INFECTIONS IN BIRDS
By Dr Colin Walker BSc, BVSc, MRCVS,
MACVSc (Avian health)
Streptococcus is the name given
to a group of dot-shaped bacteria that are capable of causing disease
in birds. They are everywhere in the environment, mainly in the
dust and air. Many species have been isolated from birds and they
are considered part of the normal bacteria found on the skin and
the lining of the digestive, respiratory and reproductive tracts.
There are different types of Streptococcus that vary in their ability
to cause disease. Transition from a normal bacterial inhabitant
to a disease agent depends on how effectively the birds’ immune
system is operating.
Experimentally, researchers have deliberately infected budgerigars
with disease-causing strains of Streptococci, both by intravenous
injection and by mouth. Many of those infected by the intravenous
route became sick, developing a variety of symptoms. Interestingly
however, in the birds inoculated with the organism by mouth,
none became sick, although the organism could be cultured from
the droppings or mouth of at least half of the birds in the month
following infection. This experiment helps to explain the nature
of the disease process with Streptococcus. Birds are obviously
being exposed to the organism intermittently but when an otherwise
healthy bird ingests the organism, disease is unlikely to occur.
Once the organism, however, gains entry to the blood stream,
the bird can become unwell. In some studies, potentially harmful
species of streptococci have been recovered from the intestines
from up to 40% of healthy budgerigars. Many budgerigars obviously
carry these organisms without becoming sick. As with other diseases
in birds, there needs to be a trigger factor that enables the
organism to invade the blood stream and spread throughout the
body. This trigger is essentially any factor that runs the bird
down. Predisposing factors include poor management, poor aviary
environment and concurrent disease, but also the ability of the
type of streptococcus itself to cause disease.
Signs associated with disease
Once the bacteria have invaded the body of a vulnerable bird,
it can spread to a variety of sites. This, together with the
fact that the severity of the disease can vary, leads to a
wide variety of symptoms that often mimic other diseases. It
is therefore important that bird fanciers do not jump to a
premature conclusion that this is the problem with any unwell
birds they may have.
Once the organism invades from the bowel or skin, etc, into
the blood stream, it can be carried to a wide variety of sites.
The symptoms displayed by the birds depend on the actual site
within the body that the bacteria infect and also the severity
of the infection. Disease displayed by the birds can be per acute
or chronic. Some birds develop a severe overwhelming disease
and will die so quickly that they do not have time to lose condition.
These birds become quiet, fluffed up and die within 2 – 3
days. Other birds, develop a chronic ill-thrift type condition
that may persist for as long as 6 – 8 weeks. Some of these
birds with treatment will recover, while others will eventually
die. In some apparently recovered birds, relapses can occur.
In still other birds, the disease may be transient and mild.
In some infected birds, the organism will localise in the respiratory
system, leading to red watery eyes, a nasal discharge and difficulty
breathing. In other birds, the liver can be affected, leading
to a green diarrhoea and weight loss. In some birds, the heart
itself may become infected. If these birds survive, they may
develop long-term heart problems, leading to a chronic shortage
of breath. The organism can also infect the membrane around the
brain (leading to poor coordination, loss of balance, or a head
tilt), the muscles (leading to bleeding and inflammation), the
joints (leading to swollen red painful joints, in particular
in the wings and legs), the kidney (leading to a thirst and excessive
urination), the bowel (leading to diarrhoea), the abdomen (leading
to fluid accumulation and a swollen abdomen) and testicles (leading
to premature infertility in young cocks). Notably, the organism
can also infect the ovary and fallopian tube of hens. This can
lead to interference with ovulation, meaning that some hens will
become sterile or lay eggs late or irregularly. In those that
do lay, the organism can be incorporated in the egg at the time
of its formation, leading to embryonic death during incubation
or a weakened chick that dies during hatching or shortly after.
Because the organism is found in birds droppings, it can contaminate
the nest box and infect the healing navel of recent hatchlings.
Because of the wide variety of symptoms associated with the disease,
the disease cannot be diagnosed by the signs displayed by the
birds. Similarly, the disease cannot be diagnosed through examination
of the droppings as it is found there normally in many budgerigars
and most of these will be quite healthy. The only way to diagnose
the disease is by culturing the organism from certain organs
during autopsy. Swabs for culture are usually taken from the
heart, brain, liver or a visible lesion.
Treatment and control
As always, good ongoing care will mean that most birds are able
to resist the disease and those that do get sick are in the best
situation to recover. When Streptococcal disease is diagnosed,
it is vital for the bird fancier to identify and correct the
flaw in his management or aviary environment that has enabled
the disease to flare up in the first place. Otherwise, a poor
response to any medication can be anticipated.
Being a bacterial infection, the organism responds to antibiotic
treatment. And so, what are the best antibiotics to use? The
best way to treat is to have your veterinarian culture the Streptococcal
organism involved in your outbreak and also have him do what
is called a sensitivity test in order to ascertain what is the
most effective antibiotic for that particular strain of Streptococcus.
Studies do, however, show that 80% of organisms are controlled
by the antibiotics ampicillin (a synthetic penicillin) and doxycycline,
while 70% are sensitive to erythromycin, 30% are sensitive to
enrofloxacin (Baytril) and only 10% are sensitive to sulfur-based
antibiotics. Obviously, the two poorest drugs are Baytril and
the sulfur-based antibiotics, so they are not likely to be the
first choice for treatment of this disease (although obviously
they are useful in other situations). In the absence of testing,
doxycycline is the usual choice as it is equally effective as
the synthetic penicillins but is more economical.
As with other bacterial bowel diseases, probiotics have a significant
role to play in the control of Streptococcal infections. They
can be used in times of stress when the normal bowel bacteria
are disrupted to minimise the risk of Streptococcal invasion
and also to preventatively treat healthy birds that have been
in contact with birds infected with Streptococcus. Gerald Binks,
in his excellent book The Challenge, discusses how Streptococcal
diarrhoea can be avoided in birds taken to shows if the birds
are treated with probiotics, eg Probac, for several days before
and after the show.
Maintenance of a clean, dry aviary will minimise exposure to
the organism. If necessary the aviary can be disinfected. Streptococci
are sensitive to most of the commonly used disinfectants.
When Streptococcal infection occurs in an aviary, it will spread
slowly through the flock and some birds will start to die. When
testing by your veterinarian confirms the disease, the following
protocol can be followed:-
Unwell birds are separated and either treated intensively in
a hospital cage environment (heat, fed and medicated by crop
tube etc.) or culled.
Aviary cleaned and disinfected.
Trigger factors such as overcrowding, poor diet, low hygiene,
inadequate parasite control, cold or damp conditions etc etc,
are identified and corrected.
Start in-contact healthy birds on probiotics.
If further birds continue to become unwell while on the probiotic
treatment, then start a flock treatment of antibiotic eg. Doxycycline, “Doxyvet”.