ENTOMOLOGY 299 



basin and the latter in Algeria. T. dispar is transmitted by Hya- 

 lomma mauritanicum Senevet, and it is of interest to note that the 

 survival of infected nymphs, which hibernate during the winter 

 months, is largely responsible for the carrying-over of the disease 

 from year to year. 



In East Africa, it has been shown by Montgomery (191 7) and 

 Daubney and Hudson (1931a) that Nairobi sheep disease, a highly 

 fatal virus disease of sheep and goats, is mainly transmitted by R. 

 appendiculatus, the common vector of east coast fever, but that in 

 certain areas where R. appendiculatus does not occur, the virus may 

 also be transmitted by Amblyomma variegatum (Daubney and Hud- 

 son 1931a and 1934). 



Another disease of cattle, sheep, and goats which can occasion 

 severe mortality is heart- water. The causal parasite of this disease, 

 Rickettsia ruminantium, was discovered by Cowdry (1925) working at 

 Onderstepoort. In South Africa heart-water is transmitted by 

 Amblyomma hebraeum (Lounsbury 1902a and b), and it is likely that 

 this tick continues to serve as a vector for heart-water up to the nor- 

 thern limit of its distribution in East Africa, which is probably 

 somewhere in the south of Tanganyika. In Kenya it has been 

 shown that heart- water is naturally transmitted by A. variegatum, 

 which is widely distributed throughout the Colony (Daubney 

 1930). It is possible that another menl^ber of the genus Amblyomma 

 may, in certain areas, also act as a vector of heart- water. 



The only satisfactory means of controlling the tick-borne proto- 

 zoan diseases is dipping or hand-dressing of stock, coupled with 

 fencing of pastures to prevent trespass of undipped cattle. The 

 manner in which these measures affect the ticks is mentioned in 

 Chapter XIV. 



Myiasis or Screw-worm of cattle, sheep, horses, and dogs is 

 common in many parts of Africa. It is due to infection by blow- 

 flies, of which Chrysomyia bezziania Villen is the commonest in 

 Rhodesia, and is widely distributed in Kenya, although Lucilia 

 cuprina Wied. also causes myiasis in sheep in both territories, as 

 shown by Smit (1931) and Lewis (1933). A good deal of valuable 

 research has been done on various dressings for large open wounds 

 and on substances to be applied after larval and egg-masses have 

 been removed from infected animals. The necessity of ensuring 



