Histomonads

Histomonads are a group of microscopic, single-celled organisms belonging to the phylum Percolozoa. They are primarily known for their parasitic nature, causing significant diseases in various animal hosts, most notably poultry. The most well-known species, Histomonas meleagridis, is responsible for histomoniasis, also known as blackhead disease, which can be devastating to turkey flocks.

These protozoa typically reside in the cecum and liver of infected animals. The life cycle of histomonads often involves an intermediate host, commonly earthworms, which ingest the parasite from contaminated droppings. Birds then become infected by consuming these earthworms. The parasite causes inflammation and lesions in the ceca and liver, leading to characteristic symptoms such as droopiness, ruffled feathers, and darkening of the head, from which the disease derives its name.

Histomoniasis affects a range of gallinaceous birds, including chickens, pheasants, and partridges, but turkeys are particularly susceptible and often experience high mortality rates. Control measures focus on preventing infection through biosecurity, managing parasite transmission via earthworms, and in some cases, medication. Research continues to explore effective treatments and preventative strategies for histomonad infections due to their economic impact on the poultry industry.