Abstract
Ranaviruses are pathogenic viruses for poikilothermic vertebrates worldwide. The identification of a common midwife toad virus (CMTV) associated with massive die-offs in water frogs (Pelophylax spp.) in the Netherlands has increased awareness for emerging viruses in amphibians in the country. Complete genome sequencing of 13 ranavirus isolates collected from ten different sites in the period 2011–2016 revealed three CMTV groups present in distinct geographical areas in the Netherlands. Phylogenetic analysis showed that emerging viruses from the northern part of the Netherlands belonged to CMTV-NL group I. Group II and III viruses were derived from the animals located in the center-east and south of the country, and shared a more recent common ancestor to CMTV-amphibian associated ranaviruses reported in China, Italy, Denmark, and Switzerland. Field monitoring revealed differences in water frog host abundance at sites where distinct ranavirus groups occur; with ranavirus-associated deaths, host counts decreasing progressively, and few juveniles found in the north where CMTV-NL group I occurs but not in the south with CMTV-NL group III. Investigation of tandem repeats of coding genes gave no conclusive information about phylo-geographical clustering, while genetic analysis of the genomes revealed truncations in 17 genes across CMTV-NL groups II and III compared to group I. Further studies are needed to elucidate the contribution of these genes as well as environmental variables to explain the observed differences in host abundance.
Highlights
Ranaviruses are double-strandedDNA viruses, known to cause disease in fish, reptiles, and amphibians[1,2,3] and are notifiable to the World Organization for Animal Health (OIE)[4]
Dutch ranavirus groups based on their phylogenetic relationship to other fully sequenced common midwife toad virus (CMTV) ranaviruses, and to obtain insights in the correlation between distinct genotype features with in vitro growth kinetics and/or effects in wild host populations
Complete genome sequencing revealed at least three ranavirus groups belonging to the CMTV clade in the Netherlands
Summary
DNA viruses, known to cause disease in fish, reptiles, and amphibians[1,2,3] and are notifiable to the World Organization for Animal Health (OIE)[4]. They are the second most common infectious cause of mortality in amphibians worldwide, after the fungus Batrachochytrium dendrobatidis (Bd)[1, 5]. The oldest records of CMTV ranaviruses are from 1995 and correspond to Saucedo et al Emerging Microbes & Infections (2018)7:56 isolates from pike perch in Finland[10] and common frogs in Great Britain[11]
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