SEH grants 2024

Testing for a Trojan Horse effect: can microplastics enhance the transmission of deadly ranaviruses between amphibians in the aquatic environment?

Plastic debris is an environmentally persistent contaminant of growing concern globally. We consider plastic debris as microplastics (MP), if its particle size falls between 1 mm and 1 μm in diameter. Larval amphibians are exposed to microplastics in the aquatic environment via respiration and ingestion of contaminated food sources. Besides their malign effects on the physiology, life history and survival of amphibians, MP are capable of absorbing diverse groups of microbes, including pathogenic viruses in the aquatic environment. Ranaviruses (Rv) are a group of aquatic pathogens with a wide host range among amphibians. Rv transmission mainly occurs via direct contact between individuals but can happen also indirectly via circulating virions in the water. Therefore, there is a possibility that MP particles may absorb Rv in amphibian breeding waters, and, by locally enhancing the density of the virus or increasing their availability for ingestion, the presence of MP may increase disease risk and exacerbate disease outcomes where Rv and MP co-occur. 

During this project, I aim to test how different MP sizes and concentrations following an accumulation period in the liquid culture of Rv influence the virus absorbance rate to the MP polymers in vitro. Also, I will examine MP and Rv co-occurrence in situ, and plan to sample 15 amphibian breeding ponds in central Hungary along an urbanisation gradient. To assess MP, I plan to collect both water and sediment samples. Additionally, to assess Rv prevalence, I plan to collect both environmental (water) and in vivo samples from two widespread amphibian species (Rana dalmatina and Bufo bufo). My investigations could be groundbreaking in the sense that even though the sole effects of emerging Rv on amphibian populations are frequently examined, their interaction with MP pollution is unstudied yet. Therefore, the combination of in vitro, in vivo and in situ investigations can reveal the cumulative effects of the two environmental stressors of growing concern in amphibian conservation.

First in situ study on the effects of Ranid Herpesvirus 3 on the fate of an amphibian population

The sixth mass extinction in Earth's history is occurring right now. One of the major causes of the biodiversity crisis is the spread of infectious diseases in wildlife populations. This is especially the case for amphibians, which have become the most vulnerable class among vertebrates. While the most fatal amphibian diseases (chytridiomycosis and ranavirosis) are intensively studied, many gaps remain in our knowledge about other transmissible viral diseases. Ranid Herpesvirus 3 (RaHV3) has been described recently and detected in common anuran species in European countries. The pathogen causes proliferative skin lesions, but information is scarce about its effects on individual fitness and thus population survival. 

Last year in a pilot study, we detected RaHV3 infection in 6 adult agile frogs (Rana dalmatina) in Hungary. This frog is an ideal model species for studying the fitness consequences of RaHV3 infection, because it is categorized as "Least Concern" by IUCN and it is still found in relatively large numbers across its European range. Its decline is attributed, besides habitat loss by anthropogenic land-use conversion and climate change, to skin diseases putatively associated with viral infection.

In this study, we aim to investigate how the RaHV3 prevalence and intensity of infection are correlated with various measures of the individuals' fitness, including their annual survival rate, date of migrating to the breeding pond, body condition, abnormalities of sexual phenotype development, and composition of the microbiome of the skin and gut. Learning about the consequences of RaHV3 infection for individual health and population dynamics can help decide whether the presence of this virus would need to be widely monitored and whether it requires further conservation intervention. Furthermore, we would like to address an essential methodological question for conservation monitoring programs: how much do infection prevalence and intensity correlate with the severity of skin symptoms? If the correlation is strong, a simple scoring system of skin symptoms could be used as a cost-efficient indicator for monitoring RaHV3 infection in a wide range of populations.