Monitoring Ranavirus-Associated Mortality in a Dutch Heathland in the Aftermath of a Ranavirus Disease Outbreak

Abstract

The ranaviruses are an emerging group of viruses that infect amphibians, fish, and reptiles. Although ranaviruses have not been linked to extinctions, emergence in amphibian communities has resulted in population declines for some species. We present the results of ranavirus-associated mortality in a Dutch national park in the aftermath of an outbreak associated with a common midwife toad virus (CMTV)-like ranavirus. We monitored five bodies of water across Dwingelderveld National Park, the Netherlands, in 2011-13. Dead and live amphibians were counted weekly July-September and every 2 wk in June and October. Dead amphibians were collected and tested for ranavirus infection. In addition, we measured biologic, chemical, and physical site characteristics to test for a correlation with ranavirus-associated mortality. Ranavirus infection was widespread in our study area and we observed nearly continuous presence of dead, ranavirus-infected amphibians in the presence of asymptomatic, live amphibians throughout our study. Fatalities occurred in larval, subadult, and adult amphibians. Ranavirus infection prevalence (based on fatal cases) was significantly associated with increasing fractions of adults and subadults compared to juveniles and larvae in the population, but was unrelated to any other measured site characteristics. Our findings showed that a CMTV-like ranavirus can persist long term in an ecosystem, affecting a diversity of amphibian species and life stages for a prolonged period. This study illustrates the importance of monitoring the modes of spread for ranaviruses and their impact on amphibian populations.

Ranavirus genotypes in the Netherlands and their potential association with virulence in water frogs ( Pelophylax spp.)

“…Additionally, mortality at DNP, while not massive, did remain constant and involved all life stages of water frogs throughout the visits. Constant CMTV-NL I-associated mortality was also observed in water frogs at DNP during the monitoring period from 2011 37 and in populations of spadefoot toad larvae and smooth newts at another northern location in a later study 38 .…”

“…The study area in the north was Dwingelderveld National Park (DNP) located in the province of Drenthe, and the one in the south was a natural area, De Driestruik (DD), located in the province of Limburg. The first recorded ranavirus outbreak in wild amphibians in the Netherlands occurred in a pond in DNP in 2010, caused by a virus belonging to the CMTV-NL group I, and ranavirus-associated mortality has been detected in DNP since then 8 , 37 . In DD a ranavirus-associated die-off occurred in 2014, affecting adult water frogs and common spadefoot toad larvae 52 , but there was no evidence for ranavirus-associated mortality in 2015.…”

“…The waterbodies monitored in 2016 consisted of three ponds in DD and two ponds and one fen in DNP. Ranavirus was previously shown to occur at all waterbodies from DNP 37 , whereas at DD, it was only known to be present in two waterbodies (DD-II and DD-III) 52 . However, a third pond at DD (DD-I) was in close proximity (300–900 m) to the affected ponds and made it a likely target for ranavirus spread mediated by amphibians, birds, or humans.…”

“…Both DNP and DD were monitored simultaneously every two weeks in 2016, i.e., on seven occasions. Population counts were performed using a previously established protocol 37 . For counts along the shoreline, ponds were fully circled and in the case of the fen only partly, due to lack of full access.…”

Hemoparasites Do Not Affect Life-History Traits and Cellular Immune Response in Treefrog Hosts Boana cordobae

“…The major threats among them are habitat loss and infectious diseases, including parasitism [3]. Fungal infections such as chytridiomycosis have gained global attention, but viruses, protozoan, and metazoan parasites may negatively affect life-history traits as well [4][5][6][7][8]. Yet, hemoparasites have received little attention [9], though anurans host a wide variety of hemoparasites, such as protozoans, microfilariae, nematodes, rickettsians, and viral inclusions [10][11][12][13][14][15][16].…”