232 Arthropods as Essential Hosts of Pathogenic Protozoa 



The evidence that the fever is transmitted by this tick is con- 

 clusive. Koch found that from five per cent to fifteen per cent, and 

 in some places, fifty per cent of the ticks captured, harbored the 

 spirochaete. The disease is readily transmitted to monkeys, rats, 

 mice and other animals and the earlier experiments along these lines 

 have been confirmed by many workers. 



Not only are the ticks which have fed on infected individuals 

 capable of conveying the disease to healthy animals but they trans- 

 mit the causative organism to their progeny. Thus Mollers (1907), 

 working in Berlin, repeatedly infected monkeys through the bites 

 of nymphs which had been bred in the laboratory from infected ticks. 

 Still more astonishing was his discovery that ticks of the third genera- 

 tion were infective. In other words, if the progeny of infected ticks 

 were fed throughout life on healthy animals, and on maturity de- 

 posited eggs, the nymphs which hatched from these eggs would still 

 be capable of carrying the infection. 



The developmental cycle of the spirochsete within the tick has not 

 been fully worked out, though the general conclusions of Leishman 

 (1910) have been supported by the recent works of Balfour (1911 

 and 1912), and Hindle (1912), on the life cycle of spirochaetes affect- 

 ing fowls. 



Spirochceta duttoni ingested by Ornithodoros moubata apparently 

 disappear within a few days, but Leishman believed that in reality 

 they break up into minute granules which are to be found in the 

 alimentary canal, the salivary glands and the Malpighian tubes of 

 the tick. These granules, or "coccoid bodies," as Hindle calls them, 

 are supposed to be the form in which the spirochaetes infect the new 

 host. We shall see later that Marchoux and Couvy (1913) dis- 

 sent wholly from this interpretation. 



According to Leishman, and Hindle, the coccoid bodies are not 

 injected into the vertebrate host with the saliva of the tick, as are 

 the sporozoites of malaria with that of the mosquito. Instead, they 

 pass out with the excrement and secondarily gain access to the 

 wound inflicted by the tick. 



Nuttall (1912) calls attention to the fact that the geographical 

 distribution of Ornithodoros moubata is far wider than our present 

 records show for the distribution of the relapsing fever in man and 

 that there is every reason to fear the extension of the disease. Huts 

 where the ticks occur should be avoided and it should be remembered 

 that in infected localities there is special danger in sleeping on the 

 ground. 



