transmission of tropical diseases. 13 



Spirochaetes. 



These give rise to relapsing fever in man. The term 

 relapsing is a very appropriate one, for after a fever lasting 

 some days and a period of apyrexia, the whole train of symptoms 

 recurs again. There may be more than one relapse, but the 

 succeeding relapses are not so intense as the original fever. 

 The disease is due to the presence of spirochaetes in the blood 

 which, however, disappear therefrom in the interval between 

 the attacks. There are many species of spirochaete described 

 in man. It will suffice to mention two only, viz., Sp. duttoni, 

 producing the African disease, and Sp. recurrentis, producing 

 the European form. The African disease is transmitted by 

 ticks and the European probably by lice. In the African 

 form the tick involved is known as Ornithodorus moubata. 

 It is a dirty-looking, brown, wrinkled tick, and frequents 

 rest-houses where it is found in the walls, thatch, etc., and 

 is found in the dust around trees where caravans halt. 

 Unlike most ticks, after feeding it crawls away. The tick 

 is infective probably directly after biting. The life cycle 

 of the spirochaete is, however, believed to be the following. The 

 spirochaete in the gut of the tick breaks up into numerous 

 ovoid granules resembling small bacilli. These pass into the 

 cells of the malpighian tubules and into the ovary. When 

 the tick bites, these ovoid bodies are voided in the faeces 

 and so contaminate the coxal fluid which is secreted when 

 the tick bites, and so presumably the wound. Those that 

 reach the ovary pass through the egg and nymph into the 

 adult tick, so that the disease is transmitted from mother to 

 offspring. This is said to hold good also for a second generation . 

 Others, however, doubt the infective nature of the ovoid 

 granules. 



Nothing much is known at present as to the mode of 



