THE TICK GROUP 



1319 



the name 5. rossi Nuttall, 1908, for this new species; but recent 

 researches seem to have proved the identity of the two conditions. 



Climatology. — ^The disease is found in Angola, the Congo Free 

 State, Uganda, late German East Africa and Portuguese East 

 Africa, and in the Valley of the Zambesi. Franco, Robledo, and 

 others have described a spirochaetiasis in Colombia, which is caused 

 by a spirochaete morphologically resembling S. diittoni, and said 

 to be spread by Ornithodoros turicatus, with reference to which it 

 may be noted that Biildow observed relapsing fever in the Andes 

 in 1865. Robledo asserts that it is spread by the bite of Orni- 

 thodoros megnini. 



The climatic conditions required appear to be heat and moisture, 

 but according to Franco's observations, the disease can occur at an 

 altitude of 7,000 feet. No observations appear to be recorded as 

 to variations due to season. Carter's investigations would tend 

 to show that Arabian relapsing fever is either a separate form of 

 fever, or is allied to this West African form, as it may be spread by 

 an Ornithodoros. 



-ffitiology.— The cause of the fever is S. duttoni Novy and Knapp, 

 1906, which is proved to be distinct from the other spirochsetes, 

 because an animal immunized against one of these is capable of 

 being successfully inoculated by it. S. duttoni can be inoculated 

 into a number of animals — namely, dogs, goats, sheep, rabbits, 

 guinea-pigs, rats, and mice — ^but not into cats, chickens, pigeons, 

 or goldfish. The spirochaetes can pass through the placenta into 

 the circulation of the foetus, which they infect. These organisms 

 are easily seen in the blood during an attack, but disappear during 

 an apyrexial interval. The spirochaete is described on p. 444. 



The life-history in the vertebrate has been worked out by Breinl, 

 who, as already described, showed that just before the crisis the 

 spirochaetes become encysted and undergo schizogony into small 

 bodies, from which the new generation develop. Leishman has 

 demonstrated that when the spirochaetes pass into the intestinal 

 sac of the tick they lose their motility and their characteristic 

 appearance, while the central core of chromatin segments into 

 small masses, which are set free into the lumen of the gut. These 

 small bodies, which resemble small rods, or are rounded, like 

 micrococci, appear to multiply in the body of the tick, and to pass 

 into the cells of the Malpighian tubules and into the tissue of the 

 ovary. In the latter position they enter the immature eggs, and 

 can be traced through all stages of development into the adult 

 ticks. In the embryo, and in all the later stages of development up 

 to and including the adults, they are found as small chromatin 

 bodies lying in the cells of the Malpighian tubules. Inoculation of 

 crushed tissue containing these bodies produces a typical infection. 

 From his experiments, Leishman concludes that it is by these 

 chromatin bodies that the disease is carried from the egg to the 

 new generation of ticks, and that infection of man does not take 

 place via the salivary glands, but by the small bodies gaining access 



