Question

how the parasitic worm protect themselves in the body of their host

Answer 1

Parasitic worms have several ways in which they manage to stay in good shape in face of immune response of a host. We can divide their strategy into four groups:

Parasites can locate themselves in places where immune responses are likely to be weak or ineffectual.
Parasites can repair damage inflicted upon them quickly enough to remain viable.
Parasites can harden themselves and become relatively insensitive to mechanism of immune responses.
Parasites can direct immune response towards ineffectual pathways.