The name is absent

Host-Parasite Relations in Amebiasis 25

According to his view, the large race of amebae with quadrinucleate cysts
comprises two types, which he regarded as independent species, E. dis-
par and E. dysenteriae (= our E. histolytica'). While E. dispar is a non-
pathogenic ameba inhabiting the human intestine throughout the world,
E. dysenteriae is the only pathogenic form responsible for amebic dysen-
tery and other clinical manifestations in warm and hot countries to which
this parasite is confined, though its virulence may be in abeyance in
carriers. Brumpt thus believed that the only ameba indigenous to coun-
tries with a temperate climate was the harmless E. dispar, while the
pathogenic E. dysenteriae is only occasionally introduced there by persons
who contracted their infection in hot countries. Among tire arguments in
favor of the independence of these two species Brumpt (1928) pointed
out that none of the factors which promote the development of clinical
symptoms in infections with E. dysenteriae has any effect on carriers of
E. dispar in temperate climates: thus, despite the presence of typhoid
fever and bacillary dysentery in France, amebic dysentery does not occur
there. On the other hand, in convalescent carriers, who had settled in
France, the exotic E. dysenteriae does not lose its virulence. In other
words, E. dispar and E. dysenteriae ‘Breed true.”

Strain variation. Brumpt’s ideas, which were based on epidemiological
data, were received with some scepticism during his life, but they have
now been vindicated by experimental investigations on the virulence of
strains of E. histolytica isolated from patients with different types of
amebiasis. Although recent work on these lines fully supports Brumpt’s
main thesis, the conclusions derived from earlier experiments were con-
tradictory (Dale & Dobell, 1917; Kessel, 1928; Meleney & Frye, 1933,
1935, 1937 and others), owing to misleading results obtained with kittens,
whose susceptibility and vulnerability to infection with E. histolytica are
exceptionally high. But with the introduction of rodents as experimental
hosts this question could be studied under conditions more closely re-
sembling those found in the human host. During the last few years this
subject has been thoroughly investigated by Neal (1951a, b; 1954, 1956a;
1957; Neal & Vincent, 1955, 1956), who demonstrated that strains from
symptomless human infections were invariably avirulent, producing no
lesions in experimentally infected rats, whereas strains from clinical cases
invaded the gut wall, causing typical ulceration. It was also shown that
the invasiveness of these strains was a stable property which could not be
modified by interchange of their floras, by diet, or by animal passages, for
through all these manipulations the strains retained their original peculi-
arities. The avirulence of strains from symptomless cases and the viru-
lence of strains from clinical cases were recently confirmed in rabbits by
Hunninen & Boone (1957), while Beaver et al. (1956), who infected 46

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