The name is absent

THE ENIGMA OF HOST-PARASITE RELATIONS
IN AMEBIASIS

Cecil A. Hoare, F.R.S.

Wellcome Laboratories of Tropical Medicine, London, England

“The clear definition of a difficulty frequently hastens the advance
of science by indicating a pitfall or a wrong road of inquiry."”

Clifford Dobell. 1919.

IN A GENERAL way it may be said that the host-parasite relationship
in any infection is concerned with the interaction between parasite
and host, which are in constant conflict, the virulence of the former strug-
gling to overcome the resistance of the latter. In the case of amebiasis,
the progress in our knowledge of the actions and reactions of the two
components of the host-parasite system has been unequal, and certain
aspects of their association are still obscure.

The successful maintenance of Entamoeba histolytica in cultures and
recent developments in the technique of animal experimentation have
provided useful tools for the study of this problem, but, while notable
advances have been made in our knowledge concerning the life history
of the parasite and its effect upon the host, very little is known about the
way the host reacts against the amebic infection. And indeed, most of the
information regarding immunity and resistance in amebiasis is based
upon circumstantial evidence rather than upon experimentally estab-
lished facts.

Action of Pabasγγe on Host

Unicism. For a critical appraisal of the role played by the human host
in the course of amebiasis, it will be necessary to review the available
data regarding the behavior of E. histolytica in the infection. One of the
most important facts concerning the etiology of amebiasis is that, in the
great majority of cases of infection throughout the world, E. histolytica
lives in the lumen of the human gut as a commensal without causing any
damage to its wall or detectable symptoms of disease (Hoare, 1952). Fur-
thermore, among these symptomless infections a distinction should be
made between those with the small and large races of E. histolytica. It is
now generally admitted that the small race is inoffensive and—as far as
its medical importance is concerned—should therefore be placed among
the other non-pathogenic amebae of man, such as E. coli, Endolimax and
Iodamoeba (Hoare, 1952, 1957; RidIey & Schofield, 1957). Moreover, the

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