236 TABANIDAE AND DISEASE [CH. 



Generally the infection lasts at least one year in camels, 

 and in the month of June practically every herd contains 

 several individuals with numerous trypanosomes in the blood. 

 These animals would act as centres from which the infection 

 could be spread by the Tabanids. These latter feed during 

 the sunny hours of the day and usually attack the herd in 

 swarms. As a result of the active movements of the camels, 

 the insects are continually flying from one animal to another, 

 and the conditions are very favourable to the spread of any 

 infection. 



Horses may also be infected by the agency of these same 

 insects, but such cases are rare, as horses are not usually kept 

 in the neighbourhood of herds of camels. 



Three other trypanosome diseases, viz. Nagana, Mai de la 

 Zousfana and Dourine, have been transmitted experimentally 

 by the bites of various species of Tabanidae in Algeria. 



Transmission was only effected when the insects fed on the 

 healthy animals immediately after having bitten an animal 

 containing a great many trypanosomes in its blood. In no 

 case was any infection produced if there was an interval of 

 more than a few minutes between the two bites. A single 

 bite was sometimes sufficient to cause inoculation of the disease, 

 and therefore, under suitable conditions, it is probable that this 

 mode of transmission can assume great importance. 



According to Cazalbou, the disease of dromedaries at 

 Timbuctoo known as Mbori, and also Souma (T. cazalboui) at 

 Segou, a disease affecting horses and cattle, are both propagated 

 by Tabanus tceniatus, Macq. and T. biguttatus, Wied. 



There is evidence showing that Tabanidae are agents for the 

 transmission of Surra (T. evansi}. Thus Rogers, in the Fede- 

 rated Malay States, invariably produced the infection in dogs 

 and rabbits by the successive bites of many Tabanids. A dog 

 bitten by 12 flies that had just previously sucked blood from 

 another dog, heavily infected with T. evansi, shewed parasites 

 after an incubation period of seven days. 



Fraser and Symonds repeated these experiments employing 

 various species of Tabanus, Hczmatopota and Stomoxys. With 

 four species of Tabanus T. fumifer, T. partitus, T. vagus, and 



