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Blackhead Disease

Other Names: Histomonosis, Histomoniasis, Infectious Typhlohepatitis, Infectious Enterohepatitis

Histomoniasis, also known as blackhead disease, is a parasitic disease found worldwide, caused by the anaerobic protozoan parasite, Histomonas meleagridis. It is characterized by cecal mucosal-to-transmural necrosis with formation of luminal cores. The severity of the infection depends on the protozoal genetics, infectious dose, and influence of cohabiting cecal bacteria (Escherichia coli, Clostridium perfringens) and protozoa (Eimeria tenella).


Transmission occurs primarily via ingestion of embryonated eggs of the cecal worm (Heterakis gallinarum) containing H. meleagridis trophozoites, or by ingestion of earthworms that have ingested cecal worm eggs. The eggs are resistant to environmental conditions and may remain infective in the soil for 2–3 years.


H. meleagridis can cause disease in most gallinaceous birds, including turkeys, chickens, partridges, peacocks, pheasants and quail. Ring-necked pheasants are relatively resistant to disease and are considered a reservoir host for the pathogen. Turkeys are notoriously susceptible to infection, with outbreak mortality rates approaching 100%.

Incubation period

Disease develops when H. meleagridis penetrate the cecal wall, multiply, enter the bloodstream, and eventually parasitize the liver. Overt signs of histomoniasis are apparent from 7–12 days but occur most commonly 11 days post-infection (PI).

Clinical signs

Turkeys usually develop more severe disease then chickens. But severe outbreaks have also been documented in chickens. Variation in susceptibility has been found among different breeds and strains of chickens. The most characteristic sign of histomoniasis, observed during the later stages of the disease, is sulfur-colored droppings, resulting from severe damage to the liver and bile pigments are excreted through the kidneys. Other non-specific signs include drowsiness, dropped wings, stilted gait, closed eyes, loss of appetite, head down close to the body or tucked under a wing, and sick birds seen huddling together.

Gross lesions

The primary lesions of histomoniasis develop in the ceca and liver. Lesions are observed initially in the ceca. After tissue invasion by histomonads, cecal walls become thickened and hyperemic. Serous and hemorrhagic exudate from the mucosa fills the lumen of ceca and distends the walls with a caseous or cheesy core, and ulceration of the cecal wall may lead to perforation of the organ and cause generalized peritonitis.

Clinical Signs

Sulfur-yellow droppings
Increased drinking
Dull and ruffled feathers
Loss of appetite
Pale, shrunken comb (anemia)


  • History
  • Clinical signs
  • Blood testing

Reported Cases

  • Case 1: Blackhead disease in a Chickens Blackhead disease was found in five backyard flocks; three involving 4– to 6-week-old chickens and two involving 2– to 3-month-old turkeys. Signs ranged from weakness, depression, droopy wings, stumbling with or without bloody droppings, to sudden death. Two of the three chicken cases had lesions limited to the ceca, while the third chicken case and both turkey cases had more classic involvement of both the liver and ceca. Ref

  • Case 2: Blackhead disease in a Bobwhite quail Three dead females and one dead male, 8-month-old, Bobwhite quail were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) with a clinical history of increased mortality. History indicated the flock exhibited enteritis and had been dewormed the previous month. Upon necropsy examination, multifocal, pale and irregular in size foci were seen scattered over the surface of the liver. Both ceca were dilated with yellowish-tan caseous cores in the lumen and small raised nodules on the mucosa. Histologically, large numbers of protozoal organisms consistent with Histomonas meleagridis associated with inflammatory cells were seen in the submucosa and muscular layer of ceca. In liver sections extensive areas of necrosis with vacuoles, some containing protozoal organisms undergoing degeneration, were seen. Ref

  • Case 3: Blackhead disease in a Turkeys Histomoniasis was diagnosed in 8- to 13-week-old turkeys on three separate premises. All affected groups of birds had classic cecal necrosis (cores) and targetoid liver lesions. All flocks had increased mortality. One flock reported weight loss and another reported weak birds unable to roost. Ref

  • Case 4: Blackhead disease in a Broiler breeder pullets There was increased mortality of 3-4 days duration in a flock of 7-week old broiler breeder pullets. Affected birds were lethargic, inappetent, and had ruffled feathers and mild to moderate loss of pectoral muscle mass. A few birds had red-brown feces. Moderate to marked loss of pectoral muscle mass was present. Gross lesions varied with chronicity, ranging from marked hyperemia and mild ulceration of the cecal mucosa to extensive ulceration of the cecal mucosa with large fibrinonecrotic casts within the lumens. In virtually all birds, there was moderate to marked thickening of the cecal walls. The livers of several birds contained variably-sized, often coalescing, foci of necrosis. In a few of the birds, there was rupture of the cecum with extensive fibrinous peritonitis and airsacculitis. Small numbers of cecal worms (Heterakis gallinarum) were variably present in the cecal lumen. Liver: Hepatitis, granulomatous, necrotizing, multifocal to coalescing, moderate, with numerous protozoa, chicken, avian. Cecum: Typhlitis, lymphoplasmacytic, histiocytic, and heterophilic, diffuse, moderate, with protozoa and cecal core. Some microslides contain cross-sections of intraluminal cecal nematodes. Ref

  • Case 5: Blackhead disease in a Chickens Preliminary diagnosis of clinical symptoms and gross lesions with subsequent histopathologic and PCR analyses revealed histomoniasis in 276 chicken flocks in Jiangsu Province, China, and surrounding areas from January 2012 to December 2015. Detailed statistical analysis was performed to explore the occurrence and epidemic characteristics of histomoniasis in chicken flocks. The results indicated that histomoniasis usually occurred in free-range flocks of local broilers and laying hens. Also, 2- to 3-mo-old chickens were most susceptible to infection, and adult chickens rarely developed infection. The morbidity rate of chickens was generally 10%–30%, with mortality rates of less than 10%. Moreover, histomoniasis is a seasonal disease, occurring most often from April to June, and the rate of coinfection with heterakids in the ceca of infected chicken was 50.8%. The symptoms of diseased chickens included mental fatigue, bowing of the head and wings, and yellowish green droppings, with bloody stool in very limited cases. Most of the pathologic changes were characteristic of the disease, but there were also some atypical lesions confirmed by laboratory techniques. Ref

  • Case 6: Blackhead disease in a Peacock Histomoniasis was diagnosed in a 2-year-old, male peacock from a flock of five peacocks and two chickens. Target-shaped lesions and large caseous cores were noticed in liver and ceca respectively. Histologically, hepatitis and typhlitis were associated with large numbers of protozoa compatible with histomonads. In addition, a few roundworm eggs, compatible with Heterakis spp., were detected in the cecal lumen. Ref


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
AnthelminticAdminister to kill off any cecal worms. Refer to cecal worms page for details.
AntiprotozoalMetronidazole (110 mg/kg PO q12h), Ronidazole (0.1-0.2 g/L drink, QD) or Dimetridazole (0.5-1.0 g/L in drink, QD)K Marx
Papaya (Carica papaya) seeds extractAdministration of papaya seed extract both in powdery (300 mg/day/bird) and aqueous (110 ml water required/day) reduced the fecal egg counts of Heterakis gallinarum in commercial laying hens.



  • Practice good sanitation, promptly remove feces from the environment.
  • Don't allow chickens access to areas where wild turkeys roam.
  • Regularly deworm chickens, to get rid of caecal worms (Heterakis gallinarum), which are carriers of the protozoa.


It is associated with a high mortality rate in turkeys, ranging from 80 to 100%.

Scientific References


Risk Factors

  • Poor sanitary practices
  • Ingestion of earthworms
  • Raised on property previous inhabited by turkeys
  • Wild turkeys on the premises.
  • Periods of heavy rainfall - This is due to the association of earthworms, which commonly surface from the soil after heavy rains.