Ebola is one of the deadliest diseases on Earth, with a fatality rate as high as 90%. It’s among a handful of illnesses so dangerous that governments consider them threats to national security. An epidemic in West Africa that began in late 2013 and faded in 2016 killed more than 11,000 people, exceeding the counts from all previous waves combined. Now Ebola has flared again, with the latest outbreak declared a global emergency by the World Health Organization.

1. What’s causing alarms?

A new outbreak in the Democratic Republic of Congo that began in August 2018 has infected more than 2,400 people and killed more than 1,500 -- making it the deadliest since the 2013 crisis. Several cases were confirmed in neighboring Uganda in June and one near Rwanda in July, raising fears again of a wider contagion. Ebola disease is endemic to Congo, meaning it’s constantly present but generally under control.

2. Where does Ebola come from?

Scientists say the virus that causes Ebola jumps to humans through contact with secretions from animals such as chimpanzees, gorillas and bats that are infected with it. The virus passes among people through direct contact with the bodily fluids of someone who is infected with the disease or has died from it. Medical workers and family members are the most at risk. Ebola doesn’t travel through the air, making it less easily transmitted than many other pathogens, as long as proper health-care practices are followed.

3. How does it affect people?

According to the WHO, symptoms of Ebola can include fever, fatigue, muscle pain, sore throat and headache, followed by diarrhea, vomiting and sometimes bleeding inside and outside the body. It damages the immune system and organs, leading to massive internal bleeding and death from multi-organ failure and shock.

4. Is it treatable or preventable?

There are no specific drugs for treating Ebola. Tackling symptoms early on increases the patient’s chances of survival. This includes administering fluids and body salts intravenously to prevent dehydration, providing oxygen, and using drugs to support blood pressure and control vomiting and diarrhea. An experimental vaccine produced by Merck & Co. has proved effective in human trials at fending off the disease. It has not yet been licensed anywhere, but Congo’s government has approved the drug for use in the face of the current outbreak. Merck says it has donated 195,000 doses of the V920 vaccine to the WHO for use in Congo and has another 245,000 available for shipment. The WHO has backed the introduction of a second vaccine, with Johnson & Johnson’s experimental treatment the most likely candidate.

5. How far could Ebola spread?

The WHO had previously stopped short of declaring the current outbreak a global emergency. But on July 17, Director General Tedros Adhanom Ghebreyesus said the organization had become more concerned the virus could spread outside Congo. The global emergency declaration can help mobilize international response to an outbreak, provide more resources, and focus government attention on the issue. In the previous big epidemic, Ebola spread from three epicenter countries -- Guinea, Liberia and Sierra Leone -- to Nigeria, Senegal and Mali. And, for the first time, Ebola infection occurred outside Africa. That provoked panic in the U.S. and Europe, but in all there were just 11 cases and one death from Ebola there.

--With assistance from William Clowes and Paul Richardson.

To contact the reporters on this story: Albertina Torsoli in Geneva at atorsoli@bloomberg.net;Mike Cohen in Cape Town at mcohen21@bloomberg.net

To contact the editors responsible for this story: Karl Maier at kmaier2@bloomberg.net, ;Paul Richardson at pmrichardson@bloomberg.net, Andy Reinhardt

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