single egg results in the production of hundreds (or
more) asexual larvae within the same snail, thereby sterilizing the host. These larvae then
encyst in the snail, but they can be easily removed by dissection.
Experimental infections
Infections of Potamopyrgus were carried out in the laboratory (Edward Percival Field
Station in Kaikoura, New Zealand) in January 1997 using mice as the ®nal host. Parasite
lines were created within 12 laboratory mice by feeding each mouse the metacercarial cysts
from 24 infected snails. Four Lake Poerua parasite lines were created using cysts dissected
from 24 infected snails collected from the Lake Poerua shoreline; similarly, 4 Lake Ianthe


Source: Autumn, Kellar - Department of Biology, Lewis and Clark College
Fearing, Ron - Department of Electrical Engineering and Computer Sciences, University of California at Berkeley


Collections: Biology and Medicine; Engineering; Materials Science