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'Bird Flu' Origin, How It Spreads Remain Mysteries

By Keith B. Richburg
Washington Post Foreign Service
Sunday, December 28, 1997; Page A21

HONG KONG, Dec. 27—Since a mysterious and deadly new "bird flu" began claiming human victims here last May, local health officials and international scientists have made progress identifying the virus. But they remain puzzled by its origin, its progress through the human population and its potential to erupt into a pandemic.

Among the mysteries, scientists say, is how the virus, originally found in birds, made the jump to humans; whether infected persons can pass the virus to other humans; why four people known or suspected to have contracted it have died while others have been successfully treated; and why more than half of the 22 known victims have been young children.

Also unanswered -- and politically sensitive here to even ask -- is the suspected role of the rest of China as the incubator of the deadly influenza.

"Right now there is clearly a lot we don't understand," said Dr. Keiji Fukuda, the epidemiology chief for the Atlanta-based Centers for Disease Control and Prevention, who is leading a team of investigators here. "One of the most pressing questions to figure out is, 'Is there human-to-human transmission?' "

The likelihood that the disease could be passed between humans seemed to increase today after the preliminary blood test results of 502 people were released. All of those tested either were poultry workers with prolonged exposure to chickens, laboratory workers who handled the virus or people who had contact with the first bird flu victim, a 3-year-old boy who contracted the disease last May and later died.

Nine of the 502 people were found to have antibodies for the disease. Five of the nine were poultry workers, suggesting to scientists that prolonged exposure to chickens -- or bird-to-human transmission -- was the most efficient way for the disease to spread. But in three other cases, there was no known exposure to chickens or to the virus in laboratories, "leaving open the possibility of human-to-human transmission," according to the study's preliminary findings.

One member of that group, described only as a health-care worker who was in contact with the boy, tested positive for antibodies to the bird flu virus, although the health worker has not been ill.

Margaret Chan, Hong Kong's director of health, said the bird flu, called A H5N1, is not thought to be an airborne virus, and that the health-care worker may have gotten it from contact with the patient's body secretions.

The presence of the bird flu antibodies in the group of nine has raised additional questions, such as whether the virus could have existed undetected here for many years, and why some people who were exposed to the virus and developed antibodies become ill and others did not.

Bird flu symptoms are similar to normal flu symptoms -- fever and chills, sore throat and muscle aches. Scientists are intrigued as to why children have been most affected.

As of today, Hong Kong health officials have recorded 11 confirmed and 11 suspected cases of bird flu. In what has become an almost daily occurence, two new cases were announced today -- a 1-year-old boy and a 72-year-old man, both said to be hospitalized in satisfactory condition.

Among the 22 recorded cases, 14 have been children between the ages of 1 and 6.

"The lack of direct exposure to poultry, and the fact that the kids clearly are not poultry workers, doesn't rule out or rule in other possibilities" for contracting the odd virus, Fukuda said. "The question is extremely important, and as more data becomes available the evidence of human-to-human transmission could become stronger."

As mysterious as the virus's transmission patterns are its origins, and evidence points increasingly to the farms across the border in southern China as the source of the virus.

So far, Hong Kong agriculture officials have said their surveillance of 70 of Hong Kong's domestic chicken farms has not turned up the virus in the birds. But on Dec. 22, workers from the Agriculture and Fisheries Department discovered three samples of the virus and traced the infected birds through a chicken wholesaler across the border. The next day, the Hong Kong government banned all chicken imports from the rest of China until a system of border controls and checks could be put in place.

Until the ban, Hong Kong's largest source of chickens was the rest of China, from which about 75,000 of the birds were shipped in each day.

Officials here, however, were careful today not to blame other Chinese regions for the disease.