Mussels are a vital part of any freshwater ecosystem, playing a part in water filtration, food webs, and habitat stabilization. However, mussel populations have been declining.
“Freshwater mussels are dying all over the world. We don’t know why,” says UW–Madison researcher Tony Goldberg, Ph.D., DVM, professor of Pathobiological Sciences in the School of Veterinary Medicine and John D. MacArthur Research Chair. “Let’s look and see if it’s infectious disease.”
This hunt led to a paper published three years ago, showcasing the first evidence of a possible infectious cause of mussel die-off. More recently, though, Goldberg and colleagues found another novel virus when researching mussels in Washington State, their research findings published in Journal of Virology earlier this month.
Goldberg and colleagues, including Emilie Blevins of the Xerces Society for Invertebrate Conservation, discovered a new rhabdovirus in Western Pearl Shell mussels. Although they suspect this virus is not responsible for mussel die-offs, the discovery sheds unexpected light on another group of viruses that infect fish.
Viruses in the Rhabdoviridae family infect a variety of animals, plants, fish, and fungi, impacting animal populations and agriculture. The novirhabdoviruses, a distinct genus within the rhabdovirus family, all infect fish and have caused large fish kills around the world, including in Wisconsin.
Viral hemorrhagic septicemia virus (VHSV), which occurs in Wisconsin, is a deadly fish virus that caused large fish kills in 2005 and 2006 and continues to be a problem today. The virus, a part of the Novirhabdovirus genus, afflicts a variety of fish species, like walleye, muskies, and yellow perch, throughout the Great Lakes region.
Novirhabdoviruses infect only fish and have, until now, existed alone with no close relatives, making these viruses difficult to study. However, Goldberg and colleagues discovered the first close relative of these viruses in mussels in Washington. They named the virus “chemarfal virus 1” to indicate its discovery in the Chehalis River in Margaritifera falcata, the western pearlshell mussel.
“We stumbled upon the closest relative of the novirhabdovirus when studying freshwater mussels,” Goldberg says. “It’s so close to these fish viruses that it could almost be considered a member of the same genus, but it has some significant differences in the way its genome is organized. With this new virus, Goldberg and colleagues can better understand how this particular branch of the rhabdovirus family tree evolved.
“You usually need some sort of comparison, but there never has been one,” Goldberg said. “We now have a near neighbor virus that we can use for comparison to understand other viruses we want to prevent or treat.”
They will also investigate how mussels contracted the virus. One hypothesis is from fish. “Baby mussels clamp on to the gills and fins of fish in order to disperse. They are in direct contact with the bloodstream of a fish for several weeks,” Goldberg says. “It is not a bad way to transmit a virus.”
– Britta Wellenstein
This article was featured in the Winter 2023-24 issue of On Call.