Killer viruses have slinked into the pristine “Peaks of Europe” in Spain, and recent outbreaks have caused mass mortalities in half a dozen amphibian species. Their gruesome symptoms include vomiting blood, systemic hemorrhaging, open sores, and the death of limb tissues. Worryingly, the declines show no sign of rebound, and the viruses appear to be on the move.
Before they were devastating populations in a protected national park, two closely related emerging ranaviruses have been infecting amphibians, fish, and reptiles on multiple continents. This study, published in Current Biology this week, is the first to document the deadly infection striking several species all at once—and with such serious impact.
Having the capacity to infect multiple species means they could force their hosts to become locally extinct. "Pathogens that can exploit more than one host simultaneously are able to persist even when one host drops to low numbers, and eventually zero, because there is another susceptible host available,” University College London’s Stephen Price explains in a news release.
The first mass mortality events in northern Spain’s Picos de Europa were witnessed in 2005. Park biologists and researchers from Madrid's Museo Nacional de Ciencias have been monitoring their six common amphibians closely ever since. Over the next couple of years, the pathogen was identified as the common midwife toad virus (CMTV), which has previously only been known to affect small numbers of the toad in the U.K.
The team traced the infection's impact across 15 locations in the park between 2005 and 2012. They found dead or dying amphibians from all six species, but the hardest hit are the common midwife toad (Alytes obstetricans), common toad (Bufo bufo), and alpine newt (Mesotriton alpestris). Price tells New Scientist: "We saw declines ranging from 60 to almost 100 percent.” Entire communities were killed off.
Based on genetic analyses of viruses recovered from infected animals, the team believe the pathogens came from a single CMTV source introduced at multiple sites across the park beginning sometime before 2005. Because the infected ponds are separated by many kilometers of rugged terrain, they suspect humans rather than amphibians spread the virus within the park. “Muddy boots are about my best guess right now,” Price tells Science.
Amphibians 200 kilometers away have been dying with similar symptoms caused by the closely related Bosca’s newt virus (BNV). And there’s also a third, more distantly related ranavirus that hasn’t caused mass death thus far. But not only are the viruses spreading and thriving, they’re “repeatedly overcoming the species barrier with catastrophic consequences,” Price says in a university statement. While related viruses are emerging in other European locations, back at the park, the team observed an instance where a snake became sick and died after eating an infected amphibian.
Over 40 percent of salamander and frog species are declining. But there is one thing Price is thankful for: The viruses haven’t overlapped anywhere with the killer chytrid fungus yet. The team’s now gathering more samples from around the world to build a viral family tree.
Images: Stephen Price
