Inclusion Body Disease of Snakes

Date Published: 05/12/2017

Ultimately fatal, inclusion body disease (IBD) is a transmissible and progressive disease first described several decades ago. IBD is the most commonly diagnosed disease suspected to originate with a virus in captive boid (boas and pythons) snakes. No treatments or vaccines are available. 

Affected snakes usually die from secondary infections, such as bacterial (salmonellosis), fungal (aspergillosis), protozoal (amoebiasis), and blood infections that take over due to a weakened immune system. These infections cause diseases of the brain, lungs (pneumonia), liver, stomach, intestine, bones, and cancers of the blood (lymphoma). This is probably a consequence of immunosuppression since both red and white blood cells, as well as the cells of the bone marrow, also develop the typical inclusion bodies that probably impair the function of these cells.

In boas, the disease outcome varies; affected animals either die within weeks or months or become healthy-looking carriers of the disease. In contrast, pythons generally develop severe fatal neurological symptoms within a few weeks.

In boas and pythons with the disease, the main clinical signs of IBD are central nervous system (brain) symptoms, such as head tremor (shaking), pupils of uneven size, muscle spasms that cause the head to arch backwards (sometimes called stargazing), and regurgitation (vomiting) on and off. A lack of appetite is also a main sign. Snakes usually have multiple signs, which may also include a swollen mouth, poor body condition, skin disease, difficulty breathing, lethargy and decreased mental activity, impaired righting reflex (the ability to orient the body back to an upright position), decreased muscle tone, and constipation.

Snakes living in mixed species collections that add new snakes regularly and have poor quarantine protocols have a higher risk of getting IBD. The risk is particularly high when the captive collection has a snake mite (Ophionyssus natricis) infestation. Inadequate husbandry is the most common cause of immune suppression in snakes, often related to improper temperature and humidity, poor hygiene, and stress from excessive handling.

The cause of IBD is not yet confirmed; however, a viral infection (a type of retrovirus) has historically been considered the most likely cause. Recently, mounting evidence has pointed to a new and unusual arenavirus in the genus Reptarenavirus as the cause of IBD. While we do not understand how IBD is transmitted, it nonetheless spreads rapidly between captive animals, particularly when there is a snake mite infestation. Under specific laboratory conditions, a Reptarenavirus is zoonotic but the likelihood of people getting this virus from their snake is unknown and very unlikely.

Affected Snakes

IBD is most commonly known to affect boas and pythons from several genera. Snakes who can get this include Boa constrictors (Boa constrictor), green anacondas (Eunectes murinus), Haitian boas (Epicrates striatus), ringed tree boas (Corallus annulatus), garden tree boas (Corallus hortulanus), Burmese pythons (Python molurus), reticulated pythons (Malapython (Python) reticulatus), ball pythons (Python regius), and Australian pythons (Morelia spilota variegata and Morelia spilota spilota).

A similar disease has been described in colubrid species of snakes, such as the Californian king snake (Lampropeltis getula) and corn snakes (Pantherophis guttaus) and in viperids, i.e., captive palm vipers (Botriechis marchi).

Given the variety of snake species that have been diagnosed with IBD, it is likely that any species of snake can be infected. Age or sex predispositions have not been well documented.

Diagnosis

Your veterinarian will start by taking a thorough medical history and give a physical examination. The snake should also have blood taken for a complete blood count and plasma chemistry in addition to X-rays.

Until now, the diagnosis of IBD relied entirely on looking under the microscope and seeing the inclusion bodies in blood cells and organ biopsy specimens. Thanks to the identification of Reptarenavirus, there is now a laboratory test (reverse transcription-PCR  or RT-PCR) to diagnose IBD. The most sensitive test is a consensus PCR with sequencing to identify the type of Reptarenvirus that your snake has.  Mouth swabs, blood samples and organ tissue samples can be used for the RT-PCR test.

Treatment

Treatment of individual animals has not been effective. Because IBD is fatal, the vast majority of snakes confirmed to have it should be humanely euthanized, and a complete necropsy (the veterinary term for autopsy) should be performed.

However, in some cases with just one snake in the collection, supportive treatment measures including fluids, antibiotics, and force feeding) may be attempted. We don't know which snakes might respond, and it may not help at all.

A recent study suggested that some snakes may be able to clear (cure themselves) an IBD infection but this is preliminary and more studies are needed to confirm that this is true.

Prevention

The goal is not to allow the disease to enter the collection. Quarantine monitoring is critical: all snakes coming into a collection should have esophageal tonsils or whole blood tested for Reptarenavirus by consensus PCR with sequencing. After adding a new snake, all of the individuals in a collection should be tested this way and re-evaluated in six to 12 months. False negative tests (which says the snake does not have IBD but really does) are unfortunately possible, however.

Getting rid of any mite infestation is essential.

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