Ranavirus invasions: 50 years of research- now let's do something about it!
Gray, M. J.  2019.  Zoological Society of London Symposium, London, England. April, 2019.  (invited)

Abstract:
Pathogens have been linked to the declines of cold-blooded vertebrates across the globe. Ranaviruses were discovered over 50 years ago, and can infect fish, reptiles and amphibians. Transmission occurs efficiently by direct contact between animals, through water, and via contaminated surfaces or substrates. Ranaviruses attack multiple organ systems, and cause a hemorrhagic disease similar to Ebola. Mortality can exceed 90% during a ranavirus outbreak, and occurs rapidly (<2 weeks) in highly susceptible species. Significant economic loss in captive populations, and local population decline and extirpation in the wild can occur. Global translocation of ranavirus species and variants through unclean and unregulated international trade has contributed to the introduction and emergence of ranaviruses. Trade and other captive conditions also facilitate genetic recombination among ranaviruses, and evolution of more virulent strains. Increase in anthropogenic stressors on landscapes and co-infections with other pathogens has played a role in ranavirus emergence. With the accumulation of research, commonsensical biosecurity practices and disease management, strategies can be used to prevent and control ranavirus invasions. For example, pet industries and zoological facilities can reduce spread of ranaviruses by acquiring animals that have been verified as infectionfree, designing captive housing so that animal isolation is possible if an outbreak occurs, and using disinfectants that inactivate ranaviruses. In the wild, management strategies that reduce host contact rates, maintain normal water temperature and biochemistry, and limit contaminant exposure will help reduce ranavirus enzootic cycles. In aquatic breeding sites where water levels can be controlled, dewatering a site for >12 months might be sufficient duration to inactivate ranavirus and for the pathogen to be cleared in reservoir host species. Prudent biosecurity practices in the field include changing examination gloves between handling animals and decontaminating footwear and gear before moving among breeding sites. Currently, there is no therapeutic treatment for ranavirusinfected animals; however, heat-inactivated and yeast-derived vaccines have shown promise. Geneediting technologies such as DNA aptamers and CRISPR have been used to modify ranaviruses to less virulent variants, although application in captive and field settings needs further investigation. Importantly, as we progress through the 21st century, we know that ranaviruses and other pathogens can significantly impact ectothermic vertebrate populations; however, we also have the capability of implementing regulations and disease management strategies that prevent careless translocation of invasive pathogens and can negatively impact pathogen epidemiology such that host species are benefited.