Blackhead disease (histomoniasis) is an important poultry disease that affects turkeys, chickens, and game birds such as partridges, pheasants, and quail. The disease is caused by the protozoa Histomonas meleagridis, tiny, single-celled organisms that are spread to the bird by the roundworm Heterakis gallinarum.
Lifecycle and Signs of Disease
The lifecycle of the protozoa H. meleagridis is complex:
- The protozoa multiply in an infected bird’s cecum, a part of its digestive tract;
- They move to the bird’s intestines where the roundworm H. gallinarum lives;
- The roundworm eats the protozoa;
- The roundworm’s eggs become infected with the protozoa;
- The bird sheds the protozoal-infected roundworm eggs in its droppings.
Healthy birds become infected when they eat food, invertebrates (such as earthworms), or bird droppings that are contaminated with the protozoa. Direct bird-to-bird transmission can also occur within a flock. Because chickens, partridges, and pheasants commonly have the roundworm in their intestines, they often are the source of the protozoal infection for other birds.
Birds with blackhead disease are usually listless and have drooping wings, unkempt feathers, and yellow droppings. Typically, the cecum and liver of an infected bird will become inflamed and develop ulcers. Young birds become sick quickly and usually die within a few days after signs appear. The disease develops more slowly in older birds and they often become emaciated and may eventually die.
Turkeys are highly susceptible to blackhead disease. Once a turkey flock has been infected, 70 to 100% of the birds may die. In one survey, U.S. turkey industry professionals reported at least 50 outbreaks of the disease each year since 2009.1 Blackhead disease is less severe in chickens but can lead to poor health and reduced egg production.
No Approved Treatments
Histostat (nitarsone), an arsenic-based animal drug, was the only FDA-approved drug to prevent blackhead disease in poultry. But in 2015, the drug company voluntarily stopped marketing Histostat and asked FDA to withdraw the drug’s approval due to concerns about inorganic arsenic levels in birds treated with the drug. Currently, there are no animal drugs approved to prevent, treat, or control blackhead disease in the U.S.
More Information on the withdrawal of Histostat (nitarsone):
- Arsenic-based Animal Drugs and Poultry
- Federal Register Notice (80 FR 78970)
- 2015 Letter from Zoetis to FDA
What is FDA doing about the lack of approved drugs against blackhead disease in poultry?
FDA determined that controlling blackhead disease in turkeys qualifies as a “minor use in a major species.”
The National Turkey Federation asked FDA to determine if controlling blackhead disease in turkeys qualifies as a “minor use in a major species.” Based on information provided to the agency by the federation and on information from other references, FDA’s Office of Minor Use and Minor Species Animal Drug Development determined that using a drug to control mortality caused by blackhead disease in flocks of turkeys diagnosed with the disease qualifies as a minor use. Because of this assessment, any drug company or other group that is pursuing an approval of a new animal drug for this specific use is entitled to various incentives, including user fee waivers, grants, exclusive marketing rights, and eligibility for conditional approval.
FDA has raised awareness about the lack of approved drugs against blackhead disease in poultry. As part of this outreach effort, the agency has:
- Presented posters at poultry scientific and industry meetings
At various meetings of poultry scientists, poultry industry professionals, and animal drug companies, FDA presented posters about the agency’s concerns. The posters highlighted the potential approval pathways available for new animal drugs to treat, control, or prevent blackhead disease.
FDA’s posters about blackhead disease:
- Met with poultry industry professionals and animal drug companies
FDA met with the National Turkey Federation, the American Association of Avian Pathologists (AAAP), poultry veterinarians, and poultry researchers to discuss the lack of approved drugs against blackhead disease. The agency also met with animal drug companies to discuss the potential approval pathways available for new animal drugs to treat, control, or prevent the disease.
- Supported AAAP’s blackhead disease symposium
In August 2016, FDA participated in a symposium on blackhead disease hosted by AAAP. The agency sponsored video conferencing of the symposium, which allowed many participants, both inside and outside FDA, to attend virtually. The symposium provided a much-needed platform for poultry researchers, poultry industry professionals, and animal drug companies to share information about the status of blackhead disease, research updates, and strategies to prevent and control the disease.
- Published a paper on regulatory considerations for drugs against blackhead disease
FDA published a paper in the journal Avian Diseases outlining the agency's regulatory process for approving new animal drugs against blackhead disease in turkeys, chickens, and game birds. The paper also discussed the various incentives available to drug companies for developing drugs for minor species or minor uses in a major species (such as for blackhead disease in poultry). Drug companies may be able to use these incentives to work toward a streamlined approval of drugs against blackhead disease.
FDA’s paper in Avian Diseases:
Because of FDA's outreach effort, more people are aware of the lack of approved treatments against blackhead disease. The agency encourages poultry researchers, the poultry industry, and animal drug companies to work together to identify and invest in promising therapies, such as drugs or vaccines, to treat, control, or prevent the disease. When developing a new drug, the agency encourages these groups to work with FDA to ensure they are following the requirements for drug approval (for vaccines, these groups should contact the U.S. Department of Agriculture). This collaboration will hopefully speed up the approval of much needed safe and effective therapies against blackhead disease in poultry.
If you have questions, please contact FDA at AskCVM@fda.hhs.gov or 240-402-7002.
1 Clark S, Bailey A. Turkey industry annual report—current health and industry issues facing the US turkey industry, in Proceedings. 119th Annual Meeting of the United States Animal Health Association 2015;433-442. Available at: http://www.usaha.org/upload/Proceedings/2015_Proceedings_web2.pdf