MONROVIA (Reuters) - Liberia is on the verge of containing the spread of the Ebola virus with only two of its 15 counties reporting new infections, the head of the country's Ebola response said on Tuesday.

Tolbert Nyenswah, who is also a deputy health minister, said the new cases were reported in Montserrado county, which includes the capital Monrovia, and Grand Cape Mount, on the border with Sierra Leone.

Bong, Nimba, Sinoe, and Margibi counties have not reported a single case since the end of December, he said. According to the World Health Organization (WHO), Bong, Nimba and Sinoe have gone 21 days without a positive case - the maximum incubation period for the virus.

"If we can go at this rate ... and maintain this trend, we will advance to zero for the entire country soonest," Nyenswah said, without setting a specific date.

Liberian officials had previously set a December 31 target for zero new infections. The rate of Ebola transmission has slowed in recent weeks in Liberia, one of the West African nations hardest hit by the outbreak.

The worst epidemic of the virus on record has killed more than 8,371 people and infected some 21,171 in Liberia, Sierra Leone and Guinea, according to WHO figures released on Monday. More than 3,515 of the dead were from Liberia, it said.

United States aid agency USAID said on Tuesday that new Ebola cases in Liberia have plunged while Sierra Leone, currently the worst-affected country, was beginning to turn the corner in dealing with the virus.

But focus was now Guinea, where the infectious hemorrhagic fever was first detected in March, a USAID official said.

Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, said on Tuesday that he was confident that the outbreak can be brought under control.


(Reporting by James Harding Giayhue; Writing by Bate Felix; Editing by Dominic Evans)