AMES, Iowa — Iowa State University veterinary researchers have pinpointed the cause of a mysterious disease that makes piglets involuntarily shake, using new DNA sequencing techniques to trace the tremors to a virus dating back nearly 100 years.

According to Bailey Arruda, DVM, an assistant professor and veterinary pathologist in the ISU Department of Veterinary Diagnostic and Production Animal Medicine at the College of Veterinary Medicine, vets have recognized the congenital tremors for years but could never pinpoint the cause until now.

"It’s been a mystery in the veterinary community for over 90 years," she said. "Unfortunately, we didn’t have the technology to find the virus before."

The virus, known as "pestiviruses," infects young pigs and can cause them to shake involuntarily, which have been referred to as "shaker pigs" or "dancing pigs."

In severe cases, the tremors prevent pigs from nursing and can lead to starvation.

Kent Schwartz, DVM, senior clinician at ISU’s College of Veterinary Medicine and a veterinary diagnostician at its Veterinary Diagnostic Laboratory in Ames, said congenital tremors, also known as myoclonia congenita, are a sporadic but not uncommon affliction in newborn pigs.

"Several causes, including hog cholera virus, have been associated with this disease," he said, "but in the last 40 years, the etiology of this condition in the U.S. has remained a mystery in most cases."

Working in collaboration with Boehringer Ingelheim Vetmedica, Inc., a St. Joseph, Mo.-based based animal health company, ISU veterinarians used next-generation DNA sequencing techniques to detect the virus in samples from affected pigs. Arruda said the team used those results to experimentally reproduce the tremors in newborn pigs.

Earlier sequencing techniques, such as polymerase chain reaction or PCR, require researchers to identify a target before beginning the process. "But that approach wouldn’t be useful in this case because we didn’t know exactly what we were looking for," she explained.

She said now that researchers have identified the virus, the ISU Veterinary Diagnostic Laboratory can use PCR tests to confirm cases from samples sent in from local vets, adding "the next step is to develop a vaccine to combat the virus."

Paulo Arruda, DVM, an assistant professor in veterinary diagnostic and production animal medicine, said piglets with congenital tremors are fairly uncommon, though the virus can appear in cycles. Schwartz said the prevalence of congenital tremors in pestivirus-inoculated litters varied from 57 percent (4 of 7 piglets affected) to 100 percent.

While the virus isn’t creating widespread problems for the pork industry, he said the mysterious bug could become particularly problematic on individual farms. Drew Magstadt, DVM, a clinician in veterinary diagnostic and production animal medicine, and research team member, said the virus doesn’t make pork unsafe to eat and stressed the virus isn’t known to infect humans.

Ron Birkenholz, communications director for the Iowa Pork Producers Assoc., agreed. "Pig farmers are concerned about pig health and welfare, and do everything possible to keep their animals healthy and safe because healthy hogs make for safe food," he explained.

"We’re confident that scientists will be able to find a vaccine that will give pork producers a tool to treat this particular virus and save more piglets."

Schwartz said ISU’s Veterinary Diagnostic Laboratory is currently offering a qPCR to detect the virus in sample types, which include serum, whole blood, central nervous tissue and lymph nodes.