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

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.

Diversity-Stability Dynamics of the Amphibian Skin Microbiome and Susceptibility to a Lethal Viral Pathogen

“…Finally, Warne et al (2019) recently showed that disruption of the gut microbiome in early life can influence host metabolism and susceptibility to ranavirus in later life. Given that the oral cavity and alimentary canal are major routes of infection for ranaviruses (e.g., Robert et al, 2011;Saucedo et al, 2019), one possibility is that measurements of skin microbiome diversity in amphibians are also reflective of gut microbiome diversity. Future work should quantify this covariation between multi-site microbiome dynamics and seek to understand the functional consequences of increased skin and gut microbiome diversity in hosts vulnerable to ranavirus.…”

Virus-Targeted Transcriptomic Analyses Implicate Ranaviral Interaction with Host Interferon Response in Frog Virus 3-infected Frog Tissues

“…FV3 represents the most frequently reported iridovirus for anurans. In North America, FV3 is widespread in wild amphibians and the only ranavirus detected in turtles [6,9,10]. A recent study detected different FV3 lineages in wild amphibians in Canada, and these new FV3 isolates appears to have undergone genetic recombination with the common midwife toad virus (CMTV) [9].…”

Amphibian ranaviruses in Europe: important directions for future research

“…Several strains of CMTV are known to be circulating in Europe, and experimental work has revealed these strains to vary markedly in pathogenicity (Saucedo et al 2018(Saucedo et al , 2019. A lack of genetic diversity in CMTV isolates collected from various outbreaks and a high number of genetic loci that appear to be under strong selection has led to the hypothesis that CMTV is an invasive pathogen on continental Europe (Price 2015;Price et al 2017b), though the route of invasion remains unknown.…”

“…Overlap also exists between CMTV and the amphibian chytrid fungi, and co-infections are known to establish (Rosa et al 2017); however, little evidence currently exists that either pathogen exacerbates the impact of the other (Rosa et al 2017). The gross pathology of ranavirosis caused by CMTV is identical to that which is caused by FV3 (e.g., Cunningham et al 1997;Balseiro et al 2009); however, CMTV is known to replicate initially in the oral cavity of infected amphibians, before invading the connective tissues and subsequently the organs, including the skin (Saucedo et al 2019). Research that focused on an alpine population of R. temporaria in France has also been key in proving the efficacy of environmental DNA or "e-DNA" at detecting the presence of ranaviruses in European amphibian populations (Miaud et al 2019).…”