g04 Tn'panosome Diseases. 



Prevention. Excepting dourine, wliicli can be controlled 

 by comparatively simple measures in the supervision of breed- 

 ing and may be entirely eradicated, the prophylaxis of the 

 tr^^^anosome diseases consists above all in the eradication of 

 the flies which play a part as transmitters, and probably also 

 as hosts for the virus. The procedure must of course be suited 

 to their habits of life and their modes of de^^elopment. In the 

 glossinae and tabanidae, which confine themselves to certain 

 forests and marshy localities, and probably also to certain wild 

 species of animals, the eradication in practice succeeds at least 

 in small territories, by cutting of the bushes, and draining of 

 the meadows. Besides regular cultivation of the soil, the de- 

 struction of the game, or keeping it from the roads of traffic, 

 or confining it to certain reservations would aid in the elimina- 

 tion of the source of infection. The species of stomoxys which 

 exist in close proximity to living houses and stables, may be 

 reduced in numbers by cleanliness, as well as by the destruction 

 of all vegetable refuse. 



As the flies do not accompany the cattle herds for great 

 distances, and as they do not swarm during the night, threatened 

 herds may be protected from infection by driving them at night 

 to non-infected localities, avoiding rivers, thus keeping them 

 from the virus carriers. 



In practice the control of trypanosomiasis is rendered more 

 difficult by the fact that not only affected, but also apparently 

 perfectly healthy, and especially the animals which have re- 

 covered from the disease harbor trypanosomes in their blood 

 for years. Such virus carriers constantly produce virulent 

 material for flies in infected territories, and may, on the other 

 hand, disseminate the virus into previously non-infected terri- 

 tories. By the destruction of all such virus carriers the source 

 of the infection for the flies could be destroyed, but such a pro- 

 cedure could only come into consideration in small, freshly 

 infected territories. 



For countries which are free of certain trypanosome affec- 

 tions careful quarantine measures, or even the prohibition of 

 the importation of susceptible species of animals from infected 

 territories, comes into consideration. 



Immunization. Immunization experiments with senim of recov- 

 ered animals and those repeatedly treated with virulent blood (Zie- 

 mann), or with blood containing parasites and subjected to high or low 

 temperatures, have not yet given manifest results (Uhlenhuth, Gross & 

 Biekel). The same applies to the experiments which have been carried 

 out by passage of the virus through various species of animals (Koch, 

 Schilling, Martini). In the efforts to work out a method for active im- 

 munization the fact must be considered that the immunized animals 

 harbor the parasites for years, and these may later become virulent, and 

 sometimes may be transmitted to healthy animals in such a condition. 



The fact that animals acquire, through recovery from certain trypanosomiasis, 

 a lasting although not an absolute immunity against the same and not against other 



