What virus was caused by Nurse Mayinga and WHY?

The Nurse does not cause the virus, she contracts the virus. Nurse Mayinga falls under the care of Dr. Margaretha Isaacson, who initially treats her while wearing a gas mask. Unable to function well in the oppressive heat, Dr. Isaacson eventually abandons the mask and treats her patient face-to-face. Despite Dr. Isaacson’s best efforts, Nurse Mayinga dies from a heart attack caused by the virus.