Blackhead Also called
Common in turkeys, rare in chickens
General signs -
Sometimes no symptoms. Other times, lack of appetite, lethargy, huddling near heat source and fluffed up feathers. Loss of appetite, increased demand for water, loss of condition, flushed face.
Cardinal or diagnostic signs -
Occasionally bloody droppings. Lab diagnosis. Postmortem: sunken spots on liver (look like blackheads), cecal changes
Histomonas meleagridis, which are protozoa that occur all over, but especially in soils that are moist or don't drain well.
Yes. It can be spread by wild birds, insects, earthworms, and even by foraging in areas where infected droppings have fallen. It can occur as a secondary issue if your birds are suffering from cecal worms.
Communicability to humans
One to two weeks
Yes, chickens who recover carry the protozoa. However, this is not a huge danger to healthy birds. You will want to put your flock on a regular worming schedule, though, to decrease the amount of protozoa they're exposed to. You will not want to start keeping turkeys with your chickens, either, as the turkeys are likely to get sick.
Yes. The protozoa causing this infection are found naturally almost everywhere. However, chickens tend to be fairly resistant. If you keep turkeys with chickens (or live in an area with lots of wild turkeys), it's more likely your chickens will catch an infection from the turkeys, who are far more susceptible to this illness.
Home treatment and/or prevention
Prevention: The protozoa is ubiquitous, and spread by insects and wild birds, so keeping it out of your coop and run area can be difficult. That said, infection is unlikely if your chickens are kept in a clean, dry area, and any infestation of cecal worms is treated promptly.
Treatment: None known.
Consult a vet to get a firm diagnosis and treatment for any other illnesses, infections or infestations (like worms) that may complicate blackhead or increase mortality.
Some birds--about 1/3--may die, but most will recover.
Other conditions, illnesses and/or diseases with similar signs:
Many other conditions have a similar appearance to the layman's eye, since the outward signs of this illness are general signs of feeling ill (lethargy, ruffled feathers). Bloody droppings are common with other infections, like coccidiosis and digestive issues. Consult a vet for a firm diagnosis.