The dimorphic fungi causing systemic disease belong to the class
Eurotiomycetes
, order
Onygenales
. This chapter covers the dimorphic members of the families
Onygenaceae
and
Ajellomycetaceae
.
Ajellomycetaceae
contains the species
Ajellomyces dermatitidis
,
A. capsulatum
,
A. duboisii
, and
A. crescens
, the anamorphs of which have been placed in the genera
Blastomyces
and
Histoplasma
. DNA sequence data place
Paracoccidioides
in the family
Ajellomycetaceae
as well. However, it is important to appreciate that tissue‐form cells of
Histoplasma
and
Blastomyces
can appear similar to each other as well as to yeast cells of various Candida species,
Cryptococcus neoformans
,
Cryptococcus gattii
, and
Talaromyces marneffei
and to endospores of
Coccidioides
species.