Free-living forms do not survive long in nature, but organisms contained within cecal worm eggs may survive for years. Chickens frequently are infected with blackhead without showing signs of the disease. These chickens may shed enormous numbers of blackhead organisms, many of which are protected by cecal worm eggs. Because of this, outbreaks in turkeys often can be traced to direct or indirect contact with ranges, houses or equipment previously used by chickens. Free-flying birds also may introduce an infection.
Losses usually are low for chickens.
Lesions of uncomplicated blackhead are confined to the ceca and liver, thus the reason for the synonymous term, enterohepatitis. The ceca are ballooned and walls may be thickened, necrotic and ulcerated. Peritonitis may be present if ulcers have perforated the ceca walls. Lesions are yellowish to yellow-green and extend deeply into the underlying liver tissue. Healing lesions may resemble those seen in visceral leukosis.