Kinshasa, Zaire -- With authorities searching for at least two individuals believed to be at large here in the capital, Zaire's chief health official warned yesterday that the quarantine of disease-stricken areas was being violated, and "if the quarantine cannot be held, the country will be closed."

The death toll in Zaire's Ebola outbreak has risen to 77, the World Health Organization reported, out of 84 confirmed cases of the virus.

In Kikwit, the center of the outbreak, authorities acknowledged that more than 100 additional deaths had probably occurred, but had gone uncounted, because the victims died at home. "People do not want to go to hospitals, knowing that the epidemic started there," a WHO statement said.

"Here in Kikwit, the problem is bigger than in Yambuku," where the Ebola virus first broke out in 1976, Zairean microbiologist Jean-Jacques Muyembe told reporters Sunday, "because the town has more than 400,000 people. It is a very big city. Yambuku was just a village."

In Kinshasa, Ministryof Health officials confirmed that two individuals -- a nurse and a Congo River boat worker -- were being sought by police. The nurse, who was exposed to Ebola in Kikwit, reportedly fled to the capital and disappeared.

Loyangela Bompenda, Zaire's secretary general of health, said yesterday that people are evading roadblocks and violating the quarantine imposed on Kikwit and neighboring villages. "If the quarantine cannot be held, the country will be closed," he said at a briefing.

Air France, Sabena and other international air carriers have already announced plans to limit flights to the Central African nation.

There is no cure or vaccine for Ebola, which kills up to 90 percent of those it infects. No one knows where the virus hides between epidemics -- in some animal or insect population, for instance. There have been three previous outbreaks, in Zaire in 1976 and in Sudan in 1976 and 1979.