It multiplies in the ovary and invades the oocysts. When embryonated Heterakis eggs are ingested by the susceptible host, the Histomonas escapes into the lumen of the caecum. Young birds usually have an acute form of the disease while older birds may appear sick for several days prior to becoming emaciated. Heaviest losses occur at 3 to 12 weeks of age. Many other species of birds including quail and pea fowl are also susceptible to infection.
Treatment is with nitroimidazole.
Separation of species and ages is vital in preventing this disease. The most important genera are Trypanosoma and Leishmania.