Prevention of Blackhead in Turkeys
Blackhead (or Histomoniasis) is a disease which affects the lower digestive tract (usually the caeca and the liver) of the bird. The organism is the protozoan Histomonas meleagridis. Clinical signs are non-specific and birds may exhibit some or all of the following: a stilted gait when walking, loss of interest in food, wasting, and yellow droppings, occasionally darkening of the skin and wattles, and death. The darkening of skin and wattles on the head provides the common name of “blackhead”.
Although the disease primarily affects turkeys the organism is also found in chickens and other galliform birds (i.e. members of the poultry, turkey and gamebird family of birds), and whilst it doesn’t normally cause the same mortality in these species as it does in turkeys they can act as a vector of infection. It is transmitted from one bird to another by direct contact with faecal material containing the parasite, or by eating the eggs of parasitic worms (particularly Heterakis gallinarum) that act as a host for the organism or by eating earthworms that contain the organism. It can also be spread by other vectors, including arthropods, humans (on dirty clothing, boots etc) and possibly rodents. However, the disease is not transmissible to humans.
In the past the incidence of the disease has been reduced by the use of medication, however there are currently no authorised treatments available to prevent the disease. Nifursol (salfuride) and dimetridazole or DMZ (Emtryl) were previously available as feed additives but lost their EU authorisations on a precautionary basis to protect consumer safety because there was insufficient data presented to show that they were safe to use.
Blackhead is a worldwide disease in farmed turkeys and is endemic in the UK with a small number of incidents being diagnosed each year mainly in smaller flocks. In the absence of medication, owners need to reduce the risk of turkey flocks coming into contact with the parasite. Good biosecurity is a key factor in preventing the spread of this disease and is important whether birds are housed on concrete, on earth floors or with access to outside runs. One way of reducing the likelihood of disease is by reducing parasitic worm burdens in flocks. Defra advises all turkey producers (as well as other livestock producers) to look to their biosecurity arrangements and step up precautions where possible. Further details on biosecurity can be found on the Defra website.
A question and answers page on Blackhead disease can be found here.
Notes for Editors
1. Both DMZ and Nifursol were authorised for use across the EU and were
subject to review under Directive 70/524. These reviews are either routine,
designed to bring product authorisations up to modern standards, or
targeted to address a specific concern. Companies will reach a commercial
decision whether it is economic for them to go to the expense of producing
additional data to support the continued authorisation of a substance
as a feed additive.
2. The manufacturer for DMZ decided not to produce the necessary data to support the continued authorisation of its use in feed additive products. Without the data to support DMZ and with Nifursol available for the prevention of blackhead, the UK supported the proposed ban. The authorisation for DMZ was withdrawn in May 2002.
3. For Nifursol, the European Commission asked the Scientific Committee for Animal Nutrition (SCAN) to make a new scientific risk assessment. SCAN adopted an opinion that on the basis of mutagenicity, genotoxicity and carcinogenicity studies provided by the manufacturer and because of a lack of data on developmental toxicity, it was not possible to set an Acceptable Daily Intake (ADI). Consequently, it was not possible to provide adequate assurances of the safety of the product to consumers.
The manufacturer of Nifursol provided additional data that they hoped would satisfy the requirements of SCAN and prevent the withdrawal of the product. However, SCAN identified a number of deficiencies in these data and concluded that they still could not provide assurances of the safety of the product to consumers. The Commission, therefore, decided to apply the precautionary principle and to withdraw the authorisation.
The UK, along with other Member States, accepted the validity of the concerns that SCAN raised. However, the UK expressed concern at having reached a position where the last available authorised treatment for blackhead was lost for use in turkeys. We emphasised the very serious consequences that this was likely to have for the turkey industry in the UK and across the EU. The UK negotiated a six-month transitional period between the date the Regulation banning the product was published and the implementation of the ban. Such transitional periods are normal where there is no specific and immediate safety risk from the continued use of the substance.
The UK, as rapporteur, wrote to the company manufacturing Nifursol to advise them that should they wish to have Nifursol re-authorised they will have to make a new application and provide the necessary data. No such application has been received. Ultimately, the decision to provide additional data is a commercial decision for the company.
4. The UK is encouraging the European Commission to review the balance between banning products that present a hypothetical risk to human health and at the same time creating known animal health and welfare problems by removing suitable treatments for serious conditions.
5. Blackhead in turkeys is not comparable to an acute viral epidemic such as Foot and Mouth Disease. However it is possible there may in the future there may be sufficient build up of the parasite for the condition to become a cost limiting factor for turkey production on some farms, possibly even in housed birds. For this reason it is important that poultry keepers implement good biosecurity measures.
Reviewed:
28 August, 2008