Inclusion Body Disease (IBD) of Boid Snakes:
Boa constrictors and several species of pythons are most commonly affected by IBD. Boas are considered to be the normal host for this retrovirus because so many (up to 50% of those tested) are infected and they can harbor the virus for years without symptoms. Early symptoms, possibly precipitated by any factor causing immune suppression, include a history of unthriftiness, anorexia, weight loss, secondary bacterial infections, poor wound healing, dermal necrosis, and regurgitation. In essence, IBD should be considered in every sick boa. Typical findings in the acute phase of the disease include leukocytosis and a normal chemistry panel. As the disease progresses, white cell counts tend to decline to subnormal levels. Blood chemistry results are variable depending on how debilitated and dehydrated the boa becomes, but organ damage may appear. As the disease becomes chronic, some boas will exhibit neurologic symptoms ranging from mild facial tics and abnormal tongue flicking to failure of the snake to right itself when placed in dorsal recumbency and severe seizures.
Pythons are thought to be an abnormal host to the IBD retrovirus because the course of disease is more acute and neurologic symptoms more profound. In most pythons the acute symptoms that boas exhibit will be missed, and they will be presented with severe neurologic disease. While the active disease can linger for months or more in boas, most pythons die within days or weeks of the onset of clinical signs.
Exposure to this retrovirus appears to be due to a transfer of body fluids. Breeding, fight wounds, and fecal/oral contamination are common ways of transfer. Casual handling of an infected specimen and then a normal specimen does not appear to create enough viral exposure to cause infection. However, any immunocompromised reptile may be susceptible under the right circumstances. The snake mite is assumed to be responsible for the spread of the virus in large, well-maintained collections.
A tentative diagnosis is based on the history and clinical signs. Blood work will vary depending on the stage of the disease, but few diseases in snakes will cause such elevated white cell counts in the early stages. On blood smears, inclusion bodies are frequently found in the cytoplasm of leukocytes. One strain (3 strains have been isolated) of the virus frequently produces inclusion bodies in the cytoplasm of erythrocytes. The inclusion bodies are highly suggestive, but not 100% reliable. A definitive diagnosis is obtained via biopsy of internal tissues in which the characteristic inclusion bodies are found, eg, the liver, kidney, esophageal tonsils, and stomach. An ELISA is being developed.
IBD is not curable, and many clients may choose euthanasia. However, individuals may elect to isolate their snakes and treat with supportive and palliative measures. It is essential to educate clients not to sell infected specimens or their offspring, as this has caused the disease to spread worldwide.
