Only a few cases of the newly discovered Bourbon virus have been reported, and two of them ended in death, partly because no specific treatments are available for the tick-borne illness. Now, researchers at Washington University School of Medicine in St. Louis have identified an experimental antiviral drug that cures mice infected with the potentially lethal virus. The drug, favipiravir, is approved in Japan but not the U.S. for treatment of influenza, a related virus.
“Without the flu drug, 100 percent of the infected mice died, and with the treatment, 100 percent survived,” said Jacco Boon, assistant professor of medicine and the paper’s senior author. “Up until now, doctors have not had any way to treat Bourbon virus. We’ve found something that works, at least in mice, and it suggests that antivirals for flu are a good place to start looking for a treatment for Bourbon.”
The findings are published June 13 in the journal PLOS Pathogens.
Bourbon virus was first identified in 2014 in a previously healthy middle-aged man in Kansas. The man arrived at the hospital with flu-like symptoms and a history of tick bites. Thinking he had ehrlichiosis, a tick-borne bacterial infection that causes similar symptoms and often affects people in the Midwest, doctors started him on antibiotics. But the man continued to decline, and further testing for ehrlichiosis and every other infection the doctors could think of came up negative. After his death 11 days later, a sample of his blood was sent to experts at the Centers for Disease Control and Prevention (CDC) who specialize in mysterious infections. The CDC researchers identified a new virus and named it Bourbon after the county where the patient had lived.
A second case appeared in the St. Louis area in 2017, in a woman who arrived at Barnes-Jewish Hospital in St. Louis complaining of fever, fatigue and body aches. Washington University infectious disease specialist Jennie Kwon, DO, an assistant professor of medicine, worked with the CDC to identify Bourbon virus—which has similarities to flu virus—as the cause.
The woman’s case caught the eye of Boon, an influenza virus researcher who works with Kwon and other infectious disease physicians. As influenza virus is a distant cousin of Bourbon virus, Boon and his colleagues set about seeing whether any of the drugs approved or in development for influenza could stop Bourbon virus.
The researchers quickly narrowed the list of potential drugs down to one—favipiravir—that inhibits a key protein the virus needs to multiply. Other available influenza drugs were unlikely to work because they target parts of the influenza virus that differ from Bourbon virus.
Since Bourbon virus infections are rare, Boon and colleagues could not study the potential drug in people. Instead, they infected mice with the virus, using a strain of mice with weakened immune systems since healthy mice were able to fight off the virus. All of the immunocompromised mice died six to eight days after they were injected with the virus.