The World Health Organization is facing its ‘most challenging’ outbreak of Ebola yet. The outbreak is contained within two countries in western Africa, although WHO officials are trying to determine if people in other countries are also infected.

However, the WHO recently announced that the outbreak is still contained to Guinea and Liberia, offsetting rumors that the disease had spread to other places.

The number of suspected Ebola cases in Guinea has risen to 157, with a total of 101 deaths. So far, 67 of those deaths have been confirmed as Ebola. The numbers are smaller in Liberia, with a total of 21 cases reported and 10 deaths. Of those cases, five are confirmed to be from Ebola.

According to ABC News, Doctors Without Borders is resuming care for Ebola patients after an attack from an angry crowd at a Guinean health center caused the aid workers to flee.

Sam Taylor, spokesman for the organization, said that the organization had resumed work at Macenta, the location where the mob accused the aid workers of beginning the outbreak. Up until these cases, Guinea has never before had a confirmed case of Ebola.

For those who contract the usually fatal disease, there is no cure or vaccine. At least 110 deaths from the disease have been reported in portions of western Africa, although Doctors Without Borders says that a few patients with the disease have been treated and released.

The WHO is currently tracking down suspected cases in other countries, as an estimated 600 people are thought to be at risk of becoming infected.

Dr. Keiji Fukada, assistant director-general for health security at the WHO, says that this outbreak of Ebola is one of the most challenging that the organization has ever faced.

Outbreaks are occurring in Guinea’s capital, Conakry, as well as remote locations.