Amphibian ranaviruses in Europe: important directions for future research

Abstract

Ranaviruses are an emerging group of pathogens capable of infecting all cold-blooded vertebrates. In Europe, ranaviruses pose a particularly potent threat to wild amphibian populations. Since the 1980s research on amphibian-infecting ranaviruses in Europe has been growing. The wide distribution of amphibian populations in Europe, the ease with which many are monitored, and the tractable nature of counterpart ex situ experimental systems have provided researchers with a unique opportunity to study many aspects of host–ranavirus interactions in the wild. These characteristics of European amphibian populations will also enable researchers to lead the way as the field of host–ranavirus interactions progresses. In this review, we provide a summary of the current key knowledge regarding amphibian infecting ranaviruses throughout Europe. We then outline important areas of further research and suggest practical ways each could be pursued. We address the study of potential interactions between the amphibian microbiome and ranaviruses, how pollution may exacerbate ranaviral disease either as direct stressors of amphibians or indirect modification of the amphibian microbiome. Finally, we discuss the need for continued surveillance of ranaviral emergence in the face of climate change.

Diet- and salinity-induced modifications of the gut microbiota are associated with differential physiological responses to ranavirus infection in Rana sylvatica

“…We investigated how the environment affects infection severity and physiological host responses, and whether these outcomes were associated with altered microbiome assembly within the wood frog : ranavirus host–pathogen system. Ranaviruses (family Iridoviridae) are a leading cause of die-offs of amphibian larvae in North America [31] and post-metamorphic amphibians in Europe [32,33]. Initial ranavirus infection in tadpoles occurs through the gastrointestinal system [34], then spreads through infected immune cells to the body (e.g.…”

Gene functions of the Ambystoma altamirani skin microbiome vary across space and time but potential antifungal genes are widespread and prevalent

“…For example, bacteria present in amphibian and bat microbiomes can inhibit the growth of fungal pathogens that have caused severe population declines in both groups of vertebrates [3,5,23,24]. Amphibians nowadays are considered the most vulnerable group of vertebrates due to habitat reduction, introduction of invasive species, and the emergence of infectious diseases such as chytridiomycosis [3,[25][26][27]. This disease is caused by the fungal pathogens Batrachochytrium dendrobatidis (Bd) [28] and B. salamandrivorans (Bsal) [29], and it has been linked to population declines of more than 500 amphibian species worldwide [3].…”

Ontogeny drives shifts in skin bacterial communities in facultatively paedomorphic salamanders

“…These periods may indicate ontogenetic drivers of host immune function, including shifts in the abundance of beneficial skin microbes during development [35,36], which can alter susceptibility to pathogen infection [37,38]. Most of the work examining amphibian microbiomes and immunity has focused on the susceptibility of a single life stage to Bd [4,19], while studies incorporating a range of development stages and other pathogens are uncommon [16,36,39]. Determining the contributions of processes that influence microbial assembly and disruption is essential to understand how host-microbe interactions shape variable patterns of disease through seasonal and developmental shifts.…”