An electron micrograph scan shows the Ebola virus emerging from an infected cell.

Researchers have long known that the Ebola virus can linger in certain bodily fluids even after an infected person begins to recover. But a new study shows that remnants of the virus remained in the semen of some male survivors in Sierra Leone for 9 months after the onset of symptoms, raising new questions about how long Ebola might remain transmissible.

"These results come at a critically important time, reminding us that while Ebola case numbers continue to plummet, Ebola survivors and their families continue to struggle with the effects of the disease," Bruce Aylward, the World Health Organization's top Ebola official, said in a statement. "[The study] provides further evidence that survivors need continued, substantial support for the next 6 to 12 months to meet these challenges and to ensure their partners are not exposed."

The findings, published Wednesday in the New England Journal of Medicine, are part of a long-term effort to decipher the mysteries that still surround the deadly disease. While the unprecedented Ebola outbreak in West Africa has killed more 11,000 people, it also has left behind something previous outbreaks did not -- thousands of survivors that researchers hope can teach us more about the virus.

Wednesday's study involved analyzing semen samples from 93 Sierra Leonean men who had survived Ebola. Researchers detected the presence of the virus's genetic material in the semen of all nine men tested in the first three months after their illness began. More than half of the 40 men tested between four and six months after the onset of their symptoms also tested positive, as did a quarter of the 43 men tested between seven to nine months after their illness began.

[Sex in a time of Ebola]

The findings shed new light on how long the virus can remain in the body. As recently as last October, the WHO noted that while the virus is spread primarily through contact with blood, feces and vomit -- and typically during the height of illness -- it also had been detected in breast milk, urine and semen. "In a convalescent male, the virus can persist in semen for at least 70 days; one study suggests persistence for more than 90 days," the organization wrote then. Wednesday's study suggests that the virus can hang around even longer than many researchers expected.

But plenty of questions remain. The authors acknowledged that they still lack data about how the presence of Ebola virus RNA in semen relates to the likelihood of actual transmission. Despite some suspected instances of Ebola being spread through sexual activity, it is exceedingly rare, and "the risk of sexual transmission ... is unknown and is being investigated," the study states.

The explanation for why some men retain fragments of the Ebola virus in their semen for months while others clear the virus also remains unclear. Researchers at the Centers for Disease Control and Prevention are conducting more tests on the samples to determine whether the virus is live and potentially infectious. In the meantime, health officials have urged the more than 8,000 male Ebola survivors to abstain from sex or use condoms until no remnants of the virus remain in their semen.

Wednesday's study, conducted jointly by the CDC, the WHO and the Sierra Leone Ministry of Health, comes as the countries hard-hit by the Ebola crisis are pushing to end the outbreak nearly two years after it began. The epidemic is now confined to small areas of Guinea and Sierra Leone, the WHO said. Liberia remains free of Ebola. In general, the epidemic is considered over in a country when no new cases are identified for 42 days, twice the incubation period of the virus.

[How the microscopic Ebola virus kills thousands]

But Ebola isn't entirely over for some survivors, who continue to wrestle with the aftermath of the disease.

Pauline Cafferkey, a 39-year-old nurse who contracted Ebola while doing aid work in Sierra Leone and appeared to have recovered in January, is now in critical condition due to a complication from the virus. She was re-admitted to the Royal Free Hospital in London last week after she fell ill and is being treated in an isolation unit. The hospital released a statement on Wednesday stating, "We are sad to announce that Pauline Cafferkey's condition has deteriorated and she is now critically ill."

Ian Crozier, an American doctor also thought to have been cured of Ebola last year, experienced severe vision problems two months after leaving the hospital. In addition to swelling and vision problems, the virus also appeared to have turned one of his eyes from blue to green. Nina Pham, the Dallas nurse infected while treating an Ebola patient last year, has said she suffers from an array of health problems, including fatigue, insomnia, body aches and liver problems. Survivors in West Africa have reported similar problems, ranging from headaches to problems with eyesight.

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