More than 100 people in Angola have died so far in an outbreak of the deadly Marburg virus, a close relative of Ebola. If you have to fall sick with a viral hemorrhagic fever from the Marburg-Ebola family, which one should you choose?
Go with Marburg. Though we don't know very much about how these viruses work, history suggests that between a quarter and half of all people who get Marburg die from it; there is a 90 percent mortality rate among those who contract Ebola. These numbers may be revised in light of the Marburg outbreak in Angola, however. Early reports indicate a mortality rate of nearly 100 percent.
Symptoms of the two diseases are very similar. Both begin with the sort of muscle pain, fever, headaches, and nausea that you might see in response to any viral infection. About five days later, a rash appears on the chest and back, and the victim's face may appear vacant and expressionless, as the virus begins to affect the brain. Both Marburg and Ebola are hemorrhagic fevers, which means they cause bleeding from multiple organs within the body. In the grisly later stages of the illness, the victim may start to ooze blood from orifices or the sites of injections.
Hemorrhagic fevers come in four basic flavors, the most deadly of which—Filoviridae—comprises the four known subtypes of Ebola as well as the Marburg virus (each of these has its own sequence of genetic material). These "filoviruses" have a shape that differentiates them from the other types of viral hemorrhagic fevers, which include dengue and yellow fever. A filovirus particle consists of a strand of RNA and some viral proteins wrapped in a long, skinny package made of fatty membrane. (The elongated shape gives it a "filamentous" appearance; particles from the other families are smaller and more spherical.) Filovirus particles can come in one of several varieties: straight, U-shaped, ring-shaped, curled over, or shaped like a "shepherd's crook." Some scientists surmise that certain shapes are more infectious than others; some assume the differences are random and of little consequence.
You can't treat Ebola or Marburg with any antiviral drug; the only thing a doctor can do is keep the patient hydrated and provide drugs that help blod clot. To make matters worse, both viruses reproduce rapidly all over the body, and they produce proteins that dampen the immune response. No one knows why Marburg outbreaks have been less deadly than Ebola outbreaks. It could be something about the virus itself—i.e., the Marburg virus may not be as effective at countering the body's immune response—or it could be something about the available medical care at the site of the outbreak.
A significant amount of the data on Marburg virus, for example, comes from Europe, where the first known cases turned up in 1967. Several dozen researchers contracted the illness at around the same time in three different cities—Belgrade, Frankfurt, and, naturally, Marburg. The virus appeared to have come from a set of green monkeys that had been captured in Uganda and sent to Europe for laboratory use.
Explainer thanks Graham Simmons of the University of Pennsylvania and Michael Bell of the Centers for Disease Control and Prevention.