Host-Parasite Relations in Amebiasis 27
The changing views on the etiology of amebiasis are summarized in
the following table:
Etiology of Amebiasis
|
HYPOTHESES |
UNICISTIC 1913- |
DUALISTIC 1925- |
Neo-Dualistic 1957 |
|
E. histolytica | |||
|
Non-Pathogenic |
SSlfΛΛ. RACE |
E. hartmanni |
E. hartmanni |
|
amebiasis |
LARGE RACE: Commensal phase I I I I I |
E. dispar |
E. histolytica |
|
PATHOGENIC AMEBIASIS |
E. Iysenteriae |
E. histolytica Virulent large race: | |
|
Subelinical |
I I |
Dormant in lumen of ↑ I | |
|
Clinical |
I . I Virulent (tissue) phase |
I 1 |
Pathogenesis. We now turn to a consideration of the factors which are
held to be responsible for the activation of the dormant virulence of the
invasive race of E. histolytica. One of the most important factors influenc-
ing the course of amebic infection is the intestinal flora. It is well known
that the role played by bacteria in the life of E. histolytica is so essential
that their association appears to be almost symbiotic. Thus, there is con-
clusive evidence that bacteria (or other suitable living cells) are indis-
pensable for the maintenance and development of this ameba in vitro
(cf. Dobell & Neal, 1952), and it has been demonstrated in vivo that the
amebae are unable to establish an infection in “germ-free” animals (Phil-
lips et al., 1955). The intestinal flora not only serves as a source of food
and of some unknown growth factors promoting the survival of E. histoly-
tica in the lumen of the host’s gut, but, according to many authors (West-
phal, 1937, 1938; Deschiens, 1938; Phillips et al., 1955, and others), it
plays a major part in the pathogenesis of amebiasis, especially when viru-
lent bacteria are present (Westphal, 1937, 1948). According to this view,
the normal mucosa of the gut wall is resistant to penetration by the