INFECTION IN BIRDS
By Dr Colin Walker BSc, BVSc, MRCVS,
MACVSc (Avian health)
Megabacteria are cigarette-shaped organisms
about 20 times the size of most common bacteria, which live in
the digestive tract of some birds. First identified in Australia
in budgerigars in the early 1990s, they have the potential to ulcerate
the lining of the bird’s Glandular Stomach. This leads to
loss of blood and tissue fluid, predisposes the bird to secondary
infection with other organisms and interferes with normal digestion.
Initially, as the ulceration begins, the birds develop diarrhoea
and become fluffed and quiet. As the disease progresses, the birds
start to lose weight and as the ulcers deepen and start to bleed
the birds become anaemic. This means they have trouble maintaining
their normal blood pressure and, as a result, their feet become
pale and cold to the touch. In severe outbreaks, 50% or more of
the birds can die.
Megabacteria infection is diagnosed usually by microscopic examination
of a bird’s dropping. However, our understanding of the
disease that Megabacteria causes has changed since the organism
was first identified. What we used to believe was that if the
organism was found in a bird’s dropping, then this would
be the cause of any digestive tract health problem it was experiencing
and that the bird should be immediately treated. We now realise
that this is not necessarily the case. We now know that although
the organism can cause disease in its own right, it is more often
a secondary agent, only becoming involved after some other disease
or poor management practice has already weakened the birds, making
them more vulnerable to disease generally.
Also, recent work at the University of Melbourne has shown that
the organism is not a bacterium at all but rather a yeast and
indeed the pattern of disease it causes is more typical of yeasts
rather than many bacteria. As a result of this recent work, the
organism has been renamed and now should be called by its correct
name Avian Gastric Yeast. However, the term Megabacteria is so
entrenched that its use is likely to persist.
It seems that Megabacteria are now fairly endemic in our Australian
budgerigar flocks and other types of birds, with many young birds
being passively exposed to the organism either directly from
their parents or other birds or droppings in the aviary from
a young age. With ongoing good care, fortunately in many cases
this low-grade ongoing exposure does not cause disease but rather
encourages the development of a natural immunity to the organism.
Disease comes when birds are exposed to a level of organism to
which the natural immunity they have developed is not strong
enough to protect them.
Typically, because of these factors, disease is seen most commonly
in the post-weaning time. Young birds have simply not been alive
long enough to develop the strong natural immunity of the adult
and yet are under multiple stresses that are inherent in the
weaning process such as separation from their parents, establishing
themselves in the new aviary, and learning to feed and water
themselves. Superimposed on this, any other stresses such as
overcrowding, low hygiene, poor nutrition or failure to provide
good control of other diseases during this time sets the stage
for a massive outbreak and particularly high losses.
Around the time the organism was first being identified, Dr
Fillipich of Queensland University trialled an extensive range
of antimicrobial agents to see which were effective against Megabacteria.
He found only one, an antiyeast/antifungal drug called Amphotericin
B. In Australia, this is available under several brand names.
There used to be a Squibb product called Fungilin, which contained
Amphotericin B as a thick orange syrup. Birds would not drink
this but it was useful in crop tubing individual birds. Unfortunately,
Squibb no longer manufacture this product. Squibb also produces
Amphotericin B in tablets, called Fungilin lozenges. Although
designed for human use, they can be adapted for use in birds
under veterinary advice. Usually a tablet is crushed into 6 ml
of water and 0.25 ml per 50g body weight of this solution is
given to sick birds daily. The tablet is not easy to dissolve,
however, it eventually forms a yellow suspension that will flow
through a crop needle. Alternatively, one tablet can be dissolved
into 80 ml of water and provided ad lib to unwell birds. The
usual suggested treatment time is at least 30 days. Do, however,
remember that many birds such as budgies are not obligate drinkers.
Unlike other birds, such as pigeons, which will rush to a drinker
if deprived of water for only a few hours, budgies and some other
birds can go without water for 20 days and still look basically
normal on the perch. This means that just because medicated water
is in front of them, there is no guarantee that they are getting
Another group of therapeutic agents which may help in managing
Megabacteria, which initially might seem a little bit strange,
are the acids. Stress disrupts the normal bowel bacteria, in
the process interfering with their lactic acid production. This
lactic acid keeps the pH of the healthy bird’s bowel on
the weakly acidic side, in the process helping to protect it
from disease. With stress, this innate protective mechanism can
be lost. It is thought that by lowering (ie acidifying) gastric
pH, an intestinal and stomach environment is created that not
only makes it difficult for Megabacteria to establish in uninfected
birds but also makes it difficult for Megabacteria to multiply
in birds that are already infected. Usually, either citric acid
(a white crystalline powder) at a dose of 1 teaspoon (3 g) to
4.5 – 6 litres or apple cider vinegar (acetic acid) 5 – 10
ml to 1 litre, are used. Being natural nutrients, at the above
doses, there is no risk of a toxic reaction and so they can be
used fairly freely. Their use also helps ensure that droppings
passed build up an acidic dressing in the aviary, helping to
inhibit Megabacterial survival in the environment.
Probiotics are also thought to be of use through promoting health
generally and by helping lower digestive tract pH through the
production of lactic acid.
So, what should you do if your veterinarian tells you that your
birds have Megabacteria? The correct answer depends on whether
the birds are unwell and if so, how many are affected. Being
a stress-based disease, only part of the answer involves the
use of medication.
If all of the birds appear clinically normal, the appropriate
thing to do is simply provide ongoing good care. With ongoing
good management practices and the maintenance of a good aviary
environment, the organism is unlikely to cause disease and the
low-grade ongoing exposure is likely to strengthen the birds
If small numbers of birds occasionally become unwell (and the
majority of aviaries fit into this group), a three-point plan
Megabacteria exposure to further birds is reduced by separation
of the unwell birds and a super thorough clean of the aviary.
Unwell birds are treated with Amphotericin B (usually Fungilin
lozenge solution, 0.25 ml per 50g body weight daily for at least
10 days via crop tube). There may also be benefit in treating
severely unwell birds with a broad-spectrum antibiotic to control
any secondary bacterial infection. Baytril 1 drop per 100g body
weight twice daily per bird is a good choice.
Aviary management and environment are reviewed to identify any
predisposing stresses that may have triggered the outbreak. To
be thorough, this should involve a veterinary health profile
to screen for any other concurrent health problems.
Ongoing good care is provided so that the majority of birds are
best placed to resist the disease. Acids or probiotics can be
placed in the water, mixed freshly each day, until a period without
new birds becoming unwell occurs.
If large numbers of birds become unwell, then the same basic
procedure is followed. It may no longer however be practical
to crop tube individual unwell birds with Amphotericin B, and
so water-based medications containing Amphotericin B (Fungilin
lozenge or Megabac S) may need to be used. In aviaries with severe
ongoing problems, the regular use of acids or probiotics, eg
2 days per week, may decrease the chance of severe disease outbreaks.