Studies on the Etiology of Blackhead Disease: The Roles of Histomonas meleagridis and Candida albicans in the United States

ALTHOUGH it has been 73 years since Cushman (1893) first described blackhead disease of turkeys (also known by the more descriptive “infectious enterohepatitis”), there is still sharp disagreement as to the etiological agent responsible for production of the disease. Smith (1895, 1910) found a protozoan, Amoeba meleagridis (now known as Histomonas meleagridis Tyzzer, 1920) to be present in diseased ceca and livers. He reported that this protozoan was the apparent causative agent. Cole and Hadley (1908) and Cole et al. (1910) reported that coccidia were the etiologic agents of the disease, but later abandoned this theory (Hadley, 1916a). Jowett (1911) and Hadley (1916a, b) stated that trichomonads were in fact the true disease agents. Allen (1936) and Walker (1948) have stated that a Pentatrichtomonas species, probably actually Trichomonas gallinarum (Allen, 1940), was a causative agent. However, Kemp and Reid (1965) concluded, on the basis of egg production and weight …