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Amoeba
are essentially everywhere and have probably existed in something like
there present form, long before the appearance of macroscopic
animals. Throughout our entire existence therefore, we have lived
in intimate association with amoebae. It is consequently no
surprise that some amoeba have adapted to take advantage of us.
However, the vast majority of amoeba collected from the environment are
found to be none pathogenic in the usual mouse model (Brown
et al, 1982).
By
far the most important pathogenic amoeba for humans is Entamoeba
histolytica, but Naegleria fowleri, Acanthamoeba, Balamuthia
and Hartmannella, have all been identified as being pathogenic
for humans. All these amoeba give rise to infections that are
treatable if their nature is recognised in time. More insidiously,
however, is that some amoebae play host to serious bacterial pathogens,
protecting them from disinfectants and allowing their multiplication
within amoebal cysts. These cysts can then enter the body where
they can constitute a lethal dose. It is even possible that amoeba
are the actual target that bacteria have evolved toxins for and that its
our bad luck that the biochemistry of our cells too are compatible with
these toxins as the machinery for all eukaryotes is so remarkably
conservative!
The fact that
common genera of amoebae give rise to medical problems in humans takes
the challenge of deriving a rational classification scheme for amoeba
(such as Naegleria and Acanthamoeba) from being an academic
exercise to being of immediate importance.
Entamoeba histolytica
This organism leads to 100,000 mortalities every year! (W.H.O.
1985). The amoeba
does not always kill the victim directly but so weakens that the
infected individuals succumb to other (mainly bacterial) pathogens.
Naegleria
A few species produce encephalitis. See Naegleria
pathogenesis.
Acanthamoeba
Some strains
(mainly from the T4 group) are pathogenic, causing keratitis and PAM. See Acanthamoeba
pathogenesis.
Balamuthia
Only one species of this genus is currently known, Balamuthia
mandrillaris and this produces a fatal encephalitis. See
Balamuthia.
Hartmannella
Accused by some of producing human keratitis. Amoeba that
are pathogenic for other species
Although less studied many amoeba cause devastating disease in plants
and animals, and some of these impact the environment and economy
indirectly. |
