LONDON (AP) — The World Health Organization urged nations worldwide to donate money and resources to stop the spread of Ebola as it declared the outbreak in West Africa to be an international public health emergency.

The latest Ebola outbreak is the largest and longest ever recorded for the disease, which has a death rate of about 50 percent and has so far killed at least 961 people, according to the U.N. health agency. It emerged in Guinea in March and has since spread to Sierra Leone, Liberia and Nigeria.