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Distribution
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Distribution of blackhead ranges from the eastern to midwestern U.S., according to the Michigan Department of Natural Resources and Environment. Serious outbreaks occur in wet seasons, especially in spring and fall. In Queensland, Australia, this disease occurs more commonly in young birds three to four weeks old in summer.
Symptoms
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After a fowl contracts the infection, the incubation period may be 15 to 21 days. Although blackhead is named for the symptom of blue or black skin color of the head caused by poor oxygenation of the blood, not every head becomes dark. Young chickens tend to show clinical signs such as partly closed eyes, darkened comb, drooping wings and tail, drowsiness, weakness and depression. Turkeys with infected livers may excrete yellow droppings; chickens, however, do not often show this symptom. According to the Queensland Government, anorexia and death occurs in up to 10 percent of cases.
Diagnosis and Pathology
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Flock owners should contact a veterinary diagnostic clinic to confirm blackhead. Coccidiosis, a disease caused by parasites in the chicken's intestinal tract, often precedes blackhead disease. Infection occurs initially in the ceca where hemorrhaging and inflammation form lesions in the cecal walls. Thick, greenish white liquid or yellowish-gray plugs may fill the ceca. A diseased liver may contain dead and degenerated tissue and concentric lesions.
Transmission
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Chickens ingest the cecal worm and its eggs in droppings passed by infected birds. Worm eggs can resist temperature extremes and cleaning agents and remain viable for more than four years. Earthworms carrying the parasite Histomonas meleagridis are another source of transmission. Contaminated facilities also spread the blackhead organism among birds that eat this protozoan parasite. Susceptible chickens can transmit the disease to turkeys.
Treatment and Control
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Chick on a wire cage Treatment of blackhead can include drugs applied through feed or water. Prevention includes medicating birds annually, when feasible. Flock owners can reduce contamination by providing clean feeders and waterers. Turkeys and chickens should be reared separately to avoid transmission. Raising chickens on wire reduces exposure to parasites from infected droppings and earthworms. In ground rearing facilities, layers of crushed limestone and dry litter help deter infected earthworms from entering the food chain.
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Blackhead Disease in Chickens
Blackhead disease in chickens damages the blind pouches of the large intestine called the cecal wall and possibly infects the liver. Blackhead, also known as enterohepatitis and histomoniasis, affects other fowl, especially turkeys. The protozoan parasite Histomonas meleagridis and a second parasite, the cecal worm Heterakis gallinarum, reproduce and multiply in the cecal wall. The cecal worm measures about one-third to one-half inch long. Not all cecal worms carry the blackhead organism.