The current Ebola outbreak is worrying the World Health Organization’s chief as the “scale and speed” of the virus’s spread increases. The number of deaths has also risen sharply as reports of illness roll in.

At least 131 people are believed to have died and 531 to have been infected, central African health authorities say. An American missionary was among those who tested positive, accoridng to a report by NBC News. 

The number of suspected cases has risen dramatically from the 300 believed infected and 88 killed as of Monday.

The Ebola Scare Begins: The Worst Outbreak Of Bundibugyo Virus Disease In World History

This outbreak went undetected for weeks, allowing the virus to continue to spread and deaths to coalesce.

Global health experts are worried about the capacity of this outbreak to cause widespread illness and death in central Africa, not least because this rare strain of Ebola, the Bundibugyo virus, has no approved vaccine or treatment and a shortage of available tests.

WHO Director-General Tedros Adhanom Ghebreyesus said early Tuesday that he was “deeply concerned about the scale and speed of the epidemic.” This comes as the United States State Department also said in a statement on Tuesday that the U.S. will fund up to 50 Ebola response clinics.

“The United States is committing to rapidly supporting the Ebola outbreak response by funding up to 50 treatment clinics, and associated frontline costs being established in Ebola-affected regions of the DRC and Uganda,” the State Department said of the outbreak. “This U.S. funding commitment will accelerate the delivery of frontline medical care, life-saving humanitarian assistance, and critical outbreak response capabilities to communities at greatest risk,” it added.

The State Department also stated that it was “strongly” urging Americans not to travel to the Democratic Republic of Congo, South Sudan, or Uganda “for any reason.”

Unfortunately, cases of Ebola have been reported as far away as the rebel-held city of Goma, 230 miles from the outbreak’s epicenter in the eastern Ituri province, as well as in neighboring Uganda.

The WHO has already declared this outbreak a global “emergency.”

WHO Declares A Global Ebola “Emergency”