June 26, 2000

Some May Carry Ebola Virus Without Having the Symptoms

By LAWRENCE K. ALTMAN

he Ebola virus, which has caused deaths from high fever and bleeding in African outbreaks, can also infect without producing illness, according to a new finding by African and European scientists.

The possibility of asymptomatic infection was only suggested in earlier studies, they said in last week's issue of The Lancet, a medical journal published in London. Now they said they had documented such infections for the first time. They found that the Ebola virus could persist in the blood of asymptomatic infected individuals for two weeks after they were first exposed to an infected individual. How much longer the virus can persist is unknown.

All outbreaks of Ebola have been controlled by standard infection control measures such as effective body disposal, destroying or sterilizing contaminated equipment and appropriate use of gloves. But if people can be carriers without showing symptoms, it means control might be more difficult.

"This degree of containment would be virtually impossible if symptom-free carriers posed a significant threat of infection," Dr. Alan G. Baxter of Newtown, Australia, wrote in an editorial in the same issue of The Lancet.

Scientists have known that Ebola usually spreads from an infected person to another individual and through contamination in clinics or hospitals. The new finding suggests that some cases may result from healthy carriers. How often is unknown. The finding could help scientists in their long-term quest to develop effective therapies to treat the virus or perhaps even a vaccine to prevent infection.

But an immediate effect is to raise the need to reasses health policy about one of the most virulent viruses known and to determine how often healthy carriers transmit it, said the scientific team headed by Dr. E. M. Leroy of Franceville, Gabon.

One concern is transmitting Ebola through blood transfusions. Dr. Thomas G. Ksiazek, an expert in Ebola at the Centers for Disease Control and Prevention, a federal agency in Atlanta, said that such concern would be much greater in Africa than in the United States, where blood banks usually ask people who have been in Africa in recent months not to donate because of the threat of transmitting malaria.

Dr. Leroy's team said another public health concern was transmission of Ebola virus from healthy carriers through sex. Other scientists have detected Ebola in semen.

About 70 percent of people with symptoms of Ebola have died in widely publicized outbreaks in the central African countries of Gabon, the Democratic Republic of the Congo and Sudan.

Illness often begins abruptly, from 5 to 10 days after exposure to Ebola virus, with symptoms like fever, headache, vomiting and diarrhea. Then bleeding can occur internally or ooze from needle sites and through the nose and mouth. Death usually occurs from five to seven days after the onset of illness.

Dr. Leroy's team studied 25 individuals who never developed symptoms although they lived with family members and cared for them without using gloves and other precautions in two outbreaks in Gabon in 1996.

Using standard virologic techniques, the scientists from Gabon, Germany and France said they could not detect the virus in the blood of the healthy contacts. But Dr. Leroy's succeeded by using a technique known as polymerase chain reaction to grow the tiny amount of virus present.