Biomedical Engineering Reference
In-Depth Information
characteristic of their superclass. All members of Class Euglenozoa that
are pathogenic in humans fall under one class: Class Trypanistomatida.
Class Trypanistomatida contains two infectious genera: Leishmania and
Trypanosoma, and these two genera account for three of the most debilitat-
ing, widespread, and prevalent diseases of humans: leishmaniasis, Chagas
disease, and sleeping sickness.
Euglenozoa
Kinetoplastida
Trypanosomatida
*Leishmania
*Trypanosoma
Class Trypanistomatida is a subclass of Class Kinetoplastida. As members
of a subclass of Class Kinetoplastida, members of Class Trypanistomatida con-
tain a unique and perplexing structure known as a kinetoplast. A kinetoplast is
a clump of DNA composed of multiple copies of the mitochondrial genome,
tucked inside a mitochondrion. All the members of Class Trypanistomatida are
parasitic (i.e., they spend much of their lives inside a host organism).
The members of class Trypanistomatida that are pathogenic in humans all
have a primary host (humans) and an insect serving as an intermediate host.
Members of Class Trypanistomatida have features that are either unique
to these organisms or that are seldom found in other organisms:
1.
Cell division is neither mitotic nor meiotic in members of Trypanistomatida.
The organelle in which the division process is focused is the kinetoplast
(a condensed mitochondrial genome). Each cell has one mitochondrion
containing one kinetoplast, and the time at which division of the organism
occurs is regulated by the cell cycle of the kinetoplast. The kinetoplast
divides, while the flagellum, anchored to the kinetoplast at the basal body,
replicates, permitting the cell to bifurcate into separate flagellate cells.
The nucleus replicates its DNA but never condenses into chromosomes; no
mitotic spindle is formed. Nuclear DNA migrates to the new cell when the
replicated kinetoplast and flagellum are formed. This features is completely
unique to Class Trypanistomatida.
2.
Replication occurs in primary and intermediate hosts. In most cases,
wherein a parasite has multiple hosts, reproduction occurs in the primary
host, and maturation occurs in the secondary host. In the case of members
of Class Trypanistomatida, parasites replicate in the primary (animal) and
the secondary (insect) hosts.
3.
Intracellular forms have flagella. Most flagellate parasites live extracellular
lives. Presumably, the flagella makes it hard to live inside a cell. It would
be like trying to open your umbrella in a phone booth. Most members of
Class Trypanistomatida have a so-called amastigote phase characterized by
a very small cell with a tiny, virtually invisible flagellum. Amastigotes are
