CHICAGO, June 15 (Xinhua) -- Researchers at Washington University School of Medicine in St. Louis, Missouri, have identified an experimental antiviral drug that cures mice infected with tick-borne Bourbon virus.

The drug, favipiravir, is approved in Japan for treatment of influenza.

As influenza virus is a distant cousin of Bourbon virus, the researchers quickly narrowed the list of potential drugs down to favipiravir that inhibits a key protein the virus needs to multiply.

Since Bourbon virus infections are rare, the researchers 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.

Tick-borne infections are a growing problem in the U.S. Midwest.

Favipiravir is not approved by the U.S. Food and Drug Administration yet. 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.

The findings were published Thursday in the journal PLOS Pathogens.