Further Studies on "Blackhead" in Turkeys, with Special Reference to Transmission by Inoculation

Abstract

Although the parasite causing the disease in* turkeys popularly known as was discovered many years ago, the mode of its transmission has not been satisfactorily demonstrated. Several distinct problems are involved in this question of transmission: (1) the source of the parasite; (2) the route by which it enters the body of the turkey, and (3) its pathogenic properties or virulence. Whether the parasite of blackhead, Histomonas meleagridis, occurs only in association with the disease, and is thus to be regarded as uniformly pathogenic, or is widely prevalent in the cecal contents of normal turkeys, and only invades the tissues under conditions which lower the host's resistance, has, up to the present, been regarded as a more or less open question. The possibility that this organism, while pathogenic for the turkey, may occur commonly in the intestinal tract of other species, such as the common fowl in which it may rarely produce lesions, should also be considered. The determination of any of these various points concerned in the transmission of blackhead may prove of practical importance in the rearing of turkeys. Source.?Considerable information is already available as to the sources of the infection. That the disease may be acquired by the exposure of normal turkeys to those which have shown evidence of infection, has been experimentally demonstrated by Theobald Smith,1 and Tyzzer.2 Smith3 concludes that turkeys which have passed through an attack are more dangerous as sources of infection than are those showing symptoms of active disease. Blackhead occurs chiefly in young turkeys during the summer months, and acute cases are often lacking throughout the greater portion of the year. It is obvious, therefore, that other sources of infection exist. We are not warranted, however, in assuming from Smith' s results that the acute