Biomedical Engineering Reference
In-Depth Information
Class Microsporidia is not your typical fungus. Unlike all other fungal clas-
ses, the members of Class Microsporidium are obligate intracellular para-
sites, that have adapted themselves to parasitic lives in a wide range of
eukaryotic organisms. Unlike virtually all other members of Class Fungi, the
members of Class Microsporidia lack mitochondria. As with other so-called
amitochondriate eukaryotic classes (e.g. Class Metamonada, Chapter 16 [65],
and Class Amoebozoa, Chapter 22 [66]), the members of Class Microsoridia
have retained remnant forms of mitochondria (i.e. mitosomes, hydrogeno-
somes) [67]. Unlike most other fungi, the microsporidia lack a hyphal form
and do not produce multicellular tissue structures. With all these non-fungal
properties, taxonomists never entertained the notion that the microsporidia
were fungi; until recently. Several molecular phylogenetic studies suggest
that microsporidians are fungi [111].
All members of Class Microsporidia form spores, thick-walled cells that
can survive in the environment. Infected animals pass spores in their urine
and feces, and the spores infect humans by contact or inhalation. The spores
pass to the intestines, where they extrude a polar tube into the intestinal lin-
ing cells. Through the polar tube, the cytoplasm of the spore (sporoplasm)
enters the host cell and organizes into a cell capable of division. Eventually,
more spores are formed. When the host cells lyse (break open and die),
spores are released into the intestine, and are passed with feces into the
environment.
A wide variety of animals are reservoirs for the various species of
Microsporidia: mammals, birds, and insects. The spores are passed in the
stools, and infect humans through direct contact, water contamination, or
through respiration of airborne spores. Preliminary evidence suggests that
microsporidial infections are common [112]. Most, but not all, cases of
symptomatic microsporidiosis occur in immune-compromised individuals,
particularly in patients who have AIDS.
Although microsporidiosis is considered a rapidly emerging disease, we
lack important and fundamental epidemiolologic information. How prevalent
is the organism in the immune-competent population? How prevalent is the
organism in the population of immune-deficient but asymptomatic patients?
How often is a microsporidium the causative agent of diarrheal diseases
among different age groups? In which geographic regions does microspori-
diosis occur? What are the most
important animal reservoirs for human
microsporidiosis?
Microsporidia
Encephalitozoonidea
*Encephalitozoon
Enterocytogoonidea
*Enterocytozoon
