In this photo taken on Monday, July 28, 2014, people hang out in a street under a banner which warns people to be cautious about Ebola, in Monrovia, Liberia. Two American aid workers in Liberia have tested positive for the virus and are being treated there. U.S. health officials said Monday that the risk of the deadly germ spreading to the United States is remote. (AP Photo/Jonathan Paye-Layleh)

(AP)—Authorities say the top doctor treating Ebola in Sierra Leone has died from the disease.

Dr. Shek Umar had been hospitalized in quarantine since he contracted the virus that has killed more than 670 people across West Africa this year.

His death Tuesday was confirmed by chief medical officer Dr. Brima Kargbo.

Health workers have been especially vulnerable to contracting Ebola, which is spread through bodily fluids such as saliva, sweat, blood and urine. Two American health workers are currently being hospitalized with Ebola in neighboring Liberia.

The Ebola outbreak is the largest in history with deaths blamed on the disease in Sierra Leone, Liberia, Guinea and also Nigeria.

This photo provided by the CDC shows an ebola Virus. U.S. health officials are monitoring the Ebola outbreak in Africa but say the risk of the deadly germ spreading to the United States is remote. (AP Photo/CDC)

The disease has no vaccine and no specific treatment, with a fatality rate of at least 60 percent.

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