Ecopathology of Ranaviruses Infecting Amphibians

Abstract

Ranaviruses are capable of infecting amphibians from at least 14 families and over 70 individual species. Ranaviruses infect multiple cell types, often culminating in organ necrosis and massive hemorrhaging. Subclinical infections have been documented, although their role in ranavirus persistence and emergence remains unclear. Water is an effective transmission medium for ranaviruses, and survival outside the host may be for significant duration. In aquatic communities, amphibians, reptiles and fish may serve as reservoirs. Controlled studies have shown that susceptibility to ranavirus infection and disease varies among amphibian species and developmental stages, and likely is impacted by host-pathogen coevolution, as well as, exogenous environmental factors. Field studies have demonstrated that the likelihood of epizootics is increased in areas of cattle grazing, where aquatic vegetation is sparse and water quality is poor. Translocation of infected amphibians through commercial trade (e.g., food, fish bait, pet industry) contributes to the spread of ranaviruses. Such introductions may be of particular concern, as several studies report that ranaviruses isolated from ranaculture, aquaculture, and bait facilities have greater virulence (i.e., ability to cause disease) than wild-type isolates. Future investigations should focus on the genetic basis for pathogen virulence and host susceptibility, ecological and anthropogenic mechanisms contributing to emergence, and vaccine development for use in captive populations and species reintroduction programs.

Sequencing and analysis of the complete genome of Rana grylio virus (RGV)

“…Ranaviruses have a wide range of hosts, including fish, amphibians and reptiles, and they can be translocated across large distances with ecological and economic consequences [36]. There is evidence that the ancestral ranavirus was a fish virus and that several recent host shifts have taken place, with subsequent speciation of viruses in their new hosts [11].…”

Rana grylio virus TK and DUT gene locus could be simultaneously used for foreign gene expression

“…They have been involved in epizootics and mass die-offs of amphibian population, identifying them as emerging infectious pathogens (Chinchar and Waltzek, 2014;Jerrett et al, 2015). In the case of amphibians, at least 70 individual species from 14 families could be infected by one or more ranaviruses (Miller et al, 2011). Ranavirus-associated mortality has been global distributed and reported on 5 continents (Gray et al, 2009).…”

Design and Analysis of Ranavirus Studies: Surveillance and Assessing Risk

“…Currently, there are few proposed control options for ranavirus, but vaccine development is possible in the future (Miller et al 2011). Other options include quarantining individuals or populations, culling, and creating captive populations for reintroduction if disease is likely to cause extremely high mortality to populations of conservation concern.…”

“…Host species could be exposed to the virus in water, which is an efficient transmission medium, or the virus could be transmitted by direct contact or consumption of infected hosts (Miller et al 2011). There is some evidence that ranavirus transmission can be density independent, which can increase extinction probabilities (Brunner et al 2015).…”