Search for: All records

Detecting pathogens in the live animal trade is critical for tracking and preventing their movement, introduction and spillover into susceptible fauna. However, the scale of the live animal trade makes individually testing animals infeasible for all but the most economically important taxa. For instance, while the fungal pathogen,Batrachochytrium salamandrivorans(Bsal), threatens amphibian, particularly caudate diversity, in Europe and the Americas, screening even a fraction of the millions of live amphibians imported into the United States, alone, is impractically laborious and expensive. A promising alternative to individual‐level sampling (e.g. swabbing the skin of salamanders) is to instead collect DNA from the animals' environment (e.g. housing container or water) which allows us to screen a whole group of animals at a time.

We used a series of experiments withBsal‐spiked water and substrates and experimentally infected rough‐skinned newts (Taricha granulosa) to determine which methods yield the mostBsalenvironmental DNA (eDNA) and evaluate the capacity of these methods to detectBsal‐infected animals in conditions found in captive settings and trade.

We found that filtering water housing infected animals for even an hour can consistently recover detectable levels ofBsaleDNA, that there is little evidence ofBsaleDNA being clumped in housing containers or swamped or inhibited by dirty housing containers, and that eDNA‐based methods achieves an equivalent or higher chance of detectingBsalinfections in a (virtual) population of co‐housed newts with fewer samples than individual swabs.

By sampling the genetic materials accumulated from a whole group of animals, eDNA‐based methods are a powerful means of detecting pathogens, such asBsal, in shipments and captive populations. These methods bring routine pathogen surveillance into reach in many more contexts and can thus be an important tool in conservation and disease control.

 

Pathogen transmission through wildlife trade has become a significant One Health issue, but businesses involved in trade can take actions to minimize pathogen spread within and beyond trade networks. Such actions could include an industry‐led clean‐trade certification program whereby retailer costs for enhanced biosecurity and disease‐free product certification are offset by increased prices to consumers. However, we currently know little about the demand for, and value of such a program to consumers. With the case of pet amphibian owners in the United States, we assessed what characteristics make people more likely to demand certified wild animals and how much more in price premium they are willing to pay for such animals. Findings suggested that the demand for pathogen‐free amphibians was driven by the perceived risk of pathogen spillover to wild populations, behavioral control in preventing transmission, and other characteristics related to pet ownership and demographics. On average, respondents were willing to pay $38.65 per animal more for certified pathogen‐free amphibians than non‐certified amphibians. Findings lend support for the viability of an industry‐led clean‐trade program aimed at enhancing animal well‐being, increasing customer satisfaction, and reducing the risk of pathogen transmission within and beyond the pet trade network.

 

The recent decline in wild populations of amphibians worldwide coincides with the period of rapid growth in the global trade of wildlife. The potential for pathogen transmission within and beyond the pet amphibian trade network makes it important to explore the attitudes and behavior of businesses involved in the industry. We surveyed US businesses involved in the pet amphibian trade industry to characterize their attitudes and behaviors and identify business characteristics that could influence percieved risk of pathogen transmission in trade. We found that amphibian businesses acquire their animals from a variety of sources (e.g., importers, wholesalers, retailers, breeders, hobbyists, wild), are aware of the threat of emerging pathogens, and are concerned about the potential spillover of pathogens from captive to wild populations. Attitudes and behaviors of businesses toward pathogens varied among business types (e.g., size of business, the share of amphibian sales, mode of business operation). Moreover, businesses expressed a strong interest in acquiring amphibians that are free of pathogens and indicated a willingness to pay a price premium to acquire certified disease‐free animals. Our results indicate that the US pet amphibian trade industry is willing to participate in healthy (clean) trade practices and increasing product prices may be one option to compensate for expenses. A government program to support pathogen‐free certification would likely facilitate implementation.

 

Ranaviruses are emerging pathogens of poikilothermic vertebrates. In 2015 the Global Ranavirus Reporting System (GRRS) was established as a centralized, open access, online database for reports of the presence (and absence) of ranavirus around the globe. The GRRS has multiple data layers (e.g., location, date, host(s) species, and methods of detection) of use to those studying the epidemiology, ecology, and evolution of this group of viruses. Here we summarize the temporal, spatial, diagnostic, and host-taxonomic patterns of ranavirus reports in the GRRS. The number, distribution, and host diversity of ranavirus reports have increased dramatically since the mid 1990s, presumably in response to increased interest in ranaviruses and the conservation of their hosts, and also the availability of molecular diagnostics. Yet there are clear geographic and taxonomic biases among the reports. We encourage ranavirus researchers to add their studies to the portal because such collation can provide collaborative opportunities and unique insights to our developing knowledge of this pathogen and the emerging infectious disease that it causes.

 

The stress-induced susceptibility hypothesis, which predicts chronic stress weakens immune defences, was proposed to explain increasing infectious disease-related mass mortality and population declines. Previous work characterized wetland salinization as a chronic stressor to larval amphibian populations. Thus, we combined field observations with experimental exposures quantifying epidemiological parameters to test the role of salinity stress in the occurrence of ranavirus-associated mass mortality events. Despite ubiquitous pathogen presence (94%), populations exposed to salt runoff had slightly more frequent ranavirus related mass mortality events, more lethal infections, and 117-times greater pathogen environmental DNA. Experimental exposure to chronic elevated salinity (0.8–1.6 g l −1 Cl − ) reduced tolerance to infection, causing greater mortality at lower doses. We found a strong negative relationship between splenocyte proliferation and corticosterone in ranavirus-infected larvae at a moderate elevation of salinity, supporting glucocorticoid-medicated immunosuppression, but not at high salinity. Salinity alone reduced proliferation further at similar corticosterone levels and infection intensities. Finally, larvae raised in elevated salinity had 10 times more intense infections and shed five times as much virus with similar viral decay rates, suggesting increased transmission. Our findings illustrate how a small change in habitat quality leads to more lethal infections and potentially greater transmission efficiency, increasing the severity of ranavirus epidemics. 

Mechanistic models are critical for our understanding of both within-host dynamics (i.e., pathogen replication and immune system processes) and among-host dynamics (i.e., transmission). Within-host models, however, are not often fit to experimental data, which can serve as a robust method of hypothesis testing and hypothesis generation. In this study, we use mechanistic models and empirical, time-series data of viral titer to better understand the replication of ranaviruses within their amphibian hosts and the immune dynamics that limit viral replication. Specifically, we fit a suite of potential models to our data, where each model represents a hypothesis about the interactions between viral replication and immune defense. Through formal model comparison, we find a parsimonious model that captures key features of our time-series data: The viral titer rises and falls through time, likely due to an immune system response, and that the initial viral dosage affects both the peak viral titer and the timing of the peak. Importantly, our model makes several predictions, including the existence of long-term viral infections, which can be validated in future studies.