Dose-dependent morbidity of freshwater turtle hatchlings, Emydura macquarii krefftii, inoculated with Ranavirus isolate (Bohle iridovirus, Iridoviridae).

Ranaviral infections cause mass die-offs in wild and captive turtle populations. Two experimental studies were performed to first determine the susceptibility of an Australian turtle species (Emydura macquarii krefftii) to different routes of infection and second examine the effect of viral titre on the morbidity in hatchlings. All inoculation routes (intracoelomic, intramuscular and oral) produced disease, but the clinical signs, histopathology and time to onset of disease varied with the route. The median infectious and lethal doses for intramuscularly inoculated hatchlings were 102.52 (1.98-2.93) and 104.43 (3.81-5.19) TCID50 ml-1, respectively. Clinical signs began 14 to 29 days post-inoculation and the median survival time was 22 days (16-25) across all dose groups. For every 10-fold increase in dose, the odds of developing any clinical signs or severe clinical signs increased by 3.39 [P<0.01, 95 % confidence interval (CI): 1.81-6.36] and 3.71 (P<0.01, 95 % CI: 1.76-7.80), respectively. Skin lesions, previously only reported in ranaviral infection in lizards, were observed in the majority of intramuscularly inoculated hatchlings that developed ranaviral disease. The histological changes were consistent with those in previous reports for reptiles and consisted of necrosis at or near the site of injection, in the spleen, liver and oral cavity. Systemic inflammation was also observed, predominantly affecting necrotic organs. The estimates reported here can be used to model ranaviral disease and quantify and manage at-risk populations.

A novel virus (order Bunyavirales) from stressed redclaw crayfish (Cherax quadricarinatus) from farms in northern Australia.

Athtabvirus, a bunya-like virus and chequa iflavirus infect redclaw crayfish (Cherax quadricarinatus) and they may cause mortality reaching 20-40% after about three weeks following transportation stress. Lesions were seen in the muscles of broodstock and juveniles and nerve cords of craylings. Using NextGen sequencing, the whole transcriptomes of a farmed case crayfish and a tank-reared, unaffected crayfish were assembled producing over 500,000 contigs. The average depth of reads was 18 replicates with a range from 15 to 44. The near complete sequences of the large and middle genome segments of a bunya-like virus were detected along with chequa iflavirus. The internal bunya-like motifs; RNA-dependent RNA polymerase on the L segment, and glycoprotein n (Gn) on the M segment were easily identified. In the opposite, positive-sense direction on the M segment, another presumed glycoprotein (glycoprotein c) with a low-density lipoprotein receptor (cysteine-rich) motif was identified by position specific iterated (psi)-BLASTp. The athtabvirus was related to Whenzhou Shrimp Virus 2 (E = 0.0, 43% amino acid identity), an unassigned, -ve sense ssRNA virus, and to peribunyaviruses (E = 10-50-20). In descending order of the number of RNA copies/0.2 mg of tissue, the organs most heavily infected were muscle (9.4 × 106), nerve cord (5.24 × 106), heart (4.07 × 106), gills (3.96 × 106), hepatopancreas (1.58 × 106) and antennal gland (6.6 × 105). Given the tissue tropism (muscle and nerves) of athtabvirus and the original lesions, this virus is implicated in being involved in the mortalities in crayfish after transportation.