A Ranavirus-associated Mass Mortality Event in an Illinois Amphibian Community [78th MWFW]

Ranavirus is an infectious disease of poikilotherms that is associated with global amphibian declines and is one of two notifiable amphibian diseases to the World Organization for Animal Health. We monitored eight ponds for ranaviral disease in Vermilion Co., Illinois using the Wood Frog (Rana sylvatica) as a sentinel species due to its reported ranavirus sensitivity. During tadpole development, we documented a ranavirus-associated mass mortality event and characterized the spatial and temporal extent of the die-offs. We collected >3000 deceased individuals of six observed species over eight weeks at the original eight ponds and at 15 additional ponds with observed mortalities. The largest number of mortalities were observed in R. sylvatica (n=752); Silvery Salamanders, Ambystoma platineum (n=303); and Chorus Frogs, Pseudacris spp. (n=105). We confirmed the pathogen isolate as an FV3-like ranavirus using a sequence from the major capsid protein gene, the DNA polymerase gene, the V1F-2a gene, the neurofilament triplet H1-like gene and a variable microsatellite region. This FV3-like ranavirus was detected at 10 of the 23 ponds sampled (44%), and infection prevalence ranged from 0% to 100% among ponds. The scale of this mortality event and the conservation status of the species affected highlight the need to continue to monitor this geographical region for amphibian disease. The mortalities in any given pond occurred over one to three weeks, so common monitoring methods have likely failed to detect ranavirus die-offs. The impact ranavirus has had on amphibian populations is underestimated, and this impact needs to be addressed so conservation action can be made if necessary.