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This is the worst Ebola outbreak in history. Here’s why you should be worried.

The worst Ebola outbreak in history has put a number of countries in West Africa in lockdown, led to the deaths of nearly 700 people since February and brought new reports of doctors, including Americans, contracting the virus they are attempting to contain. The situation is undeniably scary. Here's what you need to know.

What is Ebola?

Ebola viral disease is a highly infectious illness with fatality rates up to 90 percent, according to the U.N. World Health Organization. Symptoms initially include a sudden fever as well as joint and muscle aches and then typically progress to vomiting, diarrhea and, in some cases, internal and external bleeding — you can see a full, grim description of symptoms compiled by the Centers for Disease Control and Prevention (CDC) here.

The virus spreads through contact with bodily fluids of someone who is infected. Reports of human infections usually first emerge in remote areas that are in proximity to tropical rain forests, where humans can come into contact with animals such as chimpanzees, gorillas and forest antelope. The consumption of bush meat is often a precursor to such outbreaks. The WHO says fruit bats are probably the natural host for the virus.

Why is it called Ebola?

It's named after a tributary river in northern Congo. In 1976, a village near the river was the site of one of two simultaneous outbreaks of the disease (the other was in Sudan). Of the five known strains of Ebola, the four that are transmittable to humans are found in Africa. A fifth, the Reston virus, ravaged monkey populations in the Philippines, but no humans in its environs have contracted the illness.

Can Ebola be cured?

Ebola can spread in alarming ways; there have been incidents in which the disease has spread at funerals for victims. Public health officials deem an outbreak to be over only after 42 days have elapsed without any new confirmed cases, which is leading some to predict that the current crisis may last well into the autumn.

How bad is the current outbreak?

Bad — very, very bad. It's concentrated in three small West African states: Sierra Leone, Liberia and Guinea, where reports of Ebola infections first emerged in February. The outbreak has claimed more than 670 lives and, worryingly, infected medical personnel attempting to stop its spread. A prominent Liberian physician died Sunday.

What's particularly scary, though, was the recent death of a Liberian man in Lagos, the bustling coastal mega-city in Nigeria, Africa's most populous country. The man, a consultant for the Liberian government, had traveled from Liberia through an airport in Lome, the capital of Togo, before arriving in Nigeria. The hospital where he died is under lockdown, and the WHO has sent teams to Togo and Nigeria.

So what can be done now?

Those who have contracted the virus and the medical personnel treating them need to be kept under strict quarantine. That's easier said than done, especially in countries where resources are limited and public health protocols are not always heeded. On Monday, Liberia sealed off most of its border crossings (it has kept its main airport open). Nigeria has placed all entry points into the country on "red alert." The threat of the virus spreading beyond the immediate region remains real, and authorities have to be vigilant. A patient may manifest symptoms of the virus only three weeks after getting infected.

One of the continuing challenges is getting local populations to abide by the edicts of government authorities and foreign health workers. The WHO has repeatedly warned about the risk posed by mourners reclaiming the bodies of the deceased for traditional burial ceremonies. But in some cases during the current outbreak, families have refused to hand over the bodies to officials; some communities have staged roadblocks to halt ambulances and launched protests outside hospitals and clinics.

Wait, why would they do that?

The hysteria caused by the spread of Ebola has led also to the spread of rumor and conspiracy theories. Angry crowds have accused foreigners of bringing the virus in their midst: In April, the threat of violence forced MSF to evacuate all its staff from a treatment center in Guinea. In Sierra Leone, which has the largest number of Ebola cases at present, thousands protested over the weekend outside the country's main Ebola treatment facility in the eastern city of Kenema.

Police had to disperse the crowd with tear gas and a 9-year-old was injured in the leg by a police bullet, Reuters reports. The demonstration was sparked, the news agency claims, by a rumor spread in a nearby market that the disease was a ruse used to justify "cannibalistic rituals" being carried out in the hospital.

Liberia and Sierra Leone have societies that still live with the traumas of brutal civil wars. Susan Shepler, a professor at American University who is conducting field work in both countries, writes that such concerns and hysteria have as much to do with systemic failures in governance as they do with local superstitions:

Really who among us would want to turn a sick loved one over to a hospital staffed with foreigners, knowing we might never see them again? And hospitals in this part of the world have notoriously poor service. Families routinely have to prepare meals and bring them to patients. Families have to go to local pharmacies to buy drugs and even gloves or needles from India or Nigeria because hospital storerooms are routinely not stocked. People’s apprehensions about the failings of the healthcare system come from experience, not from ignorance.

And so as the outbreak rumbles on, the panic surrounding it may be spreading just as virulently.

Related: West Africa struggles to contain Ebola outbreak