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Pathogenic Amoebae

Page updated 13.8.03

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. 

 

References:-

Brown, T. J., Cursons, R. T. M. & Keys, E. A. (1982) Amoebae from Antarctic soil and water.  Appl.Environmental Microbiol. 44, 491-493.

World Health Organisation (1985). WHO Bull. 63, 417-426.

 
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