PROTOZOAN PARASITES OF MONKEYS AND MAN 



2.2.J 



Hundreds of different species of intes- 

 tinal protozoa have been reported from 

 man, but careful study indicates that most 

 of these are not separate species. On the 

 basis of our present knowledge we may 

 recognize six species of amoebae (Sarco- 

 dina), seven species of flagellates (Ma- 

 stigophora), one species of coccidium 

 (Sporozoa), and one species of ciliate 

 (Infusoria). All of these protozoa appear 

 to be world wide in their distribution, 

 and no differences as regards racial suscep- 

 tibility have been established with cer- 

 tainty; resistance of the individual, how- 

 ever, appears to increase with age. The 

 location of these species in the body and 

 the approximate incidence of infection 

 among the general population are as 

 follows : 



Mouth: percent 



Endamoeba gingivalis 



(Amoeba) 50 



Trichomonas buccalis 



(Flagellate) 10-30 



- Small intestine: 



Giardia lamblia (Flagel- 

 late) 10 



Isospora hominis (Coc- 

 cidium) ? 



Large intestine: 



Endamoeba histolytica 



(Amoeba) 10 



Endamoeba colt 



(Amoeba) 50 



Endolimax nana 



(Amoeba) 15 



lodamoeba williamsi 



(Amoeba) 10 



Dientamoeba fragilis 



(Amoeba) ? 



Trichomonas hominis 



(Flagellate) 5-zo 



Chilomastix mtsnili 



(Flagellate) 10 



Embadomonas intestin- 



alts (Flagellate) ? 



Tricercomonas intestinalis 



(Flagellate) ? 



Balantidium coli 



(Ciliate) ? 



Vagina and urinary tract: 

 Trichomonas vaginalis 



(Flagellate) 10-50 (in women) 



Two points of particular interest 

 brought out by these data are the high 

 incidence of infection with certain species 

 and the differences in incidence among the 

 various species. It is evident that man 

 is very susceptible to infection with 

 such species as Endamoeba gingivalis, Tricho- 

 monas buccalis, Endamoeba coli, and Tricho- 

 monas vaginalis. It is also obvious that 

 these species have little difficulty in 

 gaining entrance to the human body. 

 The two species that inhabit the oral 

 cavity are no doubt frequently passed from 

 mouth to mouth during kissing, and 

 probably no one escapes contamination 

 with these protozoa. The intestinal 

 species are mostly transmitted in the cyst 

 stage and the high incidence of infection 

 indicates that contamination of food and 

 drink with feces containing cysts is 

 frequent and widespread. 



The facts regarding the pathogenicity 

 of human intestinal protozoa may be 

 stated briefly as follows. Endamoeba 

 histolytica is pathogenic especially in 

 tropical and semitropical regions; it is the 

 etiological agent of amoebic dysentery and 

 amoebic liver abscess, and is frequently 

 fatal. Most of those infected with this 

 species are carriers and do not exhibit 

 symptoms. Endamoeba coli and Endamoeba 

 gingivalis may be pathogenic but this has 

 not yet been definitely proven. The other 

 species of amoebae appear to be harmless. 

 Of the flagellates, Giardia lamblia, Tricho- 

 monas hominis, and Chilomastix mesnili, 

 have been accused of causing "flagellate 

 diarrhea;" but their actual relation to the 

 diarrheic condition is not certain; Tricho- 

 monas buccalis seems to be more frequent in 

 persons suffering from pyorrhea, acute 

 gingivitis, or abscessed teeth than in 

 normal mouths (Hogue, 19x6; Hinshaw, 

 19x6), but are probably not responsible for 

 these diseases; Trichomonas vaginalis is 

 more common when the vaginal mucus 

 is in an abnormal condition but its relation 

 to the host is still uncertain; the other 



