THE AMOEBAE 



135 



4. GINGIVALIS GROUP. The nucleus 

 has a small, central endosome and a 

 ring of small peripheral granules. 

 There are no cysts. Members of this 

 group are found in the mouth. 



Entamoeba gingivalis of man, other 



primates, the dog and cat. 

 E)ita>noeba equibuccalis of the horse. 

 Entamoeba suigingivalis of the pig. 



5. INSUFFICIENTLY KNOWN SPECIES. 

 This group includes Entamoeba gedo- 

 etsti of the horse and E. caudata of 

 the dog. The nucleus of E. caudata 

 resembles that of E. coli, while the 

 nucleus of E. caudata resembles that 

 of E. histolytica. The cysts of these 

 species are unknown. 



The only species of Entamoeba patho- 

 genic for mammals is E. histolytica. The 

 fact that it has been recorded in an aver- 

 age of about 18% of the people examined in 

 various surveys thruout the world and yet 

 only about 1/5 of them have signs or symp- 

 toms of disease has puzzled epidemiolo- 

 gists for many years. Two other facts 

 contribute to the problem. One is that 

 there are two different sizes of these 

 amoebae, the smaller of which is not asso- 

 ciated with disease; it has been encountered 

 in about 1/3 of the people in these surveys. 

 The other is that amoebic dysentery occurs 

 mostly in the tropics. Autochthonous cases 

 occur so seldom in western Europe that 

 many European parasitologists believe that 

 cases of amoebic dysentery which occur in 

 their countries have been imported from 

 the tropics either directly or thru contact 

 with infected persons. These parasitolo- 

 gists have not had the benefit of the Amer- 

 ican experience with the disease. There 

 is no question that indigenous cases occur 

 in the temperate ZQne of this country. 



Several hypotheses have been advanced 

 in explanation (see Hoare, 1958). The 

 first theory, suggested about 1913 and still 

 held by perhaps the majority of parasitolo- 

 gists, is based on an unwillingness to 

 assign separate specific names to protozoa 

 which differ only in size and pathogenicity. 

 According to this view, the species Enta- 

 moeba histolytica is composed of a small 



race and a large race. The small race is 

 not pathogenic, while the large race may 

 or may not be. In its virulent phase the 

 latter invades the tissues; the tropho- 

 zoites of this phase are large- -the "magna" 

 form. In its commensal phase it remains 

 in the lumen of the intestine, feeding on 

 bacteria and saprozoically. The tropho- 

 zoites of this phase are small--the "minuta" 

 form. Under proper conditions, this non- 

 pathogenic "minuta" form can invade the 

 intestinal mucosa and turn into the patho- 

 genic "magna" form. The trophozoites of 

 the small race of E. histolytica are usually 

 12 to 15 |U in diameter and the cysts are 5 

 to 9|Li in diameter with a mean of 7 to 8/1. 

 The trophozoites of the "magna" form of 

 the large race are 20 to 30 jj, and those of 

 the "minuta" form 12 to 15 |U. in diameter. 

 However, the cysts of both the "magna" 

 and "minuta" forms are the same size, 10 

 to 20 jj, in diameter, with a mean of about 

 12^. 



The second theory was proposed by 

 Brumpt in 1925. He recognized 3 species. 

 He called the small, non- pathogenic race 

 Enta?noeba liartmanni, and divided the 

 large race into 2 species. Of these, E. 

 dispar is non- pathogenic and occurs thru- 

 out the world, while E. dysenteriae is 

 pathogenic, altho it may cause no apparent 

 symptoms in carriers, and occurs only in 

 warm and hot countries. 



The third theory was formulated for- 

 mally by Hoare in 1957. It calls the small, 

 non- pathogenic race E. hartmanni, but re- 

 tains the name E. histolytica for the large 

 race of the first theory. It then divides E. 

 histolytica into an avirulent race (corres- 

 ponding to Brumpt' s E. dispar) and a viru- 

 lent race (corresponding to Brumpt's E. 

 dysenteriae) which may invade the gut wall 

 or live in the lumen without causing symp- 

 toms. 



This view has a great deal to recom- 

 mend it. By giving the non- pathogenic 

 small form a separate name, it makes it 

 easier for the physician to interpret lab- 

 oratory reports and prevents faulty diag- 

 noses and needless treatment. However, 

 the question whether there actually are 

 completely non- pathogenic strains of E. 



