The natural form of blackhead, although very fatal to young turkeys, is favorably influenced by treatment with certain of the newer arsenical compounds.
Neoarsphenamine injected intravenously in toxic doses has a somewhat favorable effect on the course of the spontaneous disease and evidently lowers the mortality. Its instability, its pronounced toxicity for young turkeys, as well as the difficulty of obtaining amounts suitable for the cases to be treated on any one occasion, serve to make its employment impracticable.
Less favorable results were obtained with atoxyl.
Arsenious acid fed daily in small doses failed to prevent blackhead and possibly increased the incidence of infection. In larger doses it failed to cure spontaneous blackhead.
Tryparsamide may be injected in cases of spontaneous blackhead in doses as high as 1 gm. per kilo of body weight either intravenously or subcutaneously without serious toxic effect. Prompt clinical improvement usually follows and the mortality is undoubtedly greatly lowered.
With inoculated blackhead recovery is more difficult to obtain. Birds treated by injections of either neoarsphenamine or atoxyl failed to recover. There were two recoveries among three tryparsamidetreated cases. An attempt to cure inoculated blackhead at an advanced stage by the injection of tryparsamide failed.
The study of the lesions of treated turkeys shows that tryparsamide, and to some extent neoarsphenamine, have a more pronounced effect on the liver lesions than on the disease in the lung, which accounts for the discrepancy in the results of the treatment of spontaneous and inoculated blackhead. There is histological evidence of prompt absorption of necrotic liver parenchyma; moreover, the protozoa are destroyed more rapidly in the liver than in the lung.
Tryparsamide has the most pronounced curative action on blackhead infection of any of the drugs thus far tested. Either intravenous or subcutaneous injection of appropriate doses of this drug at the first appearance of symptoms should serve to cure the majority of cases of blackhead.