June 1, 2018 - Blackhead disease (histomoniasis) is an important poultry disease that affects turkeys, chickens, peafowl, and game birds such as partridges, pheasants, and quail. The disease is caused by Histomonas meleagridis, a protozoan that is transmitted to the bird by the parasite Heterakis gallinarum, a type of nematode, or roundworm.
Lifecycle and Clinical Signs
The lifecycle of H. meleagridis is complex. The protozoa multiply in an infected bird’s cecum (a part of its digestive tract). The protozoa move to the bird’s intestines where the roundworm H. gallinarum lives. The roundworm eats the protozoa, causing the roundworm’s eggs to become infected with H. meleagridis. The protozoal-infected eggs are then shed in the bird’s droppings.
Healthy birds become infected with H. meleagridis 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 H. gallinarum 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 clinical 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, mortality can reach 70 to 100%. A survey of professionals representing the U.S. turkey industry 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 requested withdrawal of the drug’s approval due to concerns about inorganic arsenic levels in treated birds. 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 is involved in an outreach effort to raise 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 has presented posters about the agency’s concerns regarding the lack of approved drugs against blackhead disease in poultry. The posters also highlighted the potential approval pathways available for new animal drugs to treat, control, or prevent the disease.
FDA’s posters about blackhead disease:
- Increased Concerns for the Lack of Therapeutic Interventions against Histomoniasis (Blackhead Disease) in Turkeys
- Regulatory Considerations for Approval of Drugs against Histomoniasis in Turkeys and Game Birds
Met with poultry industry professionals and animal drug companies
FDA has met with the National Turkey Federation, the American Association of Avian Pathologists (AAAP), poultry veterinarians, and researchers working in the poultry field to discuss the lack of approved drugs against blackhead disease. FDA has 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. FDA 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 peer-reviewed paper in the journal Avian Diseases outlining FDA’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. Drug companies can potentially use these incentives to work toward a streamlined approval of drugs against blackhead disease.
FDA’s paper in Avian Diseases:
- Regulatory Considerations for the Approval of Drugs Against Histomoniasis (Blackhead Disease) in Turkeys, Chickens, and Game Birds in the United States (Avian Diseases 60:725-730, 2016)
Because of this outreach effort, FDA thinks that more people are aware of the lack of treatments against blackhead disease in poultry. FDA encourages academic institutions, 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. The agency also encourages these groups to work with FDA to ensure their research efforts align with the requirements for drug approval (or to work with the U.S. Department of Agriculture for vaccine development). This collaboration will hopefully lead to much needed safe and effective approved therapies against blackhead disease getting to the marketplace efficiently and quickly.
If you have questions, please contact Dr. Prajwal Regmi at prajwal.regmi@fda.hhs.gov.
