Page 914 - Veterinary Immunology, 10th Edition

Infectious diseases, as pointed out earlier, rarely result from the
VetBooks.ir deliberate activities of a malicious microorganism. In most cases,

disease occurs because of the host's reaction to the infection or
because the invader inadvertently causes damage to its host. Well-

adapted parasites do not make these mistakes. They exploit the
host's resources without causing irreparable damage or triggering a
destructive defensive response.
A consistent feature of all parasite infestations, however, is that

they block or delay host defenses so that they may survive for
sufficient time to reproduce. Some parasites may simply delay their
destruction until they complete a single life cycle. Other well-
adapted parasites may contrive to survive for the life of their host,

protected from immunological attack by highly evolved evasive
mechanisms (Fig. 28.1).

FIG. 28.1 Evasion of the immune response is critical to parasite
survival. Some of the many ways by which parasites evade immune
destruction or exclusion are shown.

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