PROTOZOAN PARASITES OF MONKEYS AND MAN 



z 4 i 



set up in the laboratory, but the lower 

 animals are obviously not natural hosts 

 of human protozoa and only become 

 infected with them in nature under 

 extraordinary conditions (Hegner, 19x6a). 

 In susceptible lower animals the course of 

 the infection is often very different from 

 that in monkeys and man. For example, 

 the course of amoebiasis in man usually 

 includes a rather long incubation period, 

 followed by acute dysentery from which 

 the patient recovers in a carrier condition, 

 i.e., the infection continues but is kept 

 down by the resistance of the body below 

 the point at which symptoms appear. 

 Active amoebae only are present during 

 the dysenteric period and chiefly cysts are 

 passed during the carrier period; whereas 

 in cats the incubation period is short, 

 death usually occurs as the result of 

 acute dysentery, and no cysts are formed 

 at any time. In monkeys amoebic dysen- 

 tery runs a course similar to that in man. 



PROTOZOAN PARASITES AND THE GENETIC 

 RELATIONSHIP OF HOSTS 



Parasites have been used to a slight 

 extent in the study of the genetic relation- 

 ships of hosts. Von Jhering in 1901 was 

 among the first to discuss this problem in 

 cases of parasitic worms. He argues that 

 two species of hosts are of common 

 descent if they are parasitized by the same 

 species or nearly related species of para- 

 sites. He believes that the close relation- 

 ship of the parasites indicates that they 

 come from a common ancestor and that 

 the different species of hosts involved 

 descended from an ancestral host that was 

 infected by the ancestral parasite. The 

 most important work of this type involv- 

 ing protozoa is that of Metcalf (192.3) on 

 frogs and their ciliate parasites of the 

 family Opalinidae. Metcalf discusses, for 

 example, the distribution of the family 

 Leptodactylidae. These are "frogs" 



characteristic of two widely separated 

 geographical regions, (1) tropical and 

 semi-tropical America and (2.) Australia 

 and Tasmania; they have been reported 

 from no other parts of the world. There 

 are two hypotheses that may account for 

 this discontinuous distribution: (1) there 

 may have been a former connection 

 between Patagonia and Australia by way 

 of Antarctica over which these frogs 

 were continuously distributed, or (2.) re- 

 semblances of the frogs of America and 

 Australia may be due to convergent or 

 parallel evolution. 



Frogs of the family Leptodactylidae 

 contain, in the rectum, opalinid parasites 

 of the genus Zelkriella. These parasitic 

 ciliates are present in frogs of this family 

 living in both America and Australia. 

 They are so nearly alike in the frogs of the 

 two regions that they can be separated 

 specifically only with difficulty. It is 

 possible that either the frogs or the 

 opalinid ciliates may have arisen by 

 convergent or parallel evolution. It 

 seems very improbable, however, that 

 both the frogs and opalinids arose in this 

 way. The conclusion is reached that the 

 first hypothesis is correct and that a 

 former land connection existed between 

 Patagonia and Australia by means of 

 which frogs of this family, together with 

 their opalinid parasites, migrated to 

 Australia. 



PROTOZOAN PARASITES AND THE GENETIC 

 RELATIONSHIPS OF MONKEYS AND MAN 



So far as known to the writer no studies 

 have been made to determine genetic 

 relationships among monkeys with the 

 aid of their parasitic protozoa. In fact, 

 probably not enough is known regarding 

 the protozoa of monkeys to make such a 

 study profitable at present. However, as 

 the data compiled in this paper indicate, 





