Survivors of infection by Ebola virus, already known to face vision, hearing and other problems during their recovery, may also be plagued with health issues such as depression, anxiety and nerve damage that surface after they leave the hospital, according to a small spot survey of victims whose care was managed in the U.S.

Some of the signs and symptoms can persist for months, researchers from the Centers for Disease Control and Prevention in Atlanta found.

The data, reported in the New England Journal of Medicine, offer a snapshot of what eight patients, most of whom had been discharged at least four months earlier, had experienced - and were continuing to experience - during their recovery. A ninth patient was still recovering in the hospital at the time of the March survey and was included in the survey.

The results add "a few more observations to the growing body of knowledge on (what is coming to be known as) post-Ebola virus disease syndrome," Dr. Christopher Dye, director of strategy in the Office of the Director-General at the World Health Organization, told Reuters Health in an email.

"We're happy that most of the EVD patients who were managed in the U.S. survived, but surviving EVD is not the end of the story," said lead author Dr. Timothy Uyeki, clinical team lead for the CDC's Ebola response team. "There are complications, sequelae and symptoms reported by these survivors, and we need a lot more research into the frequency, duration and the pathogenesis of the post-Ebola signs and symptoms, and how to manage them."

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As of early December, WHO had logged 17,300 Ebola survivors worldwide for the most recent outbreak, which began in 2013.

Larger studies "are very much needed so that we can properly anticipate, and provide for, the health needs of the many thousands of Ebola survivors in West Africa," Dye said. "This small study helps to signal those needs in West Africa."

In the case of the U.S. survivors, many after-effects were obvious when the eight patients left the hospital.

Two had short-term memory loss. One recovered after four weeks. The other had not recovered when surveyed.

Six had joint pain, six had lethargy or fatigue, four had palpitations or tachycardia and three had shortness of breath. Most, but not everyone, recovered.

Some people were also plagued with muscle pain, depression or anxiety, or nerve pain, burning or tingling in their extremities. But in some of those people, the symptoms took as long as 12 weeks to appear.

Recovery typically required another four to six weeks, but only one of the four patients who fell into the anxiety or depression category had experienced a total recovery.

Five survivors had developed insomnia within two weeks of leaving the hospital, and only one had recovered completely.

Five developed blurred vision, typically after four weeks, and two had not fully recovered. Two experienced inflammation in one eye. One patient had begun to experience it at the two-week mark; the other after eight weeks. Both recovered.

Six had experienced temporary hair loss, usually on the head. The hair loss took anywhere from four to 16 weeks to appear and two to eight weeks to resolve.

One person experienced hearing loss on one side and had not recovered.

"Although most symptoms resolved or improved over time, only one survivor reported complete resolution of all symptoms," the CDC team writes.

There was no indication that the aftereffects were unique to U.S. patients, Uyeki told Reuters Health, but the U.S. patients "received not only better and more advanced supportive care, but they also received some investigational therapeutics not available to West African disease patients. We don't know the impact of those therapeutics. Also, the general health status of the patients before they developed EVD was probably better."

Previous research has shown that the virus can be detected in semen as many as 101 days after symptoms appear. It is also known to lurk in eye tissue.

Ebola virus was first detected in 1976, but previous outbreaks have been much smaller, making it harder to study the survivors.