This 2003 electron microscope image made available by the Centers for Disease Control and Prevention shows mature, oval-shaped monkeypox virions, left, and spherical immature virions, right, obtained from a sample of human skin associated with the 2003 prairie dog outbreak. The World Health Organization will convene an emergency committee of experts to determine if the expanding monkeypox outbreak that has mysteriously spread outside its usual zones should be considered an international public health emergency. (Cynthia S. Goldsmith, Russell Regner/CDC via AP, file)