Researches on the Intestinal Protozoa of Monkeys and Man

Abstract

Amoebae of the genusEndolimaxhave been found naturally inhabiting the large intestine of 3 species ofMacacus (M. sinicus [= radiatus], M. rhesus [= mulatto], M. nemestrinus).In all these hosts the amoebae are morphologically and culturally identical, at all stages of development, and are indistinguishable by any structural or cultural character fromEndolimax nanaof Man—with which they have been carefully compared. The several forms have been studied in “pure” culture (i.e., free from all other protozoa, but accompanied by bacteria suitable for their growth).TheEndolimaxofM. sinicus, isolated in “pure” culture, has been experimentally transmitted to an uninfected man by the natural route (cystsper os): and in this human subject it has produced an infection indistinguishable from a natural one withE. nana. The induced infection has now persisted unchanged for close on 8 years.From the experimentally infected man the amoeba has been artificially transmitted to an uninfectedM. rhesus, in which it gave rise to an infection—likewise indistinguishable from a natural simian infection—which persisted for the rest of the monkey's life (2½ years).Some further information is given about the distribution, cultivation, emetine-resistance, and other peculiarities of the forms ofEndolimaxfound in Macaques and Man; and the findings of other workers with similar organisms are briefly considered. From all the evidence available it is concluded thatE. nananaturally lives not only in Man but also in at least 3 different species of Macacus, and probably in monkeys of this genus generally. As yet there is no evidence that more than one species ofEndolimaxinhabits any of these hosts.Infections withE. nana, whether in Man or Macaques, have usually been found to endure indefinitely; but a case (M. rhesus) has been observed in which the infection appears to have died out spontaneously after persisting for a known period of over 6 years.Attempts to infect kittens withE. nanahave all been unsuccessful hitherto, but there is evidence (from the work of others) that this amoeba may inhabit some other domestic mammals. Its host-distribution in nature needs further investigation.