300 SCIENCE IN AFRICA 



that all larvae removed from wounds are effectively destroyed has 

 been demonstrated, especially in Southern Rhodesia by Lawrence 

 and Cuthbertson (1934). This is a precaution which is apt to be 

 neglected, with the result that large numbers of adult flies are bred 

 unnecessarily, and the mustering pens tend to become centres of 

 infestation. 



There are several important non-contagious virus diseases of 

 stock in Africa. Blue-tongue of sheep and horse-sickness have much 

 the same distribution in South Africa and Kenya, the two coun- 

 tries where they have been investigated. At Onderstepoort exten- 

 sive observations have been made on the capacity of these two 

 viruses to survive in mosquitoes. In two out of thirty-five experi- 

 ments the virus of horse-sickness was shown to have survived in 

 Aedes cab alius and A. lineatopennis, but the results of the whole series 

 of experiments forced the workers to the conclusion that Aedes 

 species are very probably not the natural transmitters of horse- 

 sickness (Nieschulz, Bedford, and du Toit 1934a). In the experi- 

 ments with blue-tongue virus, A. lineatopennis was twice shown to 

 have retained virus from fifteen to nineteen days, but the same 

 workers ( 1 934b) conclude that the problem of natural transmis- 

 sion has not been solved. 



A virus disease of sheep, cattle, and man, which has resemblances 

 to both dengue and yellow fever, was discovered in 1930 in Kenya 

 and named rift valley fever by Daubney and Hudson (1931b). Its 

 existence has recently been suspected in the French West African 

 territories. It has been shown by Findlay and Daubney (1931) 

 that rift valley fever is immunologically distinct from yellow fever 

 and dengue, and that mosquitoes of the genus Mansonia are ex- 

 perimental vectors (Daubney and Hudson 1933). There is evi- 

 dence also that one of these species, Mansonia fuscopennata (Theo- 

 bald), may acquire infection during the course of a natural out- 

 break. 



