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Chapter 16

“The moulds of man”

This chapter is divided into the following major sections:

• the major fungal pathogens of humans and other
  mammals


• the dermatophytic fungi


• Candida albicansand other Candidaspecies


• opportunistic and incidental pathogens: Aspergillosis


• endemic dimorphic fungi: Coccidioides, Blastomyces,
  Histoplasma, andParacoccidioides


• Cryptococcus neoformans


• Pneumocystisspecies

In contrast to the many thousands of fungi that infect

plants, only about 200–300 fungi are reported to cause

diseases of humans and other warm-blooded animals

• diseases that are collectively termed mycoses. We
  can be thankful for this, although it remains to be
  explained satisfactorily in evolutionary terms. Even the
  fungi that do infect humans and other warm-blooded
  animals are, for the most part, opportunistic or cause
  only mild symptoms in normal, healthy individuals. But
  the situation has changed drastically in recent years,
  with the increasing use of immunosuppressant drugs
  in transplant surgery and cancer therapy, and the
  advance of HIV/AIDS. Fungal infections can be life-
  threatening in these situations, and we shall see in
  Chapter 17 that there are few really satisfactory drugs
  to control them without causing adverse side effects.
  In addition to the invasive mycoses, fungi pose a
  threat to health by producing mycotoxins in foodstuffs
  and animal feeds (Chapter 7), and airborne fungal
  spores can be significant causes of asthma, hay fever,

and more serious occupational diseases, discussed in

Chapter 10. Taking all these factors together, fungi can

have a significant impact on human and animal health.

In this chapter we consider the major fungi that infect

humans and some other warm-blooded animals.

Major fungal pathogens of humans and

other mammals

The human-pathogenic fungi can be grouped into five

categories based on features such as their primary

route of entry into the host, the type of disease that

they cause, and their natural sources of inoculum

(Table 16.1). An outline of these groups is given below

and will provide the basis for more detailed treatment

in later sections of this chapter:

1 The dermatophytes, also known as ringworm

fungi, grow in the dead, keratinized tissues of the skin,

nails, and hair. They are very common, and infect

large sections of the human and animal populations.

The diseases that they cause are superficial, being

confined to the dead tissues, but they can cause severe

irritation of the underlying living tissues, leading to

secondary invasion by bacteria. Many of these fungi

show a degree of specialization for particular hosts

(humans, cats, cattle, etc.) but can cross-infect other

hosts. The source of inoculum is usually the shed

keratinized tissues (flakes of skin, hairs, etc.) in which

the fungus can persist in a dormant phase. As a group,

the dermatophytes are successful parasites with a

clearly defined niche.

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