Ebola may linger in men's semen for more than two years, a new study suggests.

What's more, at least one man who survived Ebola and then tested negative for the presence of the virus in his semen later tested positive, the new study found.

The findings raise questions about how long Ebola can linger in special immune hideouts in the body. However, the new findings only show some men carry RNA or genetic material from Ebola long after recovering from the disease. They don't necessarily mean all men who test positive for Ebola RNA are still capable of transmitting the virus. [What Are the Long-Term Effects of Ebola?]

Rare and deadly virus

Ebola virus is a rare and deadly virus that starts with common flu-like symptoms, such as fever, muscle and joint pain, and headache, according to the Centers for Disease Control and Prevention. As the virus progresses, however, people suffer from extreme diarrhea and vomiting, and in the late stages of the disease, people's blood vessels may become leaky, causing bleeding from the rectum, nose or mouth. People infected with the virus can transmit it through bodily fluids — such as blood, vomit, diarrhea or semen — and are infectious only once they start showing symptoms of the disease. Between 2014 and 2016, there were nearly 30,000 cases of Ebola reported in Sierra Leone, Guinea and Liberia, according to the World Health Organization. Many of the people who survive the initial deadly phase of the disease may still face lingering problems, such as headache, vision problems, fatigue, joint pain and hearing loss, a 2015 study in the New England Journal of Medicine found.

The finding that Ebola can linger in semen even after men recover from the infection is not a surprise to researchers. Studies of men in Sierra Leone, Liberia and Guinea after the 2014-2016 Ebola outbreak found that anywhere from 28 percent to 100 percent of men harbored the RNA, or genetic material, from the Ebola virus in their semen up to three months after infection. Another study found that a minority of men who contracted the virus tested positive for Ebola in their semen seven to nine months after recovering from the infection. In 2015, scientists reported that a man who had recovered from the disease six months earlier had transmitted Ebola to a sexual partner.

The World Health Organization currently recommends that people who recover from the virus be tested for any lingering presence of Ebola RNA three months after recovering, and then again until the test is negative on two consecutive monthly tests. If men have not been tested, they should abstain from sex for 12 months, or use condoms every time they have sex, according to WHO guidelines.

Another study found that a man transmitted the virus to his partner more than 500 days after he began showing symptoms of the illness.

Unknown persistence

But exactly how long does the virus linger in reservoirs in the body — and for how long can it be transmitted?

To answer that question, Dr. William Fischer II, a critical care specialist at the University of North Carolina at Chapel Hill, and colleagues analyzed semen donated by 149 men who had recovered from the virus up to almost three years earlier.

They found that 13 of these men tested positive for the presence of Ebola RNA; 11 of these men had recovered more than two years earlier. One of the 13 men tested positive for Ebola RNA after having tested negative on two prior occasions, the researchers reported July 22 in the journal Open Forum Infectious Diseases. The men who tested positive for Ebola virus in their semen were, on average, older than men who never tested positive. In addition, they were likelier to report the post-Ebola symptoms of vision problems and fatigue, compared with men who tested negative, the study found.

The significance of the findings is still not clear, the researchers noted in the paper.

"While the persistence of EBOV [Ebola virus] RNA in semen is concerning, it is not known if the detection of EBOV RNA in genital fluids is a surrogate for the presence of infectious virus," the researchers wrote in the paper.

But the prolonged presence of Ebola virus RNA in men should prompt organizations to rethink their sexual transmission prevention guidelines, the researchers wrote. Further research should aim to eliminate Ebola that may be hiding in these reservoirs, the authors added.

Immune hideouts

One possibility is that Ebola may hide in specific spots in the body that are somewhat protected from the immune system, such as the eye and the testes, the researchers wrote. These "privileged" areas of the body are less prone to inflammatory attack by the immune system when foreign substances are found. The fact that men who reported vision issues after their recovery were likelier to harbor Ebola RNA seems to bolster this notion, the researchers wrote.

As people age, perhaps their immune system becomes less robust, the researchers suggested. Their weakened immune systems may enable the Ebola virus to hide out in these certain immune-privileged sites, such as the testes.

However, figuring out how to provide new information on how to prevent the sexual transmission of Ebola, without making things worse for Ebola survivors, could prove tricky, the researchers noted.

"For many survivors, the physical manifestations of the disease have been compounded by the stigma encountered with their return to their communities," the researchers wrote in their paper. "Survivor messaging regarding viral persistence, if demonstrated, must provide information that can be used to protect loved ones but at the same time not risk further ostracizing by society."

Originally published on Live Science.