Xenopus Laevis: A Possible Vector of Ranavirus Infection?

Abstract

ABSTRACT:Frog virus 3 (FV3) or FV3-like viruses (Iridoviridae) infect a wide range of amphibian species, and they are becoming increasingly and causally associated with amphibian disease outbreaks worldwide. We have established the frog Xenopus laevis as an experimental model to study host defense and pathogenesis of FV3 infection. Although X. laevis adults usually clear FV3 infection within a few weeks, viral DNA has been detected in the kidneys several months after they had been experimentally infected; virus also has been detected in seemingly healthy nonexperimentally infected adults. Based on this information, we hypothesized that covert FV3 infection may occur in Xenopus. We first conducted a survey that detected FV3 by polymerase chain reaction (PCR) in the kidneys (the main site of FV3 infection) in a significant fraction of X. laevis raised in five different locations in the United States. Asymptomatic FV3 carriers also were detected by initiation of an acute systemic FV3 infection in frogs that had been immunosupressed by sublethal c-irradiation. Finally, we focused on macrophages as a potential site for viral persistence, and we showed that FV3 can infect peritoneal macrophages in vitro as determined by reverse transcriptase-PCR detection of viral mRNAs. Unlike kidney cell lines that are readily killed by FV3, infected macrophages, like uninfected macrophages, survived up to 12 days. Viral transcription also was detected in macrophages from animals up to 12 days after infection. These results suggest that FV3 can become quiescent in resistant species such as Xenopus, thereby making these species potential viral reservoirs.

Ranavirus Ecology and Evolution: From Epidemiology to Extinction

“…Alternatively, individuals of certain species or life history stages that are carriers (i.e., remain infected and infectious for long periods without clearing or succumbing to the infection) may act as reservoirs for more susceptible species or stages (Haydon et al 2002 ). In general, only a small fraction of individuals survive for weeks or months with inapparent infections (Langdon 1989 ;Cullen and Owens 2002 ;Brunner et al 2004 ;Robert et al 2007 ;Haislip et al 2011 ;Hoverman et al 2011 ;Brenes 2013 ;Brenes et al 2014b ). For example, of the 43 ectothermic vertebrate species challenged with FV3-like ranaviruses by Hoverman et al ( 2011), Brenes ( 2013), and Brenes et al ( 2014b, there was about an 85 % correlation between infection and mortality after 28 days.…”

Clinical signs, pathology and dose-dependent survival of adult wood frogs, Rana sylvatica, inoculated orally with frog virus 3 Ranavirus sp., Iridoviridae

“…Thus, the variability in experimental designs provides an abundance of valuable information but complicates comparisons and extrapolations. Amongst the multiple host species used in research, it is arguably in the African clawed frog, Xenopus laevis, that the host response of adult frogs to, and pathogenesis of, FV3 infection have been most extensively studied (Gantress et al, 2003;Robert et al, 2007Robert et al, , 2011. Adult X. laevis inoculated intraperitoneally with 10 7.7 p.f.u.…”

Efficacy of select disinfectants at inactivating Ranavirus

“…Ranaviruses cause disease in fish, reptiles and amphibians (Chinchar 2002, Converse & Green 2005, Robert et al 2007. Ranaviruses have been implicated in large-scale die-offs of amphibians in Europe, Asia, Australia, and the Americas (Converse & Green 2005, Picco et al 2007).…”

“…In May 2008, the World Organization for Animal Health (OIE) classified Ranavirus as a notifiable pathogen (OIE 2008), imposing guidelines for the importation of amphibians across international borders. There are no treatments or vaccinations currently available for ranaviruses (Robert et al 2007). …”