Emerging infectious diseases are one of the biggest challenges in a globalized world. To date, resources have been allocated to prevent and control the spread of zoonotic and livestock pathogens. We argue that, in line with the One Health approach, equitable efforts, financial resources, attention, and coordination are required for wildlife-only pathogens to halt biodiversity loss. Deploying the amphibian fungus Batrachochytrium salamandrivorans as a model, we demonstrate the unbalanced efforts among countries in Europe regarding surveillance, disease response, prevention, public outreach, and research. We compare investments with B. salamandrivorans l-free countries such as the United States, concluding that structural resources are urgently needed to curb the effects of this fungus within Europe and beyond. We encourage dialogue among authorities, researchers, and stakeholders and propose a coordinated European Union-level program of €6-10 million over 5-7 years to implement B. salamandrivorans action plans and define structural funding requirements for future wildlife disease mitigation.

The global amphibian biodiversity crisis is significantly driven by the fungal pathogen Batrachochytrium dendrobatidis (Bd), contributing to declines in populations of hundreds of species and dozens of species extinctions over the last half-century. While the pathogen is widely distributed across at least 26 European nations, it remains undocumented in many regions of the Balkans. This study reports the first detection of Bd within populations of the genus Bombina in Croatia, based on field surveys conducted during the vernal and autumnal seasons of 2023 and 2024. Surveys targeted 19 distinct sites in Papuk Nature Park across an altitudinal gradient (87 m to 864 m), focusing on ephemeral aquatic microhabitats such as shallow temporary ponds and roadside ditches. Molecular screening of 82 individuals via quantitative PCR (qPCR) confirmed the pathogen in eight individuals across four ponds. Infections were identified in yellow-bellied toads (Bombina variegata) and their hybrids, while all sampled fire-bellied toads (B. bombina) tested negative. These results confirm the regional establishment of Bd in Croatia. Given the relative isolation of the infected locations and the low likelihood of the pet trade as a distribution factor, spread via biological vectors or natural hydrological connectivity seems likely. The presence of Bd in these isolated populations introduces a serious long-term threat to their viability, emphasizing the need for monitoring, targeted conservation, and in situ mitigation strategies to prevent sudden population collapses.

Populations of amphibians and reptiles have undergone substantial declines in recent decades worldwide. The Iberian Peninsula, a European diversity hotspot for this group, is suffering severe droughts, rising temperatures, and abandonment of traditional agricultural practices. Despite the importance and sensitivity of Iberian herpetofauna, a data-driven, national, long-term, and multi-species analysis of the distribution and demographic situation of amphibians and reptiles has been lacking. We used dynamic occupancy models to study how the distributions of 25 amphibian and 37 reptile species have changed over the last three decades in Spain. We analysed a detection dataset compiled from multiple sources including citizen science, monitoring programmes and opportunistic observations. Our results showed widespread declines in amphibian and reptile occupancy, which could also suggest generalised population declines. Moreover, we observed a mismatch between the IUCN Red List categories and the estimated occupancy trend, with some species appearing stable at the IUCN global level but presenting substantial range contractions at the regional level. The causes for these declines are unclear. According to our models, amphibian persistence was negatively correlated with rainfall and colonization negatively correlated with altitude. Reptile persistence was negatively correlated with temperature. Our analysis highlights the value of national-scale assessments to identify occupancy trends at fine resolution and investigate regional threats driving these changes. We encourage further research and early conservation action before regional trends and threats become global issues. We further highlight the need for long-term, standardized monitoring programmes to contribute high-quality data to regional and global assessments.

Abstract Evolutionary and demographic processes such as selection, drift and migration shape the genetic variation of populations. Genetic diversity is often lower in populations toward higher latitudes. This decrease potentially threatens their survival as several factors are putting more pressure on the populations, including the spread of infectious diseases. In this study, we combined whole-genome re-sequencing with MHC class II genotyping and skin microbiome profiling in Bufo bufo and B. spinosus, two closely related European toad species. We investigated the underlying immunogenetic and microbial variation resulting from different demographic histories and environmental conditions to identify their potential impact on infection outcomes in these two species. We found lower immunogenetic diversity in B. bufo compared to B. spinosus , with highly significant differences in genes related to adaptive and innate immunity. We found lower overall MHC class II diversity and skin microbiome diversity at the species level in B. bufo , compared with B. spinosus . In contrast, at the individual level, B. bufo showed higher MHC allelic diversity and greater diversity in the core skin microbiota than B. spinosus . Together, our findings suggest that divergence in immunogenetic background and host-associated microbial communities may underlie differences in susceptibility to emerging infectious diseases. This integrative framework provides new insight into how host genetics and microbial communities jointly influence disease outcomes across environmental gradients.

Amphibians are undergoing a dramatic global decline. This massive biodiversity loss, which is critically impacting public and planetary health, has been attributed to multiple causes including infectious diseases. Of the known pathogens associated with obvious diseases in amphibians, herpesviruses have recently raised attention secondary to the discovery of two new species, both associated with skin diseases. Here, we provide the detection and characterization of a novel amphibian herpesvirus associated with a proliferative skin disease, closely resembling that previously described in association with Batravirus ranidallo3 (previously Ranid herpesvirus 3-RaHV3) and Bufonid herpesvirus 1 (BfHV1). The novel virus, tentatively named candidate Batravirus ranidallo5 is genetically related, but distinct from the previously described Batraviruses and it is the first amphibian herpesvirus described in Spain. The full-length genome obtained for this novel herpesvirus is approximately 220 kb and it contains the homologues of herpesvirus hallmark genes, which allows us to propose its unambiguous classification as a herpesvirus. Interestingly, a number of predicted ORFs showed to match closer to fish Alloherpesviruses homologues than Batraviruses. The discovery within a limited time span of three distinct herpesviruses, all associated with obvious skin diseases in Europe is alarming and may have significant implication for amphibian conservation.

Emerging infectious diseases (EIDs) pose a major threat to global amphibian populations, contributing to widespread mortality and species extinctions. Among EIDs, those caused by the fungal pathogens Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), and viruses in the genus Ranavirus (Rv), represent the most significant threats to amphibian biodiversity. Here, we tested for occurrence of Rv in 3 different locations in southeastern Sweden. Using a quantitative PCR assay, complemented by a secondary PCR-based validation method targeting the viral major capsid protein gene and additional 5 partial sequences, we detected Rv in 2 of 3 locations and in 5 out of 43 individuals tested. This is the first record of Rv occurrence reported at such high latitudes in northern Europe and the first from the Scandinavian peninsula, contributing important insights into infection prevalence in northern amphibian populations. These findings establish a basis for the conservation of vulnerable populations.

Ecological niche models (ENMs) have been used frequently to predict the distribution and future spread of the pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd). Based on the assumption that chytridiomycosis outbreaks are most likely to occur where the conditions are ideal for Bd, many studies have identified high‐risk areas for chytridiomycosis and its associated mortality risk using only known Bd occurrences. However, the presence of a pathogen does not necessarily indicate high infection, disease or associated mortality. We used the BIOMOD2 package implemented in R, 19 bioclimatic variables, and 267 locality records, covering three levels of infection progress (occurrence, high infection loads and disease‐associated mortality), to calculate the potential areas where: (1) Bd is likely to be present, (2) amphibians are prone to harbour high infections and (3) chytridiomycosis‐related mortalities are likely to occur. We evaluate discrepancies among the three potential areas projected by the models, encompassing their spatial extent and associated environmental conditions. When all the Bd occurrences were used, the predicted area subjected to Bd risk covered 17% of the study area. However, when just mortality records were used, the predicted area decreased three‐fold. Notably, the three predicted areas only overlapped in 3% of the total study area, suggesting that the region at risk of mortality plus high infections constituted only one‐fifth of the predicted area for Bd presence. Mean temperature during the wettest and warmest 3 months of the year together with isothermality emerged as the most robust negative predictors in each of the three models. Synthesis and applications . Ecological niche models (ENMs) based on the presence data of Batrachochytrium dendrobatidis (Bd) can overestimate the mortality risk of chytridiomycosis because the environmental conditions suitable for Bd presence do not always correspond to those conducive to significant host mortality. Distribution modelling can be a powerful tool when used correctly, and this study highlights the significance of careful data selection to ensure alignment with intended objectives. Considering the widespread use of ENMs to inform policy, meticulous design and comprehensive evaluation are imperative.

Mauritius hosts two established non-native amphibian species: the Mascarene Grass Frog (Ptychadena mascareniensis) and the Guttural Toad (Sclerophrys gutturalis). In this study, we screened individuals of both species for the presence of Batrachochytrium dendrobatidis (Bd), Batrachochytrium salamandrivorans (Bsal), and Ranavirus (Rv). Our results showed no evidence of Rv or Bsal, but Bd was detected with low to moderate infection loads. None of the sampled individuals exhibited clinical signs of chytridiomycosis. Despite the extensive global research on Bd, this study represents the first report of this fungus in amphibian populations in Mauritius.

The thermal mismatch hypothesis (TMH), the notion that cool- and warm-adapted hosts have higher infection risk during unusually warm and cool spells, respectively, was recently proposed to explain how temperature shifts driven by climate change influence host susceptibility to infections at a global scale.1 Despite substantial support for the TMH in the chytrid fungus (Batrachochytrium dendrobatidis, also commonly referred to as Bd) that is devastating amphibians worldwide,2 it remains unknown whether precipitation mismatches, in addition to temperature ones, affect infection risk. Here, we introduce the thermal-hydric mismatch hypothesis (THMH), which proposes that infection risk is shaped by mismatches resulting from the combined effects of temperature and precipitation. We tested this hypothesis using a large-scale survey of B. dendrobatidis and Ranavirus in over 5,800 adult amphibians across the Iberian Peninsula, a climate change hotspot in Europe that is heavily affected by both pathogens.3,4,5,6 We found that the combined effect of thermal and precipitation mismatches increased infection risk for both pathogens. Cool-and-wet-adapted amphibians were more infected with B. dendrobatidis during warm-and-dry spells, while warm-and-dry-adapted hosts showed higher B. dendrobatidis infection during cool-and-wet spells. For Ranavirus, mismatches occurred under opposite climatic conditions to those of B. dendrobatidis, which is consistent with the limited temporal overlap between the two pathogens, despite their frequent geographical co-occurrence.7 Finally, the fact that thermal mismatches alone did not predict B. dendrobatidis infection, and precipitation mismatches alone did not predict Ranavirus infection, suggests that infection risk in the study region is driven by their combined effects, supporting the THMH proposed here.

Because host species tend to harbor multiple parasitic species, coinfection in a host is common. The chytrid fungus Batrachochytrium dendrobatidis (Bd) and the viruses in the genus Ranavirus (Rv) are responsible for the decline of amphibians worldwide. Despite wide geographical co-occurrence and the serious conservation problem that coinfection with these pathogens could represent, little is known about their possible synergistic interactions and effects in a host community. We investigated the occurrence and associations between these two pathogens in an amphibian community after Rv-driven disease outbreaks were detected in four populations of the Iberian ribbed newt (Pleurodeles waltl) in northwestern Spain. We collected tissue samples from amphibians and fish and estimated Bd and Rv infection loads by qPCR. A few months after the most recent mass mortality event, Rv infection parameters at the affected sites decreased significantly or were lower than such registered at the sites where no outbreaks were recorded. Both pathogens were simultaneously present in almost all sites, but coinfection in a single host was rare. Our findings suggest that the co-occurrence of Bd and Rv does not predict adverse outcomes (e.g., enhanced susceptibility of hosts to one pathogen due to the presence or infection intensity of the other) following an outbreak. Other variables (such as species identity or site) were more important than infection with a pathogen in predicting the infection status and severity of infection with the other pathogen. Our results highlight the importance of host-specific and environmental characteristics in the dynamics of infections, coinfection patterns, and their impacts.

Chytridiomycosis caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd) is pushing amphibians towards extinction. Whilst mitigation methods were suggested a decade ago, we lack field trials testing their efficacy. We used the agrochemical fungicide, tebuconazole, to treat Bd infected breeding waterbodies of an endangered species that is highly susceptible to the fungus. Just two applications of tebuconazole led to a significant reduction in infection loads in the vast majority of sites, and at six sites the disinfection remained one/two-years post-application. Tebuconazole values drastically decreased in the waterbodies within a week after application, with no significant effects on their hydrochemical and hydrobiological characteristics. Although the use of chemicals in natural populations is undesirable, the growing existential threat to amphibians all over the world indicates that effective interventions in selected populations of endangered species are urgently needed.

Los anfibios son los vertebrados más amenazados. Las enfermedades emergentes de los anfibios, como la quitridiomicosis y ranavirosis, constituyen una de sus amenazas más relevantes, causando mortalidades masivas, declives poblacionales y extinciones. Dada la preocupación internacional por la crisis de los anfibios, en las últimas décadas han surgido muchas iniciativas para el seguimiento de poblaciones. Desgraciadamente, muchas de estas iniciativas no resultan eficaces para determinar la emergencia de estas enfermedades ni para evaluar su impacto real en las poblaciones, dado que: no se centran en las especies, los estadios de desarrollo y las épocas del año adecuadas, y no incluyen la toma de datos de infección de manera regular. En el caso de las poblaciones con incidencia de patógenos conocida la situación no es mejor, dado que raramente se llevan a cabo programas de seguimiento a largo plazo una vez que los brotes de mortalidad han cesado. Por lo tanto, mientras que cada vez son más frecuentes los casos publicados de mortalidades masivas de anfibios asociados a las enfermedades emergentes, existe un vacío de conocimiento significativo sobre la incidencia real de estas enfermedades y de sus efectos a medio y largo plazo.

In 2020 and 2021 we detected in Catalonia (NE Spain) six new episodes of mortality or presence of dying specimens in introduced Mediterranean painted frogs (Discoglossus pictus). All affected individuals were positive to the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). Histological examinations showed intense involvement of the superficial layers of the epidermis and qPCR analyses yielded infection loads greater than 100 000 genomic equivalents of zoospores. These results suggest that this introduced species could behave as a Bd 'supershedder', and recommend to control its expansion due to its important role in the dynamic of chytridiomycosis.

Chytridiomycosis is affecting hundreds of amphibian species worldwide, but while in tropical areas, adult individuals have been the focus of most investigations, the exact role played by infection intensity of breeding adults is not well understood in temperate areas. We conducted mark–recapture–capture surveys during spiny common toad breeding seasons from 2006 to 2018 at the site of the first recorded outbreak of chytridiomycosis in Europe, the Peñalara Massif (Sierra de Guadarrama National Park, central Spain), and collected infection samples and several variables related to the reproductive effort of male individuals. We used general linear mixed models to evaluate the contribution of study variables on the infection loads of adult male toads exhibited at their capturing date. We also analysed the differences on several male characteristics between the pond with the largest breeding population against the rest of the ponds. We found that the duration of time spent in the waterbody and the condition of the host predicted infection loads. Animals of good physical condition, that spent longer in water, have higher infection levels than individuals with the opposite set of traits. The pond supporting the largest breeding population housed smaller male toads and in poorer condition. Our results are consistent with a shift in reproductive strategy in response to infection and potentially a strategy of tolerance, rather than resistance to infection. These findings have applications for disease mitigation and theoretical implications related to the trade-offs made and the evolution of traits in response to the disease.

Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal), has had an unprecedented impact on amphibian biodiversity. Although Bd is globally widespread, Bsal is currently spreading, increasing the probability that these pathogens will co-occur in individual amphibians. Interactions among coinfecting parasites can have significant outcomes on disease dynamics and impact and, therefore, may have important consequences for amphibian conservation. We analyzed the patterns of Bd-Bsal co-infections in two species of free-ranging urodeles during an outbreak of chytridiomycosis in Spain. Our goals were to assess 1) the probability of co-occurrence of both chytrid species and 2) the correlation of pathogen loads in coinfected hosts. We detected coinfections in 81.58% of Triturus marmoratus (n=38) and in 18.75% of Ichthyosaura alpestris (n=16). Histopathologic lesions of chytridiomycosis were observed only in T. marmoratus. Our results demonstrate a positive relationship between Bd and Bsal loads in T. marmoratus, whereas the co-occurrence analysis showed a random association among pathogens in both urodele species. Overall, we show that Bd-Bsal coinfections intensify pathogen load in T. marmoratus and could, therefore, increase disease severity and have important consequences for the conservation of some amphibian species.

Multiple threats, including emerging infectious diseases, are contributing to the extinction of amphibians worldwide. One of the most devastating diseases is the fatal amphibian skin disease chytridiomycosis caused by the fungus Batrachochytrium dendrobatidis (Bd). The presence of Bd in North Africa was described in 2011 and this included the distribution range of the endemic Moroccan midwife toad (Alytes maurus). Here we report new Bd positive occurrences across several distant regions of Morocco, augment the known number of infected species, and describe the first evidence of lethal chytridiomycosis in A. maurus. Although population declines in this species were not recorded, the family Alytidae has been identified as the most susceptible taxonomic group to chytridiomycosis of the Palearctic. An environmental niche model, taking into account new records of Bd in the country, confirms the Mediterranean coast and the Rif and Middle Atlas Mountains as very favourable areas for Bd. Our results suggest that the real impact of chytridiomycosis in North Africa is poorly understood, and that this continent cannot be identified as a region less impacted by chytridiomycosis, as was previously proposed.