June 12, 2019 -- Findings of the treatment of Bourbon disease in mice were published on June 13 in PLOS Pathogens. 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, often used to treat the flu, that cures mice infected with the potentially lethal virus.
Bourbon virus is a novel RNA virus in the genus Thogotovirus (family Orthomyxoviridae) that was discovered in Bourbon County, Kansas in 2014, according to the Center of Disease Control and Prevention (CDC). Bourbon disease is a tick-borne illness.The virus was identified when a previously healthy man arrived at the hostipal in Kansas with flu-like symptoms and a history of tick-bites. After being treated with antibiotics for 11 days and being tested for any infection doctors could think of, he died. His blood was immediately sent to the CDC where researchers identified a new virus and named it after the county where the patient lived in Kansas.
A second case appeared in the St. Louis area in 2017, in a woman in Missouri came to the hospital 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. Doctors were able to tell the patient's family that they had identified the cause but that there was no treatment available.
Infectious disease researchers identified Bourbon virus as a distant cousin of influenza virus and narrowed potential therapeutic drugs down to one - favipiravir - that inhibits viral RNA-dependent RNA polymerasem, which is required for the virus to multiply. To study the potential of the drugs, 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.
In a separate experiment, the researchers treated infected mice with the flu drug or a placebo for eight days. When the mice were given the antiviral at the same time or within one day of becoming infected with the virus, all survived without becoming visibly ill. In contrast, none of the infected mice that received a placebo survived. When the researchers gave the antiviral treatment three days after infection - a time when the mice already looked sick and had lost weight - all of the treated mice recovered.
There are very few cases of Bourbon virus, however, there was a third case where the patient survived in Oklahoma. "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" said Jacco Boon, PhD, an assistant professor of medicine at Washington University of Medicine.
Since favipiravir is not approved by the FDA, it is not clear whether doctors in the U.S. would be able to obtain it for their patients. The best protection against Bourbon virus is to avoid tick bites by wearing insect repellent and long pants and sleeves, and doing regular tick checks after outdoor activity, the researchers said.
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