Page 839 - Veterinary Immunology, 10th Edition

the body surface. The development of disease is related to many
VetBooks.ir other factors, including the response of the host, the presence of

damaged tissues, the location of the bacteria, and their disease-
producing power (or virulence).

The ability of many bacteria to survive within an animal also
depends on virulence factors. Many of these virulence factors are
encoded on mobile genetic elements that can be transmitted
between species (e.g., plasmids). These virulence factors permit the

bacteria to adapt to a specific environment and promote their
transmission between hosts. Depending on their niche within the
body, bacteria can use virulence factors to penetrate surface
epithelia, to bind to cell surfaces, to acquire iron, to evade immune

responses, to hide within cells, and to promote transmission to
another host. Some of these strategies result in damage to host
tissues and must be blocked by the immune system. It should also
be pointed out that many bacteria are unable to invade and cause

disease in healthy normal hosts but will take the opportunity
offered by immunosuppression or other weaknesses in host
defenses to invade the body.

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