First evidence of amphibian chytrid fungus (Batrachochytrium dendrobatidis) and ranavirus in Hong Kong amphibian trade

FIRST RECORD OF BATRACHOCHYTRIUM DENDROBATIDIS IN THE NORTHERN NETHERLANDS

Batrachochytrium dendrobatidis (Bd) infects amphibians and has been linked to the decline of hundreds of anuran amphibians all over the world. In the province of Groningen in the Netherlands, this fungal pathogen was not detected before this study. To determine whether Groningen was Bd-free, we surveyed 12 locations in this province in 2020 and 2021. Samples were then used to quantify the presence of Bd with a qPCR assay. In total, 2 out of 110 (∼0.02%) collected in 2020 and 11 out of 249 samples collected in 2021 tested positive for Bd. Infected amphibians were found in 4 out of the 12 sites, and the prevalence of Bd was estimated at 4% for both years combined. Our study provides the first record of Bd in Groningen, and we hypothesize that Bd is present throughout the Netherlands in regions currently considered "Bd-free." Furthermore, we warn scientists and policymakers to be apprehensive when calling a site free from Bd when sampling is limited or not recent.

OCCURRENCE OF PATHOGENIC CHYTRID FUNGI BATRACHOCHYTRIUM SALAMANDRIVORANS AND BATRACHOCHYTRIUM DENDROBATIDIS IN THE HONG KONG NEWT (PARAMESOTRITON HONGKONGENSIS) AND OTHER WILD AND IMPORTED AMPHIBIANS IN A SUBTROPICAL ASIAN REGION

One of the major threats for the massive loss in global amphibian diversity is chytridiomycosis, caused by chytrid fungi Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal). Following its discovery in 2013, Bsal has emerged as a severe threat to the global survival of urodelans. In 2018, a study reported a high prevalence of Bsal (65.6%) in the Hong Kong newts (Paramesotriton hongkongensis, Near Threatened) of a southern China population adjacent to Hong Kong (HK). Uncertainty regarding the Bsal infection status of P. hongkongensis inhabiting HK raised deep concern over the risk of introducing Bsal from that population. We screened the skin swabs from wild individuals of P. hongkongensis, 15 sympatric amphibian species, and 16 imported amphibian species in HK for chytrids. We found that both Bsal and Bd occur in low prevalences in P. hongkongensis (Bsal 1.7%, 5/293; Bd 0.34%, 1/293), Hong Kong cascade frog, Amolops hongkongensis, family Ranidae (Bsal only, 5.26%, 1/19), and Asian common toad, Duttaphrynus melanostictus, family Bufonidae (Bsal only, 5.88%, 1/17), populations of HK, with infected individuals being asymptomatic, suggesting a potential role of these species as reservoirs of Bsal. Conversely, Bd, but not Bsal, was present on 13.2% (9/68) of imported amphibians, indicating a high chytrid introduction risk posed by international amphibian trade. Long-term surveillance of the presence of Bd and Bsal in wild and captive amphibians would be advisable, and we recommend that import and export of nonnative chytrid carriers should be prevented, especially to those regions with amphibian populations naïve to Bd and Bsal.

Attitudes and Behavioral Intentions of Pet Amphibian Owners About Biosecurity Practices

Global trade has been linked with the emergence of novel pathogens and declines in amphibian populations worldwide. The potential for pathogen transmission within and between collections of captive amphibians and spillover to wild populations makes it important to understand the motivations, knowledge, attitudes and behaviors of pet amphibian owners. We surveyed US pet amphibian owners to understand their characteristics and evaluated whether and how they were associated with behavioral intentions to adopt biosecurity practices. We found that the majority of pet amphibian owners are aware of the threat of emerging pathogens, concerned about potential spillover of pathogens from captive to wild populations and willing to adopt biosecurity practices to mitigate pathogen threats. Intentions to adopt such practices were driven more by psychosocial constructs such as attitudes, perceptions and beliefs than demographic characteristics. Pet amphibian owners also expressed a strong interest in acquiring, and willingness to pay a price premium for, certified disease-free animals. These findings advance our understanding of the characteristics, motivations and behaviors of pet owners, a key stakeholder in global amphibian trade, which could help to inform new policies and outreach strategies to engage them in mitigating pathogen threats. Moreover, our results imply the economic viability of a market-based program to promote pathogen-free, sustainable trade of amphibians.

Novel chytrid pathogen variants and the global amphibian pet trade

Global wildlife trade spreads emerging infectious diseases that threaten biodiversity. The amphibian chytrid pathogen Batrachochytrium dendrobatidis (Bd) has caused population declines and species extinctions worldwide except in Asia. Fire-bellied toads (Bombina orientalis), exported in large numbers from Asia, are tolerant of Bd and carry hypervirulent ancestral chytrid BdAsia-1 variants. We assayed the virulence of a new isolate of BdAsia-1 on the model Australasian frog host Litoria caerulea. Infected individuals (n = 15) all showed rapid disease progression culminating in death, whereas sham-inoculated individuals (n = 10) presented no clinical signs of disease and all survived (log rank test, χ² = 15.6, df = 1, p < 0.0001). The virulence of the new isolate of BdAsia-1 is comparable to the one we assayed previously (χ² = 0.0, df = 1, p = 0.91). Internationally traded wildlife, even when they appear healthy, can carry hypervirulent variants of pathogens. Once new pathogen variants escape into the environment, native species that have had no opportunity to evolve resistance to them may perish. Our study suggests that hypervirulent pathogens are being spread by the international pet trade. Notifiable wildlife diseases attributable to locally endemic pathogens often fail to generate conservation concern so are rarely subject to border surveillance or import controls. Because of the danger novel variants pose, national border control agencies need to implement disease screening and quarantine protocols to ensure the safety of their endemic fauna.

Predicted Batrachochytrium dendrobatidis infection sites in Guyana, Suriname, and French Guiana using the species distribution model maxent

The fungal pathogen Batrachochytrium dendrobatidis (Bd) which causes that amphibian disease chytridiomycosis is expanding its worldwide range from an Asian origin, infecting amphibians in a growing number of countries. Modelling the potential range of this amphibian pathogen using environmental variables and presence data could advance our understanding of at-risk areas and species in locations with limited surveillance to date. We used a species distribution model to assess Bd habitat suitability in the three Guiana's (Guyana, Suriname, and French Guiana) in South America. The model output showed that all three countries have substantial areas where Bd could grow and proliferate, and maximum temperature of the warmest month was the top predictor of suitable Bd habitat, inversely correlated with modeled Bd occurrence. Predicted Bd infection areas in Guyana and French Guiana were large and localized whereas possible sites in Suriname were more scattered throughout the country. The areas projected as potential suitable in Suriname were mostly high elevation regions. These results could help inform efficiencies for development of a proactive monitoring program that could alert managers of novel Bd outbreaks for focused mitigation actions to forestall the spread of this amphibian disease.

Patterns of infection, origins, and transmission of ranaviruses among the ectothermic vertebrates of Asia

Ranaviral infections, a malady of ectothermic vertebrates, are becoming frequent, severe, and widespread, causing mortality among both wild and cultured species, raising odds of species extinctions and economic losses. This increase in infection is possibly due to the broad host range of ranaviruses and the transmission of these pathogens through regional and international trade in Asia, where outbreaks have been increasingly reported over the past decade. Here, we focus attention on the origins, means of transmission, and patterns of spread of this infection within the region. Infections have been recorded in both cultured and wild populations in at least nine countries/administrative regions, together with mass die-offs in some regions. Despite the imminent seriousness of the disease in Asia, surveillance efforts are still incipient. Some of the viral strains within Asia may transmit across host-taxon barriers, posing a significant risk to native species. Factors such as rising temperatures due to global climate change seem to exacerbate ranaviral activity, as most known outbreaks have been recorded during summer; however, data are still inadequate to verify this pattern for Asia. Import risk analysis, using protocols such as Pandora+, pre-border pathogen screening, and effective biosecurity measures, can be used to mitigate introduction of ranaviruses to uninfected areas and curb transmission within Asia. Comprehensive surveillance using molecular diagnostic tools for ranavirus species and variants will help in understanding the prevalence and disease burden in the region. This is an important step toward conserving native biodiversity and safeguarding the aquaculture industry.

Chytridiomycosis Outbreak in a Chilean Giant Frog (Calyptocephalella gayi) Captive Breeding Program: Genomic Characterization and Pathological Findings

Emerging infectious diseases in wildlife are increasingly associated with animal mortality and species declines, but their source and genetic characterization often remains elusive. Amphibian chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has been associated with catastrophic and well-documented amphibian population declines and extinctions at the global scale. We used histology and whole-genome sequencing to describe the lesions caused by, and the genetic variability of, two Bd isolates obtained from a mass mortality event in a captive population of the threatened Chilean giant frog (Calyptocephalella gayi). This was the first time an association between Bd and high mortality had been detected in this charismatic and declining frog species. Pathological examinations revealed that 30 dead metamorphosed frogs presented agnathia or brachygnathia, a condition that is reported for the first time in association with chytridiomycosis. Phylogenomic analyses revealed that Bd isolates (PA1 and PA2) from captive C. gayi group with other Bd isolates (AVS2, AVS4, and AVS7) forming a single highly supported Chilean Bd clade within the global panzootic lineage of Bd (BdGPL). These findings are important to inform the strengthening of biosecurity measures to prevent the impacts of chytridiomycosis in captive breeding programs elsewhere.

Illegal Wildlife Trade and Emerging Infectious Diseases: Pervasive Impacts to Species, Ecosystems and Human Health

Simple Summary

Wildlife is trafficked illegally across the globe every day. The illegal wildlife trade (IWT) creates opportunity for emerging infectious disease (EID) events to occur. EIDs are a major threat to wildlife, ecosystems, and public health. This study addresses the lack of comprehensive review of pathogens identified in IWT and highlights the expansion of literature on this subject over the past 30 years. We reviewed 82 scientific papers and conference proceedings from 1990 to 2020. Trends in EIDs identified in IWT have significantly increased over the past decade. Cases covered 240 pathogens across all taxa. Approximately 60% of the pathogens identified were zoonotic (transmissible between animals and humans) and threaten public health. Based on our findings, we recommend further research is needed to monitor and prevent the IWT.

Abstract

Emerging infectious disease (EID) events can be traced to anthropogenic factors, including the movement of wildlife through legal and illegal trade. This paper focuses on the link between illegal wildlife trade (IWT) and infectious disease pathogens. A literature review through Web of Science and relevant conference proceedings from 1990 to 2020 resulted in documenting 82 papers and 240 identified pathogen cases. Over 60% of the findings referred to pathogens with known zoonotic potential and five cases directly referenced zoonotic spillover events. The diversity of pathogens by taxa included 44 different pathogens in birds, 47 in mammals, 16 in reptiles, two in amphibians, two in fish, and one in invertebrates. This is the highest diversity of pathogen types in reported literature related to IWT. However, it is likely not a fully representative sample due to needed augmentation of surveillance and monitoring of IWT and more frequent pathogen testing on recovered shipments. The emergence of infectious disease through human globalization has resulted in several pandemics in the last decade including SARS, MERS, avian influenza H1N1,and Ebola. We detailed the growing body of literature on this topic since 2008 and highlight the need to detect, document, and prevent spillovers from high-risk human activities, such as IWT.

A review of the introduced herpetofauna of Mexico and Central America, with comments on the effects of invasive species and biosecurity methodology

Among the principal causes producing detrimental effects on global biodiversity are introductions of alien species. Very few attempts to control introduced amphibians and reptiles in Middle America (Mexico and Central America) can be identified, so listings are provided for 24 exotic species, 16 translocated species, and 11 species that were removed from the introduced species listing because of lack of substantiating evidence that they are from established populations. Biosecurity methods are also identified that can be applied for preventing, controlling, and managing introduced and especially invasive species.

Using the 2020 global pandemic as a springboard to highlight the need for amphibian conservation in eastern Asia

Emerging infectious diseases are on the rise in many different taxa, including, among others, the amphibian batrachochytrids, the snake fungal disease and the Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) virus, responsible for Coronavirus disease 2019 (COVID-19) in mammals. Following the onset of the pandemic linked to COVID-19, eastern Asia has shown strong leadership, taking actions to regulate the trade of potential vector species in several regions. These actions were taken in response to an increase in public awareness, and the need for a quick reaction to mitigate against further pandemics. However, trade restrictions rarely affect amphibians, despite the risk of pathogen transmission, directly, or indirectly through habitat destruction and the loss of vector consumption. Thus, species that help alleviate the risk of zoonoses or provide biological control are not protected. Hence, in view of the global amphibian decline and the risk of zoonoses, we support the current wildlife trade regulations and support measures to safeguard wildlife from overexploitation. The current period of regulation overhaul should be used as a springboard for amphibian conservation. To mitigate risks, we suggest the following stipulations specifically for amphibians. I) Restrictions to amphibian farming in eastern Asia, in relation to pathogen transmission and the establishment of invasive species. II) Regulation of the amphibian pet trade, with a focus on potential vector species. III) Expansion of the wildlife trade ban, to limit the wildlife-human-pet interface. The resulting actions will benefit both human and wildlife populations, as they will lead to a decrease in the risk of zoonoses and better protection of the environment.

SIGNIFICANCE STATEMENT

There is an increasing number of emerging infectious diseases impacting all species, including amphibians, reptiles and mammals. The latest threat to humans is the virus responsible for COVID-19, and the resulting pandemic. Countries in eastern Asia have taken steps to regulate wildlife trade and prevent further zoonoses thereby decreasing the risk of pathogens arising from wild species. However, as amphibians are generally excluded from regulations we support specific trade restrictions: I) Restrictions to amphibian farming; II) regulation of the amphibian pet trade; III) expansion of the wildlife trade ban. These restrictions will benefit both human and wildlife populations by decreasing the risks of zoonoses and better protecting the environment.

First Detection of Batrachochytrium dendrobatidis in Wild Frogs from Bangladesh

Global amphibian populations are facing a novel threat, chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), which is responsible for the severe decline of a number of species across several continents. Chytridiomycosis in Asia is a relatively recent discovery yet there have been no reports on Bd-presence in Bangladeshi amphibians. We conducted a preliminary study on 133 wild frogs from seven sites in Bangladesh between April and July 2018. Nested PCR analysis showed 20 samples (15.04%) and 50% of the tested taxa (9 species from 6 genera and 4 families) as Bd-positive. Eight of the nine species are discovered as newly infected hosts. Analysis of Bd-positive samples shows prevalence does not significantly vary among different land cover categories, although the occurrence is higher in forested areas. The prevalence rate is similar in high and low disturbed areas, but the range of occurrence is statistically higher in low disturbance areas. Maximum entropy distribution modeling indicates high probabilities of Bd occurrence in hilly and forested areas in southeast and central-north Bangladesh. The Bd-specific ITS1-5.8S-ITS2 ribosomal gene sequence from the Bd-positive samples tested is completely identical. A neighbor-joining phylogenetic tree reveals that the identified strain shares a common ancestry with strains previously discovered in different Asian regions. Our results provide the first evidence of Bd-presence in Bangladeshi amphibians, inferring that diversity is at risk. The effects of environmental and climatic factors along with quantitative PCR analysis are required to determine the infection intensity and susceptibility of amphibians in the country.

“Saving Lives, Protecting Livelihoods, and Safeguarding Nature”: Risk-Based Wildlife Trade Policy for Sustainable Development Outcomes Post-COVID-19

The COVID-19 pandemic has caused huge loss of life, and immense social and economic harm. Wildlife trade has become central to discourse on COVID-19, zoonotic pandemics, and related policy responses, which must focus on “saving lives, protecting livelihoods, and safeguarding nature.” Proposed policy responses have included extreme measures such as banning all use and trade of wildlife, or blanket measures for entire Classes. However, different trades pose varying degrees of risk for zoonotic pandemics, while some trades also play critical roles in delivering other key aspects of sustainable development, particularly related to poverty and hunger alleviation, decent work, responsible consumption and production, and life on land and below water. Here we describe how wildlife trade contributes to the UN Sustainable Development Goals (SDGs) in diverse ways, with synergies and trade-offs within and between the SDGs. In doing so, we show that prohibitions could result in severe trade-offs against some SDGs, with limited benefits for public health via pandemic prevention. This complexity necessitates context-specific policies, with multi-sector decision-making that goes beyond simple top-down solutions. We encourage decision-makers to adopt a risk-based approach to wildlife trade policy post-COVID-19, with policies formulated via participatory, evidence-based approaches, which explicitly acknowledge uncertainty, complexity, and conflicting values across different components of the SDGs. This should help to ensure that future use and trade of wildlife is safe, environmentally sustainable and socially just.

A historical overview of Batrachochytrium dendrobatidis infection from specimens at the National Zoological Collection Suriname

The amphibian skin disease chytridiomycosis, caused by the pathogenetic fungus Batrachochytrium dendrobatidis (Bd) has become one of the major contributors to global amphibian population declines and extinctions. This fungus has spread globally and has caused mortalities in nearly every continent. In South America, Suriname, Guyana and Paraguay are among the remaining three countries where Bd has not been detected to date. To complete the assessment of the possible presence of Bd in Suriname, 205 specimens from the Zoological Collection of Suriname, compromising 6 frog families and 15 genera were sampled for chytrid fungus. No specimens were found to be infected by this fungus and as such the outcome strengthens the previous result of field sampling that there is no support that Bd has spread to Suriname.

Pooled samples and eDNA-based detection can facilitate the "clean trade" of aquatic animals

The regional and international trade of live animals facilitates the movement, spillover, and emergence of zoonotic and epizootic pathogens around the world. Detecting pathogens in trade is critical for preventing their continued movement and introduction, but screening a sufficient fraction to ensure rare infections are detected is simply infeasible for many taxa and settings because of the vast numbers of animals involved—hundreds of millions of live animals are imported into the U.S.A. alone every year. Batch processing pools of individual samples or using environmental DNA (eDNA)—the genetic material shed into an organism’s environment—collected from whole consignments of animals may substantially reduce the time and cost associated with pathogen surveillance. Both approaches, however, lack a framework with which to determine sampling requirements and interpret results. Here I present formulae for pooled individual samples (e.g,. swabs) and eDNA samples collected from finite populations and discuss key assumptions and considerations for their use with a focus on detecting Batrachochytrium salamandrivorans, an emerging pathogen that threatens global salamander diversity. While empirical validation is key, these formulae illustrate the potential for eDNA-based detection in particular to reduce sample sizes and help bring clean trade into reach for a greater number of taxa, places, and contexts.

Phylogenomic characterization of ranaviruses isolated from cultured fish and amphibians in Thailand

Ranaviruses are emerging pathogens associated with worldwide epizootics in farmed and wild ectothermic vertebrates. In this study, we determined the full genomes of eight ranaviruses isolated from marbled sleeper goby ( Oxyeleotris marmorata), goldfish ( Carassius auratus), guppy ( Poecilia reticulata), tiger frog ( Hoplobatrachus tigerinus), Asian grass frog ( Fejervarya limnocharis), and East Asian bullfrog ( H. rugulosus) cultured or imported into Thailand. These ranaviral isolates induced the same cytopathic effects (i.e., progression of coalescing round plaques) in epithelioma papulosum cyprini (EPC) cell cultures. Transmission electron microscopy of infected EPC cells revealed cytoplasmic viral particles with ultrastructural features typical for ranaviruses. Pairwise genetic comparisons of the complete major capsid protein coding sequences from the Thai ranaviruses displayed the highest identity (99.8%–100%) to a ranavirus (tiger frog virus; TFV) isolated from diseased tiger frogs cultured in China, a slightly lower identity (99.3%–99.4%) to a ranavirus (Wamena virus; WV) isolated from diseased green tree pythons ( Morelia viridis) illegally exported from Papua New Guinea, and a lower identity to 35 other ranaviruses (93.7%–98.6%). Phylogenomic analyses supported the eight Thai ranaviruses, Chinese TFV, and WV as a subclade within a larger frog virus 3 clade. Our findings confirm the spread of TFV among cultured fish and amphibians in Asia and likely in reptiles in Oceania. Biosecurity measures are needed to ensure TFV does not continue to spread throughout Southeast Asia and to other parts of the world via international trade.

Evaluating Potential Distribution of High-Risk Aquatic Invasive Species in the Water Garden and Aquarium Trade at a Global Scale Based on Current Established Populations

Aquatic non-native invasive species are commonly traded in the worldwide water garden and aquarium markets, and some of these species pose major threats to the economy, the environment, and human health. Understanding the potential suitable habitat for these species at a global scale and at regional scales can inform risk assessments and predict future potential establishment. Typically, global habitat suitability models are fit for freshwater species with only climate variables, which provides little information about suitable terrestrial conditions for aquatic species. Remotely sensed data including topography and land cover data have the potential to improve our understanding of suitable habitat for aquatic species. In this study, we fit species distribution models using five different model algorithms for three non-native aquatic invasive species with bioclimatic, topographic, and remotely sensed covariates to evaluate potential suitable habitat beyond simple climate matches. The species examined included a frog (Xenopus laevis), toad (Bombina orientalis), and snail (Pomacea spp.). Using a unique modeling approach for each species including background point selection based on known established populations resulted in robust ensemble habitat suitability models. All models for all species had test area under the receiver operating characteristic curve values greater than 0.70 and percent correctly classified values greater than 0.65. Importantly, we employed multivariate environmental similarity surface maps to evaluate potential extrapolation beyond observed conditions when applying models globally. These global models provide necessary forecasts of where these aquatic invasive species have the potential for establishment outside their native range, a key component in risk analyses.

Low intraspecific variation of Frog virus 3 with evidence for novel FV3-like isolates in central and northwestern Canada

Frog virus 3 (FV3) and FV3-like ranaviruses can infect a variety of cold-blooded aquatic species and present a primary threat to amphibians across the globe. Previous studies of FV3-like viruses have largely investigated higher-level phylogenetic distinctions of these pathogens via portions of the conserved major capsid protein (MCP), and the putative virulence gene vIF-2α. Few studies, however, have investigated the spatial distribution of FV3 variants at the population level3-data that can be used to further understand the spatial epidemiology of this disease. In this study, we sequenced the MCP and vIF-2α of 127 FV3-positive amphibians sampled from Canadian water bodies in Ontario, northeastern Alberta, and southern Northwest Territories to explore whether intraspecific genetic variation exists within FV3. There was a lack of variation at the 2 markers across these regions, suggesting that there is a lack of FV3 sequence diversity in Canada, which may hint at a single source of infection that has spread. However, an undocumented variant termed Wood Buffalo ranavirus (WBRV) was detected in samples from 3 sites in Alberta and Northwest Territories that clustered within the FV3-like lineage with 99.3% sequence homology for MCP. For vIF-2α, all sequences were the expected truncated variant except for 6 samples in Ontario. These latter sequences were suggestive of recombination with common midwife toad virus (CMTV). The lack of variation suggests that higher-resolution genome analyses will be required to further explore the spatial spread and intraspecific variation of the disease.

Interaction between temperature and sublethal infection with the amphibian chytrid fungus impacts a susceptible frog species

The amphibian chytrid fungus Batrachochytrium dendrobatidis is an emerging infectious pathogen present on every continent except Antarctica. It causes the disease chytridiomycosis in a subset of species but does not always result in disease or death for every host. Ambient temperature influences both amphibian metabolism and chytrid pathogenicity, however the interactive effects on host physiology is not well understood. We investigated the sublethal effect of B. dendrobatidis infection on a susceptible host, Litoria aurea to test (1) whether the infection load, metabolic activity, body fat and gonad size differed in L. aurea at either 24 °C or 12 °C ambient temperatures and (2) whether previous Bd infection caused long-term changes to body fat and gonad size. Litoria aurea in 12 °C treatments had higher infection loads of B. dendrobatidis and lower survivorship. Metabolic rate was higher and fat mass was lower in infected individuals and in animals in 24 °C treatments. Male L. aurea previously infected with B. dendrobatidis had smaller testes 5 months-post clearance of infection, an effect likely to translate to fitness costs in wild populations. These experiments demonstrate a physiological cost to sublethal B. dendrobatidis infection, which suggests a reduction in host fitness mediated by temperature in the host's environment regardless of whether infection leads to mortality.

Pathogen Risk Analysis for Wild Amphibian Populations Following the First Report of a Ranavirus Outbreak in Farmed American Bullfrogs (Lithobates catesbeianus) from Northern Mexico

Ranaviruses are the second deadliest pathogens for amphibian populations throughout the world. Despite their wide distribution in America, these viruses have never been reported in Mexico, the country with the fifth highest amphibian diversity in the world. This paper is the first to address an outbreak of ranavirus in captive American bullfrogs (Lithobates catesbeianus) from Sinaloa, Mexico. The farm experienced high mortality in an undetermined number of juveniles and sub-adult bullfrogs. Affected animals displayed clinical signs and gross lesions such as lethargy, edema, skin ulcers, and hemorrhages consistent with ranavirus infection. The main microscopic lesions included mild renal tubular necrosis and moderate congestion in several organs. Immunohistochemical analyses revealed scant infected hepatocytes and renal tubular epithelial cells. Phylogenetic analysis of five partial ranavirus genes showed that the causative agent clustered within the Frog virus 3 clade. Risk assessment with the Pandora⁺ protocol demonstrated a high risk for the pathogen to affect amphibians from neighboring regions (overall Pandora risk score: 0.619). Given the risk of American bullfrogs escaping and spreading the disease to wild amphibians, efforts should focus on implementing effective containment strategies and surveillance programs for ranavirus at facilities undertaking intensive farming of amphibians.

Ranaviruses and reptiles

Ranaviruses can infect many vertebrate classes including fish, amphibians and reptiles, but for the most part, research has been focused on non-reptilian hosts, amphibians in particular. More recently, reports of ranaviral infections of reptiles are increasing with over 12 families of reptiles currently susceptible to ranaviral infection. Reptiles are infected by ranaviruses that are genetically similar to, or the same as, the viruses that infect amphibians and fish; however, physiological and ecological differences result in differences in study designs. Although ranaviral disease in reptiles is often influenced by host species, viral strain and environmental differences, general trends in pathogenesis are emerging. More experimental studies using a variety of reptile species, life stages and routes of transmission are required to unravel the complexity of wild ranavirus transmission. Further, our understanding of the reptilian immune response to ranaviral infection is still lacking, although the considerable amount of work conducted in amphibians will serve as a useful guide for future studies in reptiles.

Fungal infections in animals: a patchwork of different situations

The importance of fungal infections in both human and animals has increased over the last decades. This article represents an overview of the different categories of fungal infections that can be encountered in animals originating from environmental sources without transmission to humans. In addition, the endemic infections with indirect transmission from the environment, the zoophilic fungal pathogens with near-direct transmission, the zoonotic fungi that can be directly transmitted from animals to humans, mycotoxicoses and antifungal resistance in animals will also be discussed. Opportunistic mycoses are responsible for a wide range of diseases from localized infections to fatal disseminated diseases, such as aspergillosis, mucormycosis, candidiasis, cryptococcosis and infections caused by melanized fungi. The amphibian fungal disease chytridiomycosis and the Bat White-nose syndrome are due to obligatory fungal pathogens. Zoonotic agents are naturally transmitted from vertebrate animals to humans and vice versa. The list of zoonotic fungal agents is limited but some species, like Microsporum canis and Sporothrix brasiliensis from cats, have a strong public health impact. Mycotoxins are defined as the chemicals of fungal origin being toxic for warm-blooded vertebrates. Intoxications by aflatoxins and ochratoxins represent a threat for both human and animal health. Resistance to antifungals can occur in different animal species that receive these drugs, although the true epidemiology of resistance in animals is unknown, and options to treat infections caused by resistant infections are limited.

Multiplex real-time PCR assay to detect illegal trade of CITES-listed shark species

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is a multilateral environmental agreement to ensure that the international trade of threatened species is either prohibited (Appendix I listed species) or being conducted legally, sustainably, and transparently (Appendix II listed species). Twelve threatened shark species exploited for their fins, meat, and other products have been listed under CITES Appendix II. Sharks are often traded in high volumes, some of their products are visually indistinguishable, and most importing/exporting nations have limited capacity to detect illicit trade and enforce the regulations. High volume shipments often must be screened after only a short period of detainment (e.g., a maximum of 24 hours), which together with costs and capacity issues have limited the use of DNA approaches to identify illicit trade. Here, we present a reliable, field-based, fast (<4 hours), and cost effective ($0.94 USD per sample) multiplex real-time PCR protocol capable of detecting nine of the twelve sharks listed under CITES in a single reaction. This approach facilitates detection of illicit trade, with positive results providing probable cause to detain shipments for more robust forensic analysis. We also provide evidence of its application in real law enforcement scenarios in Hong Kong. Adoption of this approach can help parties meet their CITES requirements, avoiding potential international trade sanctions in the future.

Enzootic frog pathogen Batrachochytrium dendrobatidis in Asian tropics reveals high ITS haplotype diversity and low prevalence

Emerging Infectious Diseases (EIDs) are a major threat to wildlife and a key player in the declining amphibian populations worldwide. One such EID is chytridiomycosis caused by Batrachochytrium dendrobatidis (Bd), a fungal pathogen. Aetiology of Bd infection is poorly known from tropical frogs in Asian biodiversity hotspots. Surveys were carried out in four biodiversity hotspots to ascertain the status of Bd fungus. We collected a total of 1870 swab samples from frogs representing 32 genera and 111 species. Nested PCRs revealed low prevalence (8.4%) and high Bd haplotype richness was revealed after sequencing. We document 57 Bd Internal Transcribed Spacer region (ITS) haplotypes, of which 46 were unique to the global database. Bd ITS region showed indels at the Taqman binding site and qPCR reverse primer binding site, suggesting qPCR is unsuitable for diagnosis in Asian Bd coldspots. Our median-joining network and Bayesian tree analyses reveal that the Asian haplotypes, with the exception of Korea, formed a separate clade along with pandemic BdGPL (Bd Global Panzootic Lineage) haplotype. We hypothesise that the frog populations in Asian tropics might harbour several endemic strains of Bd, and the high levels of diversity and uniqueness of Bd haplotypes in the region, probably resulted from historical host-pathogen co-evolution.

Does forest extent affect salamander survival? Evidence from a long-term demographic study of a tropical newt

Forest loss has been associated with reduced survival in many vertebrates, and previous research on amphibians has mostly focused on effects at early life stages. Paramesotriton hongkongensis is a tropical newt that breeds in streams but spends up to 10 months per year in terrestrial habitats. Populations are threatened by habitat degradation and collection for the pet trade, but the cryptic terrestrial lifestyle of this newt has limited our understanding of its population ecology, which inhibits development of a species-specific conservation plan. We conducted an eight-year (2007-2014) mark-recapture study on four P. hongkongensis populations in Hong Kong and used these data to evaluate relationships between forest cover, body size, and rainfall on survival and to estimate population sizes. Hong Kong has been subjected to repeated historic territory-wide deforestation, and thus, we wanted to determine whether there was a link between forest extent as a proxy of habitat quality and newt demography. Annual survival was positively associated with forest cover within core habitat of all populations and negatively related to body size. Mean annual survival (~60%) was similar to that of other stream-dwelling amphibians, but varied among years and declined substantially in 2012-2013, perhaps due to illegal collection. Despite the link between forest extent and survival, population sizes declined at the most forested site by 40% and increased by 104% and 134% at two others. Forest protection and consequential secondary succession during recent decades in Hong Kong may have been responsible for persistence of P. hongkongensis populations.

Future of keeping pet reptiles and amphibians: towards integrating animal welfare, human health and environmental sustainability

The keeping of exotic pets is currently under debate and governments of several countries are increasingly exploring the regulation, or even the banning, of exotic pet keeping. Major concerns are issues of public health and safety, animal welfare and biodiversity conservation. The keeping of reptiles and amphibians in captivity encompasses all the potential issues identified with keeping exotic pets, and many of those relating to traditional domestic pets. Within the context of risks posed by pets in general, the authors argue for the responsible and sustainable keeping of reptile and amphibian pets by private persons, based on scientific evidence and on the authors' own expertise (veterinary medicine, captive husbandry, conservation biology).

Batrachochytrium salamandrivorans not detected in U.S. survey of pet salamanders

We engaged pet salamander owners in the United States to screen their animals for two amphibian chytrid fungal pathogens Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal). We provided pet owners with a sampling kit and instructional video to swab the skin of their animals. We received 639 salamander samples from 65 species by mail, and tested them for Bd and Bsal using qPCR. We detected Bd on 1.3% of salamanders (95% CI 0.0053–0.0267) and did not detect Bsal (95% CI 0.0000–0.0071). If Bsal is present in the U.S. population of pet salamanders, it occurs at a very low prevalence. The United States Fish and Wildlife Service listed 201 species of salamanders as “injurious wildlife” under the Lacey Act (18 U.S.C. § 42) on January 28, 2016, a precautionary action to prevent the introduction of Bsal to the U.S. through the importation of salamanders. This action reduced the number of salamanders imported to the U.S. from 2015 to 2016 by 98.4%. Our results indicate that continued precautions should be taken to prevent the introduction and establishment of Bsal in the U.S., which is a hotspot of salamander biodiversity.

Complete Genome Sequence of Frog virus 3, Isolated from a Strawberry Poison Frog (Oophaga pumilio) Imported from Nicaragua into the Netherlands

Frog virus 3 was isolated from a strawberry poison frog (Oophaga pumilio) imported from Nicaragua via Germany to the Netherlands, and its complete genome sequence was determined. Frog virus 3 isolate Op/2015/Netherlands/UU3150324001 is 107,183 bp long and has a nucleotide similarity of 98.26% to the reference Frog virus 3 isolate.

Ranavirus phylogenomics: Signatures of recombination and inversions among bullfrog ranaculture isolates

Ranaviruses are emerging pathogens of fish, amphibians, and reptiles that threaten aquatic animal industries and wildlife worldwide. Our objective was to genetically characterize ranaviruses isolated during separate bullfrog Lithobates catesbeianus die-offs that occurred eight years apart on the same North American farm. The earlier outbreak was due to a highly pathogenic strain of common midwife toad virus (CMTV) previously known only from Europe and China. The later outbreak was due to a chimeric ranavirus that displayed a novel genome arrangement and a DNA backbone typical for Frog virus 3 (FV3) strains except for interspersed fragments acquired through recombination with the CMTV isolated earlier. Both bullfrog ranaviruses are more pathogenic than wild-type FV3 suggesting recombination may have resulted in the increased pathogenicity observed in the ranavirus isolated in the later outbreak. Our study underscores the role international trade in farmed bullfrogs may have played in the global dissemination of highly pathogenic ranaviruses.

The Emerging Amphibian Fungal Disease, Chytridiomycosis: A Key Example of the Global Phenomenon of Wildlife Emerging Infectious Diseases

The spread of amphibian chytrid fungus, Batrachochytrium dendrobatidis, is associated with the emerging infectious wildlife disease chytridiomycosis. This fungus poses an overwhelming threat to global amphibian biodiversity and is contributing toward population declines and extinctions worldwide. Extremely low host-species specificity potentially threatens thousands of the 7,000+ amphibian species with infection, and hosts in additional classes of organisms have now also been identified, including crayfish and nematode worms.Soon after the discovery of B. dendrobatidis in 1999, it became apparent that this pathogen was already pandemic; dozens of countries and hundreds of amphibian species had already been exposed. The timeline of B. dendrobatidis's global emergence still remains a mystery, as does its point of origin. The reason why B. dendrobatidis seems to have only recently increased in virulence to catalyze this global disease event remains unknown, and despite 15 years of investigation, this wildlife pandemic continues primarily uncontrolled. Some disease treatments are effective on animals held in captivity, but there is currently no proven method to eradicate B. dendrobatidis from an affected habitat, nor have we been able to protect new regions from exposure despite knowledge of an approaching "wave" of B. dendrobatidis and ensuing disease.International spread of B. dendrobatidis is largely facilitated by the commercial trade in live amphibians. Chytridiomycosis was recently listed as a globally notifiable disease by the World Organization for Animal Health, but few countries, if any, have formally adopted recommended measures to control its spread. Wildlife diseases continue to emerge as a consequence of globalization, and greater effort is urgently needed to protect global health.

Xenopus-FV3 host-pathogen interactions and immune evasion

We first review fundamental insights into anti-ranavirus immunity learned with the Xenopus laevis/ranavirus FV3 model that are generally applicable to ectothermic vertebrates. We then further investigate FV3 genes involved in immune evasion. Focusing on FV3 knockout (KO) mutants defective for a putative viral caspase activation and recruitment domain-containing (CARD)-like protein (Δ64R-FV3), a β-hydroxysteroid dehydrogenase homolog (Δ52L-FV3), and an immediate-early18kDa protein (FV3-Δ18K), we assessed the involvement of these viral genes in replication, dissemination and interaction with peritoneal macrophages in tadpole and adult frogs. Our results substantiate the role of 64R and 52L as critical immune evasion genes, promoting persistence and dissemination in the host by counteracting type III IFN in tadpoles and type I IFN in adult frogs. Comparably, the substantial accumulation of genome copy numbers and exacerbation of type I and III IFN gene expression responses but deficient release of infectious virus suggests that 18K is a viral regulatory gene.

Invasive amphibians in southern Africa: A review of invasion pathways

Background: Globally, invasive amphibians are known for their environmental and social impacts that range from poisoning of local fauna and human populations to direct predation on other amphibians. Although several countries on most continents have had multiple introductions of many species, southern Africa appears to have escaped allochthonous introductions. Instead, it has a small number of domestic exotic species that have rapidly expanded their ranges and established invasive populations within South Africa. Objectives methods: We used the literature to provide a historical overview of dispersal by some of the world’s major invasive amphibians, give examples of species that are commonly moved as stowaways and discuss historical and current amphibian trade in the region. In addition, we give an overview of new South African legislation and how this is applied to amphibian invasions, as well as providing updates on the introduced populations of three domestic exotics: Hyperolius marmoratus, Sclerophrys gutturalis and Xenopus laevis. Results: We show that frogs are mainly moved around southern Africa through ‘jump’ dispersal, although there are a number of records of ‘cultivation’, ‘leading-edge’ and ‘extreme long-distance’ dispersal types. Important pathways include trade in fruit and vegetables, horticultural products and shipping containers. Conclusion: We suggest that southern Africa is becoming more vulnerable to amphibian invasions because of an increase in trade, agricultural and domestic impoundments as well as global climate change. Increasing propagule pressure suggests that preventing new introductions will become a key challenge for the future. Currently, trade in amphibians in the region is practically non-existent, suggesting potential for best practice to prevent importation of species with high invasion potential and to stop the spread of disease.

Detection of Batrachochytrium dendrobatidis in Amphibians Imported into the UK for the Pet Trade

There is increasing evidence that the global spread of the fungal pathogen Batrachochytrium dendrobatidis (Bd) has been facilitated by the international trade in amphibians. Bd was first detected in the UK in 2004, and has since been detected in multiple wild amphibian populations. Most amphibians imported into the UK for the pet trade from outside the European Union enter the country via Heathrow Animal Reception Centre (HARC), where Bd-positive animals have been previously detected. Data on the volume, diversity and origin of imported amphibians were collected for 59 consignments arriving at HARC between November 2009 and June 2012, along with a surveillance study to investigate the prevalence of Bd in these animals. Forty-three amphibian genera were recorded, originating from 12 countries. It was estimated that 5000-7000 amphibians are imported through HARC into the UK annually for the pet trade. Bd was detected in consignments from the USA and Tanzania, in six genera, resulting in an overall prevalence of 3.6%. This suggests that imported amphibians are a source of Bd within the international pet trade.

Amphibian chytridiomycosis: a review with focus on fungus-host interactions

Amphibian declines and extinctions are emblematic for the current sixth mass extinction event. Infectious drivers of these declines include the recently emerged fungal pathogens Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans (Chytridiomycota). The skin disease caused by these fungi is named chytridiomycosis and affects the vital function of amphibian skin. Not all amphibians respond equally to infection and host responses might range from resistant, over tolerant to susceptible. The clinical outcome of infection is highly dependent on the amphibian host, the fungal virulence and environmental determinants. B. dendrobatidis infects the skin of a large range of anurans, urodeles and caecilians, whereas to date the host range of B. salamandrivorans seems limited to urodeles. So far, the epidemic of B. dendrobatidis is mainly limited to Australian, neotropical, South European and West American amphibians, while for B. salamandrivorans it is limited to European salamanders. Other striking differences between both fungi include gross pathology and thermal preferences. With this review we aim to provide the reader with a state-of-the art of host-pathogen interactions for both fungi, in which new data pertaining to the interaction of B. dendrobatidis and B. salamandrivorans with the host’s skin are integrated. Furthermore, we pinpoint areas in which more detailed studies are necessary or which have not received the attention they merit.

Anthropogenic and ecological drivers of amphibian disease (ranavirosis)

Ranaviruses are causing mass amphibian die-offs in North America, Europe and Asia, and have been implicated in the decline of common frog (Rana temporaria) populations in the UK. Despite this, we have very little understanding of the environmental drivers of disease occurrence and prevalence. Using a long term (1992-2000) dataset of public reports of amphibian mortalities, we assess a set of potential predictors of the occurrence and prevalence of Ranavirus-consistent common frog mortality events in Britain. We reveal the influence of biotic and abiotic drivers of this disease, with many of these abiotic characteristics being anthropogenic. Whilst controlling for the geographic distribution of mortality events, disease prevalence increases with increasing frog population density, presence of fish and wild newts, increasing pond depth and the use of garden chemicals. The presence of an alternative host reduces prevalence, potentially indicating a dilution effect. Ranavirosis occurrence is associated with the presence of toads, an urban setting and the use of fish care products, providing insight into the causes of emergence of disease. Links between occurrence, prevalence, pond characteristics and garden management practices provides useful management implications for reducing the impacts of Ranavirus in the wild.

Terrestrial Dispersal and Potential Environmental Transmission of the Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis)

Dispersal and exposure to amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) is not confined to the aquatic habitat, but little is known about pathways that facilitate exposure to wild terrestrial amphibians that do not typically enter bodies of water. We explored the possible spread of Bd from an aquatic reservoir to terrestrial substrates by the emergence of recently metamorphosed infected amphibians and potential deposition of Bd-positive residue on riparian vegetation in Cusuco National Park, Honduras (CNP). Amphibians and their respective leaf perches were both sampled for Bd presence and the pathogen was detected on 76.1% (35/46) of leaves where a Bd-positive frog had rested. Although the viability of Bd detected on these leaves cannot be discerned from our quantitative PCR results, the cool air temperature, closed canopy, and high humidity of this cloud forest environment in CNP is expected to encourage pathogen persistence. High prevalence of infection (88.5%) detected in the recently metamorphosed amphibians and frequent shedding of Bd-positive residue on foliage demonstrates a pathway of Bd dispersal between aquatic and terrestrial habitats. This pathway provides the opportunity for environmental transmission of Bd among and between amphibian species without direct physical contact or exposure to an aquatic habitat.

Presence and prevalence of Batrachochytrium dendrobatidis in commercial amphibians in Mexico City

In Mexico City, native and exotic amphibians are commonly sold through the pet trade. This study investigates the presence of Batrachochytrium dendrobatidis (Bd) in native amphibians being sold at two commercial markets and at a herpetarium in Mexico City. A total of 238 individuals (6 genera and 12 species) were tested for Bd using real-time polymerase chain reaction (PCR) analysis. There were 197 Bd-positive individuals (prevalence 82%) from five species of amphibians. Hyla eximia from the markets had very high Bd prevalence (100%; 76/76 and 99%; 88/89) but those from the herpetarium were Bd negative (0/12). Ambystoma mexicanum from the herpetarium also had a high Bd-positive prevalence (80%; 28/35). Though A. mexicanum is nearly extinct in the wild, a commercial market continues to flourish through the pet trade. Now that captive colonies of A. mexicanum are currently used for reintroduction programs, the authors recommend quarantine to reduce spread of Bd via movement of infected animals in the trade and between colonies and via disposal of wastewater from captive collections.

Phylogeny and differentiation of reptilian and amphibian ranaviruses detected in Europe

Ranaviruses in amphibians and fish are considered emerging pathogens and several isolates have been extensively characterized in different studies. Ranaviruses have also been detected in reptiles with increasing frequency, but the role of reptilian hosts is still unclear and only limited sequence data has been provided. In this study, we characterized a number of ranaviruses detected in wild and captive animals in Europe based on sequence data from six genomic regions (major capsid protein (MCP), DNA polymerase (DNApol), ribonucleoside diphosphate reductase alpha and beta subunit-like proteins (RNR-α and -β), viral homolog of the alpha subunit of eukaryotic initiation factor 2, eIF-2α (vIF-2α) genes and microsatellite region). A total of ten different isolates from reptiles (tortoises, lizards, and a snake) and four ranaviruses from amphibians (anurans, urodeles) were included in the study. Furthermore, the complete genome sequences of three reptilian isolates were determined and a new PCR for rapid classification of the different variants of the genomic arrangement was developed. All ranaviruses showed slight variations on the partial nucleotide sequences from the different genomic regions (92.6–100%). Some very similar isolates could be distinguished by the size of the band from the microsatellite region. Three of the lizard isolates had a truncated vIF-2α gene; the other ranaviruses had full-length genes. In the phylogenetic analyses of concatenated sequences from different genes (3223 nt/10287 aa), the reptilian ranaviruses were often more closely related to amphibian ranaviruses than to each other, and most clustered together with previously detected ranaviruses from the same geographic region of origin. Comparative analyses show that among the closely related amphibian-like ranaviruses (ALRVs) described to date, three recently split and independently evolving distinct genetic groups can be distinguished. These findings underline the wide host range of ranaviruses and the emergence of pathogen pollution via animal trade of ectothermic vertebrates.

First reported outbreak of severe spirorchiidiasis in Emys orbicularis, probably resulting from a parasite spillover event

The importance of disease-mediated invasions and the role of parasite spillover as a substantial threat to the conservation of global biodiversity are now well known. Although competition between invasive sliders Trachemys scripta elegans and indigenous European turtles has been extensively studied, the impact of this invasive species on diseases affecting native populations is poorly known. During winter 2012-2013 an unusual event was detected in a population of Emys orbicularis (Linnaeus, 1758) inhabiting a pond system in Galicia (NW Spain). Most turtles were lethargic and some had lost mobility of limbs and tail. Necropsies were performed on 11 turtles that were found dead or dying at this site. Blood flukes belonging to the species Spirorchis elegans were found inhabiting the vascular system of 3 turtles, while numerous fluke eggs were trapped in the vascular system, brain, lung, heart, liver, kidney, spleen, and/or gastrointestinal tissues of all necropsied animals. Characteristic lesions included miliary egg granulomas, which were mostly found on serosal surfaces, particularly of the small intestine, as well as endocarditis, arteritis, and thrombosis. The most probable cause of death in the 3 turtle specimens which were also examined histologically was a necrotic enteritis with secondary bacterial infection associated with a massive egg embolism. The North American origin of S. elegans, the absence of prior recorded epizootics in the outbreak area, and the habitual presence of its type host, the highly invasive red-eared slider, in this area suggest a new case of parasite spillover resulting in a severe emerging disease.