Relationship between two pathogens in an amphibian community that experienced mass mortalities

Because host species tend to harbor multiple parasitic species, coinfection in a host is com-mon. The chytrid fungusBatrachochytrium dendrobatidis(Bd) and the viruses in the genusRanavirus(Rv) are responsible for the decline of amphibians worldwide. Despite widegeographical co-occurrence and the serious conservation problem that coinfection withthese pathogens could represent, little is known about their possible synergistic interac-tions and effects in a host community. We investigated the occurrence and associationsbetween these two pathogens in an amphibian community after Rv-driven disease out-breaks were detected in four populations of the Iberian ribbed newt (Pleurodeles waltl)innorthwestern Spain. We collected tissue samples from amphibians and fish and estimatedBd and Rv infection loads by qPCR. A few months after the most recent mass mortalityevent, Rv infection parameters at the affected sites decreased significantly or were lowerthan such registered at the sites where no outbreaks were recorded. Both pathogens weresimultaneously present in almost all sites, but coinfection in a single host was rare. Ourfindings 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 infectionintensity of the other) following an outbreak. Other variables (such as species identity orsite) were more important than infection with a pathogen in predicting the infection statusand severity of infection with the other pathogen. Our results highlight the importance ofhost-specific and environmental characteristics in the dynamics of infections, coinfectionpatterns, and their impacts.info:eu-repo/semantics/publishedVersio

Long-Term Monitoring of Amphibian Populations of a National Park in Northern Spain Reveals Negative Persisting Effects of Ranavirus, but Not Batrachochytrium dendrobatidis

Amphibians are the most highly threatened vertebrates, and emerging pathogens are a serious threat to their conservation. Amphibian chytrid fungi and the viruses of the Ranavirus genus are causing disease outbreaks worldwide, including in protected areas such as National Parks. However, we lack information about their effect over amphibian populations in the long-term, and sometimes these mortality episodes are considered as transient events without serious consequences over longer time-spans. Here, we relate the occurrence of both pathogens with the population trends of 24 amphibian populations at 15 sites across a national Park in northern Spain over a 14-year period. Just one out 24 populations presents a positive population trend being free of both pathogens, while seven populations exposed to one or two pathogens experienced strong declines during the study period. The rest of the study populations (16) remain stable, and these tend to be of species that are not susceptible to the pathogen present or are free of pathogens. Our study is consistent with infectious diseases playing an important role in dictating amphibian population trends and emphasizes the need to adopt measures to control these pathogens in nature. We highlight that sites housing species carrying Ranavirus seems to have experienced more severe population-level effects compared to those with the amphibian chytrid fungus, and that ranaviruses could be just as, or more important, other more high-profile amphibian emerging pathogens

Climate warming triggers the emergence of native viruses in Iberian amphibians

The number of epizootics in amphibian populations caused by viruses of the genus Ranavirus is increasing worldwide. Yet, causes for pathogen emergence are poorly understood. Here, we confirmed that the Common midwife toad virus (CMTV) and Frog virus 3 (FV3) are responsible for mass mortalities in Iberia since the late 1980s. Our results illustrate the Iberian Peninsula as a diversity hotspot for the highly virulent CMTV. Although this pattern of diversity in Europe is consistent with spread by natural dispersal, the exact origin of the emergence of CMTV remains uncertain. Nevertheless, our data allow hypothesizing that the Iberian Peninsula might harbor the ancestral population of CMTVs that could have spread into the rest of Europe. In addition, we found that climate warming could be triggering the CMTV outbreaks, supporting its endemic status in the Iberian Peninsula.info:eu-repo/semantics/acceptedVersio

Incidence of emerging pathogens in the legal and illegal amphibian trade in Spain

Amphibians are threatened globally and emerging diseases are some of the most important drivers of their catastrophic situation. There is increasing evidence that the international trade in live amphibians is one of the most important mechanisms driving pathogen pollution. Here, we report the presence of Batrachochytrium dendrobatidis (Bd) and Ranavirus in 11% of tested individuals in legal amphibian trade fairs in Spain. Although none of the Bd infected animals in trade fairs presented disease symptoms, symptoms of ranavirosis were observed in some specimens, which were nonetheless still offered for sale. None of the traders who were selling infected animals showed interest in engaging in collaboration to control infections when offered for free. In addition, a large private urodele collection confiscated by the police in Barcelona comprised a number of illegally wild-caught species. Many confiscated individuals presented signs of poor welfare and several were positive for Bd. Our results indicate the urgent need for implementation of real sanitary regulations or effective legislation governing the practice of trade in living amphibians to prevent pathogen spread in Europe.Peer reviewe

Fatal chytridiomycosis in the Moroccan midwife toad Alytes maurus and potential distribution of Batrachochytrium dendrobatidis across Morocco

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.Peer reviewe

Triple dermocystid-chytrid fungus-ranavirus co-infection in a Lissotriton helveticus

Emerging infectious diseases represent a key problem for the survival of amphibian populations. Declines related to infections of the chytrid fungus Batrachochytrium dendrobatidis and Ranavirus have been described in several areas of Northern Spain, including protected areas. Co-infection—the simultaneous infection of a host by multiple pathogen species—can increase the susceptibility to subsequent infections. Here, we describe a case of triple dermocystid-ranavirus-chytrid fungus co-infection in a specimen of palmate newt (Lissotriton helveticus) from a protected wetland of North-western Spain. Five palmate newts and one Bosca’s newt (Lissotriton boscai) were found dead, and tissue samples were analysed by using qPCR methods. Ranavirus was detected in four out of five L. helveticus and in the L. boscai individual, whereas Bd was detected only in one of the five L. helveticus. Four out of six specimens tested positive for Dermocystidium. Sequencing was performed to double-check the presence of Dermocystidium in a qPCR-positive sample for that pathogen

Stressed tadpoles mount more efficient glucocorticoid negative feedback in anthropogenic habitats due to phenotypic plasticity

Coping with anthropogenic environmental change is among the greatest challenges faced by wildlife, and endocrine flexibility is a potentially crucial coping mechanism. Animals may adapt to anthropogenic environments by dampening their glucocorticoid stress response, but empirical tests of this hypothesis have provided mixed evidence. An alternative hypothesis is that a non-attenuated stress response and efficient negative feedback are favored in anthropogenic habitats. To test this idea, we non-invasively sampled corticosterone release rates of common toad (Bufo bufo) tadpoles in agricultural, urban, and natural habitats, and quantified their stress response and negative feedback by a standardized stress-and-recovery protocol. We repeated the same sampling with tadpoles raised from eggs from the same ponds in a common-garden experiment to infer if the differences observed between populations in different habitats were due to individual phenotypic plasticity rather than microevolution or transgenerational effects. We found that, compared to tadpoles in natural ponds, urban tadpoles had higher baseline and stressed corticosterone release rates, and tadpoles in agricultural ponds had similar corticosterone release rates but greater stress-induced change, indicating stronger stress responses in both types of anthropogenic habitats. As predicted, tadpoles in both agricultural and urban ponds showed more efficient negative feedback than did tadpoles in natural ponds. Water pollution levels, as indicated by the concentrations of carbamazepine and corticoid-disrupting compounds in pond water, contributed to elevating the stress response regardless of land use. Infection by neither Batrachochytrium dendrobatidis nor Ranavirus was detected in free-living tadpoles. No habitat-related glucocorticoid differences persisted in the common-garden experiment. These results suggest that toad tadpoles in anthropogenic habitats increased their glucocorticoid flexibility via phenotypic plasticity. The coupling of stronger stress response and stronger negative feedback in these habitats supports the importance of rapidly “turning on and off” the stress response as a mechanism for coping with anthropogenic environmental change.The study was supported by a Fulbright Research Grant to CRG, and by the NRDI Fund of the National Research, Development and Innovation Office of Hungary (grants "OTKA"-115402 and 2019-2.1.11-TÉT2019-00026 to VB). GINOP-2.3.3-15-2016-00018 supported the UPLCMS/MS analysis

Coinfection of Chytrid Fungi in Urodeles during an Outbreak of Chytridiomycosis in Spain

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 coinfections 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

Batrachochytrium salamandrivorans Threat to the Iberian Urodele Hotspot

The recent introduction of the chytrid fungus Batrachochytrium salamandrivorans into north-eastern Spain threatens salamander diversity on the Iberian Peninsula. We assessed the current epidemiological situation with extensive field sampling of urodele populations. We then sought to delineate priority regions and identify conservation units for the Iberian Peninsula by estimating the susceptibility of Iberian urodeles using laboratory experiments, evidence from mortality events in nature and captivity and inference from phylogeny. None of the 1395 field samples, collected between 2015 and 2021 were positive for Bsal and no Bsal-associated mortality events were recorded, in contrast to the confirmed occurrence of Bsal outbreak previously described in 2018. We classified five of eleven Iberian urodele species as highly susceptible, predicting elevated mortality and population declines following potential Bsal emergence in the wild, five species as intermediately susceptible with variable disease outcomes and one species as resistant to disease and mortality. We identified the six conservation units (i.e., species or lineages within species) at highest risk and propose priority areas for active disease surveillance and field biosecurity measures. The magnitude of the disease threat identified here emphasizes the need for region-tailored disease abatement plans that couple active disease surveillance to rapid and drastic actions.This research was funded by the European Commission (Tender ENV.B.3/SER/2016/0028, Mitigating a new infectious disease in salamanders to counteract the loss of biodiversity), the Foundation for the Conservation of Salamanders (project “Monitoring the incidence of emerging pathogens on endemic urodeles from the Cantabrian range, Spain”). B.T. was supported by a ‘Doctorados Industriales’ grant of Comunidad de Madrid, Spain (ref. IND2020/AMB-17438). G.V.-A. was financed by the Portuguese Foundation for Science and Technology (FCT; CEECIND/00937/2018). B.C.S. was supported by an ARC DECRA (DE200100121).Peer reviewe