Cattle Ticks and Texas Fever 



225 



These results have been fully confirmed by workers in different 

 parts of the world, — notably by Koch, in Africa, and by Pound, in 

 Australia. 



The disease is apparently transmitted by Boophilus annulatus 

 alone, in the United States, but it, or an almost identical disease, 

 is conveyed by Ixodes hexagonus in Norway, Ixodes ricinus in Finland 

 and France and by the three species, Boophilus decoloratus, Hyalomma 

 CBgypticum (fig. 140 and 141), and Hcemaphysalis punctata in Africa. 

 In spite of the detailed study which it has received, the life cycle 

 of Babesia bovis has not been satisfactorily worked out. The asexual 



reproduction in the 

 ^ /^ blood of the vertebrate 



host has been described 

 but the cycle in the tick 

 is practically unknown. 

 More successful 

 attempts have been 

 made to work out the life 

 cycle of a related species , 

 Babesia canis, which 

 causes malignant jaun- 

 dice in dogs in Africa 

 and parts of Southern 

 Europe. In this in- 

 stance, also, the disease 

 is transmitted by heredity to the ticks of the second generation. 

 Yet the larval, or "seed ticks," from an infected female are not 

 capable of conveying the disease, but only the nymphs and adults. 

 Still more complicated is the condition in the case of Babesia ovis of 

 sheep, which Motas has shown can be conveyed solely by the adult, 

 sexually mature ticks of the second generation. 



In Babesis canis, Christopher (1907) observed developmental 

 stages in the tick. He found in the stomach of adult ticks, large 

 motile club-shaped bodies which he considered as ookinetes. These 

 bodies pass to the ovaries of the tick and enter the eggs where they 

 become globular in form and probably represent an oocyst. This 

 breaks up into a number of sporoblasts which enter the tissues of 

 the developing tick and give rise to numerous sporozoites, which 

 collect in the salivary glands and thence are transferred to the 

 vertebrate host. A number of other species of Babesia are known 



141. Hyalomma aegypticum. Capitulum of female; 

 (a) dorsal, (b) ventral aspect. 



