The ongoing Ebola epidemic in Western Africa is already acknowledged as horrific, with 2,000 suspected cases and over 1,000 deaths reported. But the true scale of the epidemic may actually be far greater, according to an August 14 statement from the World Health Organization.

“Staff at the outbreak sites see evidence that the numbers of reported cases and deaths vastly underestimate the magnitude of the outbreak,” the WHO statement says.

Gathering accurate data about the disease has been challenging for many reasons. Guinea, Sierra Leone, and Liberia all suffer from a shortage of medical professionals and a lack of strong health care infrastructure. Some patients have also avoided health care.

Diagnoses in Guinea have recently slowed, and no new cases have been reported in Nigeria, where the disease was brought from Liberia by an infected American traveler in late July. But in Sierra Leone and Liberia, Ebola shows no signs of faltering. Joanne Liu, head of Doctors Without Borders, estimates that it would take about six months to control the epidemic.

The map above uses data released by the WHO and the health ministries in Liberia and Sierra Leone to show how the number of cases per region has increased. At times, the availability of data has been inconsistent, with one press release reporting incidence of Ebola in one area, and the next one making no mention of the disease there. We’ve displayed information from the most recent releases, so the chart shows the best picture of the disease’s believed distribution at any given point between March 22 and Aug 14. Some suspected cases were later determined not to be Ebola, which explains why the disease’s reach appears at times to retract.