BioEd Online

An outbreak of rare and deadly Marburg haemorrhagic fever has claimed more than 100 lives in central Africa. Where does the virus come from, and how serious a potential killer is it likely to be?

What is Marburg virus, and what does it do?

Marburg is a rare and deadly virus, of the same family as Ebola, that triggers haemorrhagic fever. It infects the cells lining the blood vessels and a subset of the body's immune cells, causing capillaries to leak fluid.

The first signs of infection are fever and aches, making the disease difficult to distinguish from malaria or other viral illnesses. Although Marburg can cause severe bleeding, in most cases patients die because the circulatory system collapses, triggering shock and multiple organ failure.

Why the alarm over the current outbreak?

Marburg is dangerous because it has a high mortality rate, is very contagious and has no effective treatment. The virus kills at least 25-30% of the people it infects, although its deadlier cousin Ebola kills up to 90%. Nevertheless, "that's a scary proportion", says Sina Bavari, who studies the virus at the US Army Medical Research Institute of Infectious Diseases in Fort Detrick, Maryland.

The current outbreak, which originated in Uíge province in northern Angola, has killed more people than any before. The disease first appeared there in October 2004 but was only identified as Marburg virus last week. According to the World Health Organization (WHO), health authorities had reported 132 cases as of 30 March, of which 127 have been fatal.

The virus has also attracted attention in recent years because it is viewed as a prime candidate for a bioterror agent: it is easy to mass-produce and is stable as a powder. "It's really increased awareness," says Tom Ksiazek, who works in the Special Pathogens Branch of the US Centers for Disease Control and Prevention in Atlanta, Georgia, where experts carried out recent testing on specimens from Marburg-infected patients.

Where does the virus come from?

It was first recognized in 1967 after a shipment of monkeys from Uganda triggered outbreaks of disease in laboratory workers in Marburg and Frankfurt, Germany, as well as in Belgrade in the former Yugoslavia. Thirty-seven people fell ill.

Since then, there has been only a handful of recorded outbreaks, all originating in sub-Saharan Africa. Before the most recent outbreak, the worst epidemic was in the Democratic Republic of Congo between 1998 and 2000, during which around 150 people were infected.

Scientists have no clear idea about where the virus originated. It is unlikely to stem from monkeys or other primates, because they are also killed quickly by the disease. Scientists suspect that it lives in another animal, which could be anything from bats to mosquitoes to birds, and occasionally jumps into humans and other primates. Because outbreaks are so rare, researchers have had little opportunity to trace the source.

Can the disease be controlled?

There are no vaccines or drugs that fight off Marburg fever. The virus spreads through close contact with infected people, their body fluids or the tiny water droplets from coughs and sneezes. But its spread can be curbed using standard infection-control measures, such as the use of gloves and face masks, and the isolation of those infected.

Because of concerns that the virus could spread further in Angola, infectious-disease experts from the WHO and other medical organizations are working with local health authorities to isolate patients, trace their contacts and raise local awareness of the disease.

A smattering of groups around the world is working on prototype drugs or vaccines to combat the virus, which requires the strictest level of laboratory safety standards. A study last year showed that disabled virus particles stripped of their genetic material and injected into guinea pigs protected them from infection¹.

Is the disease really that bad?

Marburg is a dangerous virus, and an outbreak is clearly devastating for the affected communities. But in terms of death toll, it cannot rival the harm caused by persistent and widespread killers such as malaria or HIV. "It does tend to get people's attention," Ksiazek says, "but perhaps more than it deserves."