How worrying is the Ebola outbreak in DR Congo?

The outbreak of Ebola in the Democratic Republic of Congo is concerning.

It has been spreading for weeks undetected in a part of the world where civil war makes getting on top of the virus difficult, and the species of Ebola involved is rare, so there are fewer tools to stop a virus that kills between a third and half of people infected.

This is a critical moment in an outbreak where there is uncertainty about how far it has spread, but there are already almost 250 suspected cases and 80 deaths.

Most Ebola outbreaks tend to be small, but specialists are haunted by the 2014-16 outbreak. Then, 28,600 people in West Africa were infected in the largest ever outbreak of the disease.

The declaration of a public health emergency of international concern by the World Health Organization (WHO) does not mean we are in the early stages of a Covid-style pandemic.

The risk Ebola poses to the whole world remains tiny.Even in the 2014-16 outbreak, there were only three cases in the UK and all were healthcare workers who had volunteered to help.

"But it does reflect that the situation is complex enough to require international coordination," says Dr Amanda Rojek, from the Pandemic Sciences Institute at the University of Oxford.

Ebola is a severe and deadly disease, although it is thankfully rare. Ebola viruses naturally infect animals – mainly fruit bats – but people can become infected if they come into close contact.

This outbreak is being caused by the Bundibugyo species of Ebola – it is one of three species known to cause outbreaks but is relatively unfamiliar.

Bundibugyo has caused only two outbreaks before – in 2007 and 2012 – where it killed 30% and 50% of people infected.

Bundibugyo poses a series of challenges. There are no approved vaccines or drug treatments for Bundibugyo, although there are some experimental ones, unlike other species of Ebola virus.

And tests to determine whether somebody has the infection do not appear to work well. Initial results in the outbreak were negative for Ebola virus, and more sophisticated laboratory tools were required to confirm Bundibugyo was involved.

Dealing with Bundibugyo is "one of the most significant concerns" in this outbreak, says Prof Trudie Lang from the University of Oxford.

Symptoms are thought to appear between two and 21 days after somebody is infected.

Initially they are like developing the flu - fever, headache and tiredness. But as Ebola progresses, it leads to vomiting, diarrhoea, and the body's organs not working. Some patients develop internal and external bleeding.