340 



THE ARACHNOIDS 



Genus Argas. Body narrow in front. Margins thin and acute. No eyes. 

 The A. persicus (Miana bug) of Persia has been supposed to be concerned in the 

 transmission of a serious disease. Rostrum some distance from anterior margin. 

 It is also called the fowl tick and transmits fowl spirillosis. 



Genus Ornithodoros. Margins of body rounded. Skin has many irregular 

 tubercles. Rostrum even with anterior margin so that ends of palpi slightly project. 

 It is the intermediate host of Spirochata duttoni. (South African tick fever.) 



0. moubata is very common in Africa living in cracks in mud floors and bites 

 severely the sleeping natives. The larva makes its first moult inside the egg so 

 that it shows four pairs of legs when it emerges. Christy thinks it may transmit 

 Filaria perstans. 



Tick Fever. With tick fever the epidemiology rests upon the 

 life history of the tick 0. moubata. This tick infests the rest houses 



FIG. 80. Ornithodoros moubata. (Murray from Doflein.) 



along the route of travel, hiding in the crevices of floors and walls during 

 the day and coming out at night to bite the sleeping inmates. The 

 feeding occupies a long time, more than an hour. Both sexes bite man. 

 The female lays about 100 eggs, from which a nymph emerges in about 

 twenty days. The larval stage takes place in the egg. Shortly after 

 emerging the nymphs suck blood. An important fact is that the female 

 transmits the spirochaete to its ova, so that the nymphs may transmit 

 the disease. 



Natives seem to sutler severely from tick fever in childhood but in adult life 

 possess a sufficient degree of immunity so that the disease shows itself in a very 

 mild form in those harboring spiroch<etes. Ticks can be infected by these carriers. 

 In some of the rest houses 50% of the ticks may be infected. While the tick does not 



