Total Ebola Case: 2127 cases / 1145 deaths

More than 1,975 people in Guinea, Liberia, Nigeria and Sierra Leone have contracted Ebola since March, according to the World Health Organization, making this the biggest outbreak on record. More than 1,050 people have died. Two American aid workers infected with Ebola while working in West Africa were taken to a containment unit in Atlanta for treatment.

Two American aid workers infected with the Ebola virus while working in West Africa are being treated at a hospital in Atlanta, in a containment unit for patients with dangerous infectious diseases. But the risk that anyone will contract Ebola in the United States is extremely small, experts say.

Doctors across the country are being reminded to ask for the travel history of anybody who comes in with a fever. Patients who have been to West Africa are being screened and tested if there seems to be a chance they have been exposed. Heightened concern about the virus led to alarms being raised at three hospitals in New York City. But no Ebola cases have turned up. If someone were to bring the virus to the United States, standard procedures for infection control are likely to contain it.

It helps that Ebola does not spread nearly as easily as Hollywood movies about contagious diseases might suggest. In 2008, a patient who had contracted Marburg – a virus much like Ebola – in Uganda was treated at a hospital in the United States and could have exposed more than 200 people to the disease before anyone would have known what she had. Yet no one became sick.

It is the deadliest, eclipsing an outbreak in 1976, the year the virus was discovered.

You are not likely to catch Ebola just by being in proximity with someone who has the virus; it is not airborne, like the flu or respiratory viruses such as SARS.

Instead, Ebola spreads through direct contact with bodily fluids. If an infected person’s blood or vomit gets in another person’s eyes, nose or mouth, the infection may be transmitted. In the current outbreak, most new cases are occurring among people who have been taking care of sick relatives or who have prepared an infected body for burial.

Health care workers are at high risk, especially if they have not been properly equipped with or trained to use and decontaminate protective gear correctly.

The virus can survive on surfaces, so any object contaminated with bodily fluids, like a latex glove or a hypodermic needle, may spread the disease.

The epidemic is growing faster than efforts to keep up with it, and it will take months before governments and health workers in the region can get the upper hand, according to Doctors Without Borders.

In some parts of West Africa, there is a belief that simply saying “Ebola” aloud makes the disease appear. Such beliefs have created major obstacles for physicians, who are trying to combat the outbreak. Some people have even blamed physicians for the spread of the virus, opting to turn to witch doctors for treatment instead. Their skepticism is not without a grain of truth: In past outbreaks, hospital staff members who did not take thorough precautions became unwitting travel agents for the virus.

Ahmed Jallanzo/European Pressphoto Agency

Liberian health workers on the way to bury a woman who died of the Ebola virus.

Symptoms usually appear about eight to 10 days after exposure, according to the Centers for Disease Control and Prevention. At first, it seems much like the flu: a headache, fever and aches and pains. Sometimes there is also a rash. Diarrhea and vomiting follow.

Then, in about half of the cases, Ebola takes a severe turn, causing victims to hemorrhage. They may vomit blood or pass it in urine, or bleed under the skin or from their eyes or mouths. But bleeding is not usually what kills patients. Rather, blood vessels deep in the body begin leaking fluid, causing blood pressure to plummet so low that the heart, kidneys, liver and other organs begin to fail.

There is no vaccine or definitive cure for Ebola, and in past outbreaks the virus has been fatal in 60 to 90 percent of cases. The United States government plans to fast-track development of a vaccine shown to protect macaque monkeys, but there is no guarantee it will be effective in humans. The question of who should have access to the scarce supplies of an experimental medicine has become a hotly debated ethical question. Beyond this, all physicians can do is try to nurse people through the illness, using fluids and medicines to maintain blood pressure, and treat other infections that often strike their weakened bodies. A small percentage of people appear to have an immunity to the Ebola virus.

Ebola was first discovered in 1976, and it was once thought to originate in gorillas, because human outbreaks began after people ate gorilla meat. But scientists have since ruled out that theory, partly because apes that become infected are even more likely to die than humans.

Scientists now believe that bats are the natural reservoir for the virus, and that apes and humans catch it from eating food that bats have drooled or defecated on, or by coming in contact with surfaces covered in infected bat droppings and then touching their eyes or mouths.

The current outbreak seems to have started in a village near Guéckédou, Guinea, where bat hunting is common, according to Doctors Without Borders.

The biggest headlines have tended to involve outbreaks of deadly viruses that medical workers have few, if any, tools to combat. The four most prominent are compared below. No cure is known for any of them, nor has any vaccine yet been approved for human use.

	Ebola	Marburg	MERS	SARS
Emerged / identified	1976; latest outbreak in 2014	1967; latest major outbreak in 2005	2012-2013	2002-2003
Locus	Originally, Congo Basin and central Africa; latest strain, West Africa	Originally, central Europe; latest major outbreak, Angola	Arabian peninsula	Southern China
Suspected source	Fruit bats, by way of monkeys and other animals	Fruit bats, sometimes by way of monkeys	Bats, by way of camels	Bats, by way of civets
Type of virus	Filovirus	Filovirus	Coronavirus	Coronavirus
Type of illness	Hemorrhagic fever	Hemorrhagic fever	Respiratory syndrome	Respiratory syndrome
Fatality rate in outbreaks	50% to 90%	24% to 88%	About 30%	About 10%
Known cases	4,000+	570+	830+	8,200+
Known deaths	2700+	470+	290+	775+
Person-to-person transmission	Readily by close contact or fluids; not by aerosol	Readily by close contact or fluids; not by aerosol	Not very readily; mechanism unclear	Very readily by aerosol, fluids or close contact