Frogs vs fungus: the emergence of amphibian chytridiomycosis

By the late 1980s, widespread dramatic declines in amphibian populations were causing alarm. The culprit was identified as Batrachochytrium dendrobatidis (Bd), a chytrid fungus that infects the skin of various amphibian hosts, particularly anurans (frogs), and the first example of a chytridiomycete parasitising vertebrates. The disease, chytridiomycosis, has spread globally and is linked to the decline and extinction of many amphibian species. This review summarises the discovery of Bd, its emergence as a panzootic pathogen, and some current mitigation strategies to conserve amphibians

Distinct Host–Mycobacterial Pathogen Interactions between Resistant Adult and Tolerant Tadpole Life Stages of Xenopus laevis

Mycobacterium marinum is a promiscuous pathogen infecting many vertebrates, including humans, whose persistent infections are problematic for aquaculture and public health. Among unsettled aspects of host–pathogen interactions, the respective roles of conventional and innate-like T (iT) cells in host defenses against M. marinum remain unclear. In this study, we developed an infection model system in the amphibian Xenopus laevis to study host responses to M. marinum at two distinct life stages, tadpole and adult. Adult frogs possess efficient conventional T cell–mediated immunity, whereas tadpoles predominantly rely on iT cells. We hypothesized that tadpoles are more susceptible and elicit weaker immune responses to M. marinum than adults. However, our results show that, although anti–M. marinum immune responses between tadpoles and adults are different, tadpoles are as resistant to M. marinum inoculation as adult frogs. M. marinum inoculation triggered a robust proinflammatory CD8+ T cell response in adults, whereas tadpoles elicited only a noninflammatory CD8 negative- and iT cell–mediated response. Furthermore, adult anti–M. marinum responses induced active granuloma formation with abundant T cell infiltration and were associated with significantly reduced M. marinum loads. This is reminiscent of local CD8+ T cell response in lung granulomas of human tuberculosis patients. In contrast, tadpoles rarely exhibited granulomas and tolerated persistent M. marinum accumulation. Gene expression profiling confirmed poor tadpole CD8+ T cell response, contrasting with the marked increase in transcript levels of the anti–M. marinum invariant TCR rearrangement (iVα45-Jα1.14) and of CD4. These data provide novel insights into the critical roles of iT cells in vertebrate antimycobacterial immune response and tolerance to pathogens

Cryptic diversity of a widespread global pathogen reveals expanded threats to amphibian conservation

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.Biodiversity loss is one major outcome of human-mediated ecosystem disturbance. One way that humans have triggered wildlife declines is by transporting disease-causing agents to remote areas of the world. Amphibians have been hit particularly hard by disease due in part to a globally distributed pathogenic chytrid fungus (Batrachochytrium dendrobatidis [Bd]). Prior research has revealed important insights into the biology and distribution of Bd; however, there are still many outstanding questions in this system. Although we know that there are multiple divergent lineages of Bd that differ in pathogenicity, we know little about how these lineages are distributed around the world and where lineages may be coming into contact. Here, we implement a custom genotyping method for a global set of Bd samples. This method is optimized to amplify and sequence degraded DNA from noninvasive skin swab samples. We describe a divergent lineage of Bd, which we call BdASIA3, that appears to be widespread in Southeast Asia. This lineage co-occurs with the global panzootic lineage (BdGPL) in multiple localities. Additionally, we shed light on the global distribution of BdGPL and highlight the expanded range of another lineage, BdCAPE. Finally, we argue that more monitoring needs to take place where Bd lineages are coming into contact and where we know little about Bd lineage diversity. Monitoring need not use expensive or difficult field techniques but can use archived swab samples to further explore the history—and predict the future impacts—of this devastating pathogen

Genetic approaches for increasing fitness in endangered species

The global rate of wildlife extinctions is accelerating, and the persistence of many species requires conservation breeding programs. A central paradigm of these programs is to preserve the genetic diversity of the founder populations. However, this may preserve original characteristics that make them vulnerable to extinction. We introduce targeted genetic intervention (TGI) as an alternative approach that promotes traits that enable species to persist in the face of threats by changing the incidence of alleles that impact on fitness. The TGI toolkit includes methods with established efficacy in model organisms and agriculture but are largely untried for conservation, such as synthetic biology and artificial selection. We explore TGI approaches as a species-restoration tool for intractable threats including infectious disease and climate change

Host species is linked to pathogen genotype for the amphibian chytrid fungus (Batrachochytrium dendrobatidis)

Host-pathogen specificity can arise from certain selective environments mediated by both the host and pathogen. Therefore, understanding the degree to which host species identity is correlated with pathogen genotype can help reveal historical host-pathogen dynamics. One animal disease of particular concern is chytridiomycosis, typically caused by the global panzootic lineage of the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd), termed Bd-GPL. This pathogen lineage has caused devastating declines in amphibian communities around the world. However, the site of origin for the common ancestor of modern Bd-GPL and the fine-scale transmission dynamics of this lineage have remained a mystery. This is especially the case in North America where Bd-GPL is widespread, but disease outbreaks occur sporadically. Herein, we use Bd genetic data collected throughout the United States from amphibian skin swabs and cultured isolate samples to investigate Bd genetic patterns. We highlight two case studies in Pennsylvania and Nevada where Bd-GPL genotypes are strongly correlated with host species identity. Specifically, in some localities bullfrogs (Rana catesbeiana) are infected with Bd-GPL lineages that are distinct from those infecting other sympatric amphibian species. Overall, we reveal a previously unknown association of Bd genotype with host species and identify the eastern United States as a Bd diversity hotspot and potential site of origin for Bd-GPL

Essays on river mechanics

Instructor: P.Y. Julien.Presented by the Graduate Students in CE 717 River Mechanics (Spring 1988).Includes bibliographical references.May 1988

Accessible interview practices for disabled scientists and engineers

Increasing representation of people with disabilities in science and engineering will require systemic changes to the culture around support and accommodations. Equitable interview practices can help foster such changes. We, an interdisciplinary group of disabled and nondisabled early-career scientists who care deeply about making science more accessible to all, present a framework of suggestions based on Universal Design principles for improving the accessibility and equitability of interviews for people with disabilities and other underrepresented groups. We discuss potential challenges that may arise when implementing these suggestions and provide questions to guide discussions about addressing them

Rewilding immunology : integrating comparative immunology can improve human, animal, and ecosystem health

The common origin of all species provides a wealth of history recorded in DNA and a lens for understanding human biology. Immunology research has traditionally used rodents as the model of choice. However, translational success has not met its full potential. Broadening immunology research to integrate comparative approaches across species and environments can amplify the potential of immunology to improve the lives of humans and other animals. Additionally, it can lead to discoveries that are not possible in a restricted set of model organisms and environments. For example, the contemporary vaccine era arose from observing human-animal interactions in a real-world environment (cowpox infection protected milkmaids from smallpox). Most emerging infectious diseases (EIDs) originate in domestic and wild animals (1), and the coronavirus disease 2019 (COVID-19) pandemic is a stark reminder of the need to think more holistically about the health of humans and animals