Ebola

Ebola survivor Musa Pabai in Walakor, Liberia. Doctors and scientists have much to learn about the long-term health effects of the illness in those who recover. (Ricci Shryock/Reuters)

Ebola infection continues to surprise scientists. The latest twist: The deadly virus may hide in pregnant women without obvious symptoms.

A new case report describes a 31-year-old woman in late pregnancy who went to a hospital in Liberia complaining of mild stomach pain, possibly pregnancy-related.

Routine Ebola testing revealed she was infected with the virus, though she had no obvious symptoms, such as body pain, vomiting and diarrhea, or bleeding.

After three days, however, Ebola symptoms emerged. Several days later she and her fetus were dead, according to a letter published June 18 in the New England Journal of Medicine.

The researchers suspect the woman's reduced immune response — a normal part of pregnancy — could have allowed the virus to remain in her body undetected for some time.

"The unique immunologic status of pregnant women might alter disease presentation and progression," wrote Dr. Emma Akerlund of Doctors Without Borders and two colleagues. "This case highlights the challenges that clinicians may face in assessing pregnant women for possible infections, including Ebola, and the potential risk for health care staff."

It's possible that she could have infected others before her symptoms appeared, the researchers said. But experts said the implications really aren't clear.

"We don't know enough about Ebola to tell what all the complications might be," said Dr. Debra Spicehandler, co-chief of infectious disease at Northern Westchester Hospital in Mount Kisco, N.Y. She had no role in the study.

The main limitation of the study is that this is a single case, said Thomas Geisbert, a professor of microbiology and immunology at the University of Texas Medical Branch in Galveston.

"If it turns out that there are a fair number of cases where high levels of virus are detected in body fluids from asymptomatic patients, then, yes, that could have important implications in explaining the magnitude of this outbreak and certainly for how outbreaks are managed," said Geisbert, who wasn't involved in the study.

The recent Ebola outbreak in West Africa — the worst in history — has infected more than 27,000 people and killed more than 11,000 of them since late 2013. Health officials believe the worst of the epidemic is over, even though a small number of cases continue to surface.

Immune response in Ebola infection

David Sanders, an associate professor of biological sciences at Purdue University in West Lafayette, Ind., explained that it's not Ebola itself that causes the symptoms, it's the body's immune response that causes the symptoms.

It's entirely possible that someone whose immune system is suppressed can carry Ebola and not show the classic symptoms, he said.

Sanders added there may be others who carry Ebola without obvious signs because their immune system is subdued.

"Fortunately, however, this appears to be rare," Sanders said. "You have to have the conjunction of immunosuppression with the infection."

While noting this is something doctors can take into account, Sanders added, "I don't think it's something we need to panic about."

He believes the mode of transmission remains the same even when the virus is concealed.

That means someone would have to have contact with body fluids to contract the virus. Ebola appears to be most transmissible from contact with infected patients just a few days before death and by handling their dead bodies, he said.

Elsewhere on Wednesday, the U.S. National Institutes of Health announced at trial in Liberia to examine the long-term health effects of Ebola virus disease among those who recover.

Study participants will give their medical history, receive physical and vision examination and have blood samples collected so researchers can identify and track any health issues, monitor organ and eye function and record Ebola antibody levels.

There have been reports of inflammatory eye disease and vision loss among Ebola survivors. One of goals of the research is to determine the incidence and extent of Ebola-related eye disease among survivors and learn about its risk factors and best treatments. 

HealthDay News with files from CBC News