The Ebola virus has the “upper hand” in an outbreak that has killed more than 1,400 people in West Africa, a top American health official said, adding that experts have the tools to stop it.

Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, is visiting Liberia, Sierra Leone and Guinea, the three hardest hit countries, this week.

Nigeria has also recorded cases, but officials have expressed optimism that its spread there can be controlled. On Tuesday, Frieden continues his visit in Liberia, which has the most cases and deaths.

“Lots of hard work is happening, lots of good things are happening,” Frieden told a meeting attended by President Ellen Johnson Sirleaf on Monday. “But the virus still has the upper hand.”

The current outbreak is the largest ever and experts have struggled to contain it for a host of reasons: doctors took a long time to identify it, it is happening in a region where people are highly mobile, it has spread to densely populated areas and many people have resisted or hid from treatment. The disease has overwhelmed already struggling health systems in some of the world’s poorest countries.

But Frieden expressed optimism that the outbreak can be contained.

“Ebola doesn’t spread by mysterious means, we know how it spreads,” he said in his remarks, which were broadcast on Liberian TV. “So we have the means to stop it from spreading, but it requires tremendous attention to every detail.”

Liberia has resorted to some of the most stringent measures to control the disease, including sealing off an entire slum neighborhood in the capital. Sirleaf has also declared a state of emergency and ordered all her ministers and top government officials to remain in the country or return from any trips.

Late Monday, her office said in a statement that any official who defied that order had been fired. The order was issued a few weeks ago and officials had been given a week to return. The statement did not say how many or who had been fired.

According to the latest World Health Organization tally, the Ebola outbreak has killed 1,427 people of the 2,615 sickened. The U.N. health agency says that 240 health care workers have been infected with Ebola, calling that an unprecedented number. Half of those infected have died.

The agency said that the high number of infections among health workers is due to a shortage of protective gear and its improper use and a shortage of staff to treat the tremendous influx of patients.

In the current outbreak as many as 90,000 protective suits will be needed every month, according to Jorge Castilla, an epidemiologist with the European Union Commission’s Department for Humanitarian Aid. That estimate takes into account a recent increase in the number of beds available for treating Ebola patients and more stringent standards to protect health workers.

There has been a severe shortage of that equipment that is only now beginning to be resolved, he said. He did not say exactly how many suits were lacking.

The outbreak also desperately needs more workers to trace the people that the sick have come into contact with and more centers where patients can be screened for the disease in a safe way that contains any Ebola infections, said Castilla, who recently returned from a trip to Guinea, Liberia and Sierra Leone.

A separate Ebola outbreak emerged over the weekend in Congo, though experts say it is not related to the West African epidemic. Doctors Without Borders, which is running many of the treatment centers in the West Africa outbreak, said it was also sending experts and supplies to Equateur, a northwestern province of Congo. But the medical charity has already warned that the West African outbreak has stretched its resources.

“In normal times, we’re able to mobilize teams specializing in hemorrhagic fevers, but currently we are facing an enormous epidemic in West Africa, limiting our capacity to respond to the outbreak in Equateur province,” said Jeroen Beijnberger, the group’s medical coordinator in Congo. “We need other actors to rapidly mobilize with us to help the (Congolese) Ministry of Health: We won’t succeed alone.”

(AP)