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==''Histomonas meleagridis''==
[[Image:Blackhead lesions in turkey liver.jpg|thumb|right|150px|Blackhead lesions in turkey liver - Milton Friend]]
[[Image:Heterakis gallinarum.jpg|thumb|right|150px|''Heterakis gallinarum'' - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]
*Infects chickens and turkeys
*Causes '''Blackhead''' in turkeys
**Infectious entero-hepatitis or histomonosis
**Head and wattle become cyanotic
*Worldwide distribution
'''Recognition'''
*10-25μm long
*Round or oval
*1 flagellum in the intestinal form
**The tissue form has no flagellum
*Pseudopial movement
'''Life Cycle'''
*''Histomonas'' carried by larval stage inside the egg of the [[Caecum - Anatomy & Physiology|caecal]] nematode worm ''Heterakis gallinarum'' (vector)
*''Histomonas'' released from larva when egg hatches in intestine
*Penetrates [[Caecum - Anatomy & Physiology|caecal]] wall
*Carried by hepatic portal system to the [[Liver - Anatomy & Physiology|liver parenchyma]]
*Intestinal ''Histomonas'' infects ''Heterakis gallinarum'' and passes to worm [[Female Reproductive Tract -The Ovary - Anatomy & Physiology|ovary]]
*Worm passes ''Histomonas''-infected eggs in droppings
*Infected eggs swallowed by birds or earthworms
**Earthworms act as transport hosts carrying larvae in their tissues
'''Pathogenicity'''
*Necrotic circular [[Caecum - Anatomy & Physiology|caecal]] lesions and [[Liver - Anatomy & Physiology|liver]] lesions
**Lesions begin small but soon enlarge and become necrotic
**The plug detaches with the caecal contents forming a caseous plug
**Lesions can be up to 1cm in diameter
**Lesions found both on the surface and in the substance of the [[Liver - Anatomy & Physiology|liver]]
*Mortality may reach 100%
*Recovered birds may have a permanently scarred [[Caecum - Anatomy & Physiology|caecum]] and [[Liver - Anatomy & Physiology|liver]]
*Generally affects turkey poults under 14 weeks old
*A few days after infection the bird will become dull with ruffled feathers
*The faeces will become sulphur yellow in colour
*In older turkeys, recovery and immunity is likely
'''Diagnosis'''
*Clincal signs
**Cyanotic head and wattles
**Yellow droppings
*Post-mortem
**Necrotic mucosa in [[Caecum - Anatomy & Physiology|caecum]]
**Circular lesions in [[Liver - Anatomy & Physiology|liver]] 1cm in diameter which stain poorly
'''Control'''
*Do not rear turkeys on ground used by chickens
**Chickens are asymptomatic carriers
*Chemical control now withdrawn due to fears of human toxicity[[Category:Protozoa]]
[[Image:Blackhead lesions in turkey liver.jpg|thumb|right|150px|Blackhead lesions in turkey liver - Milton Friend]]
[[Image:Heterakis gallinarum.jpg|thumb|right|150px|''Heterakis gallinarum'' - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]
*Infects chickens and turkeys
*Causes '''Blackhead''' in turkeys
**Infectious entero-hepatitis or histomonosis
**Head and wattle become cyanotic
*Worldwide distribution
'''Recognition'''
*10-25μm long
*Round or oval
*1 flagellum in the intestinal form
**The tissue form has no flagellum
*Pseudopial movement
'''Life Cycle'''
*''Histomonas'' carried by larval stage inside the egg of the [[Caecum - Anatomy & Physiology|caecal]] nematode worm ''Heterakis gallinarum'' (vector)
*''Histomonas'' released from larva when egg hatches in intestine
*Penetrates [[Caecum - Anatomy & Physiology|caecal]] wall
*Carried by hepatic portal system to the [[Liver - Anatomy & Physiology|liver parenchyma]]
*Intestinal ''Histomonas'' infects ''Heterakis gallinarum'' and passes to worm [[Female Reproductive Tract -The Ovary - Anatomy & Physiology|ovary]]
*Worm passes ''Histomonas''-infected eggs in droppings
*Infected eggs swallowed by birds or earthworms
**Earthworms act as transport hosts carrying larvae in their tissues
'''Pathogenicity'''
*Necrotic circular [[Caecum - Anatomy & Physiology|caecal]] lesions and [[Liver - Anatomy & Physiology|liver]] lesions
**Lesions begin small but soon enlarge and become necrotic
**The plug detaches with the caecal contents forming a caseous plug
**Lesions can be up to 1cm in diameter
**Lesions found both on the surface and in the substance of the [[Liver - Anatomy & Physiology|liver]]
*Mortality may reach 100%
*Recovered birds may have a permanently scarred [[Caecum - Anatomy & Physiology|caecum]] and [[Liver - Anatomy & Physiology|liver]]
*Generally affects turkey poults under 14 weeks old
*A few days after infection the bird will become dull with ruffled feathers
*The faeces will become sulphur yellow in colour
*In older turkeys, recovery and immunity is likely
'''Diagnosis'''
*Clincal signs
**Cyanotic head and wattles
**Yellow droppings
*Post-mortem
**Necrotic mucosa in [[Caecum - Anatomy & Physiology|caecum]]
**Circular lesions in [[Liver - Anatomy & Physiology|liver]] 1cm in diameter which stain poorly
'''Control'''
*Do not rear turkeys on ground used by chickens
**Chickens are asymptomatic carriers
*Chemical control now withdrawn due to fears of human toxicity[[Category:Protozoa]]