Avian pox is a relatively slow-spreading
viral disease in birds, characterized by wart-like nodules on
the skin and diphtheritic necrotic membranes lining the mouth
and upper respiratory system. It has been present in birds since
the earliest history. Mortality is not usually significant unless
the respiratory involvement is marked. The disease may occur in
any age of bird, at any time.
Avian pox is caused by a virus of which
there are at least three different strains or types; fowl pox
virus, pigeon pox virus and canary pox virus. Although some workers
include turkey pox virus as a distinct strain, many feel that
is identical to fowl pox virus.
Each virus strain is infective for
a number of species of birds. Natural occurring pox in chickens,
turkeys and other domestic fowl is considered to be caused by
fowl pox virus.
Fowl pox can be transmitted by direct
or indirect contact. The virus is highly resistant in dried scabs
and under certain conditions may survive for months on contaminated
premises. The disease may be transmitted by a number of species
of mosquitoes. Mosquitoes can harbor infective virus for a month
or more after feeding on affected birds. After the infection is
introduced, it spreads within the flock by mosquitoes as well
as direct and indirect contact. Recovered birds do not remain
carriers.
Since fowl pox usually spreads slowly,
a flock may be affected for several months. The course of the
disease in the individual bird takes three to five weeks. Affected
young birds are retarded in growth. Laying birds experience a
drop in egg production. Birds of all ages that have oral or respiratory
system involvement have difficulty eating and breathing. The disease
manifests itself in one or two ways, cutaneous pox (dry form)
or diphtheritic pox (wet form).
Dry pox starts as small whitish foci
that develop into wart-like nodules. The nodules eventually are
sloughed and scab formation precedes final healing. Lesions are
most commonly seen on the featherless parts of the body (comb,
wattles, ear lobes, eyes, and sometimes the feet).
Wet pox is associated with the oral
cavity and the upper respiratory tract, particularly the larynx
and trachea. The lesions are diphtheritic in character and involve
the mucous membranes to such a degree that when removed, an ulcerated
or eroded area is left.
Fowl pox is readily diagnosed on the
basis of flock history and presence of typical lesions. In some
cases, laboratory diagnosis by tissue or transmission studies
is necessary.
There is no treatment for fowl pox.
Disease control is accomplished best by preventative vaccination
since ordinary management and sanitation practices will not prevent
it. Several kinds of vaccines are available and are effective
if used properly.
Vaccination of broilers is not usually
required unless the mosquito population is high or infections
have occurred previously. The chicks may be vaccinated as young
as one day of age by using the wing-web method and using a one
needle applicator. All replacement chickens are vaccinated against
fowl pox when the birds are six to ten weeks of age. One application
of fowl pox vaccine results in permanent immunity.
Newcastle disease is a contagious viral
infection causing a respiratory nervous disorder in several species
of fowl including chickens and turkeys. Different types or strains
of the virus (varying in their ability to cause nervous disorder,
visceral lesions and death) have been recognized.
The most severe strain is called viscerotropic
velogenic Newcastle disease (VVND) and is kept from birds in the
U.S. by enforcement of strict quarantines at our national borders.
It is often referred to as "Exotic Newcastle Disease"
and infection of susceptible fowl with this form usually causes
high mortality. Due to the reduced chance that poultry in this
country will become infected with this disease form, it will not
be discussed.
A milder form of the disease is called
"mesogenic" Newcastle disease and is the most serious
strain found in the U.S. This is the form that is referred to
as Newcastle disease in this discussion.
Newcastle disease is highly contagious.
All birds in a flock usually become infected within three to four
days. The virus can be transmitted by contaminated equipment,
shoes, clothing and free-flying birds. During the active respiratory
stage, it can be transmitted through the air. The virus is not
thought to travel any great distance by this method. Recovered
birds are not considered carriers and the virus usually does not
live longer than thirty days on the premises.
Signs of Newcastle disease are not
greatly different from those of other respiratory diseases. The
signs most frequently observed are nasal discharge, excessive
mucous in the trachea, cloudy air sacs, casts or plugs in the
air passages of the lungs and cloudiness in the cornea of the
eye.
The disease in young chickens begins
with difficult breathing, gasping and sneezing. This phase continues
for ten to fourteen days and may be followed by nervous symptoms.
If nervous disorders develop, they may consist of paralysis of
one or both wings and legs or a twisting of the head and neck.
The head often is drawn over the back or down between the legs.
Mortality may vary from none to total loss of the flock.
In adult chickens, respiratory symptoms
predominate. Only rarely do nervous disorders develop. If the
flock is laying, egg production usually drops rapidly. When this
occurs, it takes four weeks or longer for the flock to return
to the former production rate. During the outbreak, small, soft-shelled,
off-colored and irregular-shaped eggs are produced. Mortality
in adult birds is usually low but may be fairly high from some
virus strains.
In turkeys, the symptoms are usually
mild and may be unnoticed unless nervous disorders develop. During
an outbreak, turkeys will produce eggs with a chalky white shell.
Reduced production in breeder flocks is the main economic loss
from this disease in turkeys.
The flock history, signs of a respiratory
nervous disorder and other typical lesions often may be sufficient
to allow a tentative diagnosis. Usually, however, the disease
cannot be differentiated from infectious bronchitis and some of
the other respiratory infections, except by laboratory methods.
Vaccination is practiced widely and
is the recommended method for prevention. Several types of vaccines
are available but the most successful and widely used is the mild
live virus vaccine known as the B1 and La Sota types.
The vaccines may be used by drops into the nostril or eye, addition
to the drinking water or applied in spray form.
Broiler chickens are usually vaccinated
when seven to ten days of age. Chickens kept for egg production
are usually vaccinated at least three times. The vaccine is given
when birds are approximately seven days, again at about four weeks
and a third time at about four months of age. Revaccination while
in lay is commonly practiced.
Vaccination is not widely used in turkeys.
It is used to protect egg producing breeder flocks. One dose of
the mild type vaccine is given after selecting breeder birds.
There is no treatment for Newcastle
disease. The disease does not always respect even the best management
programs, but good "biosecurity" practices will help
reduce the possibility of exposure to Newcastle disease virus.
Infectious bronchitis is an extremely
contagious respiratory disease of chickens characterized by coughing,
sneezing and rales (rattling). It is caused by a virus that affects
chickens only. Other fowl or laboratory animals cannot be infected
with this virus. Several distinct strains of the virus exist.
Infectious bronchitis is considered
the most contagious of poultry diseases. When it occurs, all susceptible
birds on the premises become infected, regardless of sanitary
or quarantine precautions. The disease can spread through the
air and can "jump" considerable distances during an
active outbreak. It can also be spread by mechanical means such
as on clothing, poultry crates and equipment. The disease is not
egg transmitted and the virus will survive for probably no more
than one week in the house when poultry are not present. It is
easily destroyed by heat and ordinary disinfectants.
The infection is confined to the respiratory
system. Symptoms are difficult breathing, gasping, sneezing and
rales. Some birds may have a slight watery nasal discharge. The
disease never causes nervous symptoms. It prevails for ten to
fourteen days in a flock and symptoms lasting longer than this
are from some other cause.
In chickens under three weeks of age,
mortality may be as high as thirty or forty percent. The disease
does not cause a significant mortality in birds over five weeks
of age. Feed consumption decreases sharply and growth is retarded.
When infectious bronchitis occurs in
a laying flock, production usually drops to near zero with a few
days. Four weeks or more may be required before the flock returns
to production. Some flocks never regain an economical rate of
lay. During an outbreak, small, soft-shelled, irregular-shaped
eggs are produced.
Infectious bronchitis is difficult
to differentiate from many of the other respiratory diseases.
For this reason, a definite diagnosis usually requires a laboratory
analysis.
Infectious bronchitis is highly contagious
and does not always respect sanitary barriers. Vaccinate chickens
being retained as layers. Whether broilers should be vaccinated
depends upon many factors and is an individual decision. Numerous
vaccines are available commercially. Most of them represent a
modified or selected strain of the infectious bronchitis virus.
The vaccine used should contain virus known to be present in the
area. All vaccines contain live virus and those that give the
best protection are also capable of producing symptoms and reducing
egg production. The vaccine virus will spread to other susceptible
birds. Vaccine is usually added to the drinking water, but may
be dropped into the eye or nostril or used as a spray.
There is no treatment for this disease.
In young chickens it is helpful to increase the brooder temperature
and provide as nearly ideal environmental conditions as possible.
Quail bronchitis is a contagious, highly fatal disease in young bobwhite quail. The virus causing this disease also infects chickens and turkey. This agent is also known as a CELO (Chick Embryo Lethal Organism) virus. It has been isolated from chicken eggs but does not produce a recognizable disease in chickens or turkeys. This agent may play a part in respiratory diseases and in infertility problems, but its importance must be established by additional research. It is important because it is one of the agents that may be isolated from birds with respiratory symptoms and is difficult to separate from other agents such as infectious bronchitis virus.
Characteristically, lymphoid leukosis
is a disease of adult chickens; however, the disease appears to
be increasing in importance for turkeys and game birds. Although
the virus of lymphoid leukosis can produce various responses (blood,
bone, lymph), the lymphoid tumor response is the most common.
The disease is transmitted in a variety
of ways. The causative viral agent is passed out of the body of
infected birds via eggs and feces. The virus may be transmitted
mechanically from infected birds to susceptibles by blood-sucking
parasites or by man in such procedures as fowl pox vaccination.
Lymphoid leukosis characteristically
produces lymphoid tumors, particularly in the liver and spleen.
The tumors may also affect other visceral organs such as ovary
and lungs. Affected birds may die without preliminary symptoms,
but the disease usually is chronic in nature and affected birds
show loss of appetite, progressive emaciation and diarrhea. Clinically
affected birds invariably die. Losses due to the disease are most
severe shortly after onset of egg production, but losses will
continue for as long as the flock is retained. Total loss may
approach twenty percent during the life of a flock.
Clinical diagnosis of lymphoid leukosis
is based upon flock history and disease manifestations. The lymphoid
disease cannot be readily distinguished from the visceral response
to Marek's disease; however, there are some features that aid
in differential diagnosis.
There is no treatment for lymphoid
leukosis. Although the disease cannot be prevented completely,
there are certain steps that can be taken to help control the
level of infection within a flock. Some steps are:
Marek's disease is characteristically
a disease of young chickens but older birds can also be affected.
In contrast to the lymphoid leukosis tumor response, Marek's disease
may be observed in more diverse locations.
Marek's disease is caused by a virus
belonging to the Herpes virus group. Much is known about the transmission
of the virus; however, it appears that the virus is concentrated
in the feather follicles and shed in the dander (sloughed skin
and feather cells). The virus has a long survival time in dander
since viable virus can be isolated from houses that have been
depopulated for many months.
The usual mode of transmission is by
aerosols containing infected dander and dust. Young birds are
most susceptible to infection by Marek's disease; however, since
the incubation period is short, clinical symptoms can appear much
earlier than in the case with lymphoid leukosis.
Marek's disease may produce a variety
of clinical responses, all lymphoid in character. These are acute
visceral, neural, ocular, skin or combinations of the responses
that can be seen.
Marek's of the visceral type is characterized
by widespread involvement with lesions commonly seen in gonads,
liver, spleen, kidney and occasionally heart, lungs and muscles.
The disease is often acute, with apparently healthy birds dying
very rapidly with massive internal tumors. The disease may appear
in broiler-age birds but the most severe losses occur in replacement
pullet flocks prior to onset of egg production.
The neural type of Marek's is typified
by progressive paralysis of the wings, legs and neck. Loss of
body weight, anemia, labored respiration and diarrhea are common
symptom. If lesions are present, they are confined to the nerve
trunks and plexes enervating the paralyzed extremities. Frequently
no gross lesions can be observed.
Ocular (eye) leukosis or "gray-eye" is usually seen in early maturity. Morbidity and mortality
are
usually low but may approach twenty-five percent in some flocks.
It is characterized by the spotty depigmentation or diffuse graying
of the iris in the eye. The pupil develops an irregular shape
and fails to react to light. Emaciation diarrhea and death follow.
Skin leukosis produces the most severe
losses in broilers. The losses result from high condemnations
at the processing plant. Enlargement of the feather follicles
due to accumulations of lymphocytes is the typical lesion. This
is the most infective virus since it is produced in the regions
of the feather follicles and is shed with the skin dander.
Acute Marek's disease can be extremely
rapid in its course, producing mortality in apparently healthy
birds. However, in some cases the lesions may regress and clinically
affected birds may make complete recoveries.
Diagnosis is based upon flock history
and disease manifestations. Accurate diagnosis may depend on results
of laboratory procedures. As is the case with lymphoid leukosis,
there is no treatment for Marek's disease.
A vaccine is available that is extremely
effective (90% +) in the prevention of Marek's disease. It is
administered to day-old chickens as a subcutaneous injection while
the birds are in the hatchery. Use of the vaccine requires strict
accordance with manufacturer's recommendations in a sterile environment.
Infectious bursal disease is an acute,
highly contagious viral disease of young chickens. It is most
often found in highly concentrated poultry producing areas. It
causes marked morbidity and mortality in affected flocks. Although
the disease causes severe losses, its affect on reducing the bird's
ability to develop immunity to other diseases may be the most
serious effect produced by this disease.
The transmission or spread of the disease
can occur by direct contact (bird to bird), contaminated litter
and feces, caretaker, contaminated air, equipment, feed, servicemen
and possible insects and wild birds. It is extremely contagious.
Birds have ruffled feathers, a slight
tremor at onset of the disease, strained defecation, loss of appetite
and are dehydrated. Affected birds have a tendency to sit and
when forced to move, have an unsteady gait. Vent picking is common
and a whitish diarrhea frequently develops. A sudden rise in body
temperature is followed by a drop to subnormal temperature, prostration
and death. Birds surviving the initial infection will recover
rapidly within two weeks.
Postmortem lesions include dehydration
and changes in the bursa, skeletal muscle, liver and kidneys.
All affected birds have bursal changes characterized by swelling,
change in shape (oblong), color (pink, yellow, red, black) and
the formation of a gelatinous film around the bursa. Within a
few days the bursa shrinks to half its normal size or smaller.
Diagnosis of infectious bursal disease
is based on flock history and postmortem lesions. Laboratory procedures
may be used to substantiate the diagnosis.
Vaccines are available but must be
carefully used. If given correctly, good immunity can be developed.
There is no specific treatment for infectious bursal disease and
indiscriminate medication with certain drugs may severely aggravate
mortality. Supportive measures such as increasing heat, ventilation
and water consumption are beneficial.