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What You Need To Know About Viral Diseases in Snakes


Isolating viruses from snakes is a relatively recent event. Historically, most of the infectious diseases characterized in snakes were reported to have a bacterial origin. It is possible that some of these findings were the result of limited diagnostic capabilities. With the advent of new diagnostic methods, such as enzyme-linked immunosorbent assay and the polymerase chain reaction technique, more viral diseases can be expected to be identified in the future.

Herpes or herpes-like viruses have been isolated from Indian cobras (Naja naja), Siamese cobras (N. naja kaouthia), and banded kraits (Bungarus fasciatus).The isolates from the Indian cobra and krait were incidental findings from the snake's venom. The herpes-like virus isolated from the Siamese cobra was associated with pathological changes in the venom gland. Herpes-like virus has also been isolated from juvenile boa constrictors (Constrictor constrictor). Intranuclear inclusions were found in the liver, pancreas, kidney, and adrenal cortex in two of the snakes.

The limited number of herpes virus infections reported in snakes might suggest that the virus is rare in ophidians; however, a lack of confirmed diagnoses may also be associated with limited diagnostic test availability or a failure of veterinarians to pursue these cases. To date, there has been no specific treatment recommendation for ophidian herpes virus infections, although acyclovir may be used to suppress infections.

Adenovirus has been isolated from a single adult boa constrictor, two rosy boas (Lichanura trivirgata), and a royal python (Python regius). The histopathologic findings in the snakes were similar to those lesions described for higher vertebrates, including hepatocellular necrosis and basophilic intranuclear inclusions. The route of transmission for this virus has not been described, although minimizing contact with any secretion from an infected snake is strongly recommended.

Paramyxovirus (PMV) is one of the best-documented viral infections in snakes. The first report of this virus was from a collection of Fer-de-lance (Bothrops atrax) from Switzerland. Since that time, PMV has been isolated from both viperid and non-viperids. All snake species should be considered susceptible to PMV.

The route of transmission for this virus is likely through contact with contaminated respiratory secretions. Affected snakes may have nasal discharge and purulent hemorrhagic discharge from the glottis. Neurologic disease has also been reported to occur with PMV.

Diagnosis can be made using a hemagglutination inhibition assay or by viral isolation. Because the HI assay is a serologic assay, serial samples are required to confirm an active infection. Pulmonary hemorrhage and caseous debris are common findings at post-mortem.

There is no current therapy for this virus. Trials evaluating a PMV vaccine have proven ineffective.Quarantine of new acquisitions is strongly recommended. The quarantine period should be at least 3 months. A thorough examination and a minimum of two negative assays should be performed prior to releasing the animal from quarantine.

Legacy Reptiles @

Inclusion body disease (IBD) can be a devastating disease in snake collections. The suspected etiology of IBD is a retrovirus; however, this has yet to be confirmed. Although this disease is generally associated with boas and pythons, IBD has been reported in other species of snakes. In general, boa constrictors present with a history of regurgitation and mild central nervous system dysfunction, such as a postural change (stargazing), slowed righting reflex, and impaired locomotion. Pythons generally present for more severe disturbances of the central nervous system, including a loss of the righting response, opisthotonos, and paralysis. As the disease progresses, snakes generally experience weight loss, dysecdysis, and secondary opportunistic infections, such as stomatitis, dermatitis, and pneumonia. The severe neurologic disease characterized in pythons generally limits their ability to acquire food; therefore, regurgitation is rarely noted in pythons.

The route of transmission for IBD has not been determined. However, clinical disease has been identified in snakes that have direct contact with infected individuals and with snake mites (Ophionyssus natricis). Diagnosis can be attempted ante-mortem from biopsies of the kidney, pancreas, esophagus, and liver. Eosinophilic intranuclear inclusions may be observed within the tissues when using a hematoxyin and eosin stain. Inclusion bodies may also be observed in red blood cells (RBC). However, only trained individuals should perform this procedure, as RBC non-viral inclusions are not uncommon finding in reptiles. Because of the low sensitivity of biopsy, false negative results are possible. One of the difficulties in characterizing IBD is that boas have been shown to harbor endogenous retroviruses. Because adenoviruses and reoviruses have also been isolated from snakes with neurologic disease, it is difficult to determine if these viruses also play a role in IBD. Post-mortem examination should also include samples from the CNS. Encephalitis is a common finding on pathology.

There is no effective treatment for IBD. Because this disease appears to be highly contagious, affected snakes should be culled and euthanized after ante-mortem confirmation. Preventing the introduction of O. natricis into a collection and quarantining new arrivals is strongly encouraged to reduce the likelihood of introducing IBD into an ophidian collection.

**References available upon request.

Orlando Diaz-Figueroa, DVM, MS, Dipl. ABVP (Avian Specialty)