WHO: Ebola outbreak in West Africa an international health emergency

Guinea, Liberia and Sierra Leone are battling the Ebola virus, which has also spread to Nigeria. The virus is believed to have infected 1,779 people, killing 961, from the start of the outbreak earlier this year through Wednesday, the World Health Organization said.

"The possible consequences of further international spread are particularly serious in view of the virulence of the virus, the intensive community and health facility transmission patterns, and the weak health systems in the currently affected and most at-risk countries," WHO said Friday after two days of emergency meetings.

The U.N health agency described it as
the worst outbreak in the four-decade history of tracking the disease.

The Liberian leader declared a 90-day state of emergency this week, which will allow her government to set up a series of measures to prevent the spread of the disease.

While Liberia struggles to contain the epidemic, the United States ordered relatives of its embassy employees to leave the country. The U.S. Embassy is in the capital of Monrovia -- one of the areas hardest-hit by the epidemic.

Washington said it's sending experts to Liberia, including 12 specialists from the Centers for Disease Control and Prevention, and a 13-member disaster assistance response team from the U.S. Agency for International Development.

Two Americans who were in Liberia are undergoing treatment at Emory University Hospital in Atlanta: Dr. Kent Brantly and aid worker Nancy Writebol. Emory is one of four U.S. institutions capable of providing such treatment.

The Ebola virus causes hemorrhagic fever that affects multiple organ systems in the body.

Early symptoms include weakness, muscle pain, headaches and a sore throat. They later progress to vomiting, diarrhea, impaired kidney and liver function -- and sometimes internal and external bleeding.

Ebola spreads through contact with organs and bodily fluids such as blood, saliva, urine and other secretions of infected people. It has no known cure. The most common treatment requires supporting organ functions and maintaining bodily fluids such as blood and water long enough for the body to fight off the infection.