Download protozoan diseases

PROTOZOAN DISEASES
Coccidiosis
Coccidiosis is a disease of fowl caused by a microscopic animal or protozoa and is characterized
by diarrhea, unthriftiness and variable levels of mortality. In spite of much research to advance
the control and treatment of this disease, it remains the most costly disease of the poultry
industry.
Coccidiosis is caused by microscopic animals called coccidia. There are many species of
coccidia that can infect fowl, domestic animals and humans. Each species of coccidia is host
specific and does not infect a wide variety of animals. After an outbreak of a specific species of
coccidia, the flock will develop a resistance to the exposed coccidia species but remain resistant
to other infective species. This means that a flock may experience several outbreaks of
coccidiosis, each being caused by a different species of coccidia. Chickens are susceptible to any
of nine coccidia species, turkeys are susceptible to seven species and quail are susceptible to at
least four different species of coccidia.
Coccidiosis is transmitted by direct or indirect contact with droppings of infected birds. When a
bird ingests coccidia, the organisms invade the lining of the intestine and produce tissue damage
as the undergo reproduction. Within a week after infection, the coccidia shed immature
descendants that are referred to as oocysts. The oocysts shed in the droppings are not capable of
infecting another bird unless they pass through a maturation process (sporulation) in the litter.
This sporulation occurs within a one to three day period if the litter is warm and damp but can
take much longer if the conditions are cool and dry. After sporulation the coccidia are infective if
consumed by a new host bird.
The number of infective coccidia consumed by the host is a primary factor as to the severity of
the resulting infection. An infection may be mild enough to go unnoticed while a large infective
dose of coccidia may produce severe lesions that can cause death. Coccidia survive for long
periods outside the bird's body. They are easily transmitted from one house to another on
contaminated boots, clothing, free-flying birds, equipment, feed sacks, insects and rodents.
Coccidiosis usually occurs in growing birds and young adults. It is seldom seen in birds under
three weeks or in mature birds. Signs of an outbreak include birds that are pale, droopy, tend to
huddle, consume less feed and water, have diarrhea, and may become emaciated and dehydrated.
Laying hens will experience a reduction in rate of egg production.
Cecal coccidiosis may produce bloody droppings and anemia that is often followed by death.
Intestinal coccidiosis is not as acute and is more chronic in nature. It produces less mortality than
the cecal form.
Lesions of the infection depend on the species of coccidia causing the problem, its severity and
stage of the disease. Cecal coccidiosis may produce a ballooning of the cecal pouches that is
filled with free blood. A later stage is characterized by cecae that are filled with a material with a
cheesy consistency and being tinged with variable amounts of blood. Lesions of intestinal
coccidiosis vary from a rather mild enteritis to a severe necrotic or hemorrhagic type.
Cecal coccidiosis may be confused with blackhead and salmonellosis due to their similar lesions.
Intestinal coccidiosis may be confused with hemorrhagic anemia syndrome and other enteric
diseases. Definite diagnosis is made from the microscopic examination of scrapings of the
digestive tract and identification of the coccidia organisms. Since it is common for healthy birds
to possess some coccidia, consideration of flock history and lesions must be considered before
making diagnosis and treatment recommendations.
It is difficult, if not impossible, to prevent coccidiosis by sanitation alone. It is best prevented by
addition of a drug (coccidiostat) to the feed that controls the growth of coccidia in the digestive
tract. Many coccidiostats are available commercially. Coccidiostats should not be
indiscriminately used and recommendations must be followed precisely.
A coccidiosis vaccine is also available commercially. The product is useful only in certain types
of poultry operations and must be used as recommended. Seek expert advice before using the
vaccine.
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.
Hexamitiasis (Infectious Catarrhal Enteritis)
Hexamitiasis is an acute infectious disease of turkeys, quail, ducks, chukar partridges and
pigeons. Heavy losses have been reported in one outbreak in ring-necked pheasants. Chickens
apparently are not affected.
Hexamitiasis is a problem in every commercial turkey-producing area. It may be a major
problem in localized areas during a particular year, followed by one or more years in which
incidence is low.
Hexamitiasis is caused by a one-celled parasite of the genus Hexamita. Hexamita meleagridis is
the cause in turkeys; in pigeons it is Hexamita columbae. Experimentally, the Hexamita of
turkeys can be transmitted to young quail, chicks and ducklings, and that of quail and partridges
can be transmitted to poults. However, poults cannot be infected with the organism isolated from
pigeons.
This disease is found primarily in young birds, and outbreaks seldom occur in poults past ten or
eleven weeks. Losses are most severe in birds three to five weeks old. Apparently, resistance
develops rapidly with increasing age, regardless of previous exposure.
The primary infection source is droppings from carrier birds. About a third of recovered birds
become carriers. Most outbreaks result from a buildup of organisms through several broods of
poults, making exposure of the following brood overwhelming. Indirect transmission may result
from fecal material carried from one location to another on shoes or equipment. Free-flying birds
also may be carriers.
Primary symptoms are listlessness and foamy or watery diarrhea with rapid weight loss due to
the dehydrating effect. Birds often huddle together near the heat source and cry or "chirp"
constantly as though in pain. Convulsions due to lowered blood sugar levels shortly precede
death. Affected birds suffer losses in weight and survivors remain stunted.
Dehydration and emaciation are the principal gross lesions. Muscles are dark and dry. The
intestine usually appears to have lost muscle-tone. Intestinal contents are usually thin and watery,
or may contain mucus.
Diagnosis depends upon history, symptoms and microscopic examination of intestinal contents.
A definite diagnosis cannot be made unless typical flagellated organisms can be detected in
intestinal contents of the duodenum. Most flagellate organisms in the cecae are not disease
producers.
http://www.msstate.edu/dept/poultry/disproto.htm#blkhd