A fourth doctor from Sierra Leone has tested positive for Ebola and will be evacuated from the country for treatment abroad, according to the Associated Press. Dr. Olivette Busk is the first non-Westerner to be transported out of West Africa, where the ongoing Ebola outbreak has killed more than 2,200 people and infected thousands more, for medical treatment. The three doctors who became sick before her have died. It is unclear where Busk will be taken.

Health workers have experienced higher infection rates in this Ebola outbreak than in any previous one, according to the AP. Their proximity to the disease, which is transmitted by the bodily fluids of infected individuals, and to patients who are violently ill and may be vomiting or suffering from diarrhea, makes health workers particularly vulnerable to the virus. To make matters worse, proper protective gear is in short supply, and health clinics are often overwhelmed with more patients than they can handle.

The Ebola outbreak has killed more than 135 health workers so far, and has led in part to shortages of health workers in some areas where the virus has taken hold. “Ebola has taken the lives of prominent doctors in Sierra Leone and Liberia, depriving these countries not only of experienced and dedicated medical care but also of inspiring national heroes,” the World Health Organization said in August.

WHO officials announced Tuesday that the virus had killed at least 2,288 people in Guinea, Liberia and Sierra Leone since the outbreak began six months ago. Nearly half of those deaths occurred in the last 21 days.

"We are at war with an enemy that we don't see," Amara Mohamed Konneh, Liberia’s finance minister, told AP. "And we have to win the war."

The United Nations, the U.S. and private donors have all stepped in to help quell the Ebola epidemic, including the Bill and Melinda Gates Foundation, which donated $50 million to the U.N. and other international organizations to fight the outbreak. The U.S. donated five ambulances this week to help Sierra Leone.