The Centers for Disease Control and Prevention revised its guidelines on Ebola transmission on Sunday night, urging survivors to abstain from all forms of sex or use condoms every time “until more information becomes available,” rather than three months as previously recommended.
The World Health Organization and Liberia have issued similar recommendations in recent weeks. They were acting on evidence suggesting that a Liberian man who recovered from Ebola might have transmitted the virus to his female partner many months later.
Ebola genetic material was found in a semen sample the man provided 175 days after he developed symptoms, 74 days longer than ever before found in a survivor. Scientists in Liberia have compared the genetic sequence of the virus found in the woman, Ruth Tugbah, 44, to partial sequences obtained from the virus in her boyfriend’s semen and in blood samples taken months ago from his potential contacts with Ebola, and found that they matched at several key points.
Thus far, the information is consistent with sexual transmission, scientists said, but not conclusive, and the study is continuing. Researchers at the C.D.C. were also trying to establish whether the sample the man provided contained infectious virus, rather than only harmless genetic material or RNA.
Experts said they had expected sexual transmission of Ebola to be rare. It has not yet been proved, but “cannot be ruled out,” the C.D.C. guidance said. Marburg, a similar virus, is thought to have been transmitted sexually. The World Health Organization, the C.D.C. and the Sierra Leone health ministry are planning a study of survivors intended to help establish the range of time that various body fluids, such as semen, urine and breast milk, tend to contain Ebola after it has been cleared from the blood. That time frame has varied in the small number of survivors previously studied.
“The problem is we haven’t looked at a large number of cases,” said Stuart Nichol, an Ebola researcher at the C.D.C. Philip Ireland, a Liberian doctor who contracted Ebola while working last summer at John F. Kennedy Medical Center in Monrovia, the capital, said that despite the practical difficulty involved in collecting semen samples, all survivors should be offered the chance to know whether their body fluids still contain traces of Ebola. “Tests have to be made available, and have to be made next-to-free,” he said.
Dr. Bruce Aylward, the lead Ebola official at the W.H.O., said the agency was exploring the feasibility of just such a program. “It’s a smart thing to do,” he said.