Pathology and serological aspects of Bohle iridovirus infections in six selected water-associated reptiles in North Queensland

Ariel, Ellen (1997) Pathology and serological aspects of Bohle iridovirus infections in six selected water-associated reptiles in North Queensland. PhD thesis, James Cook University.

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Abstract

Bohle iridovirus is a pathogen with a broad host range and high virulence in susceptible native animals in northern Australia. The virus is inactivated at temperatures above 32°C and therefore potential hosts are limited to poikilothermic animals. The only vertebrate class of poikilothermic animals which has not yet been studied with respect to Bohle iridovirus infections is the Reptilia. This thesis reports on investigations of the pathological and serological responses to Bohle iridovirus in selected water-associated reptiles.

The reptiles were selected on the basis of their association with either animals or environments that were known to potentially harbour Bohle iridovirus. Certain species of fish and frogs are known to be highly susceptible to Bohle iridovirus and they are both found in or near freshwater habitats. In Australia, tortoises, freshwater crocodiles and certain species of colubrid snakes prey on fish and amphibians and dwell in aquatic or riparian habitats. The species chosen for this study are endemic to north Queensland where Bohle iridovirus was first isolated, and consist of the tortoises, Emydura krefftii and Eiseya latistemum, the freshwater crocodile, Crocodylus johnstoni, the colubrid snakes, Boiga irregularis, Dendrelaphis punctulatus and Amphiesma mairii.

An enzyme linked immunosorbent assay was developed for the detection of serum proteins reactive to Bohle iridovirus in the selected reptiles. Reptilian test sera were used as the capture antisera in a sandwich enzyme linked immunosorbent assay which constitutes the first serological test for detection of reactivity to an iridovirus in reptiles. It enabled the monitoring of possible antibody responses to Bohle iridovirus in experimentally infected reptiles.

All six species were found to be capable of producing detectable levels of serum reactivity to Bohle iridovirus. Experimental animals were monitored for four weeks following either a single inoculation of live Bohle iridovirus, cohabiting with inoculated animals or by being fed artificially infected prey. Within treatments, animals did not consistently produce a detectable response.

Tortoise hatchlings of both Emydura krefftii and Elseya latistemwn were found to be extremely susceptible to Bohle iridovirus. Within four weeks hatchlings died with pathological changes in the liver, kidney, spleen, submucosa and pancreas. The virus was re-isolated from experimentally infected individuals.

Adult tortoises, yearling freshwater crocodiles and the three species of snakes did not appear to be adversely affected during the experimental period by exposure to Bohle iridovirus. There were no mortalities or pathological changes in these animals which could be directly attributed to a Bohle iridovirus infection. The virus was re-isolated from a single Boiga irregularis individual at four weeks following inoculation with live virus.

A serum survey of wild populations of the above-mentioned reptiles in selected water courses of north Queensland revealed individuals with Bohle iridovirus-hyperimmune sera at several locations. For Emydura krefftii and especially Crocodylus johnstoni a strong trend was found for larger animals to have higher levels of serum reactivity to Bohle iridovirus than the smaller animals in the sample.

The tendency for juveniles to be highly susceptible in comparison to adults which was reported for both fish and amphibians, seems also to be true for reptiles. Bohle iridovirus is extremely virulent in hatchling tortoises under the experimental conditions used, whereas adult tortoises and snakes and yearling crocodiles are not adversely affected in the short term.

Pre-experimental mortalities and intercurrent disease were thoroughly investigated as part of the monitoring of the well-being of experimental animals, but also to determine if these incidental findings were in some way influenced by the pathogen studied, or vice versa. In the freshwater crocodiles such investigations resulted in the recording of concurrent gout and hypovitaminosis A in hatchlings and also the first diagnosis of mycobacteriosis in young freshwater crocodiles.

In the wild, juveniles exposed to the virus may either succumb to infection or they may be excluded from Bohle iridovirus infection by certain behavioural features, because only serum from the larger animals were found to have high levels of Bohle iridovirus reactivity. Adult tortoises are abundant across the Australian continent. They are easily captured and can readily survive exposure to Bohle iridovirus while producing Bohle iridovirus antibodies at levels detectable by enzyme linked immunosorbent assay. Therefore they are good indicator species for a past presence of Bohle iridovirus in a particular freshwater environment. The use of such sentinel animals together with the enzyme linked immunosorbent assay described here, can survey the spread of Bohle iridovirus in northern Australia, and help to confirm the potential dangers to native fauna from this agent.

Item ID: 27712
Item Type: Thesis (PhD)
Keywords: Bohle iridovirus; tortoises, Emydura krefftii; Eiseya latistemum; Crocodylus johnstoni; Boiga irregularis; Dendrelaphis punctulatus; Amphiesma mairii; North Queensland; serum reactivity; susceptiblity attributes
Date Deposited: 26 Jun 2013 01:04
FoR Codes: 06 BIOLOGICAL SCIENCES > 0601 Biochemistry and Cell Biology > 060101 Analytical Biochemistry @ 49%
06 BIOLOGICAL SCIENCES > 0605 Microbiology > 060502 Infectious Agents @ 51%
SEO Codes: 96 ENVIRONMENT > 9604 Control of Pests, Diseases and Exotic Species > 960402 Control of Animal Pests, Diseases and Exotic Species in Coastal and Estuarine Environments @ 49%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 51%
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