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INCLUSION
BODY DISEASE VIRUS
History:
Inclusion body disease of boid snakes has been
recognized since the mid 1970's. It is named for
the characteristic intracytoplasmic inclusions
which are seen in epidermal cells, oral mucosal
epithelial cells, visceral epithelial cells, and
neurons. In the 1970's, through the late 1980's,
this disease was most commonly seen in Burmese
pythons, Python molusus bivittatus. Starting in
the late 1980's until present, it has been seen
most commonly in boa constrictors, Boa constrictor.
Host:
All boid snakes should be considered susceptible.
While the disease has not been identified in non-boid
snakes, it is unknown whether nonboid snakes can
harbor the virus. The primary host of this virus
has not been identified.
Distribution:
Worldwide in captive boid snakes. Its occurrence
in the wild is unknown.
Ages Affected:
Has been identified primarily in adult snakes.
However, all age groups should be considered susceptible.
There are anecdotal reports of infection in neonates.
Etiologic Agent:
A retro-like virus has been incriminated as
the causative agent of IBD (Figure 1). We have
an isolate from a boa constrictor that will be
used in a transmission study to fulfill Koch's
postulates and determine if it is the causative
agent. reverse transcriptase activity has been
demonstrated in supernatant from viper heart cells
infected with this virus. This virus is currently
being purified for biochemical characterization
and production of polyclonal antibodies in rabbits.
Clinical Signs:
Clinical signs are quite variable. Regurgitation
and signs of central nervous system disease (Figure
2; Figure 3; Figure 4A and Figure 4B) are commonly
seen in boa constrictors. Stomatitis, pneumonia,
undifferentiated cutaneous sarcomas (Figure 5),
lymphoproliferative disorders, and leukemia have
all been seen. Burmese pythons generally show
signs of central nervous system disease without
manifesting any other clincal signs; regurgitation
is not seen in Burmese pythons.
Pathology:
By light microscopy, in hematoxlin and eosin
stained tissues sections of a wide variety of
epithelial and neuronal cells, characteristic
intracytoplasmic inclusions are seen. Several
snakes have been seen with proliferative pneumonia
(Figure 6). While inclusions are commonly seen
in the liver, kidney, and pancreas (Figure 7;
Figure 8; Figure 9), we have seen cases where
there are very few inclusions. In a few snakes
with signs of central nervous sytem disease, and
with a severe encephalitis, no inclusions have
been seen in any cells. While the presence of
chracteristic inclusions is diagnostic for the
disease, the absence of inclusions does not necessarily
mean the snake is disease or IBD virus free. While
cells having inclusions may show mild degeneratve
changes, inflammation is rarely seen in visceral
tissues. In the brain, mild to severe encephalitis,
with lymphocytic perivascular cuffing may be seen.
Several snakes with lymphoproliferative disorders
have been identified with lymphoid infiltrates
in multiple organs.
Transmission:
Exact route of transmission has not been identified.
Possibly by: 1) direct contact; 2) intrauterine
transmission to developing embryos in viviparous
species and eggs in oviparaous species; 3) veneral
transmission. The snake mite, Ophionyssus natricis
has been implicated as a vector for the virus
since mite intestations are commonly seen in epizootics
of IBD.
Diagnosis:
Currently there is no serologic assay available
for determining exposure. We are working toward
developing an immunoflourescence assay. At the
University of Florida College of Veterinary Medicine,
we perform complete blood counts on suspect snakes.
Infected snakes commonly have white blood cells
counts >30,000/ul. Intracytoplasmic inclusions
are occasionally seen in peripheral lymphocytes
(Figure 10). We also take esophageal, gastric,
and liver bopsies. If inclusions are identified
in any cells, euthanasia is recommended.
Control:
Identify infected snakes and euthanatize.
All new snakes should be quarantined for minimally
90 days before introduction into an established
collection. Recommendations for boas is 6 month
quarantine period. Mite control and elimination
is essential. Fibroglass cages of infected snakes
should be cleaned with chlorox and left out in
the sun to dry before being used for other snakes.
Wooden cages, unless sealed with urethane or some
other sealeant should be discarded.
Current and Future Research:
- Isolation and purification of the causative
agent.
- Development of a serodiagnostic test.
References:
- Schumacher, J., Jacobson, E.R.; Homer, B.L.;
Gaskin, J.M. 1994. Inclusion body disease in
boid snakes. J. of Zoo and Wildlife Med. 25(4):511-524.
- Axthelm, M.K. 1985. Viral encephalitis of
boid snakes. Int. Colloq. Pathol. Reptiles Amphib.
3:25. (Abstract)
For More Information Contact:
Dr. Elliott Jacobson
Box 100126
Department of Small Animal Clinical Sciences
College of Veterinary Medicine
University of Florida
Gainesville, Florida 32610
Dr. Juergen Schumacher
Box 100126
College of Veterinary Medicine
University of Florida
Gainesville, Florida 32610
UFL. 1996. IBD Virus Info. Originally published
at http://www.vetmed.ufl.edu/sacs/wildlife/IBDINFO.html.
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