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AVIAN POLYOMA VIRUS AND ITS
DISEASE
1. Causative
Agent:
Polyomaviral disease was first
documented in the early 1970's as Budgie Fledgling Disease, caused by a virus of
the Polyoma family. Because of the unenveloped nature of this virus, it is very
resistant to environmental conditions and can survive for a substantial amount
of time in the environment into which it has been shed. Polyomavirus most likely
causes the most commonly encountered infectious viral disease of young
psittacine birds, and as such, is the most economically and emotionally damaging
facing psittacine aviculture to date.
2. Susceptible Species:
Virtually all bird species of
birds are susceptible to infection. This virus, its infection and the disease it
can cause can definitely no longer be assumed to be a "Budgie's
disease", and is actually most devastatingly encountered in the larger
parrot species. There are numerous reports of polyomaviral disease in Gouldian
finches as well. Not all bird species show the same clinical signs when
infected, however. Many species demonstrate no outwardly visible signs when
infected, but generate measurable antibody, which allows us to understand that
exposure, and infection has occurred. This is particularly true when speaking of
adult birds, as opposed to young hand feeding chicks, where the fulminating
disease is more common.
3. Clinical Signs:
As described in the original
literature in Budgerigars, clinical signs were seen to vary according to the age
of the bird. The younger the bird, the more severe the signs.
Budgerigar Fledglings:
-Feather abnormalities. Particularly lack of
(14 - 21 days)
down feathers or failure of normal down
feather
growth.
-Distended abdomen
-Slow crop emptying time
-Sudden death
Budgerigar Juveniles:
- Feather abnormalities, including the lack of or
growth of malformed tail and flight feathers. Birds
with these abnormalities used to be called
"French Moult" birds.
Budgerigar Adults:
-Feather abnormalities, usually the tail, wing, or
contour
feathers. Similar in appearance in many
respects
to the juveniles.
-Asymptomatic carriers are
common. Most of the
birds
that carry this virus are believed to be
survivors
of infection at an earlier age.
Larger Psittacine
Species:
-Slow or non-emptying crops. Usually fledglings
demonstrate
a sudden onset of clinical signs.
-Depression
-Bleeding or bruising anywhere on
the body,
including the crop and entire GI tract.
-Sudden death
Larger Psittacine
-Sub normal growth rates
Juveniles:
-Recurring bacterial or fungal infections
-Painful abdomen
-Bleeding or bruising anywhere on
the body.
Remember
this can include the urinary system
and
GI tract as well.
-Yellow colored urates and urine
-Slow crop emptying time
-Reluctance to wean
-Abnormal feathering as is seen
in the Budgerigar
group.
These are the classically reported signs only. In
clinical practice, adults can also be seen to be chronically infected with this
virus. Signs in adult psittacine species may include sudden death, neurological
disease, kidney disease, chronic liver disease, as well as poor beak, feather,
and nail growth. The only physical sign of Polyomavirus infection in a juvenile
bird may be immunosuppression, and this may well be hidden from easy diagnosis
underneath the secondary infections, which can arise. In reality, this disease
is very prevalent in domestic avicultural collections. Waiting for VISIBLE
symptoms or suggestion of the carrier state is clearly not the means of choice
for identifying birds that may be carrying the virus or clinically affected.
4. Diagnosis:
Noting the clinical signs in the appropriate age group
and species makes a presumptive diagnosis.
The definitive diagnosis is made
in the following manners:
A.
Post Mortem examination and histopathology.
B.
Biopsies of affected feathers and skin of live birds.
C.
DNA probe antigen testing: The presence or absence of virus
in a swab from a suspect patient
or its tissues can be determined. A cloacal swab may or may not be meaningful as
a screening tool for polyomavirus testing, as the virus is shed very
sporadically in most birds. This same reality applies when testing random tissue
samples as well, as there is no assurance that a negative DNA probe from
internal organ biopsies cannot provide assurance as to the true viral status of
the birds in question. A positive DNA probe is indicative of the presence of
Polyomavirus at the sampled site, but does not necessarily indicate that the
bird is infected, may die, is a carrier, or will recover uneventfully if
infected.
D.
Antibody testing (serology): this type of testing will
indicate if a bird has been
vaccinated, infected or exposed to polyomavirus. The presence of antibody does
NOT necessarily indicate that infection is currently present.
5. Treatment:
There is no specific antiviral treatment available. Supportive care including
fluid therapy, blood transfusions, and vitamin K1 may help with some
individuals. Prognosis depends on the age of the bird and the severity of
symptoms. Severe bleeding should be regarded as a grave sign. Most of the
Budgerigars that survive should be regarded as likely carriers, and this is also
believed to be true in Lovebirds. Carrier status of surviving large psittacine
species is not known for certain. Mortality will be higher when other disease
organisms are also present. The vaccine is NOT intended by any means to be used
as a treatment for a diseased individual.
6. Probable Routes of Transmission:
The exact routes of transmission are not known definitively. Carrier birds and
infected individuals probably shed the virus in the urine, feces, feather dust,
and crop contents. Routes of spread of the virus would therefore be virus
inhalation through aerosolized feather dust, carrier parents or infected babies
feeding young with virus laden crop contents, nursery spread of virus on hands,
equipment, in the incubator and isolettes or brooders. Vertical transmission
(through the egg) has recently been confirmed in the Budgerigar, and this route
of transmission is suspected in larger Hookbills.
7. Control of Clinical Disease:
As with most of the viral diseases of birds, controlling
the spread of the virus and its resultant disease are the primary keys to
success. Utilizing Closed Aviary Principles, alone, it is not likely that
occasional individual deaths will be avoided. Good Closed Aviary Practices
primarily serve to prevent further spread of the virus and its disease, thus the
collection and young in the nursery can be minimized from risk of
epidemiological losses. Vaccination, when used with closed aviary principles,
should virtually eliminate the occurrence of polyomaviral disease from a flock.
In The Case Of An Outbreak, What Do We Do?
Nursery:
A.
Disinfect between individual clutches of babies being fed. This should Also apply to anything that
passes from one group of birds to another, such as your hands, feeding
instruments, scales, and incubators or brooders. Consult with your avicultural
Veterinarian regarding which disinfectants are appropriate for your particular
circumstance. Wavicide, Bleach, and Nolvasan are popular brand name
representatives of effective disinfectants.
B.
Remove visibly affected individuals from your nursery. They are only another magnified source of
virus for your remaining young that are still at risk.
C.
Minimize dust, feathers, and aerosolized particles from the nursery. Install an air filter system if
possible. Preferably, have a non-porous floor such as vinyl, which can be
cleaned easily. Don't allow older birds to flap their wings and stir up feather
dust and dander. Preferably, remove these birds from your nursery if at all
possible.
D.
Disinfect yourself between servicing your adults and their nest boxes and your nursery. Do not
risk bringing virus into your nursery from your adults, which may be
asymptomatic carriers or subclinically infected.
E.
Do not bring chicks or eggs from your collection without disinfecting appropriately.
F.
Do not bring in chicks of eggs from outside of your collection.
Aviary:
A.
Consult with your avicultural Veterinarian as to the likelihood of where this virus may have
originated. If the resulting conclusions suggest that there probably are
carriers in your collection, consider having some screening tests done to
attempt to identify those birds. Keep in mind that these tests are not yet
reliable to definitively answer the question of carrier status at present
time. Also keep in mind that the occurrence of polyomaviral disease may
suggest that there are other immunosuppressive events or agents present in
your flock/aviary.
B.
Do not condemn carriers or suspect carriers. These birds can theoretically raise healthy
offspring, which should be immunologically resistant to the virus, but may be
contaminated on their surface by the virus. Contact between those offspring and
those of the non-carrier breeders should not be allowed. Separate proven carrier
parents from non-carrier adult breeders.
C.
Disinfect or destroy the nest boxes belonging to the carrier parents at the end of that breeding season.
Consider forcing some species into sexual inactivity until next season. Again,
consult with your Veterinarian as to what action is most appropriate for your
individual circumstance.
Vaccination:
Vaccination can and will continue to prove to be an invaluable tool in the
control of polyomavirus in the future. This vaccine is proven safe and
immunogenic in multiple psittacine bird species. Keep in mind, however, that
vaccination, without closed aviary principles, will not protect your birds from
any other disease process, and may not adequately protect alone against
polyomavirus. This relatively new product is recommended to be used in the
commercial and avicultural communities in the following manners:
Vaccinate all chicks starting at
day 21 of age. Repeat this vaccination in two weeks (day 35). It is believed
that "protective status" is achieved approximately two weeks following
this second boost. (Day 49) We are currently recommending that chicks from
vaccinated adults be started at day 28, and boosted at day 42.
This emphasizes the reality that
utilization of closed aviary concepts regarding traffic flow will be mandatory
as a part of the control of this deadly viral disease. Vaccination, alone, will
not serve industry and aviculture adequately.
Vaccinate adult breeding birds
twice in the same manner, and consider boosting them annually. This practice is
intended to prevent viral infection (amplification) in the flock, and
potentially result in the passage of antibody on through the egg, providing some
protection to chicks less than 21 days of age. It is believed that vaccination
of adult breeders is an integral and key component to polyomaviral preventative
health management.
Vaccinated chicks should NOT be
intermixed with unvaccinated stock, as carriers that may be present in the
vaccinated population may result in infection and disease in the unprotected
population. Vaccination DOES NOT treat the disease, nor does it eliminate the
carrier state. Vaccination will serve to protect uninfected birds from becoming
infected and diseased following exposure - if and when this should happen.
Important Considerations Prior to
Vaccination
An almost mandatory consideration pertinent to instituting a vaccination
program is that good sound avicultural medical consultation occurs between the
aviculturalist and their veterinarian. This vaccine is costly, and may not
necessarily be the most appropriate thing to institute for all flocks as an
initial venture into a flock improvement program. Occasionally, a costly
preventative health program, although well intended, can cause more economic
damage to the aviculturalist's finances than the disease it was intended to
prevent. With this in mind, we, at this hospital strongly encourage our
avicultural clients to enter into and established an overall flock health
program, which allows for a more complete, timely and appropriate address of the
true needs that are present. The details and specifics of a flock health program
are quite variable and are dependent on facility, business philosophy, bird
health status, record review and production desired. As a result, vaccination
for avian polyomavirus should be, most appropriately, viewed as a single tool
that can be used in the "big picture" of more comprehensive flock
health management.
There is no "vaccine" to prevent disease resulting from
malnutrition, overcrowding, poor aviary design, and violations of closed aviary
concept rules, poor business management or poor fiscal management of a
psittacine aviary. If it is not Polyomavirus that serves as "The Great
Equalizer" in a poorly managed aviary, any one of MANY other infectious
agents will.
Comments:
This viral disease should be regarded as the most threatening virus in
domestic psittacine aviculture today. Every year, there are increasing numbers
of young birds lost to this disease, and major epidemics and total nursery
losses are not uncommon. The results are financially and emotionally
devastating, not to mention the losses to the genetic pool that these dead
babies represent to their respective species preservation efforts. Threats of
and actual litigation pertinent to this disease are significantly on the rise.
Unfortunately, most of these unnecessary actions are directly related to a lack
of understanding of the virus, the disease it causes, and its control and
prevention.
Please don't hesitate to contact our office for further details regarding Flock
Health Management Programs or the proper implementation of a polyomavirus
vaccination program in your aviary.
Information
Provided by:
Brian
L.
Speer
,
DVM, DIP, ABVP, ECAMS
Certified
in Avian Practice
European-Certified
Avian Specialist
The
Medical
Center
For Birds
3807
Main Street
Oakley
,
CA
94561
Phone:
925-625-1878
Fax:
925-625-8511
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