EDNA Increases the Detectability of Ranavirus Infection in an Alpine Amphibian Population.

Claude Miaud,Véronique Arnal,Alice Valentini,Tony Dejean,Marie Poulain

doi:10.3390/v11060526

Abstract

The early detection and identification of pathogenic microorganisms is essential in order to deploy appropriate mitigation measures. Viruses in the Iridoviridae family, such as those in the Ranavirus genus, can infect amphibian species without resulting in mortality or clinical signs, and they can also infect other hosts than amphibian species. Diagnostic techniques allowing the detection of the pathogen outside the period of host die-off would thus be of particular use. In this study, we tested a method using environmental DNA (eDNA) on a population of common frogs (Rana temporaria) known to be affected by a Ranavirus in the southern Alps in France. In six sampling sessions between June and September (the species’ activity period), we collected tissue samples from dead and live frogs (adults and tadpoles), as well as insects (aquatic and terrestrial), sediment, and water. At the beginning of the breeding season in June, one adult was found dead; at the end of July, a mass mortality of tadpoles was observed. The viral DNA was detected in both adults and tadpoles (dead or alive) and in water samples, but it was not detected in insects or sediment. In live frog specimens, the virus was detected from June to September and in water samples from August to September. Dead tadpoles that tested positive for Ranavirus were observed only on one date (at the end of July). Our results indicate that eDNA can be an effective alternative to tissue/specimen sampling and can detect Ranavirus presence outside die-offs. Another advantage is that the collection of water samples can be performed by most field technicians. This study confirms that the use of eDNA can increase the performance and accuracy of wildlife health status monitoring and thus contribute to more effective surveillance programs.

Highlights

Amphibians are often considered ecosystem health indicators (“the canaries in the coal mine”, [1])due to their permeable skin, their sensitivity to environmental disturbance, and their often biphasic life cycle (e.g., [2])
Emerging infectious diseases (EIDs) are causing drastic amphibian declines worldwide [4,5,6], and the chytridiomycosis panzootic has been involved in the decline of at least 501 amphibian species over the past half-century, including 90 presumed extinctions [7]
common midwife toad virus (CMTV)-related mortality has been recorded in other European countries, affecting several amphibian species in both Anura and Caudata [13,14]

Summary

Introduction

Amphibians are often considered ecosystem health indicators (“the canaries in the coal mine”, [1])due to their permeable skin, their sensitivity to environmental disturbance, and their often biphasic (requiring water and land) life cycle (e.g., [2]). Ranaviruses (family Iridoviridae)—double-stranded DNA viruses that infect fish, reptiles, and amphibians [8]—are considered the second most common infectious cause of mortality in amphibians [9,10]. These viruses have caused amphibian die-offs on Viruses 2019, 11, 526; doi:10.3390/v11060526 www.mdpi.com/journal/viruses. The common midwife toad virus (CMTV) [12] is a Ranavirus that has been causing amphibian die-offs since 2005 in Spain [10]. CMTV-related mortality has been recorded in other European countries, affecting several amphibian species in both Anura and Caudata [13,14]

Results

Discussion

Conclusion