The death of the chief Ebola treatment specialist in Sierra Leone could be considered a major setback to containment of the deadly virus that has since killed hundreds of people in the African region.

The Associated Press has received confirmation from chief medical officer Dr. Brima Kargbo that Dr. Shek Umar Khan has succumbed to the virus after he was hospitalized for Ebola infection. He has been leading a team in West Africa in treating patients who have been infected with the virus. Aside from Umar, the virus has claimed over 670 across the African region this year alone.

Ebola has been considered as an extremely dangerous virus strain, as one could get infected through bodily fuids like blood, saliva, sweat and urine. The outbreak in Africa has been considered the largest so far for the Ebola virus, and has already spread in Liberia, Guinea and Nigeria apart from Sierra Leone, AP said. At the moment, there is no vaccine for the disease, nor specific treatment to it. People who have been infected with the virus have at least 40% chance to survive from the virus.

Although it has yet to reach foreign soil like the US, Ebola has already infected two American. CNN said that social aid workers Dr. Kent Brantly and Nancy Writebol had been tested positive for Ebola. The two, like Umar, had been in close contact with infected people who are seeking treatment or in proximity to people who have yet to know that they have been infected.

On Monday, the Centers for Disease Control and Prevention hosted a media briefing and declared that there is no significant risk of a virus outbreak in the US. Although Doctors Without Borders epidemiologist Kamiliny Kalahne assured the public that it was rare for infected people to travel, the health authority has since cautioned humanitarian workers to be familiarized with infection control precautions to avoid getting infection.

Ebola has already claimed a life of an American. CNN said US national Patrick Sawyer, a top government official in the Liberian Ministry of Finance succumbed to the Ebola virus. The 40 year-old died on July 25, five days after he was admitted to the hospital.