Six U.S. military planes arrived Thursday in Liberia to deliver more Marines into the epicenter of the Ebola crisis. Meanwhile, at a World Bank meeting in Washington, West African leaders pleaded for help in dealing with the disease.
A look at the essential developments worldwide:
The fleet that landed outside the Liberian capital of Monrovia consisted of four MV-22 Ospreys and two KC-130s. The 100 additional Marines bring to just over 300 the total number of American troops in the country.
Speaking by videoconference to the World Bank meeting, Sierra Leone President Ernest Bai Koroma called the epidemic "a tragedy unforeseen in modern times." He said other countries are not responding fast enough.
In Britain, authorities said they would introduce "enhanced" screening of travelers for Ebola at Heathrow and Gatwick airports and Eurostar rail terminals. Prime Minister David Cameron's office said passengers arriving from West Africa would be questioned about their travels and contacts.
Elsewhere, University of Maryland researchers announced that the first study of a possible Ebola vaccine in Africa was underway. Scientists say three health care workers in Mali received the experimental shots developed by the U.S. government.
Ebola has killed at least 3,800 people in West Africa and infected at least 8,000, according to the World Health Organization. The virus has taken an especially devastating toll on health care workers in the hardest-hit countries of Liberia, Guinea and Sierra Leone — places that already were short on doctors and nurses.
THE U.S. PATIENTS
Two patients with Ebola are being treated in the U.S. A freelance NBC News cameraman arrived in Nebraska for treatment earlier this week. And an American aid worker has been undergoing treatment in Atlanta since last month. In total, five Americans with Ebola have returned home for treatment.
The Texas sheriff's deputy who exhibited symptoms of Ebola has tested negative for the disease, state health officials said Thursday. Michael Monnig had gone to a health clinic Wednesday, days after he was among a group of deputies who went inside the Dallas apartment where a patient from Liberia, Thomas Eric Duncan, had stayed. Duncan died Wednesday.
THE WAY IT SPREADS
The virus that causes Ebola is not airborne and can only be spread through direct contact with bodily fluids — blood, sweat, vomit, feces, urine, saliva or semen — of an infected person who is showing symptoms.
There are no approved medications for Ebola, so doctors have tried experimental treatments in some cases, including drugs and blood transfusions from others who have recovered from Ebola. The survivor's blood could carry antibodies for the disease that will help a patient fight off the virus.