Biomedical Engineering Reference
In-Depth Information
devices that provide potential entry points for fungi, the number of newly
recognized fungal pathogens will increase. It is estimated that there are
about 20 new fungal diseases reported each year [102]. If the number of
diseases caused by other types of organisms (i.e. bacteria, protists, ani-
mals, viruses and prions) remains steady, then it will not be long before
the number of different fungal diseases exceeds the number of different
diseases produced by all other organisms, combined.
2.
Increased sensitivity of diagnostic tests. It is now possible to identify
heretofore undiagnosed cases of pathogenic species [103]. In the past,
when clinical mycology laboratories had fewer of the sophisticated tests
available today, it was easier to lump diseases under a commonly encoun-
tered species or a genus. For example, Aspergillus fumigatus is a common
cause of severe pulmonary infections in immune-compromised patients.
With advanced typing techniques, an additional 34 species of Aspergillus
have been isolated from clinical specimens [102].
3.
Unstable taxonomy. Class Fungi has recently undergone profound
changes, with the exclusion of myxomycetes (slime molds) and oomy-
cetes (water molds), and the acquisition of Class Microsporidia
(Chapter 37). The instability of fungal taxonomy impacts negatively on
the practice of clinical mycology. When the name of a fungus changes,
so must the name of the associated disease. Consider “Allescheria boy-
dii”; people infected with this organism were said to suffer from the dis-
ease known as allescheriasis. When the organism's name was changed to
Petriellidium boydii, the disease name was changed to petriellidosis.
When the fungal name was changed, once more, to Pseudallescheria boy-
dii, the disease name was changed to pseudallescheriasis [102]. All three
names appear in the literature (past and present).
4.
Classification by morphologic features of reproduction. Unfortunately,
for the taxonomist, fungal organisms have two options for reproduction:
sexual and asexual. Both these forms of reproduction have their own
morphologic appearances, in the same species of organism. Factors that
determine the mode of reproduction for a cultured fungus are a mystery.
It is possible for one mycologist to observe a fungus that reproduces
exclusively asexually, while another mycologist, observing the same spe-
cies in a culture dish or growing in the wild, may observe sexual repro-
duction (e.g. fruiting bodies). Depending on the phase of reproduction
observed, and ignorant of the existence of an alternate morphologic form,
taxonomists have assigned different names (sexual and asexual) to the
same organism. Rather than harmonizing a dichotomous nomenclature
under one preferred name, the ICBN has ruled that it is acceptable to
assign two different binomials to an organism: a sexual (also called teleo-
morphic, perfect, or meiotic form), and an asexual (also called anamor-
phic, imperfect, or mitotic form). For instance, two binomials legitimately
apply to the same organism: Filobasidiella neoformans (the teleomorphic
