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IntroductionRanavirus disease, caused by viruses within the genus Ranavirus (Iridoviridae), is considered a globally emerging infectious disease linked to mass mortality events in both wild and cultured ectothermic vertebrates. Surveillance work is, however, limited in Asia hence prevalence and the dynamics of the disease remain poorly understood. To understand disease burden and the potential biotic and abiotic drivers in southern China region, we conducted a systematic surveillance of the ranavirus across Guangxi Zhuang Autonomous region (GAR).MethodsFor this, we used a multifaceted approach involving screening of amphibians and other potential hosts, diagnostic tests, phylogenetic analyses, prevalence estimation, co-infection assessments, and climatic niche analyses. Over one thousand individuals were sampled across 25 sampling sites.ResultsWe found ninety-two individuals from 18 species of ectothermic vertebrates to be infected with ranavirus. Two lineages were responsible – Rana nigromaculata ranavirus and tiger frog virus were identified using phylogenetic analysis based on the major capsid protein (MCP) gene fragment. Out of these two lineages, the presence of tiger frog virus is rare as we came across only one case. We also found evidence of a co-infection with ranavirus and Batrachochytrium dendrobatidis that can be highly detrimental to host populations; possibly the first such documentation in Asia. Our niche modelling analysis suggests that precipitation seasonality plays an important role in ranavirus prevalence in GAR – southwestern, southeastern, central and northeastern regions of GAR can be considered to be optimum habitats for ranaviruses. Infection rates in wild frog species have reached 100% in some areas, even in nature reserves.DiscussionOur research also indicates that culture facilities and pet markets are frequently infected, serving as likely vectors for the regional and global spread of ranaviruses. The knowledge generated suggests the need for systematic surveillance, stringent biosecurity measures, and control of international animal trade to prevent further transmission and protection of biodiversity and aquaculture industries across Asia.

Ranaviruses are DNA viruses (Family Iridoviridae; Subfamily Alphairidovirinae) and ranaviral disease is considered an emerging infectious disease of ectothermic vertebrates. Ranavirus infection can have varying pathological effects on infected amphibians, reptiles, and fish, most notably causing significant mortality events and population declines. Despite having a broad global range with reports from six continents, only a single incidental finding in Xenopus longipes from mainland Africa (Cameroon) is known and lacks molecular confirmation. Thus, there is a considerable knowledge gap concerning ranaviruses in Africa. We opportunistically obtained tissue samples from 160 amphibians representing five genera (Hoplobatrachus, Hylarana, Ptychadena, Pyxicephalus, and Xenopus) and two turtles (Pelomedusa sp.) from Chad, Africa. Samples were tested for ranavirus infection using a conventional PCR assay targeting the major capsid protein (MCP). A total of 25/160 (16%) frogs tested positive including 15/87 (17%) Hoplobatrachus occipitalis, 10/58 (17%) Ptychadena spp., 0/3 Pyxicephalus spp., 0/9 Xenopus spp., and 0/3 Hylarana spp. One of two turtles tested positive. Partial MCP gene sequences indicated all samples were >98% similar to several frog virus 3 (FV3)-like sequences. Additional gene targets (DNA polymerase [DNApol], ribonucleotide reductase alpha [RNR- α], ribonucleotide reductase beta subunit [RNR- β]) were sequenced to provide further detailed classification of the virus. Sequences of individual gene targets indicate that the ranavirus detected in frogs in Chad is most similar to tiger frog virus (TFV), a FV3-like virus previously isolated from diseased amphibians cultured in China and Thailand. Full genome sequencing of one sample indicates that the Chad frog virus (CFV) is a well-supported sister group to the TFVs previously determined from Asia. This work represents the first molecular confirmation of ranaviruses from Africa and is a first step in comparing ranavirus phylogeography on a local and global scale.

The seal picornavirus 1, species Aquamavirus A, is currently the only recognized member of the genus Aquamavirus within the family Picornaviridae. The bear picornavirus 1 was recently proposed as the second species in the genus under the name aquamavirus B. Herein, we determined the complete genomes of two novel pinniped picornaviruses, the harbor seal picornavirus (HsPV) and the ribbon seal picornavirus (RsPV). The HsPV and the RsPV were isolated in Vero.DogSLAMtag cells from samples collected from stranded harbor (Phoca vitulina) and ribbon (Histriophoca fasciata) seals. RsPV-infected Vero.DogSLAMtag cells displaying extensive cytopathic effects were processed for transmission electron microscopy and revealed non-enveloped viral particles aggregated into paracrystalline arrays in the cytoplasm. A next-generation sequencing approach was used to recover the complete genomes of the HsPV and the RsPV (6,709 and 6,683 bp, respectively). Phylogenetic and genetic analyses supported the HsPV and the RsPV as members of the Aquamavirus genus. Based on these results, RsPV represents a novel strain of Aquamavirus A, while the HsPV is a novel strain of the proposed species aquamavirus B. These discoveries provide information on the evolutionary relationships and ultrastructure of aquamaviruses and expands the known host range of those viruses. Our results underscore the importance of the application of classical virology and pathology techniques coupled with high-throughput sequencing technologies for the discovery and characterization of pathogens in wild marine mammals.