"We have reasons to be cautiously optimistic that this terrible outbreak can be defeated," said Ban at a press conference with Liberia's president.
"Our response strategy is working -- where people are gaining access to treatment, where contacts are being traced, burials are becoming safer, communities are mobilizing to protect themselves," he said.
Nearly 3,300 of the Ebola deaths have been in Liberia, where health officials say the spread of the virus has shown signs of slowing in recent weeks.
"Just one case can trigger an epidemic and we have a long way to go," said Ban.
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His visit to Liberia comes on the eve of crucial midterm senatorial elections. Some 139 candidates are vying for 15 seats in the senate, including former soccer star George Weah and Robert Sirleaf, the son of Liberia's president.
Health authorities have deployed 4,700 thermometers to voting places around the country to take voters' temperatures as people go to the polls.
Authorities also have deployed 10,000 bottles of sanitizers to polling places amid concerns about Ebola.
Some critics have questioned whether the polls can be credible at a time the country is battling such a deadly epidemic.