The World Health Organization says it aims to identify and isolate all new Ebola cases in West Africa by the end of May to stop the spread of the lethal virus before the rainy season.
In a new Ebola plan released on Tuesday, the U.N. health agency said it hopes to limit transmission of the virus to the coastal areas of Guinea, Liberia and Sierra Leone before the rainy season begins, normally in April or May.
WHO said the decline in Ebola's spread has "plateaued," partly due to "persistently high transmission" in Guinea and Sierra Leone. Officials say the rainy season will make it more difficult for responders to reach remote areas.
Although cases have dropped from the peaks of more than 800 cases per week in October, there is still a steady trickle of several dozen cases every week. Experts don't know where most new cases are coming from in Guinea and Sierra Leone.
The last confirmed patient in Liberia died on March 27; if no new cases are identified there by May 9, the country could be declared Ebola-free, though some experts warn no country will be safe until the entire region wipes out Ebola.
"How can we really be sure when Ebola has been eliminated in this region?" asked Peter Piot, co-discoverer of the Ebola virus, pointing out serious problems in surveillance systems.
Piot said officials are struggling to deal with questions about whether the virus might be spread via sexual transmission or other ways that could complicate declaring the epidemic over. WHO says there is no evidence the virus can be spread via sex and that studies are ongoing.
WHO said it was determined to reach "zero cases" and to ensure "a positive legacy remains after this crisis." To date, Ebola is estimated to have killed more than 10,800 people in the biggest-ever outbreak of the disease.
The U.N. had previously predicted Ebola would be contained by June but has missed numerous targets it set to stop the virus.