There\u2019s a new threat looming over amphibian populations \u2013\nRanavirus. Ranaviruses are a class of virus that pose an increasing threat to aquatic\necosystems, as infection can lead to devastating mass mortality events. A ranavirus\nis a large, double-stranded DNA virus that causes a hemorrhagic response, or\nexcessive bleeding, in young toads and\nfrogs which is often fatal. Ranavirus outbreaks may result in the decimation of\nentire generations of amphibian larvae. Even more concerning is that these\nviruses are not picky \u2013 they are capable of infecting amphibians, fish, and\nreptiles. Infection spreads rapidly through aquatic ecosystems because the\nvirus is relatively stable. This is bad news, because according to disease\necologist Erin Sauer, \u201camphibians around the globe are already in peril\u201d.\nClimate change, habitat destruction, the pet trade\u2014the odds are stacked against\nmany amphibian species, and it looks like ranavirus is just another enemy amphibians\nare up against.<\/p>\n\n\n\n
What is behavioral\nfever?<\/strong><\/p>\n\n\n\n When we get infected with a virus, one of our body\u2019s\nimmediate responses is to increase the body\u2019s temperature, which results in uncomfortable\nsweating and chills: a fever. This signals to your immune system that something\nis wrong, and the immune system responds by kicking into overdrive: all hands\non deck in an effort to destroy the pathogen. The initial fever is detected by\nthe hypothalamus, which then directs your body to warm itself up. Unlike mammals, toads are ectothermic, meaning\nthey must rely on their environment to regulate their body temperature. This is\nwhy you frequently see lizards basking in the sun, or salamanders cooling off\nunder a log. When infected by a virus, toad immune systems are incapable of\ninducing a fever on their own. However, Sauer has been studying a clever adaptation\nthat may allow herps to fight viruses: a behavioral<\/em> fever. <\/p>\n\n\n\n A behavioral fever occurs after the immune system detects the invasion of a pathogen, much like how a home security system detects an intruder. When the sensors on a home security system are triggered, a command center is alerted to the presence of the intruder; the command center will then alert the homeowner and provide instructions on how to respond. The hypothalamus in the brain of a toad acts like a command center, which, upon viral intrusion, instructs the toad to move to a warmer location, thus increasing its body temperature. This process is summarized below: <\/p>\n\n\n\n This phenomenon has been observed in many ectothermic species,\nbut it does not occur with all types of pathogens. For example, infection by\nanother infamous pathogen, chytrid fungus, does not induce toads to exhibit a\nbehavioral fever. A behavioral fever is thought to kickstart the immune system\nin a similar way to fever in endotherms, where the fever acts as a messenger\nthat facilitates a longer immune response, rather than a method to destroy the pathogens.\n<\/p>\n\n\n\n Dr. Sauer and her team designed an experiment to quantify\nthe effects of behavioral fever on ranavirus. Their experiment yielded that adult\nAnaxyrus terrestris<\/em>, or southern toads, are able to successfully reduce\ntheir viral load using this method, which is encouraging \u2013 to a point.\nRanavirus is most deadly to younger animals, where large quantities of the\nvirus may overwhelm the developing amphibian and result in a quicker death. Adult\ntoads were tested using a method similar to COVID-19 testing: a swab sample was\nused to determine the presence of the virus, based on the quantity of viral DNA\npresent. Unfortunately, the mouths of the younger toads were too small to be\nswabbed, so these frogs had to be analyzed post-mortem to determine viral\npresence; therefore, the results of this study apply more to adult toads.<\/p>\n\n\n\n Why should\nI care?<\/strong><\/p>\n\n\n\n The changing climate may increase\nthe frequency of disease outbreaks, so learning the strategies by which other\nanimals fight these pathogens may prove to be extremely important in the context\nof endangered or threatened species. Also, there are serious economic and\npublic health concerns when it comes to outbreaks\u2014according to Sauer, there are\n\u201cdirect impacts on people getting sick, economic impacts on our [livestock] getting\nsick,\u201d not to mention, \u201c these epidemic events could be an indicator that\nthere\u2019s something else going on in the ecosystem\u201d. The current global pandemic\nis indeed a good example of how disruptive a microscopic virus can be.\nSARS-CoV-2 jumped from animals to humans and has since brought the world\nto its knees. Regardless of whether a\npathogen is capable of affecting humans right now, it is essential that we\ncontinue to monitor the ecological patterns and consequences of these\noutbreaks. <\/p>\n\n\n\n <\/p>\n\n\n\n Bottom line:<\/strong><\/p>\n\n\n\n This study concluded that while cold-blooded toads could not fight infections like\nmammals do, they are able to change their behavior in a way that enhances their\nability to combat disease.<\/p>\n\n\n\n What\u2019s next: <\/strong><\/p>\n\n\n\n More research is needed before we\ncan determine if other species can use this mechanism to fight ranavirus in the\nway A. terrestris<\/em> has. As the virus mutates and infects other species,\nbehaviors and responses may shift, and it is imperative to keep studying them.\nIn Wisconsin, Sauer is continuing to study the effects of urbanization on\namphibian populations with respect to other diseases. <\/p>\n\n\n\n Where to find it:<\/strong> Sauer,\nE. L., Trejo, N., Hoverman, J. T., & Rohr, J. R. (2019). Behavioural fever\nreduces ranaviral infection in toads. Functional Ecology<\/em>, 33<\/em>(11),\n2172-2179<\/p>\n","protected":false},"excerpt":{"rendered":" By Sophie Kogut Introduction: There\u2019s a new threat looming over amphibian populations \u2013 Ranavirus. Ranaviruses are a class of virus that pose an increasing threat to aquatic ecosystems, as infection can lead to devastating mass mortality events. A ranavirus is … Continue reading ![\"\"](\"https:\/\/blog.uvm.edu\/bmosher1-fieldherp\/files\/2020\/07\/Kogut_1.png\")
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