According to a new report by the World Health Organization, the death toll continues to rise in West Africa as the Ebola epidemic moves through the three nations at the center of the pandemic to neighboring nations. The report also highlights the possible existence of "shadow zones."

New statistics released by the WHO reveal that the number of Ebola deaths has risen to 1,427 with 2,615 people infected, according to CBC News. Most of the new infections come from Liberia, where parts of the capital city Monrovia have been sealed off.

However, the disease continues to spread. Nigeria has reported two new cases of infection, reports the Associated Press. The infected are two spouses of caregivers who came in contact with Liberian-American Patrick Sawyer, who introduced the virus to Nigeria earlier this month, said Nigeria's Health Minister, Onyebuchi Chukwu.

These are the only infections to be transmitted without contact with Sawyer. He infected 11 others during his trip from Liberia to the Nigerian capital of Lagos. Despite the virus's spread into Nigeria, the WHO warns that numbers in Liberia, Sierra Leone and Guinea could be higher.

"The magnitude of the Ebola outbreak, especially in Liberia and Sierra Leone, has been underestimated for a number of reasons," said the WHO in a Situation Assessment released on Friday.

The organization explains that family members do not report infected relatives, because they see treatment centers as sources of infection, while others believe that infected relatives ought to die in the comfort of their homes. Some bury the dead without notifying officials.

The statement details the case of Liberia where, "as soon as a new treatment facility is opened, it is immediately filled with patients, many of whom were not previously identified." This "strongly suggests the existence of an invisible caseload of patients who are not being detected by the surveillance system," explains the WHO.

Ignorance and accessibility also play a role in the virus's spread. "An additional problem is the existence of numerous 'shadow-zones,'" explains the organization, present in remote villages inaccessible because of lack of staff or vehicles and local distrust of officials.

According to Joseph Fair, an infectious disease specialist advising Sierra Leone's health minister, health organizations' numbers could be off by 20 percent, he said in an interview with NPR.

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