Pathogenicity in six Australian reptile species following experimental inoculation with Bohle iridovirus

Abstract

Ranaviruses are able to infect multiple species of fish, amphibian and reptile, and some strains are capable of interclass transmission. These numerous potential carriers and reservoir species compound efforts to control and contain infections in cultured and wild populations, and a comprehensive knowledge of susceptible species and life stage is necessary to inform such processes. Here we report on the challenge of 6 water-associated reptiles with Bohle iridovirus (BIV) to investigate its potential pathogenicity in common native reptiles of the aquatic and riparian fauna of northern Queensland, Australia. Adult tortoises Elseya latisternum and Emydura krefftii, snakes Boiga irregularis, Dendrelaphis punctulatus and Amphiesma mairii, and yearling crocodiles Crocodylus johnstoni were exposed via intracoelomic inoculation or co-habitation with infected con-specifics, but none were adversely affected by the challenge conditions applied here. Bohle iridovirus was found to be extremely virulent in hatchling tortoises E. latisternum and E. krefftii via intracoelomic challenge, as demonstrated by distinct lesions in multiple organs associated with specific immunohistochemistry staining and a lethal outcome (10/17) of the challenge. Virus was re-isolated from 2/5 E. latisternum, 4/12 E. krefftii and 1/3 brown tree snakes B. irregularis. Focal necrosis, haemorrhage and infiltration of granulocytes were frequently observed histologically in the pancreas, liver and sub-mucosa of the intestine of challenged tortoise hatchlings. Immunohistochemistry demonstrated the presence of ranavirus antigens in the necrotic lesions and in individual cells of the vascular endothelium, the connective tissue and in granulocytes associated with necrosis or present along serosal surfaces. The outcome of this study confirms hatchling tortoises are susceptible to BIV, thereby adding Australian reptiles to the host range of ranaviruses. Additionally, given that BIV was originally isolated from an amphibian, our study provides additional evidence that interclass transmission of ranavirus may occur in the wild.

An unusual mortality event in Johnstone River snapping turtles Elseya irwini (Johnstone) in Far North Queensland, Australia

“…Ranavirus is capable of causing death in freshwater turtles and a strain from North Queensland has been shown to have extremely high pathogenicity in native freshwater fish, amphibians and turtles . Because of previous detection in North Queensland, and its potential to cause death in freshwater turtles, the samples were tested for the presence of ranavirus by PCR and culture, but it was not detected.…”

“…Immunohistochemistry was performed on sections using rabbit anti‐epizootic haematopoietic necrosis virus antibody (1 : 1500), according to methods previously described to detect the presence of ranavirus . Results were negative for the presence of ranavirus.…”

Serological survey of Australian native reptiles for exposure to ranavirus

“…Stock with a known history of exposure to ranavirus was not available, and antibody levels of experimentally infected animals was therefore assessed in relation to their initial levels and to that of non-exposed animals. Experimental challenge was performed as described by Ariel et al (2015). Briefly, turtles and crocodiles were assigned to 1 of 3 treatments: (1) a single intra-coelomic injection with 500 µl BIV (10 4.5 TCID 50 ml −1 ); (2) co-habitation (intra-coelomic injection with phosphate buffered saline [PBS]) housed with BIV-injected animals and (3) negative control (placebo as for the co-habitation animals).…”

“…In addition to these 3 treatments, snakes in the oral exposure group were fed 2 infected froglets inoculated in-traperitoneally with 50 µl live BIV (10 3.5 TCID 50 ) at 4 d post inoculation. At this dose rate, frogs died between 6 and 10 d after inoculation, and virus was isolated in cell culture from inoculated frogs, while samples from non-inoculated frogs did not produce cytopathic effect in cell culture via the viral isolation technique described by Ariel et al (2015). The day the infected froglets were eaten by the snakes was considered the first day of the challenge.…”

“…Experimental infections revealed that BIV is a pathogen of extreme virulence to certain Australian species with a wide host range among local species of amphibians, fish and reptiles (Moody & Owens 1994, Cullen et al 1995, Ariel et al 2015). This contrasts with the very few records of natural outbreaks in these experimentally susceptible species, which may be due to the vastness of the Australian wilderness combined with the cryptic nature of most of these species, and the low human population density to witness any such outbreaks.…”