What is Ebola and why is stopping this outbreak so difficult?

An Ebola outbreak in the Democratic Republic of Congo has been declared a public health emergency of international concern, by the World Health Organization (WHO).

Dealing with this outbreak is difficult as it involves a rare strain for which there is no vaccine and the cases have been found in an area affected by conflict.

What is Ebola and what are the symptoms?

Ebola is a rare but deadly disease caused by a virus.

Ebola viruses normally infect animals, typically fruit bats, but outbreaks among humans can sometimes start when people eat or handle infected animals.

It takes two to 21 days for symptoms to appear. They come on suddenly and start like the flu, with fever, headache and tiredness.

As the disease progresses, vomiting and diarrhoea develop and it can lead to organ failure. Some, but not all, patients develop internal and external bleeding.

The virus spreads from one person to another by contact with infected bodily fluids such as blood or vomit.

Why is this Ebola outbreak different and is there a vaccine?

This outbreak is caused by the Bundibugyo species of Ebola, which had not been seen for over a decade.

Bundibugyo has only caused two previous outbreaks, when it killed about a third of those infected.

This rarer species of Ebola is causing challenges.

Initial blood tests for Ebola were negative as they test for more common species.

There is no approved vaccine for Bundibugyo, but experimental ones are in development. It is possible that a vaccine for another species of Ebola (called Zaire) may offer some protection.

There are also no drugs developed that target Bundibugyo, making it harder to treat.

An additional complication is that the outbreak is taking place in a conflict zone, with a quarter of million people displaced from their homes and people moving across porous borders into neighbouring countries.

However, the WHO's declaration of a public health emergency of international concern does not mean we are in the early stages of a Covid-style pandemic. The risk Ebola poses outside east Africa is minimal.

How did the outbreak start?

The first known case was a nurse who developed symptoms on 24 April, so the virus had been spreading undetected for weeks.

This means that the true size of the outbreak is unknown and the task of finding infected patients and anyone they may have spread the virus to more challenging.

The nurse died in Bunia, the capital of eastern DR Congo's Ituri province, according to Congolese health minister Samuel Roger Kamba.

The nurse's body was repatriated to Mongwalu, one of two gold-mining towns where the majority of cases have been reported.

Kamba said one of the reasons the virus spread so quickly was the number of people exposed to the body during the funeral ceremony.

Africa Centres for Disease Control and Prevention's (CDC) director Dr Jean Kaseya told BBC World Service's Newsday programme that funerals were a particular concern - as they were during previous outbreaks of Ebola.

He said public health information campaigns were "providing information on how to handle funerals" and the importance of basic hygiene and sanitation, as well as providing protection measures for health workers.

Kamba said the outbreak was slow in being reported due to infected communities believing it to be "witchcraft" or a "mystical illness", resulting in people seeking treatment from prayer centres and witchdoctors rather than hospitals.

Where have cases been reported?

The first reported cases were in the Ituri towns of Mongwalu and Rwampara, as well as Bunia.

There has also been a case in eastern DR Congo's biggest city, Goma, which has a population of around 850,000 people and is under rebel control.

In Goma, the confirmed case involved a woman who had travelled to the city after her husband died of Ebola in Bunia, Jean-Jacques Muyembe, the director of the Congolese Institut National de Recherche Biomédicale (INRB), told AFP news agency.

Two people have also died in Uganda's capital, Kampala. They were Congolese nationals who had recently travelled to the country.

What is being done to tackle the outbreak?

The government has sent health teams to Bunia with protective equipment.

The WHO and medical charity Médecins Sans Frontières (MSF) are also present. They are setting up treatment centres and working on a response plan.

A toll-free number, 151, has been provided for reporting symptoms.

Residents have been urged to take measures such as:

• calling immediately when symptoms appear
• avoiding contact with bodies of people who died with symptoms, or with dead animals
• not eating raw meat, as undercooked food may transmit the virus
• practising social distancing

How are rebels responding?

Goma, the capital of the North Kivu province, is currently controlled by rebels from the AFC-M23 group, who say they are creating an Ebola response team.

On Sunday, AFC-M23 spokesman Lawrence Kanyuka said they had "immediately activated" response mechanisms in conjunction with health services and local medical facilities, to prevent the spread of Ebola in areas under their control.

However, the Congolese government is unlikely to want to work with the rebel administration, which would add another obstacle to efforts to tackle the outbreak.

What are Rwanda and other neighbouring countries doing?

Africa CDC has warned of the high risk of spread to countries that border DR Congo, specifically Uganda, Rwanda and South Sudan.

It expects to speak to the four countries on "how to strengthen the response".

Rwandan authorities have said they are reinforcing their screening for people entering the country after the confirmed case in Goma, which is on its border.

One Congolese man told the BBC that he had been blocked from crossing from Goma into Rwanda.

But he said that he was told that Rwandans were being allowed to go back home, and so were Congolese nationals living in Rwanda.

In Uganda, President Yoweri Museveni has postponed the Martyrs' Day pilgrimage, a Christian holiday held on 3 June each year, which usually draws thousands of Congolese nationals to join festivities.