black head disease

black head disease

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Blackhead (Histomoniasis, Enterohepatitis):-
Blackhead is an acute or chronic protozoan disease of fowl, primarily
affecting the cecae and liver. The disease is present wherever poultry
are raised. Blackhead is one of the critical diseases of growing turkeys
and game birds. It may cause stunted growth, poor feed utilization and
death. It is of lesser economic importance in chickens since they are
more resistant, but the incidence in chickens apparently is increasing.
Blackhead is caused by a protozoan parasite called Histomonas
meleagridis. The organism in passed in the fecal material of infected
birds. In many instances, the organism is shed within the eggs of the
cecal worm of chickens, turkeys and game birds. Free-living blackhead
organisms do not survive long in nature, but those in cecal worm eggs
may survive for years. Therefore, most blackhead transmission is
considered due to ingesting infected cecal worm eggs. Transmission may
also occur by the earthworm.
Chickens are frequently infected without showing signs of the disease.
These chickens may shed enormous numbers of blackhead organisms, many of
which are protected by cecal worm eggs. Outbreaks in turkeys can often
be traced to direct or indirect contact with ranges, houses or equipment
previously used by chickens. Free-flying birds may also contribute to
an infection.
Most blackhead losses occur in young birds (six to sixteen weeks). Among
the symptoms are loss of appetite, increased thirst, droopiness,
drowsiness, darkening of the facial regions and diarrhea. Morbidity and
mortality are variable, but mortality seldom exceeds fifteen percent;
however, it may approach one-hundred percent in uncontrolled turkey
outbreaks. Losses are usually low in chickens.
Lesions of uncomplicated blackhead are confined to the cecae and liver,
thus the reason for the synonymous term, enterohepatitis. The cecae are
ballooned and walls may be thickened, necrotic and ulcerated. Caseous
(cheesy) cores within the cecae may be blood tinged. Peritonitis may be
present if ulcers have perforated the ceca walls. Livers are swollen and
display circular depressed areas of necrosis about one-half inch in
diameter. Smaller lesions coalesce to form larger ones. Lesions are
yellowish to yellow-green and extend deeply into the underlying liver
tissue. Healing lesions may resemble those seen in visceral leukosis.
Blackhead diagnosis is made readily on the basis of the lesions.
Atypical forms, particularly in chickens, must be differentiated from
cecal coccidiosis and Salmonella infections in particular. Medications
may interfere with atypical lesions. Laboratory tests may be required
for positive diagnosis in such cases.
Good management practices can do much to control the blackhead problem.
Do not keep birds of different species on the same premises. Do not
range turkeys on ground previously used by chickens unless several years
have elapsed. Rotate ranges periodically if possible. Cecal worm
control is necessary to reduce blackhead incidence. Wire or slatted
floors reduce exposure.
Good management is the only effective method of preventing this disease
since many of the effective drugs used in past years are no longer
available commercially. Drugs that reduce the presence of cecal worms,
and thus reduce the infection rate, are available but do not have an
effect on the Histomonas organism. Refer to the cecal worm section for
recommended control practices