Common midwife toad ranaviruses replicate first in the oral cavity of smooth newts (Lissotriton vulgaris) and show distinct strain-associated pathogenicity

Bernardo Saucedo,Mark J Goodman,María J Forzán,Steven J Van Beurden,Steven J R Allain,Andrea Gröne,Trenton W J Garner,Marja J L Kik,Natasja Kruithof,Diego A Vergara,Chris Sergeant,Raymond J Cranfield

doi:10.1038/s41598-019-41214-0

Abstract

Ranavirus is the second most common infectious cause of amphibian mortality. These viruses affect caudates, an order in which information regarding Ranavirus pathogenesis is scarce. In the Netherlands, two strains (CMTV-NL I and III) were suspected to possess distinct pathogenicity based on field data. To investigate susceptibility and disease progression in urodeles and determine differences in pathogenicity between strains, 45 adult smooth newts (Lissotriton vulgaris) were challenged via bath exposure with these ranaviruses and their detection in organs and feces followed over time by PCR, immunohistochemistry and in situ hybridization. Ranavirus was first detected at 3 days post infection (p.i.) in the oral cavity and upper respiratory mucosa. At 6 days p.i, virus was found in connective tissues and vasculature of the gastrointestinal tract. Finally, from 9 days p.i onwards there was widespread Ranavirus disease in various organs including skin, kidneys and gonads. Higher pathogenicity of the CMTV-NL I strain was confirmed by higher correlation coefficient of experimental group and mortality of challenged animals. Ranavirus-exposed smooth newts shed virus in feces intermittently and infection was seen in the absence of lesions or clinical signs, indicating that this species can harbor subclinical infections and potentially serve as disease reservoirs.

Highlights

The common midwife toad virus (CMTV) is a Ranavirus, initially reported in Spain in 20081
Smooth newts are susceptible to infection with both CMTV-NL Ranavirus strains
Adults newts captured in the wild were challenged with two CMTV-NL strains or medium and euthanized at 5 post-infection (p.i.) time points to study disease progression

Summary

Introduction

The common midwife toad virus (CMTV) is a Ranavirus (family Iridoviridae), initially reported in Spain in 20081. Ranaviruses clustering genetically within the common midwife toad clade were subsequently recorded as the cause of mortality events involving various amphibian and reptile species throughout Europe[2,3,4,5] and Asia[6,7]. In the north of the Netherlands (NL), CMTV was the cause of an amphibian mass mortality event in 2010 at Dwingelderveld National Park (DNP)[8,9]. Over half of the amphibian species native to the Netherlands have been affected by CMTV ranaviruses; water frogs Dutch Ranavirus strains were designated as CMTV-NL I, II and III11. NL-I, the more virulent strain, was recently introduced into the Netherlands and that CMTV NL-III was potentially endemic with attenuated virulence[10,11].

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