Dear Dr Raad 

Some information about epidemiology, ecology and the types of diseases caused by these pathogens amoebae were reviewed in this paper:

Trabelsi, H., F. Dendana, A. Sellami, H. Sellami, F. Cheikhrouhou, S. Neji, F. Makni, and A. Ayadi. "Pathogenic free-living amoebae: epidemiology and clinical review." Pathologie Biologie 60, no. 6 (2012): 399-405.

Acanthamoeba spp. are also responsible for amoebic keratitis. Some of the infections are opportunistic, occurring mainly in immunocompromised hosts (Acanthamoeba and Balamuthia encephalitides), while others are non-opportunistic (Acanthamoeba keratitis, Naegleria meningoencephalitis, and cases of Balamuthia encephalitis occurring in immunocompetent humans). The amoebae have a cosmopolitan distribution in soil and water, providing multiple opportunities for contacts with humans and animals, as evidenced by antibody titers in surveyed human populations.

t has long been admits that not all strains of E. histolytica are pathogenic. Non-pathogenic strains can be isolated from asymptomatic patients and are prevalent among homosexual men living in the United States and England. The pathogenic strains and nonpathogenic can not be distinguished by microscopy, except for the fact that the pathogenic trophozoites often phagocyte erythrocytes. Based on biochemical, immunological and genetic data, E. histolytica was then redescribed. A new species, E. dispar, now is not the pathogenic isolates and apparently is not invasive in humans, while E. histolytica comprises only potentially pathogenic strains. Since not all potentially pathogenic strains of E. histolytica invariably produce disease, other processes undoubtedly influence the amoebic virulence.

It was developed an immunoassay to distinguish between E. histolytica and E. dispar, a lectin based on N-acetyl-D-galactosamine specific for E. histolytica. Currently, there is no method available that allows commercial diagnostic laboratories make an immediate distinction between these bodies [see Diagnostics, below], even though both may be distinguished by observing the differences in isozymes, restriction fragment patterns, repetitive DNA and riboprinting.

The cysts eliminated in human feces are the main responsible for human infections. The acquisition of infection is fecal-oral contamination and can occur via transmission by water or food, as well as via interpersonal transmission. The latter form of transmission contributes to the increased prevalence of E. histolytica infection among promiscuous homosexual men and institutions where there is fecal incontinence and poor hygiene. The amebiasis is most common in lower socioeconomic groups than in the general population due to lack of sanitation and excessive overcrowding. In the United States, there have been reports of individuals who returned from international travel or who immigrated from areas where amoebiasis is endemic.