The World Health Organization (WHO) says the ongoing Ebola outbreak in West Africa is "one of the most challenging" outbreaks of the virus it has ever faced.
WHO Assistant Director-General Keiji Fukuda says it could take four more months to contain the outbreak, which has resulted in more than 110 deaths.
Guinea remains the center of the outbreak, with 157 suspected or confirmed cases of Ebola. Another 21 cases are suspected or confirmed in Liberia.
During a Tuesday news conference in Geneva, Fukuda said the current outbreak is especially challenging because it is spread over a wide area.
The outbreak began in Guinea's forested southeastern region in February, before spreading across the border into Liberia.
Health officials are also investigating suspected cases in Mali and Sierra Leone.
Ebola is spread through contact with bodily fluids. The virus can cause hemorrhagic fever, leading to symptoms that can include muscle pain, vomiting, unstoppable bleeding and organ failure.
Health experts are warning people in the affected areas to avoid direct contact with patients or those killed by the virus.
This is the first major outbreak of Ebola in West Africa. Previous outbreaks have occurred in Central African countries, including Uganda and the Democratic Republic of Congo.