consumption of muscle tissue containing encysted larvae which
have curled up in a characteristic manner in a cyst with a calcified wall
(Figure 8.2). In this state they can survive for many years in a living host
but, once eaten by a second host, the larvae are released by the digestive
juices of the stomach and they grow and mature in the lumen of the
intestines where they may reach 3–4 mm in length. On the assumption
that uncooked human flesh is not consumed, the human host represents a
dead end for nematodes such asTrichinella. This is unlike the situation in
the Cestodes, such asTaenia, where passage of proglottids in human
faeces can complete the cycle back to domestic animals.
The adult worms do not cause any apparent symptoms but a single
female can produce more than a thousand larvae, each of which is about
100 mm long, and it is these larvae which burrow through the gut wall
and eventually reach a number of specific muscle tissues in which they
Figure 8.2 Trichinella spiralis
Chapter 8 273