Chapter 4 



HISTOMOHAS 



Histomonas belongs to the order 

 Rhizomastigorida, members of which 

 possess both flagella and pseudopods. 

 Within this order it belongs to the family 

 Mastigamoebidae, members of which have 

 1 to 4 flagella. Histo»ionas is the only 

 genus in this order occurring in domestic 

 animals. 



Genus HISTOMONAS 

 Tyzzer, 1920 



The body is actively amoeboid, 

 usually rounded, sometimes elongate, 

 with a single nucleus, and with 1 to 4 ex- 

 tremely fine flagella arising from a basal 

 granule close to the nucleus. A single 

 species, H. meleagridis is recognized. 



HISTOMONAS MELEAGRIDIS 

 (SMITH, 1895) TYZZER, 1920 



Disease : Histomonosis, infectious 

 enterohepatitis, blackhead. 



Hosts : Chicken, turkey, peafowl, 

 guinea fowl, pheasant, ruffed grouse, 

 quail, chukar partridge. 



Location : Ceca, liver. 



Geographic Distribution : Worldwide. 



Prevalence : This parasite is prac- 

 tically ubiquitous in chickens, altho it 

 seldom causes disease in them. It is one 

 of the most important causes of disease 

 in turkeys. Before control measures were 

 developed, it drove many turkey raisers 

 out of the business, and even now the United 

 States Department of Agriculture (1954) has 

 estimated that it causes an annual loss of 

 $3,815,000 in turkeys and Sl49,000 in 

 chickens due to mortality alone. 



Morphology : This parasite was first 

 recognized by Theobald Smith in 1895. He 

 thought it was an amoeba and named it 

 accordingly. It was later confused with a 

 number of other microorganisms. Some 

 workers thought that it was one of the forms 



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