Inclusion Body Disease

Inclusion bodies © RVC

Species predisposition

Inclusion body disease is seen in Boidae. In the past, the most commonly affected snakes were the Burmese pythons but the disease is now most often seen in Boa constrictors. It appears to be relatively uncommon in Royal pythons and has not been reported in Rosy boas. The occurrence of the disease in non-boids cannot be ruled out since typical signs and lesions have been reported in a Kingsnake. IBD is primarily seen in adult snakes, however all age groups should be considered susceptible. Young snakes tend to develop an acute infection with a mortality rate approaching 100%. Infected adult snakes often experience the disease in a more chronic and debilitating form.

Inclusion body disease (IBD) is a worldwide disease of Boidae and is named for the characteristic intracytoplasmic inclusions seen in the cells of affected snakes. The causative agent of has not been identified although a Retroviridae-like virus has been incriminated.

Examination

CNS derangement in Burmese python © RVC

Classically pythons developed acute CNS signs and boas presented with regurgitation. In fact clinical signs are very variable among species and individuals and may related to secondary bacterial infections in immunosuppressed boids.

Common clinical signs include the following:

• Lethargy
• Anorexia
• Weight loss
• Lack of weight gain
• Pale oral mucous membranes
• CNS problems including:
  • Incoordination
  • Disorientation
  • Loss of righting reflexes
  • Head tremors
  • Opisthotonous
  • Paresis to paralysis
• Regurgitation (partially digested possibly mucous-covered food food about one week post-prandial), stomatitis, diarrhoea, pneumonia, dermatitis and neoplasia.

For more information on physical examination of a snake, see Snake Physical Examination.

Diagnosis

Gastric mucosal inclusions© RVC

Since IBD presents with a variety of signs, any sick boid without an obvious aetiology should be suspected of IBD. Especially consider those with regurgitation, CNS signs and bacterial infections. A thorough physical examination may rule our other causes. Currently there is no serologic assay available for determining exposure. Diagnostic aids include the following:

Blood

Blood sample examination may be helpful. Haematology may show a leukocytosis with a lymphocytosis. The white blood cell count is variable, ranging from normal (immune system depression) to as high as 100,000. The leucocytes may show toxic changes. Smears are observed for the presence of inclusion bodies. Typically 1% of cells have the inclusion bodies so it is worthwhile doing a buffy coat smear. Biochemistry may show changes in liver parameters.

Note thick mucus filling the lung © Dr. Oscar Razioli

Biopsy and histology

Tissues for biopsy include oesophageal tonsils, liver, kidney and gastric mucosa. The presence of cytoplasmic inclusion bodies on histology is diagnostic for IBD. Sometimes very few inclusions are seen so absence of inclusions does not rule out the disease. For antemortem diagnosis biopsies may have be repeated several times to find inclusions. Characteristic histopathology may be seen in several tissues.

• For more infomation on taking samples from snakes, see Specimen Collection and Evaluation.

Necropsy

Necropsy shows changes associated with secondary bacterial infections. On histology, multiple tissues have been reported to contain cells with inclusions.

• For more information on postmortem of a snake, see Snake Necropsy.

Therapy

There is no known treatment. Euthanasia is recommended.

• For more information on euthanasia, see Lizard and Snake Euthanasia.

Prevention

A sound preventive medicine programme is the protection. All new snakes should be quarantined for a minimum of 90 days before introduction to others. For larger collections a quarantine of 6 months may be more appropriate. The exact route of transmission is unknown so hygiene and mite control are essential. Finally all infected snakes should be euthanased.

For more information on preventative veterinary medicine, see:

• Lizard and Snake Quarantine, and
• Lizard and Snake Day to Day Practice