Blackhead

Blackhead, more correctly known as Histomoniasis, is a disease of the digestive tract of a number of bird species caused by the parasite, Histomonas meleagridis. Increasing numbers of free range producers are coming across this disease either in their own flocks or from hearing horror stories from their colleagues. Losses of up to 20% have occurred in replacement pullets, losses in early lay have been associated with poor performance and mortality, whilst, in turkeys, losses as high as 90% have been reported. The parasite, Histomonas meleagridis, damages the lining of the caeca (part of the birds’ intestine equivalent to a human appendix) leading to a similar sort of pain and illness one would expect from appendicitis. During this stage, the parasite damages the caecal wall and affected birds may be identified as depressed and dull, being reluctant to move to take food. Feathers may be ruffled and as the gut problem develops, birds may be seen to pass foul smelling liquid faeces. As the condition progresses, the parasite moves into the blood and eventually reaches the liver which acts as a filter for most toxins and bugs. It is here that they produce their characteristic circular spots on the liver. Definite diagnosis of the condition depends on a prompt post mortem examination but the diarrhoea and excessive mortality can be useful pointers. Dull birds often go blue around the head, giving the disease its more common name of blackhead.

The life cycle of this infection is interesting in that it involves the small roundworm, Hetarakis gallinarum (the caecal worm), which is a parasite in its own right. Histomonas can infect the Hetarakis worm and this helps transmit the disease from bird to bird via the worms eggs. These worm eggs also protect Histomonas while it is outside the bird on the soil. As a result, blackhead can infect consecutive flocks and is known as one of the diseases associated with "fowl sick" land. The real dilemma facing producers now is that there is no specific drug licenced to treat blackhead. Emtryl, which contains the active drug Dimetridazole, was used in the past but this product is now banned from use in chickens. There are reports of limited success with other antibiotics.

As usual, with poultry diseases, prevention is better than cure. The best treatment is to control the Hetarakis caecal worm in the first place and this will help to break the cycle. Good worm control during rear and worming of birds in the first week of housing with Flubendazole (Flubenvet) should ensure that the pullet is "worm free" at the start of her productive life. The usual advice on worm control (as previously reported in The Ranger) is equally important here. All the following will help:

· Good drainage around the poultry house

· Keeping pasture grass short to allow ultra violet kill of worm eggs

· Pasture rotation and management of any poached areas close to the popholes.

Remember that worm eggs are sticky and therefore the use of clean boots and foot dips with effective disinfectants on entry to the site house will reduce the chance of spreading this infection. Don’t wait to be another statistic as one of the increasing unfortunates who have suffered through blackhead. Act now to ensure you have the best possible worm control strategy and think about biosecurity and the management practices on your farm that can help reduce the introduction and persistence of disease bugs.