Scientists at Rutgers University-New Brunswick have discovered a virus that caused a nationwide die-off of superworms, a common food for birds, reptiles, other pets and, increasingly, even humans as an alternative protein source. In doing so, they pioneered a different way to search for and identify emerging viruses and pathogens in humans, plants and animals.
Using chopped beetle carcasses that form a slurry and an electron microscope cooled by liquid nitrogen, the scientists reported today in Cell that they have discovered what they have called the Zophobas morio black wasting virus. The name is derived from the virus’s deadly effect on a species of dusky beetle, Zofobas morio, native to the subtropics, especially in the insect’s immature larval stage, when it hatches from its eggs as large, brown superworms. This species was called “superworm” because the larvae are larger, about 5 cm long, than any other reared for food.
The protein-rich larvae of Z. moriothat provide the staple food for captive, often exotic reptiles, birds, fish and amphibians around the world, mysteriously began going extinct in 2019, confusing pet food suppliers and pet owners.
Jason Kaelber, author of the study and associate professor at the Institute for Quantitative Biomedicine (IQB) at Rutgers-New Brunswick, worked with Judit Penzes, first author of the study and a postdoctoral associate at IQB.
“Judit wanted to figure out the reason why beetle farmers were losing all their superworm colonies to a deadly disease and I wanted to develop ways to discover new viruses that don’t rely on DNA or RNA sequencing,” Kaelber said. “We eventually discovered the virus that is sweeping the country and killing superworms.”
The scientific investigation began over a year ago, when Penzes, a molecular virologist, was contacted by beetle farm owners whose superworms were mysteriously dying at an alarming rate. Penzes was already well known in the industry for previous work in which she isolated a virus that killed crickets, another popular pet food.
She started collecting superworms from pet stores in New Jersey. “Every time I went to a pet store, I immediately went to the insect food section, opened the containers and looked at the worms,” she said. “They were all infected. I told the store owners what I saw, that I was researching this virus, and asked if I could have the container. They were on board immediately. They told me to bring as many as I needed. “
She returned to her laboratory, grabbed a Magic Bullet blender, dropped the worm carcasses into it and blended them at high speed. The process created a slurry of beetle sap that she took and processed using a virus purification method that separates the virus due to its density. In the final step, she shined a fluorescent light on the centrifuge tube and the virus glowed blue.
“I said, ‘I got you,’ when I saw it,” Penzes said. “Then I knew it was indeed a virus.”
Penzes then worked with Kaelber, a fellow electron microscopist, to examine the virus using a cryo-electron microscope, which allows a three-dimensional view of the virus, including its interior.
“You take a virus, a protein, a cell, etc., and you freeze it so quickly that the water solidifies without turning into ice crystals,” Kaelber said. “We can find out what the amino acid sequence of the protein is without analyzing the DNA, and just by looking at that 3D structure, because we have such sharp resolution.”
They compared the structure of the protein to all known proteins using the Protein Data Bank database hosted at Rutgers and found that it is similar to a virus that affects cockroaches, but not identical, and is part of a family of animal viruses known as parvoviruses.
“It’s a new one, unlike anything that has been sequenced or imaged before,” Penzes said.
The scientists are also grateful to rural superworm farmers who volunteered to send samples as soon as news of the study broke. “The eagerness of farmers to help us research the virus played a huge role in the creation of this published study,” Penzes said.
The effort, Kaelber said, provided a “proof of concept” that cryo-electron microscopy can be used to directly discover and characterize new pathogens.
“If there is ever a really significant outbreak in the future, we will want to use every resource possible to see what we can find,” Kaelber said. “We want to make diagnostic cryo-electron microscopy routine so that if there is an unknown infectious disease, we have many options for same-day identification of the causative agent.”
Cryoelectron microscopy has gained popularity in recent years and has become an increasingly common method for 3D analysis of known specimens. However, Rutgers’ work represents the first time the method has been used on an unknown pathogen.
After discovering the virus, researchers tested a way to protect against it Z. morio beetles against disease, by injecting a closely related virus from a different species that does not cause symptoms. Based on that work, they are developing a vaccine.
“The discovery is important for two reasons,” Kaelber said. “First, beetle farmers can use this information to protect their colonies and understand what actions will be effective or ineffective in controlling the epidemic. Second, the beetle epidemic was a real-world test of the technology that we hope can be useful are to quickly investigate future outbreaks in humans, plants or animals.”
Scientists Martin Holm of the Rutgers Institute for Quantitative Biomedicine and Samantha Yost of REGENXBIO Inc., in Rockville, Maryland, also authored the study.
