The World Health Organization convened an emergency meeting earlier this week, just a day after Equatorial Guinea, in West Africa, confirmed its first-ever outbreak of the highly lethal Marburg virus disease.

The WHO emergency meeting on February 14 was to discuss whether to test one of several Marburg vaccines and treatments in development during this outbreak.

WHO has already dispatched personnel and supplies – equipment such as gloves and isolation tents as well as rehydration fluids — the only current treatment for Marburg.

If an outbreak is large enough it can offer a chance to test the efficacy of vaccines in development that could prevent the disease, explains Dr. Heinz Feldmann, head of the Laboratory of Virology at the U.S.'s National Institute of Allergy and Infectious Diseases.

"A vaccine clinical trial won't help those already infected with the virus," notes Dr. Daniel Bausch, a former U.S. Centers for Disease Control and Prevention medical officer now with the non-profit FIND, which develops diagnostic tests around the world. "But an outbreak is your opportunity to see if a vaccine can potentially work in people at risk of contracting the virus."

Deadly Marburg

Marburg was first identified in 1967 among lab workers in Marburg, Germany and Belgrade, in what is now Serbia. They were exposed to the virus during research with monkeys or tissue samples of the monkeys originally from Uganda. It is a hemorrhagic fever virus, which can result in the body's organs eventually shutting down. Symptoms vary but usually start with a headache and fever.

It is "similar to many other illnesses which is why Marburg can spread before it's identified and before infected people are isolated," says Bausch. In fact, news reports say that the first case in the Equatorial Guinea outbreak may have emerged in early January of this year but only prompted alarm in early February, when a health worker saw patients who had severe symptoms of Marburg including bloody diarrhea and blood in vomit.

People can be infected and not show symptoms of Marburg for two to 21 days, followed by fever, chills, headache and body aches. A rash can appear around day five on a person's body, and additional symptoms such as nausea, vomiting, chest pain, a sore throat, abdominal pain, and diarrhea can occur in the course of the disease. The symptoms can become increasingly severe including jaundice, an inflamed pancreas, severe weight loss, delirium, massive internal bleeding, shock and multi-organ failure. The fatality rate varies widely, but the WHO puts it around 50%.

The host animal for Marburg is believe to be the fruit bat, which often is found in caves. Bats can directly infect humans or monkeys and pigs can be infected by the bats and then those animals infect humans. Marburg is spread through direct contact (through broken skin or mucous membranes) with blood, secretions, organs or other bodily fluids of infected people and through any materials such as bed sheets that become contaminated with the infected fluids. As is the case with Ebola, burial ceremonies have sometimes been a source of infection if people come in contact with secretions of someone who died of the virus.

Diagnosis is hard, says Dr. David Freedman, professor emeritus of infectious diseases at the University of Alabama at Birmingham, because many poor countries just don't have labs to test disease samples. In fact, while the health officer in Equatorial Guinea suspected Marburg on February 7, the viral sample had to be sent to Senegal, 2,000 miles away, and was only confirmed a week later.

The current outbreak

The most recent information from AfricaCDC, released earlier this week, is that Equatorial Guinea has one confirmed case of Marburg as well as nine deaths and 16 suspected cases from two communities in the Kie Ntem province in the northwestern part of the country. The patients had fever, fatigue and bloody vomit and diarrhea, though lab tests could confirm only one case. The WHO says the source is not yet known.

News reports said that an additional two cases were suspected in Cameroon, which borders Equatorial Guinea, but Cameroon's health minister dismissed those reports. Nevertheless, according to Voice of America, Cameroon is stepping up surveillance and restrictions at its border with Equatorial Guinea. As of Friday morning, there were no updates from Equatorial Guinea, AfricaCDC or WHO about the outbreak.

Countries around Equatorial Guinea are concerned that travel from the area could spread the virus, particularly among people who might have close contact with a case, even a deceased individual during funeral ceremonies. But the virus isn't transmitted through the air and is most infectious when someone has full-blown symptoms, says Bausch, so does not pose a great risk for the rest of the world. "The CDC is working closely with the World Health Organization to monitor the current outbreak of Marburg virus disease (MVD) in Equatorial Guinea," Scott Pauley, a spokesperson for the CDC, tells NPR. "So far, the outbreak is confined to Equatorial Guinea, therefore the current risk to people in the United States is extremely low."

Testing a vaccine

Daniel Bausch says it's important that the WHO convened the meeting to try to test a vaccine while the outbreak is ongoing. When it ends, if there's not a successful vaccine candidate, public health dollars may go elsewhere.

"Marburg hasn't been a super priority because there have been fewer than 15 outbreaks, most small," says UAB's Freedman. (Two exceptions have been a 1998–2000 outbreak in the Democratic Republic of the Congo that was linked to 154 cases and 128 deaths, and a 2004–05 outbreak in Angola that caused 227 deaths out of 252 reported cases.) "Given everything going on in the world you have to decide what your investment should be."

The WHO meeting concluded by calling for examining options for what could be tested during this current outbreak, building on the efforts of a working group looking at vaccine and therapeutic candidates. It hasn't said when it will reconvene.

Dr. Leana Wen, an emergency physician and professor at the Milken School of Public Health at George Washington University in Washington, D.C., says there's one more urgent reason a vaccine must be prioritized. "Health-care workers are at particular risk, and in Equatorial Guinea and surrounding countries, illness and death of the relatively few doctors and nurses they have would have tremendous lasting impact on health in their region."

Fran Kritz is a health policy reporter based in Washington, D.C., and a regular contributor to NPR. She also reports for the Washington Post and Verywell Health. Find her on Twitter: @fkritz