CHAPTER X 



ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA 



[Continued] 



ARTHROPODS AND SPIROCH^ETOSES OF MAN AND ANIMALS 



The term spirochaetoses is applied to diseases of man or animals 

 which are due to protistan parasites belonging to the group of slender, 

 spiral organisms known as spirochaetes. 



There has been much discussion concerning the relationship of 

 the spirochaetes. Formerly, they were regarded as bacteria closely 

 related to the forms grouped in the genus Spirillum. The results 

 of the detailed study which the spirochaetes have received in 

 recent years, have led most of the workers to consider them as belong- 

 ing to the protozoa. The merits of the discussion we are not con- 

 cerned with here, but rather with the fact that a number of diseases 

 caused by spirochaetes are arthropod-borne. The better known of 

 these we shall discuss. 



African Relapsing Fever of Man It has long been known to the 

 natives of Africa and to travelers in that country, that the bite of a 

 certain tick, Ornithodoros moubata, may be followed by severe or 

 even fatal fever of the relapsing type. Until recent years, it was 

 supposed that the effect was due to some special virulence of the tick, 

 just as nagana of cattle was attributed to the direct effect of the bite 

 of the tsetse-fly. The disease is commonly known as "tick-fever" 

 or by the various native names of the tick. 



In 1 904, Ross and Milne, in Uganda, and Button and Todd on the 

 Congo, discovered that the cause of the disease is a spirochaete which 

 is transmitted by the tick. This organism has been designated by 

 Novy and Knapp as Spiroch&ta duttoni. 



Ornithodoros moubata (fig. 142), the carrier of African relapsing 

 fever, or "tick-fever," is widely distributed in tropical Africa, and 

 occurs in great numbers in the huts of natives, in the dust, cracks 

 and crevices of the dirt floors, or the walls. It feeds voraciously 

 on man as well as upon birds and mammals. Like others of the 

 Argasidce, it resembles the bed-bug in its habit of feeding primarily 

 at night. Button and Todd observed that the larval stage is under- 

 gone in the egg and that the first free stage is that of the octopod 



nymph. 



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