Blackhead (also known as Entero-hepatitis and Histomoniasis) is a severe protozoan disease of turkeys and peafowls and also affects fowls and game birds. It is characterised by caecal (blind gut) and liver lesions. Fowls tend to be more resistant to Blackhead and therefore should not be run with turkeys. Blackhead mainly causes deaths in birds 3 to 18 weeks of age and is probably the most serious disease confronting the turkey producer.
Cause
Blackhead is caused by the protozoan organism Histomonas meleagridis which damages the caecal wall. Secondary infection occurs with coliform (gut) bacteria Clostridium perfringens and Bacillus subtilis . Infection may spread to the liver causing yellow droppings.
The caecal worm (Heterakis gallinae ) is always present during blackhead outbreaks, but can be present without blackhead occurring. The blackhead organism can shelter within the egg of the caecal worm. This combination can survive in the soil for up to four years. Earthworms play an important role in the spread of this disease by eating these eggs. Hence properties can be difficult to clean up once they are infected.
Species affected
Blackhead occurs naturally in chickens and turkeys, however, infection in turkeys is more serious. Peafowls and gamebirds are also susceptible. Birds with lowered resistance due to factors such as fowl pox or nutritional diseases are more severely affected.
Symptoms and expected course
Blackhead is a disease of the caeca and liver.
Fowls - young chickens show only clinical signs. Affected birds are depressed and weak and huddle with necks drawn in and wings and tails drooping. In some instances yellow droppings may be seen and in up to ten percent of cases, a rapid bodyweight loss and death can occur.
In Queensland, blackhead is more common in summer, mainly affecting birds 3 to 4 weeks old, although outbreaks can occur in older birds. Blackhead in chickens is often preceded by an outbreak of coccidiosis.
Turkeys - for poults (young turkeys), blackhead is an acute, fatal disease. There is not the same age resistance as in chickens. Turkeys are most susceptible up to the stage when they shoot the red, (about 18 to 20 weeks of age) but mature birds can also be affected.
Sick birds rapidly become weak and stand out with ruffled feathers, drooping heads and wings. Soiled vent feathers due to diarrhoea are common, and as liver involvement increases, the characteristic bright yellow-sulphur droppings appear. On occasions the head may be darkened (hence the name Blackhead).
Turkeys are clinically affected about 10 days after infection and death occurs 2 to 3 days later with up to 100% mortality.
Post mortem findings
In both chickens and turkeys, the first site of infection is the caeca (blind gut). Early signs are haemorrhage and inflammation with thickening and ulceration of the caecal walls. In the caeca there may be grey-yellow cheesy cores of necrotic tissue - often streaked with blood.
Infection may then spread to the liver. This is more common with turkeys than with chickens. Lesions on the liver are round, creamy-yellow depressions of necrotic tissue. These can vary from pinhead size up to about 1 cm in diameter.
Transmission
By eating caecal worm eggs or earthworms contaminated by Histomonas meleagridis. Rain brings earthworms to the surface. If eaten, these may cause a blackhead outbreak in the birds.
Infected birds pass droppings which are heavily contaminated with the organism. Adolescent and adult birds are not infected by eating these droppings as the organism is usually killed by acidic reaction in the proventriculus and gizzard. Birds only become infected by eating caecal worm eggs which transport the blackhead organism safely through the acidic areas. Droppings containing contaminated caecal worm eggs can be a means of rapid spread of the disease among poults.
Diagnosis
Signs - drowsiness, weakness, ruffled feathers, lowered head, darkened comb, drooping of the wings and tail, depression, weight loss, soiled vent feathers, and yellow-sulphur coloured droppings. On post mortem examination, liver and caecal lesions are found and the caeca contain firm cheesy plugs.
Microscopic or histopathological demonstration of the organism in liver and caecal tissue.
Similar diseases
Chickens
coccidiosis
heavy worm burdens
fowl cholera.
Turkeys
hexamitiasis
coccidiosis
cholera.
Treatment and control
Management
The primary means of transmission appears to be the caecal worm egg. Successful control of blackhead relies on the removal of worm eggs from the cycle and providing areas which are not heavily contaminated with the blackhead organism. The survival of Heterakis (caecal worm) eggs can be reduced by providing sunny, well-drained rearing facilities - particularly for turkey ranges.
Major management factors
keep turkeys and chickens apart ensuring drainage does not occur from chicken to turkey runs
caecal worm control - suitable treatments are available
poultry should be brooded away from ranged turkeys and chickens - avoid contamination of ground
keep turkeys away from caecal worm eggs and earthworms
ensure poult feeders and waterers are not contaminated with droppings and are moved to clean areas regularly.
Medication
Little immunity is developed to blackhead although chickens are more resistant. Treatment may be through the feed or water. Treatment in water is the most common method used, flocks normally being medicated for several days.
Preventative medications may also be administered in the water or feed. The manufacturers' direction should be closely followed. Successful control and treatment is accomplished by using drugs in combination with improved hygiene and management.
أ.د/ أكـــرم زيـن العــابديــن محـــمود محمـــد حمــدى - جامعــة المنــيا
[email protected] [01006376836] Minia University, Egypt »
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