High susceptibility of the endangered dusky gopher frog to ranavirus

Abstract

Amphibians are one of the most imperiled vertebrate groups, with pathogens playing a role in the decline of some species. Rare species are particularly vulnerable to extinction because populations are often isolated and exist at low abundance. The potential impact of pathogens on rare amphibian species has seldom been investigated. The dusky gopher frog Lithobates sevosus is one of the most endangered amphibian species in North America, with 100-200 individuals remaining in the wild. Our goal was to determine whether adult L. sevosus were susceptible to ranavirus, a pathogen responsible for amphibian die-offs worldwide. We tested the relative susceptibility of adult L. sevosus to ranavirus (103 plaque-forming units) isolated from a morbid bullfrog via 3 routes of exposure: intra-coelomic (IC) injection, oral (OR) inoculation, and water bath (WB) exposure. We observed 100% mortality of adult L. sevosus in the IC and WB treatments after 10 and 19 d, respectively. Ninety-five percent mortality occurred in the OR treatment over the 28 d evaluation period. No mortality was observed in the control treatment after 28 d. Our results indicate that L. sevosus is susceptible to ranavirus, and if adults in the wild are exposed to this pathogen, significant mortality could occur. Additionally, our study demonstrates that some adult amphibian species can be very susceptible to ranavirus, which has been often overlooked in North American studies. We recommend that conservation planners consider testing the susceptibility of rare amphibian species to ranavirus and that the adult age class is included in future challenge experiments.

Comparative Pathology of Ranaviruses and Diagnostic Techniques

“…Based on this result, the authors concluded that route of exposure and specifi c ranavirus isolate infl uenced the pathogenesis; however, both syndromes can develop within the same frog. The hemorrhagic syndrome is similar to pathological changes reported by Sutton et al ( 2014a ) in adult dusky gopher frogs ( Lithobates sevosus ).…”

“…1a, b ). Hemorrhages are most often present on the ventral surfaces near the vent, rear legs, and gular regions, but can also be observed around the eyes, ear drum, tongue, tail, and feet (Balseiro et al 2009 ;Cheng et al 2014 ;Cunningham et al 2007 ;Docherty et al 2003 ;Geng et al 2010 ;Kik et al 2011 ;Meng et al 2014 ;Sutton et al 2014a ). Raised skin plaques or polyps have been described in tiger salamanders ( Ambystoma tigrinum ) and Chinese giant salamanders (Jancovich et al 1997 ;Bollinger et al 1999 ;Geng et al 2010 ).…”

An ecological role for assortative mating under infection?

“…The same populations also show signs of directional selection at the MHC (Teacher et al 2009b) suggesting that the MHC could act as a basis for assortative mate choice. Globally, Ranavirus has been implicated in the declines of many species of amphibians, fish and reptiles (Cunningham et al 1996;Whittington et al 2010;Marschang 2011), including some of conservation concern, like the dusky gopher frog (Sutton et al 2014). They are considered such a threat to wildlife that the World Organisation for Animal Health has classified the type species, Frog virus 3, as a notifiable disease.…”

Ranavirus Host Immunity and Immune Evasion

“…In this regard, it is altogether not surprising that tadpoles are typically unable to fully control ranavirus infections and succumb to these pathogens (Bayley et al 2013 ;Grayfer et al 2014 ;Hoverman et al 2010 ;Landsberg et al 2013 ;Reeve et al 2013 ). However, it is clear that in some amphibian species, adult frogs also die from ranavirus infections (Sutton et al 2014 ). Indeed, several reports indicate that compared to larvae of given amphibian species, metamorphic (Brunner et al 2004 ;Haislip et al 2011 ;Reeve et al 2013 ) and adult (Duffus et al 2013 ) animals may be more susceptible to ranaviruses.…”