Researchers find that breast cancer and infertility drugs can keep up to 90 percent of mice infected with the Ebola virus alive.

Outbreaks of deadly viruses like Ebola, which causes flu-like symptoms and widespread bleeding, are still a pressing threat in some parts of the world. Last year, an Ebola outbreak killed 34 out of 62 confirmed cases in the Democratic Republic of Congo (DRC), according to the UN Office for the Coordination of Humanitarian Affairs.

Discovered in the DRC in 1976, Ebola is very much a contemporary disease, and unfortunately one without a cure—until now. In a new study, researchers from the U.S. Army Medical Research Institute of Infectious Diseases have found that estrogen receptor drugs used to treat infertility and breast cancer can keep mice from becoming infected with Ebola.

Ebola is a type of filovirus that can lead to hemorrhagic fever and death. Ebolavirus strains are transmitted by direct contact with the blood, bodily fluids, or tissues of infected people, although handling sick or dead animals like monkeys, antelope, and fruit bats can also spread the disease, says the World Health Organization (WHO). Normally restricted to African countries like the DRC, Sudan, Uganda, Angola, and Gavon, Ebola could pose a threat to uninfected populations if it is used as a bio-terror weapon.

“The filoviruses are grave viral threats that continue to infect humans as well as nonhuman primates. There is a great concern about the potential for accidental importation…and that filoviruses may be used as a biological weapon,” the study authors wrote in Science Translational Medicine.

Using molecular probes, the researchers identified drugs with the potential to protect against Zaire ebolavirus (EBOC), one of the deadliest strains. They found that selective estrogen receptor modulator (SERM) drugs may be the answer. “Our results indicate that both clomiphene and toremifene broadly inhibit filovirus infection,” the study authors wrote.

Perhaps even more frightening than the idea of Ebola being intentionally used as a weapon is the thought that the virus could be spread accidentally through trade or travel, with similar results.

“Although effective drugs have been found to treat several other viral diseases, there are currently no approved therapeutics (small molecule or biologic) to prevent or treat filovirus infections,” the study authors said. SERMs may change that.

Estrogen receptors are proteins found inside cells that are activated by the female hormone estrogen. Once activated, estrogen receptors bind to DNA and regulate gene activity. In the case of Ebola, SERMs inhibit Ebola infection in the body by locking onto the DNA and keeping the Ebola virus from entering the cells.

Researchers demonstrated the antiviral properties of the specific SERM drugs clomiphene and toremifene in both human and monkey cells. To confirm their findings, researchers also tested clomiphene and toremifene in mice by infecting 5- to 8-week-old females with Ebolavirus. Beginning one hour after infection, the mice were treated with clomiphene, toremifene, or a placebo for a period of 10 days.

Ninety percent of the mice treated with clomiphene and 50 percent of those treated with toremifene survived. Consider this WHO statistic: Up to 90 percent of all human cases of Ebola in Africa end in death. The significance of these surviving mice just got a whole lot bigger.