As the Ebola outbreak worsens — with the virus mutating, the death toll spiraling and the World Health Organization warning that 20,000 people could eventually be infected — another West African country has confirmed that the deadly virus has crossed its borders.

Senegal confirmed its first case of Ebola on Friday, according to a statement from Health Minister Awa Marie Coll Seck. The patient, a Guinean national who traveled to Senegal, is in quarantine.

The news brings the number of countries impacted by the outbreak up to five: Sierra Leone, Liberia and Senegal’s neighbor, Guinea, have seen the bulk of the 3,069 reported Ebola infections in the region, according to the WHO. More than half of those infected have died. The virus also spread to Nigeria recently, and a separate outbreak — unrelated to the one in West Africa — has been reported in Congo.

As the outbreak worsened in West Africa, Senegal took aggressive measures to prevent the virus from spreading across its borders. Last week, the country closed its borders with neighboring Guinea out of fear that the virus might come to Senegal. That closure prevented any flights headed to Guinea, Sierra Leone or Liberia from touching down on Senegal’s soil. The World Health Organization counts 607 confirmed and suspected cases of Ebola in Guinea alone and 406 deaths from the virus there.

Senegal is a major travel hub for the region, particularly its capital city of Dakar, the Associated Press noted.

The news gives added weight to fears that the current outbreak is far from its peak. On Thursday, the WHO warned that the outbreak could infect more than 20,000 people before it ends.

Forty percent of infections included in the current tally occurred within the past three weeks, according to the WHO. And the virus has mutated during the outbreak, which could hinder diagnosis and treatment of the disease, according to scientists who genetically sequenced the virus in scores of victims.

With 1,552 deaths recorded so far, the virus is certain to claim more lives than all of the previous Ebola outbreaks combined.

On Thursday, U.S. government researchers, in collaboration with British drugmaker GlaxoSmithKline, announced that they will begin human trials next week at the National Institutes of Health in Bethesda, Md., of an experimental Ebola vaccine. Health officials said they want to rush the drug as quickly as possible to health workers and others at risk in Ebola-ravaged West Africa.

In Liberia, where international health organizations have said the outbreak could be spiraling out of control, Centers for Disease Control and Prevention Director Tom Frieden said the situation is far worse than he anticipated.

“It’s even worse than I’d feared,” Frieden told CNN. “Every day this outbreak goes on, it increases the risk for another export to another country.”

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