CHAPTER XLVIII 



INTESTINAL PROTOZOA OF MAN AND THEIR 

 HOST-PARASITE RELATIONS 



ROBERT HEGNER ■ 



Johns Hopkins School of Hygiene and Public Health 



PROTOZOA THAT LIVE IN MAN 

 CLASSIFICATION ACCORDING TO HABITAT 



At the present time twenty-five species of protozoa are recognized by most au- 

 thorities as human parasites. Many other protozoa have been recorded from man; 

 most of these are simply well-known species that varied in certain respects from the 

 normal condition; others may be new species but have not yet been sufficiently 

 studied to warrant their inclusion here. These twenty-five species may be separated 

 into three groups according to their habitats. In the first place, the so-called "in- 

 testinal protozoa" include six species of amebae, seven species of flagellates, one 

 coccidium, and one ciliate; these live in the mouth, intestine, vagina, or urinary tract. 

 The second group contains nine species of blood-inhabiting protozoa; these include 

 three species of trypanosomes, three leishmanias, and three plasmodia. The last 

 species in the list is a muscle parasite known as Sarcocysiis. We know very little about 

 this species in man; it may be a regular inhabitant of some lower animal which on 

 rare occasions succeeds in establishing itself in a human being. In this chapter only ■ 

 the intestinal protozoa will be considered. 



THE INTESTINAL PROTOZOA LIVING IN MAN 



As indicated above, the intestinal protozoa of man include representatives of all 

 four of the major groups of protozoa. The amebae belong to the class Sarcodina; the 

 flagellates to the class Mastigophora; the coccidium to the class Sporozoa; and the 

 ciliate to the class Infusoria. The morphological characteristics of these various 

 organisms are iUustrated in the accompanying figures. 



The amebae (Figs. 1-5) are characterized by a body that changes its shape frequently 

 and possesses pseudopodia as locomotor organs. The structure of greatest importance in 

 classification is the nucleus. The genus Endamoeba (Figs, i, 2, 4) has a spherical nucleus 

 containing a spherical karyosome and a layer of chromatin granules on the nuclear mem- 

 brane. The members of the genus Endolimax (Fig. 5) have a nucleus with a large and often 

 irregular karyosome but free from chromatin granules on the nuclear membrane. lodamocba 

 ivilliamsi (Fig. 3) possesses a nucleus with a large karyosome which is surrounded by a layer 

 of achromatic granules. Dieiilamoeba fragilis frequently contains two nuclei, each of which 

 has a karyosome consisting of a number of chromatin granules embedded in an achromatic 

 matrix. 



The intestinal tlagellates (Figs. 6, 7, and 8) belong to five genera. The genus Tricho- 

 moiias (Fig. 7) is characterized b>' the presence of an undulating membrane and an axostyle 

 which extends through the center of the body antero-posteriorly. Chilomastix (Fig. 6) 



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