Continent-Wide Distribution of CMTV-Like Ranavirus, from the Urals to the Atlantic Ocean.

Abstract

Ranavirosis is an emerging infectious disease of amphibians, fish, and reptiles caused by large dsDNA viruses of the genus Ranavirus associated with morbidity and mass mortalities worldwide. They are considered to be one of the major drivers of the ongoing amphibian biodiversity crisis. In this study, we investigated the prevalence and genetic diversity of ranaviruses in native and invasive populations of water frogs (Pelophylax spp.) across Russia using the DNA sample collection established in 2006-2016. The collection included samples collected in the wild and samples from wild-caught water frogs that had been kept in laboratories for a period of time. Overall, 52 out of 590 (8.8%) of wild frogs from 18 out of 94 (19.1%) sampling sites tested positive, including samples from invasive populations. Among the captive frogs, 71 out of 263 (27.0%) were positive and they had a significantly higher relative viral load. We found six major capsid protein gene haplotypes from 22 positive samples, all belonging to the common midwife toad virus (CMTV-like) ranaviruses, at multiple sites within the basins of three of Europe's largest rivers (Volga, Dnieper, and Don). Combined with previously published data, this study provides evidence for a continent-wide distribution of CMTV-like ranaviruses in Europe and strengthens the hypothesis of their endemism on the continent. Our study also highlights that the water frogs are important hosts for ranaviruses and could potentially act as vectors for infection transmission.