What are the symptoms of Blackhead disease in turkeys?
Answer: Blackhead disease, also called Histomoniasis, is a serious disease capable of decimating turkey flocks and negatively affecting other poultry. Caused by the protozoan Histomonas meleagridis, Blackhead can also have a significant economic impact on chicken production.
Physical Symptoms of Blackhead
• Mustardy, yellowish colored stool — varies from a watery, foamy diarrhea to a dry, solid black stool with waxy yellowish streaks
• Bulls-eye-shaped necrotic pitting on liver
• Ceca filled with yellow, cheesy substance
Behavioral Signs of Blackhead
• Drooping wings
• Dry, ruffled feathers
• Suppressed appetite, increased thirst
• Decreased/lack of flight distance (distance the turkey keeps between itself and humans)
• Decreased/lack of inquisitiveness
Blackhead infections vary in the time required to manifest signs, depending on the pathway and initial amount of infection. Signs of infection begin to appear seven to 14 days after exposure. In turkeys, the yellow-colored fecal matter is the definitive symptom of Blackhead disease. From personal experience, when behavioral symptoms become apparent, mortality usually occurs in one to three days.
Positive diagnosis of dead birds can be easily obtained through a post-mortem dissection (necropsy) by the farmer. The abdominal cavity can be opened and the cecum examined. The chest/breast can then be split down the middle using heavy duty shears or tin snips to reveal the liver. Once the ceca and liver are exposed, the organs can be inspected for necrosis as described above.
Despite the descriptive name of the disease, Blackhead rarely, if ever, causes the head of the infected bird to darken or turn black, so the common name is somewhat of a misnomer.
Turkeys demonstrate the most severe symptoms of any poultry from H. meleagridis infection and, consequently, the highest mortality rates. Indeed, expectations of 80 to 100% mortality are plausible in turkey Blackhead outbreaks. Chickens are usually able to stop the disease before destruction of the ceca and degradation of the liver take place. Infections in chickens often are undiagnosed, though in chickens the impact of Blackhead has been described as being at least as severe as coccidiosis, and in some broiler breeder flocks, mortality may reach as high as 10% (McDougald, 2005). Bobwhite quail farmers have also occasionally experienced outbreaks of Blackhead disease, especially when these growers utilize old chicken houses.
You’ll benefit from reading the ATTRA publication Parasite Management for Natural and Organic Poultry: Blackhead in Turkey. This publication addresses the new research as well as focusing on the history, life cycle, diagnosis, prevention, and management of Blackhead disease, primarily in turkeys. The effect Histomoniasis has on other poultry species (chickens, gamebirds, and peafowl) is also discussed briefly.
Be sure to also check out the Poultry section of the ATTRA website, where you’ll find a host of additional useful resources.
McDougald, L.R. 2005. Blackhead Disease (Histomoniasis) in Poultry: A Critical Review. Avian Diseases. Vol. 49, p. 462-476.