EXPERIMENTAL CHALLENGE STUDY OF FV3-LIKE RANAVIRUS INFECTION IN PREVIOUSLY FV3-LIKE RANAVIRUS INFECTED EASTERN BOX TURTLES (TERRAPENE CAROLINA CAROLINA) TO ASSESS INFECTION AND SURVIVAL

Abstract

The Maryland Zoo in Baltimore experienced an outbreak of Frog virus-3 (FV3)-like ranavirus during the summer of 2011, during which 14 of 27 (52%) of its captive eastern box turtles (Terrapene carolina carolina) survived. To assess survival, immunity, and viral shedding, an experimental challenge study was performed in which the surviving, previously infected turtles were reinfected with the outbreak strain of FV3-like ranavirus. Seven turtles were inoculated with virus intramuscularly and four control turtles received saline intramuscularly. The turtles were monitored for 8 wk with blood and oral swabs collected for quantitative polymerase chain reaction (qPCR). During that time, one of seven (14%) inoculated turtles and none of the controls (0%) died; there was no significant difference in survival. Clinical signs of the inoculated turtles, except for the turtle that died, were mild compared to the original outbreak. Quantitative PCR for FV3-like ranavirus on blood and oral swabs was positive for all inoculated turtles and negative for all controls. The turtle that died had intracytoplasmic inclusion bodies in multiple organs. Three inoculated and two control turtles were euthanized at the end of the study. No inclusion bodies were present in any of the organs. Quantitative PCR detected FV3-like ranavirus in the spleen of a control turtle, which suggested persistence of the virus. The surviving five turtles were qPCR-negative for FV3-like ranavirus from blood and oral swabs after brumation. Quantitative PCR for Terrapene herpesvirus 1 found no association between ranavirus infection and herpesvirus loads. In conclusion, previously infected eastern box turtles can be reinfected with the same strain of FV3-like ranavirus and show mild to no clinical signs but can shed the virus from the oral cavity.

Xenopus-FV3 host-pathogen interactions and immune evasion

“…This suggests that adult frogs surviving a primary ranavirus infection can remain resistant to a subsequent infection for long time. Indication of immunological memory leading to increased survival and/or improved viral clearance has been reported in turtles (Hausmann et al, 2015). Evidence documenting an active adaptive immune response against ranavirus infection is also emerging from recent transcriptome studies in the non-model amphibian Rana temporari species (Price et al, 2015).…”

“…This non-permissiveness of viral replication is enhanced in IL-34-derived (Grayfer and Robert, 2014, 2015). The possible role of macrophages as reservoirs for viral persistence in resistant hosts is of relevance given that ranavirus is increasingly detected in asymptomatic amphibian populations in the wild (Brenes et al, 2014; Forzan and Wood, 2013) as well as in captive turtle species (Hausmann et al, 2015). The threat of resistant animal carriers in propagating ranavirus infection is underscored by the fact that X. laevis adults can harbor quiescent virus prone to reactivation.…”

A novel herpesvirus detected in 3 species of chelonians

“…In the box turtles, quantitative PCR (qPCR) with a standard curve for TerHV1 was initially performed using methods described previously. 14 Additional pathogen testing was performed (Table 3).…”

Herpesviruses in Reptiles

“…Disease surveillance and research in wild populations of reptiles are associated with numerous challenges including difficulties in accessing samples or field data, misleading epidemiological data and missing population data, as well as political and cultural restrictions ( 11 ). These challenges well explain the use of captive wildlife as models in many studies to acquire epidemiological information, since diseases are comparable in both wild and captive animals ( 12 – 15 ). Nonetheless, more robust and ideal epidemiological data are obtained when free ranging animals are surveyed.…”