CHAPTER IX 
DISEASES CAUSED BY PROTOZOA 
GENUS AMEBA 
General discussion of Ameba. The ameba belong to the Phylum 
protozoa, Subphylum sarcodina. They are protozoa usually with 
simple structure and characterized mainly by motile organs in the 
form of changeable protoplasmic processes called pseudopodia. The 
ameba are a sub-class of the sarcodina which include the more common 
forms of rhizopods with blunt, lobose pseudopodia which do not 
anastomose on touching one another. The genus contains a few 
species that have become parasitic in their habits. These parasites 
do not produce noxious products like bacterial toxins but whatever 
damage they may cause is due to the mechanical disturbances set up 
by their presence and multiplication. 
The genus ameba contains very few pathogenic species. Those 
best known are Ameba coli (Entamoeba colt), the cause of a dysentery 
in man, and Ameba meleagridis Smith, the cause of an infectious dis- 
ease of turkeys. Laveran and Lucet gave it the name Haemamaeba 
Smithi. Musgrave and Klegg introduced the term Amebaisis to 
denote infections caused by ameba. 
INFECTIOUS ENTERO-HEPATITIS 
Synonyms. Blackhead; amebaisis of turkeys and fowls. 
Characterization. This disease is characterized by thickening of 
areas or of the entire walls of the ceca and areas of tissue degeneration 
and necrosis in the liver. It affects turkeys largely but hens and 
young chickens are sometimes attacked. 
History. In the fall of 1893, Prof. Samuel Cushman of the Rhode 
Island State Experiment Station sent a few specimens of the affected 
organs of turkeys which had died of “blackhead”’ to the Bureau of 
Animal Industry, where they were carefully examined by Dr. Theo- 
bald Smith. In the summer of 1894, Smith made a careful study of 
this disease at the Rhode Island Experiment Station. He found that 
it was caused by one of the protozoa (Ameba meleagridis Smith). 
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