Essentials of Anatomy and Physiology

that are vectors of disease. These are listed in Table
22–8. Mosquitoes, fleas, lice, and flies are all insects.
Ticks are not insects but are more closely related to
spiders.

SUMMARY

The preceding discussion is an introduction to
microorganisms and human disease, and is only part of
the story. The rest of this story is the remarkable abil-

ity of the human body to resist infection. Although we

are surrounded and invaded by potential pathogens,

most of us remain healthy most of the time. The

immune responses that destroy pathogens and enable

us to remain healthy are described in Chapter 14. Also

in that chapter are discussions of vaccines. The devel-

opment of vaccines represents the practical applica-

tion of our knowledge of pathogens and of immunity,

and it enables us to prevent many diseases. The avail-

ability of specific vaccines is noted in the tables of bac-

terial and viral diseases that follow.

An Introduction to Microbiology and Human Disease 515

Scolex head (x20)

Hooks

Sucker

Fluke (x4) Tapeworm (actual size)

Muscle tissue

Hookworm (x3) Pinworm (x2) Trichinella (x100)

A B

C D E

Figure 22–6. Worms.
QUESTION:Which human organ
system is infested by worms A–D?

A B C

D E F

Louse (x15) Flea (x15) Mosquito (x5)

Larva

Nymph

Scabies mite (x100) Wood tick (x4) Deer tick (x12)

Figure 22–7. Arthropods.
QUESTION:Which of these arthro-
pods are not insects (an old name
for insects is hexapods)?