Essentials of Anatomy and Physiology

tance of the immune system is clearly evident if we
consider people with AIDS. Without the normal
immune responses, AIDS patients are very susceptible
to invasive fungal diseases, including meningitis
caused by Cryptococcus. Pneumocystis jiroveci(formerly P.
carinii and classified with the protozoa, its DNA
sequences suggest it is closer to the fungi) is an impor-
tant cause of pneumonia in people with AIDS. This
species is usually not pathogenic, because the healthy
immune system can easily control it. For AIDS
patients, however, this form of pneumonia is often the
cause of death.

Antifungal Medications

One of the most effective drugs used to treat serious,
systemic mycoses, amphotericin B, has great potential
to cause serious side effects. Patients receiving this
medication should have periodic tests of liver and kid-
ney function. Newer medications include ketocona-
zole, fluconazole, and caspofungin, which are less
toxic to the recipient and may prove to be as effective
as amphotericin B.
Superficial mycoses such as ringworm may be
treated with certain oral medications. Taken orally, the
drug is incorporated into living epidermal cells. When
these cells die and reach the stratum corneum, they are

resistant to the digestive action of the ringworm fungi.

An effective topical spray has also been developed.

There are several effective medications for mucosal

yeast infections, but it is important that the trigger for

the infection (such as antibiotic therapy) be resolved as

well. If it is not, the yeast infection may recur when

the medication is stopped.

PROTOZOA (SEE TABLE 22–6)

Protozoa are unicellular animals, single cells that are

adapted to life in freshwater (including soil) and salt-

water. Some are human pathogens and are able to

form cysts, which are resistant, dormant cells that are

able to survive passage from host to host.

Intestinal protozoan parasites of people include

Entamoeba histolytica, which causes amebic dysentery,

and Giardia lamblia, which causes diarrhea called giar-

diasis (Fig. 22–5 and Table 22–6). People acquire these

by ingesting food or water contaminated with the

cysts of these species. Giardiasis can become a prob-

lem in daycare centers if the staff is not careful con-

cerning hand washing and food preparation.

Plasmodium, the genus that causes malaria, affects

hundreds of millions of people throughout the world

(causing 2 to 3 millions deaths each year) and is prob-

ably the most important protozoan parasite. The

An Introduction to Microbiology and Human Disease 513

F Pneumocystis jiroveci

(x 1200)

E Cryptococcus (x 500)

B Rhizopus (x 40) C Aspergillis (x 40)

D Ringworm (x 750)

A Yeast (x 750)
Figure 22–4. Fungi.
QUESTION: Which of
the fungi shown have a
mycelium?